Dear LF-band enthusiasts,
as Gamal wrote in an earlier message, he and myself took a nice ride to the
Burg transmitter facility, took some pictures and a field strength profile
from the location back to my home QTH, approximately 120 km away. I hope to
be able to post the profile, some further information as well as
photographs of the antenna structure.
As DCF39 is one of the few LF signals that has been heard on the other side
of the atlantic, it might be interesting for further field strength
calculations to know the ERP.
With our measurements with an untuned 1m-diameter loop and a calibrated
level meter (MV61, as my Siemens D2108 gave up its work) we came to the
result, that the 50 kW DCF39 signal on 138.830 kHz mark frequency is being
transmitted from a 325m high antenna. The actual ERP we came up with
(matching the appropriate CCIR-curves with a very good correlation) is
40 kW ERP.
So for all you guys in Canada or the U.S. that are able to hear DCF39, you
might consider this ERP in relation to an amateur signal of only 1 W ERP
(but maybe 1000 km closer to you location if it is a UK or Irish station).
But that brings me to another measurement that I have made and something
that was mentioned in a previous message written by Mike, G3XDV (IO91VT)
Don't forget that the transmission was a full 1W ERP (from only
10W in!). Very few amateur stations are able to run that amount of
power even with hundreds of watts input.
I believe that most of us over-estimate their ERP by far (and I include
also those guys with 'real' antennas).
I myself calculated from the antenna current and the height of my umbrella
antenna (18m) an estimated ERP of 200 mW. With the above mentioned
equipment I actually measured the ERP to be only 30 mW (!). Field strength
measurements performed by Dick, PA0SE, Markus, DF6NM and myself also
indicate, that probably only two or three stations within Europe actually
reach the 1 Watt ERP line (considering all the difficulties of actually
measuring ERP from a distance beyond near-field). G3WSC/p obviously is one
of those stations and as I indicated earlier, their signal was exactly on
my theoretical 1 Watt ERP line.
I am still surprised that with my actual ERP being that low, my signal
still can be considered an average signal and allowed me to cover distances
of up to 1300m (one of the disadvantages of living in Central Europe is
that there simply is no active LF station further away -- yet ...).
Even more I am surprised that with an antenna by far less effective I was
able to run my first Slow-CW QSOs over a distance of 402 km with ON7YD last
year with an ERP of (theoretcically, based on my actual measurments and
calculations) less than 0.1 mW (!!) ERP. This shows me, that, providing we
select the appropriate technique, the detection of estonishing weak signals
out of the noise is possible. The only other places I personally know
working with similar techniques are military (submarine communcation),
radio astronomers, NASA, and geophysical people (seismics and oilfield
applications to transmit data wireless from the borehole bottom to surface)
as well as our EME collegues!
Geri, DK8KW (W1KW)
P.S.: what I have heard (and read on the internet somewhere), NASA people
used spectrogram-like software to look for signals of the missing MARS
vehicle last year ... so much to the application of "amateur" techniques by
the professionals and vice versa.
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