craigm wrote:

Michael Black wrote:

[...]

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





With modern circuitry, the phasing networks are near-perfect, with
far better effective shape factors than what one gets with even the
most expensive physical IF filters.

Additionally, a synchronous detector using its own phase shift
networks for USB or LSB interference cancellation has a 6 dB S/N
advantage over using IF filtration to cancel one sideband.

That is because the Q channel contains INTERFERENCE ONLY and
virtually NONE of the desired station's audio. The Q channel is in
an audio null for the DSB information. Therefore, the phase
cancellation works on interference only, and the full phase
reinforcement of the desired DSB audio gives you 6 dB stronger
desired audio (yes, 6, not 3, because of phase coincidence) than one
sideband alone.


With all good wishes,



--

Kevin Alfred Strom.

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