From: John Rabson <john.rabson@numeo.fr>
Date: Fri, 20 Aug 2010 11:49:32 +0200
Message-Id: <98D767A2-7458-4CDC-AABC-BE5C5E4C7696@numeo.fr>
Cc: Robin Gape <robingape@ukfsn.org>,
 Chris Trayner <C.Trayner@leeds.ac.uk>,
 Alan Melia <alan.melia@btinternet.com>
To: rsgb_lf_group@blacksheep.org
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Subject: LF: 137kHz tests - summary of results
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LF, Robin, Chris, Alan,

Last Tuesday morning (17 August between about 08 30 and 1030 UTC) Robin,=
 Chris and I carried out some tests on 137.000 kHz from Mare le Bas  (JN17=
vg).  I apologise for not having posted earlier.  Many thanks to those who=
 responded to my previous posting.

Transmitter: 30 W output (subsequently falling to 20 W) to an 8 m vertical=
 with two 20 m horizontal wires as a top hat.  Many thanks to Alan for adv=
ice on this.  Feed current initially 330 milliamps.  Manual ID every 15 mi=
nutes interspersed with long dashes.

Receiver: a 1.6 m mag mount whip in the centre of the roof of a Renault ka=
ngaroo, feeding a Lowe HF 250 receiver with a DVM connected to the AGC lin=
e.  Mode: CW.  Bandwidth 2.2 kHz.

Environment: the area is extensively wooded, and the underlying rock appea=
rs to be on the boundary between limestone and granite.   To the north-eas=
t there is a fairly clear view out to several kilometres, with a small bel=
t of trees cutting across it a few hundred metres from my location. To the=
 south-east there is a belt of trees nearby.

Results: rather to our surprise, we were only able to make measurements to=
 a distance of a little under 2 km to the north-east. The limitation appea=
red to be man-made interference. We suspect that this may be from the car=
 electronic system (Cam Bus?) which seems to be doing something even when=
 the ignition and all accessories are turned off.  On the return from the=
 south-east signals were noticeably weaker.

Lessons we have learned:

- the cause of the falloff in transmitter output power needs to be investi=
gated
- the calibration of the antenna current meter needs to be checked
- the bandwidth of the HF 250 is really too great for good measurements.=
  Something more appropriate is needed
- making measurements with a small loop a little way away from the vehicle=
 should enable us to deal with weaker signals
- moving to 137.700 would be a good move as it should place us within the=
 capture range of one or more grabbers

Robin and Chris have had to return to the UK but I hope to continue with=
 the work in the meantime.

We would welcome comments and advice from those who are more experienced=
 in this corner of the field.

73
John F5VLF