RadioBanter - View Single Post - Sherwood SE-3 MK III D Synchronous High-Fidelity Phase-Locked AM Product Detector

June 5th 06, 04:41 PM posted to rec.radio.shortwave

wrote:

craigm wrote:
Michael Black wrote:

HFguy ) writes:
Joe Analssandrini wrote:
John Plimmer wrote:

There was also a long thread on this newsgroup that claimed the AOR
7030 had
the best sync detector in the business, but I still punt the R8B as
the 7030
sync was NOT sideband selectable, which is required for most good
listening.

Dear John,

Contrary to what you write, the AR7030's synchronous detection
circuit IS most definitely sideband-selectable and features
double-sideband detection as well (so does the Drake R8B). It does
not feature a "fixed" sideband selection as does the Drake R8B (or
the Drake SW8/Grundig Satellit 800), but rather a "variable" one
using the passband tuning. (You can tune the circuit this way as well
on the Drake.)

If your description (above) is technically accurate, the 7030 does not
have a 'real' sideband sync' detector because it requires using the
passband tuning to select the desired sideband in the double-sideband
mode. The sideband sync' detector on the R8B uses phase cancellation
for rejecting the unwanted sideband. This is a more effective
rejection method than using only passband tuning.

But are you arguing semantics, or outcome? Because the phasing method
of selectable sideband reception is not as good as the filter method.
A filter really knocks out the unwanted sideband, while the phasing
method tends to give far less rejection of the unwanted sideband.

Michael

Both methods have their limits to unwanted sideband rejection.

For the filtering method, no physical filter has infinitely steep sides,
so closer to carrier, the unwanted sideband rejection can be poor if you
do not want to also lose part of the desired sideband.

For the phasing method, the unwanted sideband rejection is based upon the
accuracy of the phasing network. The better the network, the better the
results.

So, to say one is better than the other is challenging. If you wish to
say one is better than th other, you will need to describe the two
specific implementations in great detail. This must include the
characteristics of the filters and phasing networks over the range of
interest. Deetailed measurements of unwanted sideband rejection vs.
frequency would be good to see.

craigm

One question here is how do you know the Drake is using quadrature
techniques to kill the other sideband. You may be selecting a sideband,
but again, how do you know how it is selected. I've designed Hilbert
transformers for narrow data applications. Getting a good Hilbert
transformer for voice grade isn't as easy. The sideband cancelation
will only be as good as the Hilbert transformer allows.

by looking at the schematic?