A quest for a QRP sized Differential T matching unit


Jim, N5IB
 

With the weekend's experiments showing a continuously variable inductance is reasonably possible, it's now time to see how to make the differential capacitor.
Photo attached of a first "proof of concept" effort.
Geared together, the two air variables turn in opposite directions, so when one is at max, the other is at min, and vice-versa.
The smaller gear that drives the pair has half the teeth, so a full turn of the "knob" results in 180 degrees at the caps.

Quite a bit of mechanical details to work out - not my strongest suit - but it looks like the thing can be done, and fit in a box certainly not larger than a Bayou Jumper.

BTW - I did locate the article that shows a variable inductor made with a moving iron powder core:
Discussed in Hayward's Solid State Design p166, referencing a Feb 1976 QST article by K1KLO

Jim, N5IB


Jim Sheldon
 

Nice Jim. Great job on the gears.

On Jul 27, 2021, at 6:34 PM, Jim, N5IB <n5ib@juno.com> wrote:

With the weekend's experiments showing a continuously variable inductance is reasonably possible, it's now time to see how to make the differential capacitor.
Photo attached of a first "proof of concept" effort.
Geared together, the two air variables turn in opposite directions, so when one is at max, the other is at min, and vice-versa.
The smaller gear that drives the pair has half the teeth, so a full turn of the "knob" results in 180 degrees at the caps.

Quite a bit of mechanical details to work out - not my strongest suit - but it looks like the thing can be done, and fit in a box certainly not larger than a Bayou Jumper.

BTW - I did locate the article that shows a variable inductor made with a moving iron powder core:
Discussed in Hayward's Solid State Design p166, referencing a Feb 1976 QST article by K1KLO

Jim, N5IB





<Capacitors and Gear Train.jpg>


Johnny AC0BQ
 

Ge Jim
Another piece of art!
Good job on the gears.
72
Johnny ACØBQ 

On Tue, Jul 27, 2021 at 6:38 PM Jim Sheldon <w0eb@...> wrote:
Nice Jim.  Great job on the gears.
> On Jul 27, 2021, at 6:34 PM, Jim, N5IB <n5ib@...> wrote:
>
> With the weekend's experiments showing a continuously variable inductance is reasonably possible, it's now time to see how to make the differential capacitor.
> Photo attached of a first "proof of concept" effort.
> Geared together, the two air variables turn in opposite directions, so when one is at max, the other is at min, and vice-versa.
> The smaller gear that drives the pair has half the teeth, so a full turn of the "knob" results in 180 degrees at the caps.
>
> Quite a bit of mechanical details to work out - not my strongest suit -  but it looks like the thing can be done, and fit in a box certainly not larger than a Bayou Jumper.
>
> BTW - I did locate the article that shows a variable inductor made with a moving iron powder core:
> Discussed in Hayward's Solid State Design p166, referencing a Feb 1976 QST article by K1KLO
>
> Jim, N5IB
>
>
>
>
>
> <Capacitors and Gear Train.jpg>






--
Check out the 4SQRP website at 4sqrp.com


W6BOW
 

Dear Johnny and All,

I've been enjoying this FB discussion.

Attached find info on Antenna-Matching Devices from the 1986 ARRL publication, "QRP Notebook" By Doug DeMaw, W1F

73

W6BOW (Don)
San Francisco



-----Original Message-----
From: Johnny AC0BQ <jomatlock@...>
To: main@4sqrp.groups.io
Sent: Tue, Jul 27, 2021 6:55 pm
Subject: Re: [4SQRP] A quest for a QRP sized Differential T matching unit

Ge Jim
Another piece of art!
Good job on the gears.
72
Johnny ACØBQ 

On Tue, Jul 27, 2021 at 6:38 PM Jim Sheldon <w0eb@...> wrote:
Nice Jim.  Great job on the gears.
> On Jul 27, 2021, at 6:34 PM, Jim, N5IB <n5ib@...> wrote:
>
> With the weekend's experiments showing a continuously variable inductance is reasonably possible, it's now time to see how to make the differential capacitor.
> Photo attached of a first "proof of concept" effort.
> Geared together, the two air variables turn in opposite directions, so when one is at max, the other is at min, and vice-versa.
> The smaller gear that drives the pair has half the teeth, so a full turn of the "knob" results in 180 degrees at the caps.
>
> Quite a bit of mechanical details to work out - not my strongest suit -  but it looks like the thing can be done, and fit in a box certainly not larger than a Bayou Jumper.
>
> BTW - I did locate the article that shows a variable inductor made with a moving iron powder core:
> Discussed in Hayward's Solid State Design p166, referencing a Feb 1976 QST article by K1KLO
>
> Jim, N5IB
>
>
>
>
>
> <Capacitors and Gear Train.jpg>






--
Check out the 4SQRP website at 4sqrp.com