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LF: 73kHz Cross - band QSO's

To: [email protected]
Subject: LF: 73kHz Cross - band QSO's
From: "James Moritz" <[email protected]>
Date: Thu, 23 Mar 2000 15:02:06 +0000
Organization: University of Hertfordshire
Reply-to: [email protected]
Sender: <[email protected]>
Dear LF group,
Sent CQ's on 71.81 for cross-band QSO's from 2030 - 2250 last night, and from 0600 - 0815 this morning, but no replies that I could detect. Did see G4GVC on 71.7 or therabouts, with a just- about audible QRSS signal. Also saw G3AQC and DF6NM on 137.7. The noise level on 136kHz seemed to rise quite sharply after about 2200, and fall quite sharply at about 0730.
I will be sticking to my 71.81kHz 'channel' for the time being; the
balance of response has been in favour of this, especially since
71.82 is already being used by G3XTZ! Of course, I can always
use a different frequency if requested, no problem.
In response to some of Mal's points, I was using a Maplin MOSFET
audio amp as a PA until recently - it produced about 100W
perfectly reliably, but I had to modify it to increase slew rate in
order to get full output on 136, and also improve the heatsinking; it
wasn't very efficient, requiring well over 200W DC input.
As for 120ft verticals, well, yes please!

Using the same, small, antenna as usual, my best DX QSO has been OH1TN with normal CW on 136 kHz, but I have not managed to reach him yet on 73kHz using QRSS CW.In theory, a given antenna ought to be about 6dB less efficient on 73kHz compared to 136kHz, and the natural noise level is higher by about 6dB too, so DX contacts are unlikely ever to be easier on the lower band, in spite of reduced ground wave losses. Certainly, the stations local to me are much weaker signals on 73kHz than they are on 136kHz. But the special circumstances on 73kHz at the moment are that the noise level in the UK is extremely high due to the Rugby transmitter, whereas in Europe this is not so much of a problem, judging by the spectrogram screen shots that have been posted. Because of this, it is sometimes easier to receive a 73kHz signal outside the UK than it is over a short distance. I don't see why ionospheric propagation should not play a part on 73kHz; obviously there has not been much opportunity to investigate this.
I had a nice cross-band QSO with PA0SE last time Rugby was off
the air, using normal CW; I think we both gave each other 559 or
569 reports - copy was certainly no problem. It would be good if
Mal could activate his GI3KEV station for the next 'first Tuesday' -
assuming of course that Rugby does go off air again, G - GI cross-
band QSO's ought to be quite possible with normal CW, as possibly other countries too.
I think it's important we all do as much with 73kHz as possible in
the time there is available - after all, if we ever try to get new
bands allocated, or stop existing ones going to other users, we
won't get much sympathy from the powers-that-be if they have the
impression the bandwidth won't be utilised. Perhaps a cross-band,
QRSS contact is not ideal as a form of communications, but it is a
lot more interesting and challenging than nothing.
I intend to be QRV on 73kHz again on Friday night and over the
weekend; hope to see you there.
Cheers, Jim Moritz
73 de M0BMU







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