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From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
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Date: Mon, 7 Sep 2009 14:02:26 +0100
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Subject: LF: Re: WSPR/Questions
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Dear Laurence, Roman, LF Group,

I shut the beacon down at 0446utc this morning. The frequency was 503.975kHz 
as advertised. Thanks for the overnight reports, nice to see spots from 
W1TAG again and from Russia for the first time. I transmitted in about 75% 
of the 2 minute periods between about 1940 and 2050utc, but saw nothing like 
a signal in the BY3 grabber, although the frequency seemed mostly clear. 
Conditions were relatively noisy here with more QRN than the previous night.

The antenna is a top-loaded vertical with 3 wires in a sort of Y shape in 
the horizontal plane. Where the wires meet, it is supported by a 10m 
fibreglass mast. To "jack up" the antenna, I have an old "cherry picker" (or 
aerial access platform or whatever you wish to call it) which is slowly 
sinking into my lawn. The bottom of the mast is bolted to the cherry picker 
where the operator's basket used to be, so the whole mast can be raised into 
the air. This allows a total maximum height of about 19m if I am feeling 
brave; last night the middle of the antenna span was raised to about 17m. 
Previous FS measurements have shown this gives about 3 - 4dB improvement in 
ERP due to the increased height and radiation resistance, along with a 
slight reduction in loss resistance. The total length of wire in the antenna 
stays the same, but gets further from the ground, so antenna capacitance 
actually reduces slightly. The things we do to try and get a better 
signal...

Cross-band QSOs from M0BMU are unfortunately difficult at the moment due to 
the high QRM levels on the lower HF bands here - I am hoping some work on 
dedicated HF receiving antennas here will improve this soon.

The 504kHz signal seems to be present in many widely-seperated QTHs - don't 
know about W/VE though? It seems to be different at each location. Here it 
is a rather weak carrier with no audible modulation, on the spectrogram it 
can be seen to have a couple of stronger spectral lines and several weaker 
ones spread over a range of a few Hz. These seem to vary over time, possibly 
due to QSB. They can't all be RTE/Atlantic 252 harmonics - 504kHz is an 
integer multiple of 9kHz, so many opportunities for internal or external 
intermods due to broadcast stations. 504kHz is also a multiple of 8kHz, as 
is 136kHz - it was suggested at one time that the weak carriers audible in 
many places on 136.0kHz could be harmonics of the 8kHz clock rate used in 
wired telecomms.

I would be quite interested to try WOLF again - although it needs more 
careful coordination with frequencies than WSPR.

Roman, there are some pdf files on the UK 500kHz group site about some of my 
LF/MF gear - you are welcome to use those if you like.

Cheers, Jim Moritz
73 de M0BMU