[hard-core-dx]: NEWS: DAB

[caz.ian@xxxxxxxxxx (by way of Piet Pijpers <Piet.Pypers@xxxxxxxxxx>)]

DX Information from the British DX Club.

A few observations on the recent points raised on digital radio:-

>2. Tropospheric DX will still work with digital, even on microwave.
> The current microwave DX record is over 4000km (California to
> Hawaii) and within Europe, DX of over 2000km has been experienced
> by radio hams.

This isn't strictly true.  Digital reception is different to analogue
reception.  DX'ers will no longer be able to DX weak tropo signals,
because with digital it's a case of "all or nothing".  Once a signal
drops below a certain signal threshold, the audio will simply drop out.
No more digging out weak signals from white noise as with analogue FM at
present.  However, there's no reason why stronger tropo signals should
not be heard, and there may be the prospect of CD quality audio DX for
the better signals.  We won't know for sure till we get hold of DAB
receivers to put them to the test, but my guess is they'll be less
opportunity for DX when compared with current FM.  If DAB is anything
like digital satellite, there will probably be no opportunity of manual
tuning - only the chance to set up the receiver to download available
signals into the receiver's memory, following a sweep of the DAB band.

As DAB will be using frequencies above 200 MHz here in Europe, the
chances of any Sporadic E reception are extremely remote!

>3. I think all DAB systems will include full RDS information.  RDS
> is not very popular in the USA (and is not used on MW) so it can
> be very difficult to ID smaller USA stations.  DAB will probably
> make this much easier.
>
>73 Doug

Yes, RDS is invaluable for FM DX'ers, especially for ID'ing briefly
heard stations via Sporadic E.  But again, RDS is dependent on the
signal level being above a certain threshold to work.

>What's more, a lot of the hype about the good sound quality of DAB is
>completely irrelevant for the in-car market which DAB seems to be
>targeting: in cars you need heavily compressed signals rather than full
>dynamic range to be able to listen comfortably above road noise (at
least in
>your average small car).
>
>73s Dave

I understand that there are plans for two versions of each service on
DAB - one with the full dynamic range for the hi-fi buffs who want CD
quality; and another with compressed audio, better suited to
listening in noisy environments, like the car.  Whether this will happen
is another matter, as obviously duplicating each service in this way
would mean less services can be carried on each DAB outlet.  Will there
be the temptation to restrict the dynamic range across all services, to
enable more services to be carried on each DAB outlet?

With my DX hat on, DAB is bad news, if FM does die out.  I don't think
it will for years - after all, longwave is still expanding!  As for
general listening, I'd be a big fan if it meant an end to background
hiss and "birdies" we currently suffer on FM where signal levels are not
at powerhouse levels, or adjacent or co-channel stations are present.

Watch this space in ten year's time!

All the best - Ian Kelly, Reading




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