... I'm looking forward to this new receiver. How's the performance of
the synchronous detector?

73,

Fred E.
N8UC -- Detroit

Fred, I didn't see a response from Al on this, so I'll take
a stab...
The synchronous detector in my recently-arrived and
updated RX-350D stays in lock until it's faced with a good
jolt of static like from thunderstorms a few hundred miles
away. It also decides that it has lost lock during
significant fades. It works better during fading with the
AGC speed set to Medium rather than Slow, and better yet
with AGC set to Fast. The synchronous detector also works
better if the radio is tuned accurately to the station's
frequency. To do that, I use the 1 Hz tuning resolution as
I switch from lower side-band to upper and back, tuning for
the same pitch on the audio components of the AM signal.
Then I try the synchronous detector again. Or I just leave
it in sideband mode.
When the synchronous detector loses sync, the receiver
apparently reverts to AM mode with a click, a change of
audio level and a change in the audio frequency response.
Then the synchronous detector will reaquire the signal and
go back to the initial set of audio conditions. This
switching is quite intrusive.
So when the going gets tough, I just use the upper or
lower sideband mode. The carrier injection of this mode is
totally reliable since it is locked to a crystal in the
receiver. It also allows the use of the auto-null filter on
strong heterodynes whereas the synchronous detector disables
the null filter. The sideband modes don't boost the low
audio frequencies like the synchronous detector does.
The sideband modes are my preferred modes for marginal
AM signals. These modes behave nicely. The only downside
is the task of getting the receiver tuned exactly on
frequency. Come to think of it, I use the synchronous or AM
detector when tuning through the broadcast bands to avoid
the heterodynes. When I find a marginal signal that I want
to monitor, I'll switch to the sideband modes.
A couple days ago I ran across some marginal 'pirate'
station transmitting on 10253.250 kHz who was on a VFO and
was drifting +/- 500 Hz. It was necessary to chase him with
the frequency knob. This was one rare occasion where a
better implementation of the synchronous detector would have
helped.
I would say that if you're not listening to shortwave
primarily for non-DRM music that you ought to ignore the
synchronous detector issue.

Greetings,
Henry AC5LA



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