craigm ) writes:

With PBT, the ability to attenuate the unwanted sideband is limited by the
skirt selectivity characteristics of the filter.

With selectable sideband sync detectors, the unwanted sideband is cancelled
by the circuitry. This can be significant if the detector is well tuned.

But of course, how much a phasing type circuit attenuates the unwanted
sideband is a reflection of how precise the components are, and how
well balanced the circuit is.

And one reality is that "sync detectors" came into common use in relatively
low end receivers. Before the Sony 2010, I can't think of any receiver
that had a built in sync detector. The advantage in that and other low
end receivers is that it does allow "narrowing" the selectivity without
the cost of a filter. It is cheaper to use some passive components and
an IC than to add a good IF filter.

To make a fair comparison, one actually has to compare the receivers,
rather than compare techniques. Because while passband tuning does
indeed reflect on the skirts of the filters used, phasing-based selectible
sideband depends on the components and circuitry used.

Once you start paying for a receiver out of the portable category, chances
go up that the filters are better than run of the mill ceramic filters,
which means their passband tuning may be fine. (And I actually can't
think of an instance of passband tuning in a cheap receiver.) On
the other hand, there are lots of relatively inexpensive receivers with
not so great ceramic filters that do use the phasing method to get selectible
sideband, and since those are lower cost receivers, one might wonder how
good the phasing networks are.

Fifty years ago, people would buy phasing type SSB adaptors for their
receivers. They wanted an actual product detector, rather than the
"envelope detector" that came in their receiver, because SSB was
coming in and they wanted to adapt. The selectivity of the receivers
were often limited, because they'd been intended for AM reception.
So an ssb adaptor with the phasing method allowed for improved selectivity
with relatively low cast and no need to modify the receiver (other than
adding a point to connect the adaptor). But nobody claimed this
was better than a good IF filter in the receiver.

Michael