Jozef wrote in message
...
I have recently built a very large pi-network transmatch with two very big
homemade variable capacitors. They can be seen at:
http://www.metaphoria.us/hamradio/transmatch.html

Jozef
WB2MIC

Very nicely done...

I toyed with the idea of designing a couple of flat dies to punch out the
stator and rotor plates and market my own series of capacitors. I agree,
the high price of those capacitors are unwarranted.

There was no need for two variables in that tuner... a single DIFFERENTIAL
capacitor would do nicely and eliminate the extra adjustment during tune-up.
For some unknown reason Hams still need a tuner with two capacitors---it was
nice to see MFJ offer the Differential-T tuner Model 986.

Many years ago (before the MFJ 986 tuner) as an experiment I built a field
expedient tuner using a differential capacitor made from two telescoping
cardboard tubes and aluminum foil (two plates outer and one plate inner
tube) and slid the inner tube in and out to acheive an antenna match with a
28 microhenry tapped coil. It worked fine at 100 watts and many contacts
were made with the end fed wire but dilectric heating of the cardboard tubes
was observed.

RG

RadioGuy wrote:
Jozef wrote in message
...

I have recently built a very large pi-network transmatch with two very big
homemade variable capacitors. They can be seen at:
http://www.metaphoria.us/hamradio/transmatch.html

Jozef
WB2MIC


Very nicely done...

I toyed with the idea of designing a couple of flat dies to punch out the
stator and rotor plates and market my own series of capacitors. I agree,
the high price of those capacitors are unwarranted.

There was no need for two variables in that tuner... a single DIFFERENTIAL
capacitor would do nicely and eliminate the extra adjustment during tune-up.
For some unknown reason Hams still need a tuner with two capacitors---it was
nice to see MFJ offer the Differential-T tuner Model 986.

Many years ago (before the MFJ 986 tuner) as an experiment I built a field
expedient tuner using a differential capacitor made from two telescoping
cardboard tubes and aluminum foil (two plates outer and one plate inner
tube) and slid the inner tube in and out to acheive an antenna match with a
28 microhenry tapped coil. It worked fine at 100 watts and many contacts
were made with the end fed wire but dilectric heating of the cardboard tubes
was observed.

RG


RG, is there an example of a differential capacitor I could look at?
I'm not sure I've ever seen one? Is there a Tuner project somewhere
using one I could look at (grin)...

Regards, Mike

In a differential capacitor, as the rotor disengages from one
set of fixed plates, it engages with the other set, instead of
engaging with fresh air.

The two sets of fixed plates are adjacent to each other and
separated by a gap. (If it were not for the gap, there would
be a solid square of metal with the axle dead centre)

"Mike, K8LH" wrote in message
...

RG, is there an example of a differential capacitor I could look at? I'm
not sure I've ever seen one? Is there a Tuner project somewhere using one
I could look at (grin)...

Polymath wrote:
In a differential capacitor, as the rotor disengages from one
set of fixed plates, it engages with the other set, instead of
engaging with fresh air.

The two sets of fixed plates are adjacent to each other and
separated by a gap. (If it were not for the gap, there would
be a solid square of metal with the axle dead centre)

"Mike, K8LH" wrote in message
...

RG, is there an example of a differential capacitor I could look at? I'm
not sure I've ever seen one? Is there a Tuner project somewhere using one
I could look at (grin)...



Thank you... I have seen variable capacitors like this...

Vy 73, Mike - K8LH

"Jozef" wrote:

: http://www.metaphoria.us/hamradio/transmatch.html


excellent demonstration for others to learn from.