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Message-ID: <F1716EE11C844172ABCBBBED7E6E28CA@JimPC>
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
References: <AANLkTik=W6auBcNzge4FH_E5ukVs0dVW2r_8kve5SuaV@mail.gmail.com><003301cbb568$1a159780$0401a8c0@xphd97xgq27nyf> <AANLkTinO2vVXzA_x8xbOai1-azQFDC5pd3i7au_BwWfi@mail.gmail.com>
In-Reply-To: <AANLkTinO2vVXzA_x8xbOai1-azQFDC5pd3i7au_BwWfi@mail.gmail.com>
Date: Sun, 16 Jan 2011 18:53:35 -0000
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Subject: Re: LF: Re: Separate Receiving Antenna?
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Dear Toni, LF Group,

...>
 It will be difficult to get a receiving antenna far away enough...>

Unlike Mal, I have used seperate RX antennas for several years on 136k, due 
to local QRM picked up by the TX antenna. I am currently using both loops 
and a vertical for RX. The loops show no noticeable coupling to the TX 
antenna provided they are several metres from the downlead and loading coil. 
Actually they are directly underneath one end of the TX antenna wire at the 
moment. The vertical does have significant QRM induced by the main TX 
antenna, but this is greatly reduced by having a relay that disconnects the 
TX loading coil on receive, and de-resonates the TX antenna. The RX antennas 
are about 40m from the main noise sources, which seem to be the mains and 
telecom wiring in mine and neighbors houses. QRM is not eliminated by this 
seperation, but it is greatly reduced - enough to make operating possible, 
at least...

I have used seperate TX and RX antennas at a number of QTHs now, because 
most locations seem to have noise problems for LF reception! I have usually 
found it possible to get good improvements in reception. The main thing is 
to find the best position for the RX antenna - moving it a few metres can 
make a big difference sometimes. Another useful measure is a 1:1 RF 
isolating transformer at the RX end of the feeder, to reduce "ground loop" 
effects. A 100m reel of RG58 coax has less than 1dB loss at 136k, so it is 
not too difficult to have the RX antenna quite a long way from the TX 
antenna.

Cheers, Jim Moritz
73 de M0BMU