Stephen Mosier <mosier@uncg.edu> W3GRG, writes:
> On another note, I have an old Hallicrafters that I listen to SW on, but
> have often thought of a newer rcvr. The unsettled question that hangs
> in my mind is whether or not to get synchronous detection, a la the
> expensive Drake rcvr. Does anyone have any thoughts on adding
> synchronous detection to the TenTec kit? I think there was a
> synchronous detector project in QST a few years ago.
Synchronous AM detection is absolutely wonderful. It has two advantages:
1) The carrier is replaced by an oscillator in the receiver, locked to
the carrier frequency and phase. Selective fading, which causes that
slow, periodic "fuzz out" distortion, is often eliminated.
2) If there is an interfering signal to one side of the desired signal,
you can listen to the other sideband.
I have a Sony 2010 portable, which has arguably the best synch detector on
the consumer market. With it, listening is often a pleasure on signals
that would be unpleasantly distorted without it. With the Kiwa
aftermarket filters, it's a very good program listener's radio. It uses
phasing via an AM stereo chip, and only uses half the filter bandwidth.
You can offset the tuning a couple of hundred Hz to gain a bit more highs.
How much varies from receiver to receiver On some fluttery signals, the
Sony's AGC can pump, rendering it unintelligable.
The Drake R8 has better selectivity options, wonderful audio, crummy
ergonomics, and a synchronous detector that tends to lose lock a bit more
than the Sony, according to reviews. It also has a PBT (IF shift) control
that makes the synch detector somewhat more flexible than the Sony's.
Synch detection is more of a program listener's tool than a hard-core
DXer's. It makes listening more pleasurable and more "hi-fi" rather than
"communications" quality.
However, any ham who is skilled at tuning SSB can acheive almost the same
result as synch tuning--just tune in the AM signal as an SSB signal, and
zero beat the carrier. Speech is relatively easy. If you have a good ear
and a stable receiver, you can tweak it so that music sounds just right.
The sensation is kind of like the "THX" sound system demo that comes
before some movies--when you get it right, octaves are perfectly in tune.
If your general coverage rig allows you to switch in a wide filter in SSB,
so much the better. This technique is somtimes referred to as exalted
carrier reception.
I did this for years before I got the Sony, first on a Hallicrafters
SX-122A, and then on an ICOM 745 and 751a. I still use the technique do
when a signal is too weak or fluttery for the Sony.
I don't know anything about aftermarket synch detection kits and homebrew
retrofits. (Wasn't there a Sherwood Engineering kit in the early '80s?)
My opinion is that if you do a lot of listening to music over shortwave,
it might be worth the effort--if your receiver's audio is good enough. If
you just listen to news and speech, exalted carrier will do most of the
same job.
Doesn't the Tentec SW kit tune in 5 kHz steps? That fits most, but not
all SWBC stations. At that tuning rate, the synch PLL would have to lock
in even if slightly offtuned.
73,
--Peter (KD7MW)
Peter A. Klein (pklein@seattleu.edu) : -----==3== --- ---
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