"Kristoff Bonne" wrote in message
...
My question is what happens if you tune a normal DSB-AM decoder to a SSBc
signal (say in USB), where there happens to be another signal at the 5 Khz
below.

Actually, there is a good test for that. 7335 khz is in the middle of a
broadcasting-band.
Can you still hear CHU at that frequency (SSBc USB, carrier at 7335 Khz,
signal from 7335 to 7340 Khz) with a normal DSB-AM radio if there is a
station broadcasting at 7330 Khz in DSB-AM (i.e. signal from 7325 to 7335
Khz)?

Yes, answered before and below...

If the IF shifts the 7310 to the centre of its 5 kHz passband, then both
an envelope detector or a sync AM detector centred in the passband are
going to see the upper 2.5k of the upper sideband of the lower adjacent
freq. As you tune the receiver higher in frequency, less of the undesired
sideband and more of the desired will be seen, thus improving the S/I.

That is saying that you would tune the conventional envelope detector
receiver to the upper side of the USBc carrier in order to suppress
interference from the lower adjacent channel, just as you would if the
desired signal was DSB and there was interference from the lower adjacent
channel. The more difficult and potentially untenable situation for even the
most sophisticated receiver is if the interferer is DSB on the upper
adjacent channel of a USBc signal.


But I do think the situation in different parts of the world:
- here in Europe SW is used to beam news and information from "home" to
holidays-destinations
- in the US -as there are no "domestic" SW-broadcasts- (at least, that's
what I read somewhere) SW is probably more a "hobby" thing.
- in other parts of the world, SW is also used for "domestic"
broadcasting.

I think you are correct that the US FCC does not license SW broadcasters for
domestic coverage but many supposedly international US broadcasters have
their largest audiences within its borders. I am in Canada - we have a few
SW transmitters for domestic coverage.

But, as I already said, the question is to what degree this really
matters. The way I see it, we're asking ourself the wrong question here.
The first question would be "who are we aiming this service for and what
kind of equipement do they have now"?


I see two possibilities:
- either you direct this at a target-group which already owns a shortwave
radio, and -then- backwards compatibility with DSB-AM is important.

And that is my point - the already huge installed base, not only of SW but
also MW and LW radios....

- either you are looking at a group of people who currently do not have a
SW-radio, and they will have to buy a new one anyway, so -at that moment-
backwards compatibility of your service to existing DSB-AM receivers is
not important!

Nobody is being forced to buy a new method of reception, unless the
regulators shut down the current methods, as is intended for TV broadcast.
For radio, the US and Canadian regulators seem to be more inclined to let
market forces decide. Canada was an early adopter of Eureka 147 in a new
slice of spectrum for broadcast - the L-band. The number of receivers sold
over the course of nearly 6 years since its launch is probably numbered in
the high hundreds, certainly less than a few thousand, despite claiming
coverage of over 10 million people. The number being used is probably a tiny
fraction of that. They were not forced to buy and certainly not induced by
the supposed attractions of Program Associated Data, AF interchange with FM,
multiple services, and the claims of 'CD quality', etc. So all that
investment in DAB transmission has been wasted. Anybody mounting an
advertising-based service solely on DAB would have been foolish.

So, what is our goal?

- more robust reception?
- better audio quality.
- a better user-interface
- additional services
- reduced broadcasting-power

AND

- low transition cost, for both broadcasters and listeners
- rapid reach to a large potential audience
- economical receivers, in cost, weight and power consumption
- interference mitigation

I think the most usefull approach is to put the two techologies next to
each other and see how well they score for every element.

Of course. But it's not easy. Real-world A-B comparisons are the right way
to do some of these things, double-blind tests, controlled conditions,
etc...

We can then try to "map" these to what we think is important for the
listener, but that will also vary on the kind of listener you're aiming
this at.
And this will different for somebody who is interested to learn about
foreign countries and who also has access to the internet, then for
somebody whos SW-radio is the only way to get news, information and music
from the central island of the archipel.

Sure, the weight one puts on each criterion will be influenced by context.

73,

Tom