[TMC] PMO/VOX etc
Roy Morgan
k1lky at earthlink.net
Fri Oct 9 12:37:18 EDT 2009
On Oct 9, 2009, at 10:44 AM, Telegrapher at att.net wrote:
> ... All that is required is an RF source of modulated power, AM,
> CW,SSB etc at around 2W or less to drive the Amps you have been
> talking about...
>
> I recently picked up a radio that will allow me to run anything
> from .5 watts upward to 100 and will be using that to run my PAL-500
Larry and others,
We did not hear what radio Larry has, but with the old tube type
radios that can be throttled way back, there is something to look out
for. The problem is that when the transmitter or transceiver is set
at a very low power, the spurious signals become larger with respect
to the desired signal. They produce much cleaner signals at moderate
(or perhaps higher) output levels.
So you need an attenuator that will work at 100 watts or so and puts
out 100 to 200 mw. Bird makes/made these but they are few and far
between, and they cost a bunch even at hamfests. The Vishay company,
I believe, made small solid state type attenuators that can handle 50
or a hundred watts when mounted on a heatsink. I think they are still
available (put it on a heat sink with two connectors and it could not
be simpler), but I don't know the source(s).
As I understand it, most TMC transmitters and linears will run to full
power with a hundred milliwatts of signal or thereabouts. (Do not be
fooled when you find a 6146 or 2E26 as the "final" in their exciters
and oscillators - they were chosen for high linearity in class A
service at very modest power levels.)
One more point on the TMC SBE: If I remember correctly, and without
checking the manual, I seem to remember that the SBE needs an input
frequency (or internal oven crystal) that is offset from the desired
output frequency by something like 200 kc. This is because the mixing
scheme involves generating the SSB or other sideband signals at 200 kc
or so and mixing that with the internally generated carrier. (It will
do two separate sidebands with independent information by being fed
audio signals.)
I found that "getting my head around" the functions of the SBE was an
activity that needed concentration and some study of the manual.
Roy
Roy Morgan
k1lky at earthlink.net
529 Cobb St.
Groton NY, 13073
Home: 607-898-3607
Cell: 301-928-7794
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