From: Matti Aarnio (dhoq.pququoz@uk.com)
Date: Thu May 27 2004 - 15:53:42 EEST
On Thu, May 27, 2004 at 01:30:25PM +0200, Günther Montag wrote:
> Hello friends
>
> does someone know, is there something lik a beacon on the air
> on shortwave or medium wave, ham or radio band, which sends
> a known fixed exact frequency tone in AM, e.g. 1000 Hz or other,
> for calibration? Something like DCF77 on longwave?
>
> We have a real-time pactor program which needs an exact frequency for
> calibration, and not everyone has an DCF77 receiver.
Dear OM,
I would use GPS disciplined OCXO myself for that.
There have been numerous articles about that in QST, for example.
They are more complex than DCF77 rx, but also versatile, and work
in places where DCF77 doesn't reach -- and as a bonus, you can
get accurate timing well down to microsecond from a commercial
GPS with PPS output. Adding OCXO disciplining is another story,
of course.
The NCDXF beacon network runs with GPS synced timing, but not with
GPS disciplined frequency, I think. Those beacons exist all over
the world and frequencies, though.
Alternate methods include asking your local TV network about how
they generate and distribute their TV signals.
In Finland we used to have (during analog link era) a highly accurate
15625 Hz line frequency in TV2 network picture. Now that they distribute
the signal via digital networks (uncompressed, though) there is noticeably
larger jitter in that timing parameter, and it will end altogether, when
the analog TV system will get decomissioned in a few years time from now.
One possibility might be DVB-T symbol rate clock, which derives itself
from SDH transmission hierarchy master clocks. But a receiver to extract
that is (if possible) even more complex than GPS-OCXO. The DVB-T, and
DAB do include a possibility to send the same signal at the same frequency
from multiple transmitters, and a stationary receiver will pick it up just
fine (mobile receiver is a bit more challenged, though..)
> tnx!
> --
> 73 de
> Günther
> jtt@rele.tunk.net
73 de Matti, OH2MQK
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