|
Dick Rollema wrote:
To All from PA0SE
Not all TV-stations derive their sync-signals from
stable frequency sources. Harry, PA0LQ, has investigated this matter some
years ago and seemed to remember that BBC1, BBC2 and the German ARD are
referenced to an atomic standard and therefore very stable. But Anjo, PA0ZR,
recently found out that this was no longer the case for BBC2. But
perhaps this is due to the fact that the BBC2 signal, as distributed over
Europe, is picked up near Dover from a station in Kent and perhaps this
one does not use the atomic standard.
The digital televison network is not locked in this way. The accuracy
there is only that of a good crystal
and will vary as they switch from source to source. So you cannot use
any digital cable, satellite or
terrestial transmission as a high accuracy reference.
Also some long distance distribution, ie C4 is distributed arround the
UK is done that way and
then converted back to analogue. Only if the analogue broadcaster re-syncs
to a high
accuracy reference will that be precise.
Stewart G3YSX
73, Dick, PA0SE
At 08:13 12-4-02 -0400, you wrote:
Hello
Jim, Uwe and group,
Yes of course an LF broadcaster can
only be used as reference if he is quite close to your station. Groundwave
propagation must be dominant throughout the observation period. But there
is a way to find this out:
Use the TV sync as reference to observe
the MSF or DCF77 carrier. Requires no hardware (except for a potentiometers
to adjust the input signals to the receiver). Input signals (into
the longwave receiver) will be 4*15625 Hz and 60kHz, or 5*15625 Hz and
77.5 kHz. Fortunately, in both cases the signals fit in a standard 3kHz
IF bandwidth.
This allows checking if the reference
phase is stable enough - if you are lucky you'll never have
to let the TV turned on overnight ;-). I will try this experiment soon
and let you know the results.
Thanks Uwe for the signal gallery.
>From your QTH, you can be sure to receive Loran from Sylt via groundwave
!
Regards,
Wolf DL4YHF.
|
