Hello,
First a few assumptions:
(1) The 2 x 1625's are in push-pull and operate in "class C"
(2) The capacitance values quoted are across the whole plate coils
Center linked coils of the B&W JVL variety were originally intended for
balanced transmission lines with an impedance
of a "few" hundred ohms, but will work connected to coaxial lines.
As the coupling is variable, it only takes to first swing the link all the way
out of the
plate coils, dip the plate, then carefully meshing the link more and more with
the coil and
readjusting the plate tuning until the rated plate current flows and/or the RF
output goes through
a maximum. In order not to damage the 1625's, it is advisable to keep the
key-down periods short (< 5 s or so)
until proper resonance and loading has been found.
RF output could be monitored with an SWR meter, or to be really traditional,
with a thermocouple ammeter or a
flashlight bulb connected across a short piece of the centre conductor of the
coaxial line.
Adjusting a transmitter in this fashion has almost become a lost art since the
introduction of the pi-network,
and as usual, the precautions of keeping the fingers away from exposed plate
voltage apply.
73/
Karl-Arne
SM0AOM
----- Original Message -----
From: <StephenTetorka@cs.com>
To: <amps@contesting.com>
Sent: Monday, September 05, 2005 5:18 PM
Subject: [Amps] Xmtr output impedance?
> Hi all:
>
> I'm attempting to determine the 'output impedance' of my 1948 homebrew
> transmitter so I can obtain maximum efficiency power output to my antenna.
>
> The RF deck is two 1625's having a B&W model JVL coil link output coupling to
> the antenna posts.
>
> Per my studies, the 80 meter coil requires 46pf for resonance; the 20 meter
> coil needs 21pf.
> Therefore, I get Xc = Xl as 990 for 80 and 540 for 20.
>
> This data and $1.50 can get me a mug of beer at my watering hole.
>
> Might someone be able to help me better understand what transmission line I
> need?
>
> Thanks,
> Steve
> WA2TAK
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