At 13:48 16/03/2007, cris blak wrote:
> The broadcasting station from the MW should be OK but there is a
> little problem with an carrier amplitude modulated signal. The
> modulation could affect the measured amplitude of the carrier and
> than, instead of a steady amplitude carrier, one will see an up and
> down signal depending of the modulation. Only with the very narrow
> band (less than 50Hz) one can achieve good measurements. Another
> thing is to find a BC station which is ON 24hours a day, 365 days
> a year! You cannot control this fact. Also, in order to evaluate
> correctly the propagation path loss you should know the EIRP of
> that station and to be sure that parameter is constant. Another
> factor that cannot be controlled.
Barring disaster, Cris, a MW broadcaster's signal should be very
predictable, as their pattern and power is a condition of their
licence, and in many parts of the world, the information is in the
public domain. They can't change such things randomly, but they may
have a different power and pattern depending on whether it's night or
day; it will be predictable, however. And broadcast schedules are
often 24 hours a day 365 days a year, much to the chagrin of medium
wave DXers who might live near the transmitter. Again, schedules
change rarely on these stations, unlike shortwave broadcasters. The
engineering staffs of the stations themselves can sometimes be
helpful in describing such parameters.
Getting the carrier strength out of a broadcast station used as a
beacon can be a problem. I've found that using a 400Hz IF filter,
averaging the monitored signal, combined with corrections applied
from monitoring interference from 1 kHz either side of the desired
signal works fairly well. Interference will always be an issue for
beacon monitoring. How would one handle summer's static crashes,
random local electrical noise, or another amateur station interfering
with a beacon on 160 meters?
best wishes,
Nick
VE7DXR
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Nick Hall-Patch
Victoria, B.C.
Canada
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