Message-ID: <23068.200003291050@gemini>
From: "James Moritz" <j.r.moritz@herts.ac.uk>
Organization: University of Hertfordshire
To: rsgb_lf_group@blacksheep.org
Date: Wed, 29 Mar 2000 11:50:51 +0000
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Subject: LF: 73kHz/Decca Sites
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Dear LF Group,

	The Rugby TX is still off the air (or was at about 0730utc), as it 
has been for the last couple of days. Worked G3XTZ, G3LDO, and 
G3XDV last night, all 'armchair copy' signals. If anybody would like 
a 73kHz or cross-band sked, please let me know - hopefully we  will 
be able to take advantage of this window of opportunity.

Also listened from time to time on 136kHz - but did not hear LA1K. 
However, I dozed off some time around 2100, so might have 
missed him!

OK about the Idea of experiments to compare big and small 
antennas at a Decca site - this looks like an interesting idea, but 
perhaps 1W ERP is being a bit hopeful from the small antenna; it 
would probably be neccessary to settle for lower power from both 
antennas for the duration of the experiment. I did some EZNEC 
simulations a while ago, to follow up a suggestion by G3XDV that 
the towers at Brookmans Park MF broadcast site might be acting 
as parasitic radiators, enhancing the M0BMU signal. The result 
was essentially that, with a spacing of some hundreds of metres, 
the effect was neglegible, provided the big antenna was not 
resonated at 136kHz. This could be achieved by grounding one 
antenna whilst using the other, or similar.

A 300ft tower is still only lambda/24 at 136kHz, so should in theory 
give the same vertical radiation pattern as an 'infinitesimal' vertical, 
to all practical intents and purposes.

Hope to hear more about Decca sites soon,

Cheers, Jim Moritz
73 de M0BMU