My first TRX in 1963 was a Wireless Set No.19 MkIII equipped with the 807 in
the final.
That radio also used a variometer as an ATU, it was a very quick and
reliable means of coupling random wires or verticals to the rig from 2-8MHz.
I used 20 and 40m long wires on 40 and 80m then.
73
Peter
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Peter Chadwick
>Tom said:
>They are sometimes called variometers.
They have terrible Q at minimum inductance, especially at higher
frequencies. Of all the common methods, this is the least efficient way to
vary inductance over a wide range.< Strictly, a variometer is where the two
coils are in series, and the inductance can be adjusted from L1 + L2 + 2M to
L1 + L2 - 2M, where M is the mutual inductance. They do give a wide
inductance range, but as Tom says, the low Q at minimum inductance is a
problem. Historically, they were used a lot in long wave tx's, especially in
the marine band at 410 - 516 kHz, as well as in early (pre 1930) broadcast
radios. The roller coaster type of variable inductor gets a bit impractical
when you want a 500 or 1000 microhenry inductance change............ There
was a German WW2 military radio that used iron cored ones in the antenna
tuning, and I believe that with the core removed, they were popular with
German amateurs in the 1950's because the construction was such that they
were very stable when used in VFOs. The Collins ART13 airborne tx of WW2
used one in the output pi network as well.
For variable coupling between tuned circuits, a lot would depend on the
actual inductance value as to how useful such a device would be on any
particular band.
73
Peter G3RZP
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|