On 07/11/2013 09:38 AM, Michael Black wrote:
On Tue, 2 Jul 2013, dave wrote:


You forgot to turn on the BFO. BFO level is frequently too low for
demodding SSB hence the need to reduce RF gain.

No I didn't. It should be a given that you need the BFO. I was making
the point that it's one of those radios of the time that didn't have a
product detector, so you had to do what all the books said to do. A few
years later, most receivers did have product detectors. Indeed, the
GPR-90 came along right at the cusp, so you could get an external unit
that added a product detector (and I think some extra selectivity) and
some really fine tuning. The receiver has the an IF output jack on the
back, even has a jack for feeding audio back into the receiver (though
the TMC adapter had a built in audio amplifier). Other receivers had
similar units. The R388 and the R390 didn't have product detectors,
though they are considered some of the best receivers from the time (and
perhaps for all time).

But with that level of receiver, turning down RF gain wasn't a real
issue. I had no problem receiving SSB, even on six meters, on the SP-600
I had forty years ago.

ON the other hand, that Hallicrafters S-120A (the transistorized model)
that I got in the summer of 1971 had a horribly weak BFO, so by the time
I'd attenuated the incoming signal (a pot between the antenna and the
receiver), there weren't many signals left strong enough to receive.


I've had a couple R-390As. I used to leave them on 11175 upper with RF
gain low, carrier sliced off with 2 or 4 KC mechanical filter by
slightly tuning off center, BFO on about 1200 cycles. It was dead quiet
unless someone spoke, like dolby FM. It would stay perfectly tuned for
days, with the ovens off.

I can't afford electricity to waste on old radios.