On Sat, 13 Sep 2014, Lostgallifreyan wrote:

Michael Black wrote in
news:alpine.LNX.2.02.1407261848390.22322@darkstar. example.org:

Of course, they can't handle CW or SSB.


I found a circuit online that puts a local IF oscillation inductively
into a radio to allow some sort of USB mode tuning. I might try makign
one to feed into the ring connector of the PL-390 I modifed with a
100-turn coil. It does wonders with a longwire, and hopefully a magnetic
loop soon as well. If feeding it with this IF frquency method will allow
SSB that small modification would be an extremely good thing to do with
a PL-390 and likely other radios that use this IC. On the other hand if
the DSP means the same IF frequency method of analog systems is not used
at all, then I guess the AM to SSB trick isn't going to work at all...

I forget the block diagram, I recall the receiver converts to a low IF and
then hits the DSP. The problem is, is there an easy way to get a BFO
signal into that thing, when it's mostly one IC? ANd if it's a low IF
(traditionally the IF was 455KHz and I think this receiver has a lower
IF), any harmonics of the BFO that get into the antenna will be that more
frequent.

Also, doing it this way will be inferior to using a DSP to detect the SSB
signal. It has all the disadvantages of feeding a BFO through the IF
chain of any old receiver.

In the old days, one scheme for adapting old receivers for SSB was to use
a local signal generator of some kind on the signal frequency, coupling it
into the antenna input of the receiver. There, it only needed a weak
signal (while by the time an incoming signal reaches the detector in a
receiver, it can be quite strong, and the BFO needs to be stronger unless
there's a product detector in there), and you can adjust injection with a
simple level control on the output of the local signal generator. Another
advantage is that for receivers not meant for SSB, they would tend to
drift, while you could build a decent VFO or something that would be
stable. So the "bfo" would stay in tune with the incoming signal, even if
the old receiver would drift off. So you'd need to retune the receiver
every so often as it faded into the skirt of the selectivity, but the
"bfo" and the incoming signal would remain the same, so none of that oddly
sounding voices.

Michael