between Derek G3GRO, and Stefan DK7FC that is reproduced with permission.
Dear Derek,
Just want to give you a feedback:
A few weeks ago we ordered some 100m of ex Decca RF litz wire. It took me only a few weeks to build a new loading coil for my 137 kHz system. The wire is wound on a glass coil body of 300mm diameter, about 155 turns plus a small variometer part which is driven by a remote controlled drive engine, to accurately resonate on any frequency in the band.
I achieved a Q of about 1000 which lowers the coil losses by 6 dB, compared to the older one. This makes my system even more effective. My antenna is a 70m long wire in 30m height, with
extremely low earth losses.
Last friday it was possible to for Joe/VO1NA and me to have a first transatlantic detection of a ham generated CW signal in New Foundland, just like in Marconi's tests You can find a short
Report and a wav file to listen for my CW on his page at
http://www.ucs.mun.ca/~jcraig/lfex.html
There are many stations in Canada and the US who can receive my signals almost daily.
Thanks again for the possibility to get that most useful RF litz wire which improves my system significantly!!!
Best 73, Stefan/DK7FC
Dear Stefan,
Many congratulations on making your first transatlantic two-way QSO on the 137kHz band with Joe, VO1NA using your new high Q loading coil and variometer to tune your antenna - you must be delighted with your antenna performance. Thanks for the feedback I would be interested to know what earth system do you use at your QTH.?
The best two-way DX I ever achieved on 137 kHz was to OH1TN in Finland using hand-keyed CW. My LF antenna was then a 45m long wire with a similar loading coil to yours but the antenna was at only 12m AGL and somewhat screened by conifer trees almost as high and.fairly
close by! I did however manage to make a cross-band QSO down to a UA3 in the Russian Black Sea region at 2200km distance but that was when using the old Decca 100m mast as an antenna by special permission !! -
Unfortunately I am not currently QRV on the 137kHz band at present.
Thanks again for the feedback
73 and vy best Wishes, Derek/G3GRO
Dear Derek,
Well it was not a 2 way QSO but "just" a detection by VO1NA. There is not much going on in QSO activity you know but a lot of OMs are concentrating on beacon transmissions these days, which is interesting too. However I plan to do acty in CW, like today. But i need to improve
my RX since there have been many OMs answering my call but i didn't hear them I started with LF operation in autumn 2003 until spring 2004 and then had a break until autumn 2009 where I came back with some /p experiments using a 100m kite vertical. In 2003 i also worked OH1TN/OH5UFO and many other stations.
Well, about my earth system. The antenna is mounted here at my work which is the institute of environmental physics at the University of Heidelberg. This is a 35m high building. Since it is a German official and relatively new building they put much money in all the equipment and realized an EXCELLENT earth system. So i simply had to connect the cold end of my coil to the lightning protection system. Now, my earth losses are 1.2 Ohm! When using the new coil i am getting an overall loss resistance of 5 Ohm (recently measured 4.8 Ohm) including the PA and LPF losses, i.e. i am getting 1 A antenna current at 5 W RF I'm sure there would be no problem to appear in DFCW-60 on the G4WGT grabber when using a 9 V block battery and running 1W RF... This makes it clear why the RF litz caused a 3 dB improvement of that system. Assuming a Q of 1000 and j2500 Ohm for the coil i am at 2.5 Ohm now. Before, it was 8.7 Ohm. If someone has 50 Ohm earth losses, the improvement would have been marginal...
Best 73, Stefan/DK7FC
Stefan then sent us a photograph of his system on the roof of the University building
Stewart/G3YSX
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