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LF: O/C chasing at LF

To: "LF-Group" <[email protected]>
Subject: LF: O/C chasing at LF
From: "Alan Melia" <[email protected]>
Date: Fri, 28 Feb 2003 01:07:04 -0000
Reply-to: [email protected]
Sender: <[email protected]>
Hi all, I thought this little episode might prove interesting and it
certainly finds a use for the "below 50MHz" part of a hand-held scanner. I
have an AOR 2700 which purports to operate down to 100kHz, but like a lot of
this kind of kit is very deaf down there. I did think it might be useful for
DFing TV interfence, but it is too deaf even for that, without a pre-amp.

I restrung my 60m-top Marconi last weekend and was disappointed to see that
the tunning when paralleled with my 30m top inv-L was not at the original
position. As it is a receive aerial is is strung with 1mm PVC coated wire. A
quick measurement of the tuning inductor indicated only 80pF more capacity,
which I guessed would mean a break inside the insulation about 16m from the
feed point (5pF / m). After a little thought and a couple of coffees, I
plugged the end of the unloaded 60m wire into the 600ohm output of the PS-12
(W&G SIG GEN) turned up full and with the interenal resistor set to "0". I
then walked down the wire (now dropped to the ground again), running the
wire at right-angles over the closed telescopic aerial on the AOR2700. The
"S-meter" gave fullscale on AM, and about 15m down the wire it dropped
significantly ( to "S3"). A quick waggle of the wire confirmed two breaks at
that point. I was quite pleasantly surprised that point indicated by the
scanner s-meter was with an inch of the break. After a quick soldering job
and a tape-up the aerial tuning inductor was back to where it was expected
to be.

I know its not rocket science but its nice when these little tricks really
work. The feed voltage from the PS-12 was about 0.7V r.m.s. It also proved
my contention that a wide coverage receiver is one of the most useful bits
of test gear you can have (I might add "portable" to that as well now!!)

Cheers de Alan G3NYK
[email protected]

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