Is it practical to use a slug-tuned variable inductor in an antenna matcher (aka “antenna tuner”)?Variable phase antennaDo vacuum variable capacitors have higher Q than air variable capacitors?Stacked shell inductor — what's its function/use?Where does one find high-voltage variable capacitors and inductors for RF?Adapting an antenna tuner for use with a panel meter instead of an LEDAntenna tuner designWhat is an antenna tuner? Why bother with resonant antennas in the first place?Two devices + one antennaUsing one of two antenna tuners connected in seriesWhat dielectric strength is required for a variable capacitors in a 100W T-network antenna tuner?
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Is it practical to use a slug-tuned variable inductor in an antenna matcher (aka “antenna tuner”)?
Variable phase antennaDo vacuum variable capacitors have higher Q than air variable capacitors?Stacked shell inductor — what's its function/use?Where does one find high-voltage variable capacitors and inductors for RF?Adapting an antenna tuner for use with a panel meter instead of an LEDAntenna tuner designWhat is an antenna tuner? Why bother with resonant antennas in the first place?Two devices + one antennaUsing one of two antenna tuners connected in seriesWhat dielectric strength is required for a variable capacitors in a 100W T-network antenna tuner?
$begingroup$
I will soon need an antenna impedance match (aka "antenna tuner"), because I'll initially only have a single antenna for my HF rig (needs to cover 80m, 40m, 20m, 15m, and 10m). Obviously, in order to manage SWR, I'll need a matching network, quite likely with a wider capability than the pi network built into my Heathkit SB-102. Even if the SB-102 can manage without help, I'll also need to match my portable antenna to my portable QRP rigs.
One of the core components of any matching network -- L, T, SCS, or pi -- is a "variable" inductor. Home builders seemingly usually use a tapped coil for this, giving discrete increments of inductance and depending on a variable capacitance to finalize the match.
However, variable caps are getting harder to find; they're no longer manufactured in the old "interleaved plates, air spaced" form, and the tiny plastic dielectric ones that are still available can't take much voltage (and are difficult to adjust precisely).
It occurred to me that what's needed is to adjust the ratio of inductance to capacitance, not either one in particular; if one had an inductor with stepless adjustment over a wide range of value, one might be able to use common fixed capacitors, or possibly a switch-selected gang of parallel fixed capacitors.
Now, adjustable inductors have been around for decades; aligning an old superheterodyne receiver involves tweaking up to a couple dozen components, of which roughly half are slug-tuned variable inductors. I recall from studying for my license exam that a ferrite or iron slug will increase inductance when inserted into a coil, while a brass (or presumably copper or aluminum -- conductive but non-magnetic) slug decreases it.
What wasn't covered in the study materials is how widely one can adjust the inductance with slugs. Common variable capacitors out of old radio or TV tuners run from zero to several hundred picoFarad, and a tapped coil can likewise run near zero inductance when tapped down to two or three turns. What sort of range could I get with, say, a tuning slug that's iron on one end, brass on the other?
diy electronics antenna-system
edited May 13 at 14:11
rclocher3
3,4671625
asked May 12 at 15:33
Zeiss IkonZeiss Ikon
1,023115
$endgroup$
add a comment |
$begingroup$
I will soon need an antenna impedance match (aka "antenna tuner"), because I'll initially only have a single antenna for my HF rig (needs to cover 80m, 40m, 20m, 15m, and 10m). Obviously, in order to manage SWR, I'll need a matching network, quite likely with a wider capability than the pi network built into my Heathkit SB-102. Even if the SB-102 can manage without help, I'll also need to match my portable antenna to my portable QRP rigs.
One of the core components of any matching network -- L, T, SCS, or pi -- is a "variable" inductor. Home builders seemingly usually use a tapped coil for this, giving discrete increments of inductance and depending on a variable capacitance to finalize the match.
However, variable caps are getting harder to find; they're no longer manufactured in the old "interleaved plates, air spaced" form, and the tiny plastic dielectric ones that are still available can't take much voltage (and are difficult to adjust precisely).
It occurred to me that what's needed is to adjust the ratio of inductance to capacitance, not either one in particular; if one had an inductor with stepless adjustment over a wide range of value, one might be able to use common fixed capacitors, or possibly a switch-selected gang of parallel fixed capacitors.
Now, adjustable inductors have been around for decades; aligning an old superheterodyne receiver involves tweaking up to a couple dozen components, of which roughly half are slug-tuned variable inductors. I recall from studying for my license exam that a ferrite or iron slug will increase inductance when inserted into a coil, while a brass (or presumably copper or aluminum -- conductive but non-magnetic) slug decreases it.
What wasn't covered in the study materials is how widely one can adjust the inductance with slugs. Common variable capacitors out of old radio or TV tuners run from zero to several hundred picoFarad, and a tapped coil can likewise run near zero inductance when tapped down to two or three turns. What sort of range could I get with, say, a tuning slug that's iron on one end, brass on the other?
diy electronics antenna-system
edited May 13 at 14:11
rclocher3
3,4671625
asked May 12 at 15:33
Zeiss IkonZeiss Ikon
1,023115
$endgroup$
$begingroup$
um, "tiny plastic dielectric ones that are still available can't take much voltage" that's not actually true, see this commercially available list of >=1kV-rated variable capacitors
$endgroup$
– Marcus Müller
May 12 at 17:22
$begingroup$
@MarcusMüller I looked at that DigiKey link, and they are all trimmer capacitors, not exactly convenient to use in an HF antenna tuner. Not to mention that the ones that have a wide enough capacitance range for use in an HF tuner are $200 to well over $300.
$endgroup$
– Mike Waters♦
May 12 at 18:05
2
$begingroup$
fair point! I tend to forget that the goal wouldn't be achieving an acceptable matching for the whole band (so, you'd use a trimmer for each band of interest and trim that once), but an exact matching for the frequency of interest. My bad!
$endgroup$
– Marcus Müller
May 12 at 19:10
add a comment |
$begingroup$
I will soon need an antenna impedance match (aka "antenna tuner"), because I'll initially only have a single antenna for my HF rig (needs to cover 80m, 40m, 20m, 15m, and 10m). Obviously, in order to manage SWR, I'll need a matching network, quite likely with a wider capability than the pi network built into my Heathkit SB-102. Even if the SB-102 can manage without help, I'll also need to match my portable antenna to my portable QRP rigs.
One of the core components of any matching network -- L, T, SCS, or pi -- is a "variable" inductor. Home builders seemingly usually use a tapped coil for this, giving discrete increments of inductance and depending on a variable capacitance to finalize the match.
However, variable caps are getting harder to find; they're no longer manufactured in the old "interleaved plates, air spaced" form, and the tiny plastic dielectric ones that are still available can't take much voltage (and are difficult to adjust precisely).
It occurred to me that what's needed is to adjust the ratio of inductance to capacitance, not either one in particular; if one had an inductor with stepless adjustment over a wide range of value, one might be able to use common fixed capacitors, or possibly a switch-selected gang of parallel fixed capacitors.
Now, adjustable inductors have been around for decades; aligning an old superheterodyne receiver involves tweaking up to a couple dozen components, of which roughly half are slug-tuned variable inductors. I recall from studying for my license exam that a ferrite or iron slug will increase inductance when inserted into a coil, while a brass (or presumably copper or aluminum -- conductive but non-magnetic) slug decreases it.
What wasn't covered in the study materials is how widely one can adjust the inductance with slugs. Common variable capacitors out of old radio or TV tuners run from zero to several hundred picoFarad, and a tapped coil can likewise run near zero inductance when tapped down to two or three turns. What sort of range could I get with, say, a tuning slug that's iron on one end, brass on the other?
diy electronics antenna-system
edited May 13 at 14:11
rclocher3
3,4671625
asked May 12 at 15:33
Zeiss IkonZeiss Ikon
1,023115
$endgroup$
I will soon need an antenna impedance match (aka "antenna tuner"), because I'll initially only have a single antenna for my HF rig (needs to cover 80m, 40m, 20m, 15m, and 10m). Obviously, in order to manage SWR, I'll need a matching network, quite likely with a wider capability than the pi network built into my Heathkit SB-102. Even if the SB-102 can manage without help, I'll also need to match my portable antenna to my portable QRP rigs.
One of the core components of any matching network -- L, T, SCS, or pi -- is a "variable" inductor. Home builders seemingly usually use a tapped coil for this, giving discrete increments of inductance and depending on a variable capacitance to finalize the match.
However, variable caps are getting harder to find; they're no longer manufactured in the old "interleaved plates, air spaced" form, and the tiny plastic dielectric ones that are still available can't take much voltage (and are difficult to adjust precisely).
It occurred to me that what's needed is to adjust the ratio of inductance to capacitance, not either one in particular; if one had an inductor with stepless adjustment over a wide range of value, one might be able to use common fixed capacitors, or possibly a switch-selected gang of parallel fixed capacitors.
Now, adjustable inductors have been around for decades; aligning an old superheterodyne receiver involves tweaking up to a couple dozen components, of which roughly half are slug-tuned variable inductors. I recall from studying for my license exam that a ferrite or iron slug will increase inductance when inserted into a coil, while a brass (or presumably copper or aluminum -- conductive but non-magnetic) slug decreases it.
What wasn't covered in the study materials is how widely one can adjust the inductance with slugs. Common variable capacitors out of old radio or TV tuners run from zero to several hundred picoFarad, and a tapped coil can likewise run near zero inductance when tapped down to two or three turns. What sort of range could I get with, say, a tuning slug that's iron on one end, brass on the other?
diy electronics antenna-system
diy electronics antenna-system
edited May 13 at 14:11
rclocher3
3,4671625
asked May 12 at 15:33
Zeiss IkonZeiss Ikon
1,023115
edited May 13 at 14:11
rclocher3
3,4671625
asked May 12 at 15:33
Zeiss IkonZeiss Ikon
1,023115
edited May 13 at 14:11
rclocher3
3,4671625
edited May 13 at 14:11
rclocher3
3,4671625
edited May 13 at 14:11
rclocher3
3,4671625
3,4671625
asked May 12 at 15:33
Zeiss IkonZeiss Ikon
1,023115
asked May 12 at 15:33
Zeiss IkonZeiss Ikon
1,023115
asked May 12 at 15:33
Zeiss IkonZeiss Ikon
1,023115
1,023115
$begingroup$
um, "tiny plastic dielectric ones that are still available can't take much voltage" that's not actually true, see this commercially available list of >=1kV-rated variable capacitors
$endgroup$
– Marcus Müller
May 12 at 17:22
$begingroup$
@MarcusMüller I looked at that DigiKey link, and they are all trimmer capacitors, not exactly convenient to use in an HF antenna tuner. Not to mention that the ones that have a wide enough capacitance range for use in an HF tuner are $200 to well over $300.
$endgroup$
– Mike Waters♦
May 12 at 18:05
2
$begingroup$
fair point! I tend to forget that the goal wouldn't be achieving an acceptable matching for the whole band (so, you'd use a trimmer for each band of interest and trim that once), but an exact matching for the frequency of interest. My bad!
$endgroup$
– Marcus Müller
May 12 at 19:10
add a comment |
$begingroup$
um, "tiny plastic dielectric ones that are still available can't take much voltage" that's not actually true, see this commercially available list of >=1kV-rated variable capacitors
$endgroup$
– Marcus Müller
May 12 at 17:22
$begingroup$
@MarcusMüller I looked at that DigiKey link, and they are all trimmer capacitors, not exactly convenient to use in an HF antenna tuner. Not to mention that the ones that have a wide enough capacitance range for use in an HF tuner are $200 to well over $300.
$endgroup$
– Mike Waters♦
May 12 at 18:05
2
$begingroup$
fair point! I tend to forget that the goal wouldn't be achieving an acceptable matching for the whole band (so, you'd use a trimmer for each band of interest and trim that once), but an exact matching for the frequency of interest. My bad!
$endgroup$
– Marcus Müller
May 12 at 19:10
$begingroup$
um, "tiny plastic dielectric ones that are still available can't take much voltage" that's not actually true, see this commercially available list of >=1kV-rated variable capacitors
$endgroup$
– Marcus Müller
May 12 at 17:22
$begingroup$
um, "tiny plastic dielectric ones that are still available can't take much voltage" that's not actually true, see this commercially available list of >=1kV-rated variable capacitors
$endgroup$
– Marcus Müller
May 12 at 17:22
$begingroup$
@MarcusMüller I looked at that DigiKey link, and they are all trimmer capacitors, not exactly convenient to use in an HF antenna tuner. Not to mention that the ones that have a wide enough capacitance range for use in an HF tuner are $200 to well over $300.
$endgroup$
– Mike Waters♦
May 12 at 18:05
$begingroup$
@MarcusMüller I looked at that DigiKey link, and they are all trimmer capacitors, not exactly convenient to use in an HF antenna tuner. Not to mention that the ones that have a wide enough capacitance range for use in an HF tuner are $200 to well over $300.
$endgroup$
– Mike Waters♦
May 12 at 18:05
2
2
$begingroup$
fair point! I tend to forget that the goal wouldn't be achieving an acceptable matching for the whole band (so, you'd use a trimmer for each band of interest and trim that once), but an exact matching for the frequency of interest. My bad!
$endgroup$
– Marcus Müller
May 12 at 19:10
$begingroup$
fair point! I tend to forget that the goal wouldn't be achieving an acceptable matching for the whole band (so, you'd use a trimmer for each band of interest and trim that once), but an exact matching for the frequency of interest. My bad!
$endgroup$
– Marcus Müller
May 12 at 19:10
add a comment |
5 Answers
5
active
oldest
votes
$begingroup$
What wasn't covered in the study materials is how widely one can adjust the inductance with slugs. Common variable capacitors out of old radio or TV tuners run from zero to several hundred picoFarad, and a tapped coil can likewise run near zero inductance when tapped down to two or three turns. What sort of range could I get with, say, a tuning slug that's iron on one end, brass on the other?
The inductivity of a coil is very much dominated by the magnetic permeability of its core – use a core with a twice as high a permeability, get (pretty much) twice the inductivity. A ferrite core can have a permeability a couple thousand times higher than that of air. So, by inserting a core into an otherwise air-core coil, you could achieve that factor of variability.
Problem: Cores tend to saturate in strong fields. You'll have to dimension the core such that saturation does not occur at the powers you plan to use. That can be large, challenging and hence expensive!
answered May 12 at 17:49
Marcus MüllerMarcus Müller
8,1871031
$endgroup$
$begingroup$
Fortunately, iron and steel bar stock is cheap. Brass/copper, less so, but I only need a short piece. I have a mechanism handy that will give ~4 inches of travel in a turn and a half; I may just have to wind up a coil and give this a try. With that permeability range, I may not even want/need the brass section of the slug. Sounds like time to hit the books and figure out how many turns I need...
$endgroup$
– Zeiss Ikon
May 13 at 11:13
1
$begingroup$
Simply build /calculate an air-core coil, and do a rough estimate of the permeability of the core you're planning to insert. Take that as the factor over the air-core inductivity! In such a coil system, the vast majority of the field energy will be contained within the high-permeability core, so that the surrounding material can be disregarded.
$endgroup$
– Marcus Müller
May 13 at 11:23
$begingroup$
(also, instead of brass, try with nylon/plastic in general – if you want a large range, go for the least permeable material as contrast to iron)
$endgroup$
– Marcus Müller
May 13 at 11:28
$begingroup$
Yep, the housing for this is thermoplastic (polyethylene, I think), roughly same permeability as air anyway. I've got a spool of magnet wire; time to visit the steel shapes section at the local big box store, or prowl around Metal Shorts for a cast iron slug. Then find my tap set.
$endgroup$
– Zeiss Ikon
May 13 at 11:34
$begingroup$
I'd be totally lazy: start with a bold/screw that you've got lying around.
$endgroup$
– Marcus Müller
May 13 at 11:40
|
show 1 more comment
$begingroup$
...variable caps are ... no longer manufactured in the old "interleaved plates, air spaced" form, and the tiny plastic dielectric ones that are still available can't take much voltage (and are difficult to adjust precisely).
Thankfully, Oren Elliott is a surprisingly affordable source of brand new air-variable capacitors. I have used them successfully in several projects.
answered May 13 at 1:24
Brian K1LIBrian K1LI
2,800417
$endgroup$
$begingroup$
Yipe! 50-65 dollars each in singles isn't "surprisingly affordable" -- at least to me!
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
In my experience, this has always been the going rate for such units. A kit manufacturer used to sell them for $75.
$endgroup$
– Brian K1LI
yesterday
$begingroup$
Maybe it's just another sign I'm getting old. I remember being able to buy a new radio with one of these in it (okay, likely the light, low-voltage version) for $20 or so.
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
Any case, seems like another good reason to come up with a homebuilt way to vary the inductance instead of being tied to a $60+ varicap for each antenna matcher...
$endgroup$
– Zeiss Ikon
yesterday
add a comment |
$begingroup$
Fair-Rite makes ferrite rods which would be suitable for HF applications. It should be possible to create or repurpose a screw-operated mechanism to move the rod into and out of a cylindrical coil.
Preferably, the material will have steady permeability and low loss over the frequency range of interest. Loss is proportional to the ratio of the real and imaginary components of permeability, $fracmu'mu''$.
The properties of Material 61 are probably best, because:
$mu'$ doesn't begin to drop off until past 30MHz
$mu''$ is relatively low and doesn't rise significantly until 20MHz
The relative permeability of a wound rod depends on the ratio of the rod's length to its diameter:
So you will have to make some preliminary calculations before deciding on turns count for rods using Material 61.
answered May 13 at 23:09
Brian K1LIBrian K1LI
2,800417
$endgroup$
add a comment |
$begingroup$
Variable caps are getting harder to find; they're no longer
manufactured in the old "interleaved plates, air spaced" form.
They are not hard to find. You can buy those if you know where to look. I have managed to find more than enough for my uses. You just have to look elsewhere than those selling new components.
I have quite a stock of them (and even rotary inductors!) that I purchased very inexpensively from hamfests.
Electronics and radio surplus companies often have them. And have you looked on eBay? I've seen some real bargains from time to time!
Some places that sell surplus radio parts are Surplus Sales of Nebraska, RF Parts, and Fair Radio Sales. And those are only a few of them.
In lieu of rotary (or ferrite-core) inductors, you could use a fixed air-wound coil with taps. One of the homebrew tuners at the base of my inverted-L uses that method (photos below); the other uses just two variable capacitors in an L-network (Omega match).
The red alligator clip shorts out the unused portion of this old Barker & Williamson Air Dux coil that I bought from eBay. If you can't find one, you can wind one yourself.
This is inside the tuner that I made to match my 160m inverted-L on 80 and 40 meters.
answered May 12 at 18:17
Mike Waters♦Mike Waters
4,0422635
$endgroup$
$begingroup$
@ZeissIkon Your comment wasMike, the point of this question is that air-spaced variable caps aren't as easy to find or as cheap as they used to be, and both tapped coil and fixed coil need them. – Zeiss Ikon May 13 at 14:26 deleted by Zeiss Ikon May 13 at 14:27
$endgroup$
– Mike Waters♦
6 hours ago
1
$begingroup$
Ah, now I remember. I asked question A ("slug tuning"), and you answered question B.("air variable caps availability").
$endgroup$
– Zeiss Ikon
5 hours ago
$begingroup$
I'm well aware of tapped coils to vary inductance (I mentioned them in the question). I was looking for an alternative to the "stepwise" change in inductance in order to avoid air variable caps.
$endgroup$
– Zeiss Ikon
5 hours ago
$begingroup$
@ZeissIkon Good luck with that, because the values of both the capacitors and the inductor interact. Adjust the inductor, and you'll almost certainly have to change the value of the capacitors.
$endgroup$
– Mike Waters♦
1 hour ago
add a comment |
$begingroup$
For a variable inductor you can make two coils with a fairly large diameters. One diameter a bit larger than the other. Place the smaller one inside the larger one.
If you make the length of the inner coil fairly small you can rotate it so the coils will have the same or the opposite winding direction. This way you can get a large
tuning range for the inductance. Obviously, if you design for a very small minimum capacitance, Q will be poor since the series R will be much larger compared to a normal coil. Get inspiration from here:
http://axotron.eu/photo/2013/2013-08-18_Rundradiomuseet/slides/DSC_1812.html
This one is to tune a 150 kW transmitter. Something similar, but much smaller....
answered 2 days ago
sm5bszsm5bsz
54113
$endgroup$
$begingroup$
This is a variable coupling air-core transformer; they're used as ticklers for regenerative receivers, and as antenna couplers (especially for crystal radios), but I don't recall reading that this changes the induction of either coil -- just how well energy passes from one to the other.
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
@ZeissIkon Trust me, Leif SM5BSZ knows what he's talking about. :-) You're getting some great advice on hamSE; but respectfully, you don't know that yet. ;-)
$endgroup$
– Mike Waters♦
1 hour ago
add a comment |
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5 Answers
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5 Answers
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$begingroup$
What wasn't covered in the study materials is how widely one can adjust the inductance with slugs. Common variable capacitors out of old radio or TV tuners run from zero to several hundred picoFarad, and a tapped coil can likewise run near zero inductance when tapped down to two or three turns. What sort of range could I get with, say, a tuning slug that's iron on one end, brass on the other?
The inductivity of a coil is very much dominated by the magnetic permeability of its core – use a core with a twice as high a permeability, get (pretty much) twice the inductivity. A ferrite core can have a permeability a couple thousand times higher than that of air. So, by inserting a core into an otherwise air-core coil, you could achieve that factor of variability.
Problem: Cores tend to saturate in strong fields. You'll have to dimension the core such that saturation does not occur at the powers you plan to use. That can be large, challenging and hence expensive!
answered May 12 at 17:49
Marcus MüllerMarcus Müller
8,1871031
$endgroup$
$begingroup$
Fortunately, iron and steel bar stock is cheap. Brass/copper, less so, but I only need a short piece. I have a mechanism handy that will give ~4 inches of travel in a turn and a half; I may just have to wind up a coil and give this a try. With that permeability range, I may not even want/need the brass section of the slug. Sounds like time to hit the books and figure out how many turns I need...
$endgroup$
– Zeiss Ikon
May 13 at 11:13
1
$begingroup$
Simply build /calculate an air-core coil, and do a rough estimate of the permeability of the core you're planning to insert. Take that as the factor over the air-core inductivity! In such a coil system, the vast majority of the field energy will be contained within the high-permeability core, so that the surrounding material can be disregarded.
$endgroup$
– Marcus Müller
May 13 at 11:23
$begingroup$
(also, instead of brass, try with nylon/plastic in general – if you want a large range, go for the least permeable material as contrast to iron)
$endgroup$
– Marcus Müller
May 13 at 11:28
$begingroup$
Yep, the housing for this is thermoplastic (polyethylene, I think), roughly same permeability as air anyway. I've got a spool of magnet wire; time to visit the steel shapes section at the local big box store, or prowl around Metal Shorts for a cast iron slug. Then find my tap set.
$endgroup$
– Zeiss Ikon
May 13 at 11:34
$begingroup$
I'd be totally lazy: start with a bold/screw that you've got lying around.
$endgroup$
– Marcus Müller
May 13 at 11:40
|
show 1 more comment
$begingroup$
What wasn't covered in the study materials is how widely one can adjust the inductance with slugs. Common variable capacitors out of old radio or TV tuners run from zero to several hundred picoFarad, and a tapped coil can likewise run near zero inductance when tapped down to two or three turns. What sort of range could I get with, say, a tuning slug that's iron on one end, brass on the other?
The inductivity of a coil is very much dominated by the magnetic permeability of its core – use a core with a twice as high a permeability, get (pretty much) twice the inductivity. A ferrite core can have a permeability a couple thousand times higher than that of air. So, by inserting a core into an otherwise air-core coil, you could achieve that factor of variability.
Problem: Cores tend to saturate in strong fields. You'll have to dimension the core such that saturation does not occur at the powers you plan to use. That can be large, challenging and hence expensive!
answered May 12 at 17:49
Marcus MüllerMarcus Müller
8,1871031
$endgroup$
$begingroup$
Fortunately, iron and steel bar stock is cheap. Brass/copper, less so, but I only need a short piece. I have a mechanism handy that will give ~4 inches of travel in a turn and a half; I may just have to wind up a coil and give this a try. With that permeability range, I may not even want/need the brass section of the slug. Sounds like time to hit the books and figure out how many turns I need...
$endgroup$
– Zeiss Ikon
May 13 at 11:13
1
$begingroup$
Simply build /calculate an air-core coil, and do a rough estimate of the permeability of the core you're planning to insert. Take that as the factor over the air-core inductivity! In such a coil system, the vast majority of the field energy will be contained within the high-permeability core, so that the surrounding material can be disregarded.
$endgroup$
– Marcus Müller
May 13 at 11:23
$begingroup$
(also, instead of brass, try with nylon/plastic in general – if you want a large range, go for the least permeable material as contrast to iron)
$endgroup$
– Marcus Müller
May 13 at 11:28
$begingroup$
Yep, the housing for this is thermoplastic (polyethylene, I think), roughly same permeability as air anyway. I've got a spool of magnet wire; time to visit the steel shapes section at the local big box store, or prowl around Metal Shorts for a cast iron slug. Then find my tap set.
$endgroup$
– Zeiss Ikon
May 13 at 11:34
$begingroup$
I'd be totally lazy: start with a bold/screw that you've got lying around.
$endgroup$
– Marcus Müller
May 13 at 11:40
|
show 1 more comment
$begingroup$
What wasn't covered in the study materials is how widely one can adjust the inductance with slugs. Common variable capacitors out of old radio or TV tuners run from zero to several hundred picoFarad, and a tapped coil can likewise run near zero inductance when tapped down to two or three turns. What sort of range could I get with, say, a tuning slug that's iron on one end, brass on the other?
The inductivity of a coil is very much dominated by the magnetic permeability of its core – use a core with a twice as high a permeability, get (pretty much) twice the inductivity. A ferrite core can have a permeability a couple thousand times higher than that of air. So, by inserting a core into an otherwise air-core coil, you could achieve that factor of variability.
Problem: Cores tend to saturate in strong fields. You'll have to dimension the core such that saturation does not occur at the powers you plan to use. That can be large, challenging and hence expensive!
answered May 12 at 17:49
Marcus MüllerMarcus Müller
8,1871031
$endgroup$
What wasn't covered in the study materials is how widely one can adjust the inductance with slugs. Common variable capacitors out of old radio or TV tuners run from zero to several hundred picoFarad, and a tapped coil can likewise run near zero inductance when tapped down to two or three turns. What sort of range could I get with, say, a tuning slug that's iron on one end, brass on the other?
The inductivity of a coil is very much dominated by the magnetic permeability of its core – use a core with a twice as high a permeability, get (pretty much) twice the inductivity. A ferrite core can have a permeability a couple thousand times higher than that of air. So, by inserting a core into an otherwise air-core coil, you could achieve that factor of variability.
Problem: Cores tend to saturate in strong fields. You'll have to dimension the core such that saturation does not occur at the powers you plan to use. That can be large, challenging and hence expensive!
answered May 12 at 17:49
Marcus MüllerMarcus Müller
8,1871031
answered May 12 at 17:49
Marcus MüllerMarcus Müller
8,1871031
answered May 12 at 17:49
Marcus MüllerMarcus Müller
8,1871031
answered May 12 at 17:49
Marcus MüllerMarcus Müller
8,1871031
8,1871031
$begingroup$
Fortunately, iron and steel bar stock is cheap. Brass/copper, less so, but I only need a short piece. I have a mechanism handy that will give ~4 inches of travel in a turn and a half; I may just have to wind up a coil and give this a try. With that permeability range, I may not even want/need the brass section of the slug. Sounds like time to hit the books and figure out how many turns I need...
$endgroup$
– Zeiss Ikon
May 13 at 11:13
1
$begingroup$
Simply build /calculate an air-core coil, and do a rough estimate of the permeability of the core you're planning to insert. Take that as the factor over the air-core inductivity! In such a coil system, the vast majority of the field energy will be contained within the high-permeability core, so that the surrounding material can be disregarded.
$endgroup$
– Marcus Müller
May 13 at 11:23
$begingroup$
(also, instead of brass, try with nylon/plastic in general – if you want a large range, go for the least permeable material as contrast to iron)
$endgroup$
– Marcus Müller
May 13 at 11:28
$begingroup$
Yep, the housing for this is thermoplastic (polyethylene, I think), roughly same permeability as air anyway. I've got a spool of magnet wire; time to visit the steel shapes section at the local big box store, or prowl around Metal Shorts for a cast iron slug. Then find my tap set.
$endgroup$
– Zeiss Ikon
May 13 at 11:34
$begingroup$
I'd be totally lazy: start with a bold/screw that you've got lying around.
$endgroup$
– Marcus Müller
May 13 at 11:40
|
show 1 more comment
$begingroup$
Fortunately, iron and steel bar stock is cheap. Brass/copper, less so, but I only need a short piece. I have a mechanism handy that will give ~4 inches of travel in a turn and a half; I may just have to wind up a coil and give this a try. With that permeability range, I may not even want/need the brass section of the slug. Sounds like time to hit the books and figure out how many turns I need...
$endgroup$
– Zeiss Ikon
May 13 at 11:13
1
$begingroup$
Simply build /calculate an air-core coil, and do a rough estimate of the permeability of the core you're planning to insert. Take that as the factor over the air-core inductivity! In such a coil system, the vast majority of the field energy will be contained within the high-permeability core, so that the surrounding material can be disregarded.
$endgroup$
– Marcus Müller
May 13 at 11:23
$begingroup$
(also, instead of brass, try with nylon/plastic in general – if you want a large range, go for the least permeable material as contrast to iron)
$endgroup$
– Marcus Müller
May 13 at 11:28
$begingroup$
Yep, the housing for this is thermoplastic (polyethylene, I think), roughly same permeability as air anyway. I've got a spool of magnet wire; time to visit the steel shapes section at the local big box store, or prowl around Metal Shorts for a cast iron slug. Then find my tap set.
$endgroup$
– Zeiss Ikon
May 13 at 11:34
$begingroup$
I'd be totally lazy: start with a bold/screw that you've got lying around.
$endgroup$
– Marcus Müller
May 13 at 11:40
$begingroup$
Fortunately, iron and steel bar stock is cheap. Brass/copper, less so, but I only need a short piece. I have a mechanism handy that will give ~4 inches of travel in a turn and a half; I may just have to wind up a coil and give this a try. With that permeability range, I may not even want/need the brass section of the slug. Sounds like time to hit the books and figure out how many turns I need...
$endgroup$
– Zeiss Ikon
May 13 at 11:13
$begingroup$
Fortunately, iron and steel bar stock is cheap. Brass/copper, less so, but I only need a short piece. I have a mechanism handy that will give ~4 inches of travel in a turn and a half; I may just have to wind up a coil and give this a try. With that permeability range, I may not even want/need the brass section of the slug. Sounds like time to hit the books and figure out how many turns I need...
$endgroup$
– Zeiss Ikon
May 13 at 11:13
1
1
$begingroup$
Simply build /calculate an air-core coil, and do a rough estimate of the permeability of the core you're planning to insert. Take that as the factor over the air-core inductivity! In such a coil system, the vast majority of the field energy will be contained within the high-permeability core, so that the surrounding material can be disregarded.
$endgroup$
– Marcus Müller
May 13 at 11:23
$begingroup$
Simply build /calculate an air-core coil, and do a rough estimate of the permeability of the core you're planning to insert. Take that as the factor over the air-core inductivity! In such a coil system, the vast majority of the field energy will be contained within the high-permeability core, so that the surrounding material can be disregarded.
$endgroup$
– Marcus Müller
May 13 at 11:23
$begingroup$
(also, instead of brass, try with nylon/plastic in general – if you want a large range, go for the least permeable material as contrast to iron)
$endgroup$
– Marcus Müller
May 13 at 11:28
$begingroup$
(also, instead of brass, try with nylon/plastic in general – if you want a large range, go for the least permeable material as contrast to iron)
$endgroup$
– Marcus Müller
May 13 at 11:28
$begingroup$
Yep, the housing for this is thermoplastic (polyethylene, I think), roughly same permeability as air anyway. I've got a spool of magnet wire; time to visit the steel shapes section at the local big box store, or prowl around Metal Shorts for a cast iron slug. Then find my tap set.
$endgroup$
– Zeiss Ikon
May 13 at 11:34
$begingroup$
Yep, the housing for this is thermoplastic (polyethylene, I think), roughly same permeability as air anyway. I've got a spool of magnet wire; time to visit the steel shapes section at the local big box store, or prowl around Metal Shorts for a cast iron slug. Then find my tap set.
$endgroup$
– Zeiss Ikon
May 13 at 11:34
$begingroup$
I'd be totally lazy: start with a bold/screw that you've got lying around.
$endgroup$
– Marcus Müller
May 13 at 11:40
$begingroup$
I'd be totally lazy: start with a bold/screw that you've got lying around.
$endgroup$
– Marcus Müller
May 13 at 11:40
|
show 1 more comment
$begingroup$
...variable caps are ... no longer manufactured in the old "interleaved plates, air spaced" form, and the tiny plastic dielectric ones that are still available can't take much voltage (and are difficult to adjust precisely).
Thankfully, Oren Elliott is a surprisingly affordable source of brand new air-variable capacitors. I have used them successfully in several projects.
answered May 13 at 1:24
Brian K1LIBrian K1LI
2,800417
$endgroup$
$begingroup$
Yipe! 50-65 dollars each in singles isn't "surprisingly affordable" -- at least to me!
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
In my experience, this has always been the going rate for such units. A kit manufacturer used to sell them for $75.
$endgroup$
– Brian K1LI
yesterday
$begingroup$
Maybe it's just another sign I'm getting old. I remember being able to buy a new radio with one of these in it (okay, likely the light, low-voltage version) for $20 or so.
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
Any case, seems like another good reason to come up with a homebuilt way to vary the inductance instead of being tied to a $60+ varicap for each antenna matcher...
$endgroup$
– Zeiss Ikon
yesterday
add a comment |
$begingroup$
...variable caps are ... no longer manufactured in the old "interleaved plates, air spaced" form, and the tiny plastic dielectric ones that are still available can't take much voltage (and are difficult to adjust precisely).
Thankfully, Oren Elliott is a surprisingly affordable source of brand new air-variable capacitors. I have used them successfully in several projects.
answered May 13 at 1:24
Brian K1LIBrian K1LI
2,800417
$endgroup$
$begingroup$
Yipe! 50-65 dollars each in singles isn't "surprisingly affordable" -- at least to me!
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
In my experience, this has always been the going rate for such units. A kit manufacturer used to sell them for $75.
$endgroup$
– Brian K1LI
yesterday
$begingroup$
Maybe it's just another sign I'm getting old. I remember being able to buy a new radio with one of these in it (okay, likely the light, low-voltage version) for $20 or so.
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
Any case, seems like another good reason to come up with a homebuilt way to vary the inductance instead of being tied to a $60+ varicap for each antenna matcher...
$endgroup$
– Zeiss Ikon
yesterday
add a comment |
$begingroup$
...variable caps are ... no longer manufactured in the old "interleaved plates, air spaced" form, and the tiny plastic dielectric ones that are still available can't take much voltage (and are difficult to adjust precisely).
Thankfully, Oren Elliott is a surprisingly affordable source of brand new air-variable capacitors. I have used them successfully in several projects.
answered May 13 at 1:24
Brian K1LIBrian K1LI
2,800417
$endgroup$
...variable caps are ... no longer manufactured in the old "interleaved plates, air spaced" form, and the tiny plastic dielectric ones that are still available can't take much voltage (and are difficult to adjust precisely).
Thankfully, Oren Elliott is a surprisingly affordable source of brand new air-variable capacitors. I have used them successfully in several projects.
answered May 13 at 1:24
Brian K1LIBrian K1LI
2,800417
answered May 13 at 1:24
Brian K1LIBrian K1LI
2,800417
answered May 13 at 1:24
Brian K1LIBrian K1LI
2,800417
answered May 13 at 1:24
Brian K1LIBrian K1LI
2,800417
2,800417
$begingroup$
Yipe! 50-65 dollars each in singles isn't "surprisingly affordable" -- at least to me!
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
In my experience, this has always been the going rate for such units. A kit manufacturer used to sell them for $75.
$endgroup$
– Brian K1LI
yesterday
$begingroup$
Maybe it's just another sign I'm getting old. I remember being able to buy a new radio with one of these in it (okay, likely the light, low-voltage version) for $20 or so.
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
Any case, seems like another good reason to come up with a homebuilt way to vary the inductance instead of being tied to a $60+ varicap for each antenna matcher...
$endgroup$
– Zeiss Ikon
yesterday
add a comment |
$begingroup$
Yipe! 50-65 dollars each in singles isn't "surprisingly affordable" -- at least to me!
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
In my experience, this has always been the going rate for such units. A kit manufacturer used to sell them for $75.
$endgroup$
– Brian K1LI
yesterday
$begingroup$
Maybe it's just another sign I'm getting old. I remember being able to buy a new radio with one of these in it (okay, likely the light, low-voltage version) for $20 or so.
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
Any case, seems like another good reason to come up with a homebuilt way to vary the inductance instead of being tied to a $60+ varicap for each antenna matcher...
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
Yipe! 50-65 dollars each in singles isn't "surprisingly affordable" -- at least to me!
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
Yipe! 50-65 dollars each in singles isn't "surprisingly affordable" -- at least to me!
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
In my experience, this has always been the going rate for such units. A kit manufacturer used to sell them for $75.
$endgroup$
– Brian K1LI
yesterday
$begingroup$
In my experience, this has always been the going rate for such units. A kit manufacturer used to sell them for $75.
$endgroup$
– Brian K1LI
yesterday
$begingroup$
Maybe it's just another sign I'm getting old. I remember being able to buy a new radio with one of these in it (okay, likely the light, low-voltage version) for $20 or so.
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
Maybe it's just another sign I'm getting old. I remember being able to buy a new radio with one of these in it (okay, likely the light, low-voltage version) for $20 or so.
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
Any case, seems like another good reason to come up with a homebuilt way to vary the inductance instead of being tied to a $60+ varicap for each antenna matcher...
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
Any case, seems like another good reason to come up with a homebuilt way to vary the inductance instead of being tied to a $60+ varicap for each antenna matcher...
$endgroup$
– Zeiss Ikon
yesterday
add a comment |
$begingroup$
Fair-Rite makes ferrite rods which would be suitable for HF applications. It should be possible to create or repurpose a screw-operated mechanism to move the rod into and out of a cylindrical coil.
Preferably, the material will have steady permeability and low loss over the frequency range of interest. Loss is proportional to the ratio of the real and imaginary components of permeability, $fracmu'mu''$.
The properties of Material 61 are probably best, because:
$mu'$ doesn't begin to drop off until past 30MHz
$mu''$ is relatively low and doesn't rise significantly until 20MHz
The relative permeability of a wound rod depends on the ratio of the rod's length to its diameter:
So you will have to make some preliminary calculations before deciding on turns count for rods using Material 61.
answered May 13 at 23:09
Brian K1LIBrian K1LI
2,800417
$endgroup$
add a comment |
$begingroup$
Fair-Rite makes ferrite rods which would be suitable for HF applications. It should be possible to create or repurpose a screw-operated mechanism to move the rod into and out of a cylindrical coil.
Preferably, the material will have steady permeability and low loss over the frequency range of interest. Loss is proportional to the ratio of the real and imaginary components of permeability, $fracmu'mu''$.
The properties of Material 61 are probably best, because:
$mu'$ doesn't begin to drop off until past 30MHz
$mu''$ is relatively low and doesn't rise significantly until 20MHz
The relative permeability of a wound rod depends on the ratio of the rod's length to its diameter:
So you will have to make some preliminary calculations before deciding on turns count for rods using Material 61.
answered May 13 at 23:09
Brian K1LIBrian K1LI
2,800417
$endgroup$
add a comment |
$begingroup$
Fair-Rite makes ferrite rods which would be suitable for HF applications. It should be possible to create or repurpose a screw-operated mechanism to move the rod into and out of a cylindrical coil.
Preferably, the material will have steady permeability and low loss over the frequency range of interest. Loss is proportional to the ratio of the real and imaginary components of permeability, $fracmu'mu''$.
The properties of Material 61 are probably best, because:
$mu'$ doesn't begin to drop off until past 30MHz
$mu''$ is relatively low and doesn't rise significantly until 20MHz
The relative permeability of a wound rod depends on the ratio of the rod's length to its diameter:
So you will have to make some preliminary calculations before deciding on turns count for rods using Material 61.
answered May 13 at 23:09
Brian K1LIBrian K1LI
2,800417
$endgroup$
Fair-Rite makes ferrite rods which would be suitable for HF applications. It should be possible to create or repurpose a screw-operated mechanism to move the rod into and out of a cylindrical coil.
Preferably, the material will have steady permeability and low loss over the frequency range of interest. Loss is proportional to the ratio of the real and imaginary components of permeability, $fracmu'mu''$.
The properties of Material 61 are probably best, because:
$mu'$ doesn't begin to drop off until past 30MHz
$mu''$ is relatively low and doesn't rise significantly until 20MHz
The relative permeability of a wound rod depends on the ratio of the rod's length to its diameter:
So you will have to make some preliminary calculations before deciding on turns count for rods using Material 61.
answered May 13 at 23:09
Brian K1LIBrian K1LI
2,800417
answered May 13 at 23:09
Brian K1LIBrian K1LI
2,800417
answered May 13 at 23:09
Brian K1LIBrian K1LI
2,800417
answered May 13 at 23:09
Brian K1LIBrian K1LI
2,800417
2,800417
add a comment |
add a comment |
$begingroup$
Variable caps are getting harder to find; they're no longer
manufactured in the old "interleaved plates, air spaced" form.
They are not hard to find. You can buy those if you know where to look. I have managed to find more than enough for my uses. You just have to look elsewhere than those selling new components.
I have quite a stock of them (and even rotary inductors!) that I purchased very inexpensively from hamfests.
Electronics and radio surplus companies often have them. And have you looked on eBay? I've seen some real bargains from time to time!
Some places that sell surplus radio parts are Surplus Sales of Nebraska, RF Parts, and Fair Radio Sales. And those are only a few of them.
In lieu of rotary (or ferrite-core) inductors, you could use a fixed air-wound coil with taps. One of the homebrew tuners at the base of my inverted-L uses that method (photos below); the other uses just two variable capacitors in an L-network (Omega match).
The red alligator clip shorts out the unused portion of this old Barker & Williamson Air Dux coil that I bought from eBay. If you can't find one, you can wind one yourself.
This is inside the tuner that I made to match my 160m inverted-L on 80 and 40 meters.
answered May 12 at 18:17
Mike Waters♦Mike Waters
4,0422635
$endgroup$
$begingroup$
@ZeissIkon Your comment wasMike, the point of this question is that air-spaced variable caps aren't as easy to find or as cheap as they used to be, and both tapped coil and fixed coil need them. – Zeiss Ikon May 13 at 14:26 deleted by Zeiss Ikon May 13 at 14:27
$endgroup$
– Mike Waters♦
6 hours ago
1
$begingroup$
Ah, now I remember. I asked question A ("slug tuning"), and you answered question B.("air variable caps availability").
$endgroup$
– Zeiss Ikon
5 hours ago
$begingroup$
I'm well aware of tapped coils to vary inductance (I mentioned them in the question). I was looking for an alternative to the "stepwise" change in inductance in order to avoid air variable caps.
$endgroup$
– Zeiss Ikon
5 hours ago
$begingroup$
@ZeissIkon Good luck with that, because the values of both the capacitors and the inductor interact. Adjust the inductor, and you'll almost certainly have to change the value of the capacitors.
$endgroup$
– Mike Waters♦
1 hour ago
add a comment |
$begingroup$
Variable caps are getting harder to find; they're no longer
manufactured in the old "interleaved plates, air spaced" form.
They are not hard to find. You can buy those if you know where to look. I have managed to find more than enough for my uses. You just have to look elsewhere than those selling new components.
I have quite a stock of them (and even rotary inductors!) that I purchased very inexpensively from hamfests.
Electronics and radio surplus companies often have them. And have you looked on eBay? I've seen some real bargains from time to time!
Some places that sell surplus radio parts are Surplus Sales of Nebraska, RF Parts, and Fair Radio Sales. And those are only a few of them.
In lieu of rotary (or ferrite-core) inductors, you could use a fixed air-wound coil with taps. One of the homebrew tuners at the base of my inverted-L uses that method (photos below); the other uses just two variable capacitors in an L-network (Omega match).
The red alligator clip shorts out the unused portion of this old Barker & Williamson Air Dux coil that I bought from eBay. If you can't find one, you can wind one yourself.
This is inside the tuner that I made to match my 160m inverted-L on 80 and 40 meters.
answered May 12 at 18:17
Mike Waters♦Mike Waters
4,0422635
$endgroup$
$begingroup$
@ZeissIkon Your comment wasMike, the point of this question is that air-spaced variable caps aren't as easy to find or as cheap as they used to be, and both tapped coil and fixed coil need them. – Zeiss Ikon May 13 at 14:26 deleted by Zeiss Ikon May 13 at 14:27
$endgroup$
– Mike Waters♦
6 hours ago
1
$begingroup$
Ah, now I remember. I asked question A ("slug tuning"), and you answered question B.("air variable caps availability").
$endgroup$
– Zeiss Ikon
5 hours ago
$begingroup$
I'm well aware of tapped coils to vary inductance (I mentioned them in the question). I was looking for an alternative to the "stepwise" change in inductance in order to avoid air variable caps.
$endgroup$
– Zeiss Ikon
5 hours ago
$begingroup$
@ZeissIkon Good luck with that, because the values of both the capacitors and the inductor interact. Adjust the inductor, and you'll almost certainly have to change the value of the capacitors.
$endgroup$
– Mike Waters♦
1 hour ago
add a comment |
$begingroup$
Variable caps are getting harder to find; they're no longer
manufactured in the old "interleaved plates, air spaced" form.
They are not hard to find. You can buy those if you know where to look. I have managed to find more than enough for my uses. You just have to look elsewhere than those selling new components.
I have quite a stock of them (and even rotary inductors!) that I purchased very inexpensively from hamfests.
Electronics and radio surplus companies often have them. And have you looked on eBay? I've seen some real bargains from time to time!
Some places that sell surplus radio parts are Surplus Sales of Nebraska, RF Parts, and Fair Radio Sales. And those are only a few of them.
In lieu of rotary (or ferrite-core) inductors, you could use a fixed air-wound coil with taps. One of the homebrew tuners at the base of my inverted-L uses that method (photos below); the other uses just two variable capacitors in an L-network (Omega match).
The red alligator clip shorts out the unused portion of this old Barker & Williamson Air Dux coil that I bought from eBay. If you can't find one, you can wind one yourself.
This is inside the tuner that I made to match my 160m inverted-L on 80 and 40 meters.
answered May 12 at 18:17
Mike Waters♦Mike Waters
4,0422635
$endgroup$
Variable caps are getting harder to find; they're no longer
manufactured in the old "interleaved plates, air spaced" form.
They are not hard to find. You can buy those if you know where to look. I have managed to find more than enough for my uses. You just have to look elsewhere than those selling new components.
I have quite a stock of them (and even rotary inductors!) that I purchased very inexpensively from hamfests.
Electronics and radio surplus companies often have them. And have you looked on eBay? I've seen some real bargains from time to time!
Some places that sell surplus radio parts are Surplus Sales of Nebraska, RF Parts, and Fair Radio Sales. And those are only a few of them.
In lieu of rotary (or ferrite-core) inductors, you could use a fixed air-wound coil with taps. One of the homebrew tuners at the base of my inverted-L uses that method (photos below); the other uses just two variable capacitors in an L-network (Omega match).
The red alligator clip shorts out the unused portion of this old Barker & Williamson Air Dux coil that I bought from eBay. If you can't find one, you can wind one yourself.
This is inside the tuner that I made to match my 160m inverted-L on 80 and 40 meters.
answered May 12 at 18:17
Mike Waters♦Mike Waters
4,0422635
edited 5 hours ago
answered May 12 at 18:17
Mike Waters♦Mike Waters
4,0422635
answered May 12 at 18:17
Mike Waters♦Mike Waters
4,0422635
answered May 12 at 18:17
Mike Waters♦Mike Waters
4,0422635
4,0422635
$begingroup$
@ZeissIkon Your comment wasMike, the point of this question is that air-spaced variable caps aren't as easy to find or as cheap as they used to be, and both tapped coil and fixed coil need them. – Zeiss Ikon May 13 at 14:26 deleted by Zeiss Ikon May 13 at 14:27
$endgroup$
– Mike Waters♦
6 hours ago
1
$begingroup$
Ah, now I remember. I asked question A ("slug tuning"), and you answered question B.("air variable caps availability").
$endgroup$
– Zeiss Ikon
5 hours ago
$begingroup$
I'm well aware of tapped coils to vary inductance (I mentioned them in the question). I was looking for an alternative to the "stepwise" change in inductance in order to avoid air variable caps.
$endgroup$
– Zeiss Ikon
5 hours ago
$begingroup$
@ZeissIkon Good luck with that, because the values of both the capacitors and the inductor interact. Adjust the inductor, and you'll almost certainly have to change the value of the capacitors.
$endgroup$
– Mike Waters♦
1 hour ago
add a comment |
$begingroup$
@ZeissIkon Your comment wasMike, the point of this question is that air-spaced variable caps aren't as easy to find or as cheap as they used to be, and both tapped coil and fixed coil need them. – Zeiss Ikon May 13 at 14:26 deleted by Zeiss Ikon May 13 at 14:27
$endgroup$
– Mike Waters♦
6 hours ago
1
$begingroup$
Ah, now I remember. I asked question A ("slug tuning"), and you answered question B.("air variable caps availability").
$endgroup$
– Zeiss Ikon
5 hours ago
$begingroup$
I'm well aware of tapped coils to vary inductance (I mentioned them in the question). I was looking for an alternative to the "stepwise" change in inductance in order to avoid air variable caps.
$endgroup$
– Zeiss Ikon
5 hours ago
$begingroup$
@ZeissIkon Good luck with that, because the values of both the capacitors and the inductor interact. Adjust the inductor, and you'll almost certainly have to change the value of the capacitors.
$endgroup$
– Mike Waters♦
1 hour ago
$begingroup$
@ZeissIkon Your comment was
Mike, the point of this question is that air-spaced variable caps aren't as easy to find or as cheap as they used to be, and both tapped coil and fixed coil need them. – Zeiss Ikon May 13 at 14:26 deleted by Zeiss Ikon May 13 at 14:27$endgroup$
– Mike Waters♦
6 hours ago
$begingroup$
@ZeissIkon Your comment was
Mike, the point of this question is that air-spaced variable caps aren't as easy to find or as cheap as they used to be, and both tapped coil and fixed coil need them. – Zeiss Ikon May 13 at 14:26 deleted by Zeiss Ikon May 13 at 14:27$endgroup$
– Mike Waters♦
6 hours ago
1
1
$begingroup$
Ah, now I remember. I asked question A ("slug tuning"), and you answered question B.("air variable caps availability").
$endgroup$
– Zeiss Ikon
5 hours ago
$begingroup$
Ah, now I remember. I asked question A ("slug tuning"), and you answered question B.("air variable caps availability").
$endgroup$
– Zeiss Ikon
5 hours ago
$begingroup$
I'm well aware of tapped coils to vary inductance (I mentioned them in the question). I was looking for an alternative to the "stepwise" change in inductance in order to avoid air variable caps.
$endgroup$
– Zeiss Ikon
5 hours ago
$begingroup$
I'm well aware of tapped coils to vary inductance (I mentioned them in the question). I was looking for an alternative to the "stepwise" change in inductance in order to avoid air variable caps.
$endgroup$
– Zeiss Ikon
5 hours ago
$begingroup$
@ZeissIkon Good luck with that, because the values of both the capacitors and the inductor interact. Adjust the inductor, and you'll almost certainly have to change the value of the capacitors.
$endgroup$
– Mike Waters♦
1 hour ago
$begingroup$
@ZeissIkon Good luck with that, because the values of both the capacitors and the inductor interact. Adjust the inductor, and you'll almost certainly have to change the value of the capacitors.
$endgroup$
– Mike Waters♦
1 hour ago
add a comment |
$begingroup$
For a variable inductor you can make two coils with a fairly large diameters. One diameter a bit larger than the other. Place the smaller one inside the larger one.
If you make the length of the inner coil fairly small you can rotate it so the coils will have the same or the opposite winding direction. This way you can get a large
tuning range for the inductance. Obviously, if you design for a very small minimum capacitance, Q will be poor since the series R will be much larger compared to a normal coil. Get inspiration from here:
http://axotron.eu/photo/2013/2013-08-18_Rundradiomuseet/slides/DSC_1812.html
This one is to tune a 150 kW transmitter. Something similar, but much smaller....
answered 2 days ago
sm5bszsm5bsz
54113
$endgroup$
$begingroup$
This is a variable coupling air-core transformer; they're used as ticklers for regenerative receivers, and as antenna couplers (especially for crystal radios), but I don't recall reading that this changes the induction of either coil -- just how well energy passes from one to the other.
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
@ZeissIkon Trust me, Leif SM5BSZ knows what he's talking about. :-) You're getting some great advice on hamSE; but respectfully, you don't know that yet. ;-)
$endgroup$
– Mike Waters♦
1 hour ago
add a comment |
$begingroup$
For a variable inductor you can make two coils with a fairly large diameters. One diameter a bit larger than the other. Place the smaller one inside the larger one.
If you make the length of the inner coil fairly small you can rotate it so the coils will have the same or the opposite winding direction. This way you can get a large
tuning range for the inductance. Obviously, if you design for a very small minimum capacitance, Q will be poor since the series R will be much larger compared to a normal coil. Get inspiration from here:
http://axotron.eu/photo/2013/2013-08-18_Rundradiomuseet/slides/DSC_1812.html
This one is to tune a 150 kW transmitter. Something similar, but much smaller....
answered 2 days ago
sm5bszsm5bsz
54113
$endgroup$
$begingroup$
This is a variable coupling air-core transformer; they're used as ticklers for regenerative receivers, and as antenna couplers (especially for crystal radios), but I don't recall reading that this changes the induction of either coil -- just how well energy passes from one to the other.
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
@ZeissIkon Trust me, Leif SM5BSZ knows what he's talking about. :-) You're getting some great advice on hamSE; but respectfully, you don't know that yet. ;-)
$endgroup$
– Mike Waters♦
1 hour ago
add a comment |
$begingroup$
For a variable inductor you can make two coils with a fairly large diameters. One diameter a bit larger than the other. Place the smaller one inside the larger one.
If you make the length of the inner coil fairly small you can rotate it so the coils will have the same or the opposite winding direction. This way you can get a large
tuning range for the inductance. Obviously, if you design for a very small minimum capacitance, Q will be poor since the series R will be much larger compared to a normal coil. Get inspiration from here:
http://axotron.eu/photo/2013/2013-08-18_Rundradiomuseet/slides/DSC_1812.html
This one is to tune a 150 kW transmitter. Something similar, but much smaller....
answered 2 days ago
sm5bszsm5bsz
54113
$endgroup$
For a variable inductor you can make two coils with a fairly large diameters. One diameter a bit larger than the other. Place the smaller one inside the larger one.
If you make the length of the inner coil fairly small you can rotate it so the coils will have the same or the opposite winding direction. This way you can get a large
tuning range for the inductance. Obviously, if you design for a very small minimum capacitance, Q will be poor since the series R will be much larger compared to a normal coil. Get inspiration from here:
http://axotron.eu/photo/2013/2013-08-18_Rundradiomuseet/slides/DSC_1812.html
This one is to tune a 150 kW transmitter. Something similar, but much smaller....
answered 2 days ago
sm5bszsm5bsz
54113
answered 2 days ago
sm5bszsm5bsz
54113
answered 2 days ago
sm5bszsm5bsz
54113
answered 2 days ago
sm5bszsm5bsz
54113
54113
$begingroup$
This is a variable coupling air-core transformer; they're used as ticklers for regenerative receivers, and as antenna couplers (especially for crystal radios), but I don't recall reading that this changes the induction of either coil -- just how well energy passes from one to the other.
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
@ZeissIkon Trust me, Leif SM5BSZ knows what he's talking about. :-) You're getting some great advice on hamSE; but respectfully, you don't know that yet. ;-)
$endgroup$
– Mike Waters♦
1 hour ago
add a comment |
$begingroup$
This is a variable coupling air-core transformer; they're used as ticklers for regenerative receivers, and as antenna couplers (especially for crystal radios), but I don't recall reading that this changes the induction of either coil -- just how well energy passes from one to the other.
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
@ZeissIkon Trust me, Leif SM5BSZ knows what he's talking about. :-) You're getting some great advice on hamSE; but respectfully, you don't know that yet. ;-)
$endgroup$
– Mike Waters♦
1 hour ago
$begingroup$
This is a variable coupling air-core transformer; they're used as ticklers for regenerative receivers, and as antenna couplers (especially for crystal radios), but I don't recall reading that this changes the induction of either coil -- just how well energy passes from one to the other.
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
This is a variable coupling air-core transformer; they're used as ticklers for regenerative receivers, and as antenna couplers (especially for crystal radios), but I don't recall reading that this changes the induction of either coil -- just how well energy passes from one to the other.
$endgroup$
– Zeiss Ikon
yesterday
$begingroup$
@ZeissIkon Trust me, Leif SM5BSZ knows what he's talking about. :-) You're getting some great advice on hamSE; but respectfully, you don't know that yet. ;-)
$endgroup$
– Mike Waters♦
1 hour ago
$begingroup$
@ZeissIkon Trust me, Leif SM5BSZ knows what he's talking about. :-) You're getting some great advice on hamSE; but respectfully, you don't know that yet. ;-)
$endgroup$
– Mike Waters♦
1 hour ago
add a comment |
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$begingroup$
um, "tiny plastic dielectric ones that are still available can't take much voltage" that's not actually true, see this commercially available list of >=1kV-rated variable capacitors
$endgroup$
– Marcus Müller
May 12 at 17:22
$begingroup$
@MarcusMüller I looked at that DigiKey link, and they are all trimmer capacitors, not exactly convenient to use in an HF antenna tuner. Not to mention that the ones that have a wide enough capacitance range for use in an HF tuner are $200 to well over $300.
$endgroup$
– Mike Waters♦
May 12 at 18:05
2
$begingroup$
fair point! I tend to forget that the goal wouldn't be achieving an acceptable matching for the whole band (so, you'd use a trimmer for each band of interest and trim that once), but an exact matching for the frequency of interest. My bad!
$endgroup$
– Marcus Müller
May 12 at 19:10