I recall an article in QST or "73", I think the title was,
"For the L of it"
I'm looking for the magazine it was in and the date it was printed.
The article described a series LC, a fixed L and a air variable C.
The impedance of the L was bigger than the impedance of the C,
and by adjusting the C you caused the inductance to vary.
So in effect you have a variable inductor.
Thanks, Mikek

On Jan 20, 5:32*pm, "amdx" wrote:
* I recall an article in QST or "73", I think the title was,
* "For the L of it"
* I'm looking for the magazine it was in and the date it was printed.
*The article described *a series LC, a fixed L and a air variable C.
The impedance of *the L was bigger than the impedance of the C,
and by adjusting the C you caused the inductance to vary.
So in effect you have a variable inductor.
* * * * * * Thanks, * *Mikek

Or two caps in series connected paralell to an inductor. Input or
output at the juction of the caps. This concept of the circuit may be
more easily found in various reference manuals. You may find these
caps labeled TUNE and LOAD in some circuits.


Jimmie

Jimmie

On Jan 20, 3:32*pm, "amdx" wrote:
* I recall an article in QST or "73", I think the title was,
* "For the L of it"
* I'm looking for the magazine it was in and the date it was printed.
*The article described *a series LC, a fixed L and a air variable C.
The impedance of *the L was bigger than the impedance of the C,
and by adjusting the C you caused the inductance to vary.
So in effect you have a variable inductor.
* * * * * * Thanks, * *Mikek

I recall the article and have it around somewhere. The problem with
this (if you want to call it a problem) is it only works for a small
range of frequencies.

For instance, at 10 MHZ a series 1.6uH L and 318 pF C looks like a .
8uH inductor (good). But at 5.76 MHZ the combination looks like 30
ohm Xc capacitor. At 7.0 MHZ it looks like a short because of series
resonance.

I would not want to replace the roller inductor on my 80-10 antenna
tuner with this, but there are other applications (single frequency)
where it should work just fine.

Gary N4AST

On Thu, 20 Jan 2011 15:32:34 -0600, amdx wrote:

I recall an article in QST or "73", I think the title was,
"For the L of it"
I'm looking for the magazine it was in and the date it was printed.
The article described a series LC, a fixed L and a air variable C.
The impedance of the L was bigger than the impedance of the C,
and by adjusting the C you caused the inductance to vary.
So in effect you have a variable inductor.
Thanks, Mikek

73 magazine March 1980 page 40. I have the magazine and I have a scanner.
If you want a copy let me know.
73 de VE3JUA

"Eskay" wrote in message
...
On Thu, 20 Jan 2011 15:32:34 -0600, amdx wrote:

I recall an article in QST or "73", I think the title was,
"For the L of it"
I'm looking for the magazine it was in and the date it was printed.
The article described a series LC, a fixed L and a air variable C.
The impedance of the L was bigger than the impedance of the C,
and by adjusting the C you caused the inductance to vary.
So in effect you have a variable inductor.
Thanks, Mikek

73 magazine March 1980 page 40. I have the magazine and I have a scanner.
If you want a copy let me know.
73 de VE3JUA

Thank you VE,
I do want a scan.
Email to,

Remove NONO.
Thank you very much, Mikek

On Fri, 21 Jan 2011 11:34:39 -0600, amdx wrote:

"Eskay" wrote in message
...
On Thu, 20 Jan 2011 15:32:34 -0600, amdx wrote:

I recall an article in QST or "73", I think the title was,
"For the L of it"
I'm looking for the magazine it was in and the date it was printed.
The article described a series LC, a fixed L and a air variable C.
The impedance of the L was bigger than the impedance of the C,
and by adjusting the C you caused the inductance to vary.
So in effect you have a variable inductor.
Thanks, Mikek

73 magazine March 1980 page 40. I have the magazine and I have a scanner.
If you want a copy let me know.
73 de VE3JUA

Thank you VE,
I do want a scan.
Email to,

Remove NONO.
Thank you very much, Mikek

Coming soon. Sieb.

"Eskay" wrote in message
...
On Fri, 21 Jan 2011 11:34:39 -0600, amdx wrote:

"Eskay" wrote in message
...
On Thu, 20 Jan 2011 15:32:34 -0600, amdx wrote:

I recall an article in QST or "73", I think the title was,
"For the L of it"
I'm looking for the magazine it was in and the date it was printed.
The article described a series LC, a fixed L and a air variable C.
The impedance of the L was bigger than the impedance of the C,
and by adjusting the C you caused the inductance to vary.
So in effect you have a variable inductor.
Thanks, Mikek

73 magazine March 1980 page 40. I have the magazine and I have a
scanner.
If you want a copy let me know.
73 de VE3JUA

Thank you VE,
I do want a scan.
Email to,

Remove NONO.
Thank you very much, Mikek

Coming soon. Sieb.

I got them, look good.
Thank you, Mikek

On Jan 20, 5:47 pm, Gary wrote:

The article described a series LC, a fixed L and a air variable C.
The impedance of the L was bigger than the impedance of the C,
and by adjusting the C you caused the inductance to vary.
So in effect you have a variable inductor.

I recall the article and have it around somewhere. The problem with
this (if you want to call it a problem) is it only works for a small
range of frequencies.

They do the reverse of this in AM broadcast antenna matching
networks (doghouses) where the object is NOT to have a variable
capacitor. A fixed, high-reactance capacitor is placed in series
with a 'tappable' inductor and the capacitor is 'tuned' by adjusting
the tap on the inductor. Again, works well at one frequency,
but not over an octave bandwidth.... K7JEB

On Jan 27, 9:42*pm, K7JEB wrote:
On Jan 20, 5:47 pm, Gary wrote:

*The article described *a series LC, a fixed L and a air variable C.
The impedance of *the L was bigger than the impedance of the C,
and by adjusting the C you caused the inductance to vary.
So in effect you have a variable inductor.
I recall the article and have it around somewhere. *The problem with
this (if you want to call it a problem) is it only works for a small
range of frequencies.

They do the reverse of this in AM broadcast antenna matching
networks (doghouses) where the object is NOT to have a variable
capacitor. *A fixed, high-reactance capacitor is placed in series
with a 'tappable' inductor and the capacitor is 'tuned' by adjusting
the tap on the inductor. *Again, works well at one frequency,
but not over an octave bandwidth.... K7JEB

The OP's arrangement works well for impedance matching and is suitable
for tuning a circuit to resonance. I dont believe the circuit he
described would be much different from the resonant circuit in a
Colpitts osc.

Jimmie