From: "Mike Dennison" <mike.dennison@rsgb.org.uk>
To: rsgb_lf_group@blacksheep.org
Date: Fri, 19 Jan 2001 11:23:44 -0000
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Subject: Re: LF: Receiver insensitivity
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G8AFN wrote:

> I tried to send this message 3 times last week it apparently got held
> up as I had started the subject line with the word "help" the software
> at Blacksheep thought it was some sort of command but could not act on
> it. Hopefully with a more sensible subject line we will be alright
> this time.

I wonder what other 'commands' we might accidentally use?

> I have been investigating my receive signal to noise ratio, which
> seems to be about 20  to 30dB less than many people. [huge cut]

Peter,

It looks to me like you have a local noise source. The simplest way 
to check this is to build a directional antenna. This could be a few 
tens of turns of wire about 1m in diameter, tuned by a few hundred 
pF, and coupled via two or three turns to the Rx. You can then do 
three tests:

1) Rotate the antenna to see whether your S/N improves (or even 
gets worse).

2) If the noise appears directional, use the antenna to get a bearing 
on it.

3) If you have a 12V Rx, take your receiver out in the car with the 
loop antenna and see whether you can get a much better S//N at 
locations away from home.

Another thing to look at are the Loran lines. Do you see them clearly 
on a spectrogram? If not, you probably have a noise problem. As a 
guide, I can see them only when my neighbours are not playing 
computer games or watching their widescreeen TVs.

Good luck.


Mike, G3XDV (IO91VT)
http://www.lf.thersgb.net