Al Klein wrote:

On Sat, 08 Oct 2005 21:17:44 -0400, Dave Holford
said in rec.radio.scanner:

You can't assume that any filter over 3kHz or so is symetrical about the
'carrier' frequency just because that is the normal configuation of consumer
equipment.

You can't assume that any given SSB signal will fit in a 3 KHz
bandwidth, just because all current signals do.

But I can assume that all filters currently in production are
symmetrical about the center frequency within 10% - because they all
are.


Certainly most current crystal filters are symmetrical about the centre frequency,
as are most people symmetrical about the centre (externally at least, and I'm not
going to quibble about the orientation since I'm sure you know what I mean) - I
wrote 'carrier' frequency.

I'm not sure about current mechanicals (somewhere I have an old Collins filter
catalog with asymmetrical SSB curves).



Just for fun I am currently listening to an LSB conversation on 3763 kHz with
a 7.5 kHz filter and I cannot hear any sign of the conversation on 3765 - but,
the noise is a bit higher due to the wider filter. I wouldn't normally do this
but just had to try it. Of course, if I select DSB or ISB I get both signals,
although the 3765 conversation is inverted and shifted in frequency.

With what receiver and which filter? What kind of detector? I can
design any number of receivers that will do what you claim, but that
doesn't negate the fact that the standard filtered superhet SSB
receiver will receive a signal on the "wrong" sideband if the filter
is wide enough and the detector is set correctly.


As I stated in my first posting, a Winradio.

The rest of the paragraph is true if you are talking about 'the standard filtered
superhet SSB receiver' provided that it is also fitted with AM filters which can be
used in the SSB mode - not universally true. I can do it with my TS-450 but not my
IC-706 for example. Not all receivers have the ability to select mode and filter
independently.



I don't know how much DSB is still on the air but a quick google search for
"double side band' gets over 12 million hits. It may not be encountered in
normal voice communications on HF and scanner frequencies but it is hiding in
other places and frequencies from a quick look at some of the hits.

I said DSBSC, not DSB. There's loads of DSB on the air today, it's
just not DSBSC.

True, my mistake in assuming DSBRC or DSBSC.

Here I am trying to make a simple point that one should not assume that just
because a situation is common in one's own experience it is universal; and I make
an assumption - Hoist with my own Petard!

And, I can't help noting how a simple point can grow into a complex discussion of
differing views - I guess that's how politics and the law got started!

Dave