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Message-ID: <521F9D653DB54457B0874D0C164638BB@JimPC>
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
References: <AANLkTik=W6auBcNzge4FH_E5ukVs0dVW2r_8kve5SuaV@mail.gmail.com>
In-Reply-To: <AANLkTik=W6auBcNzge4FH_E5ukVs0dVW2r_8kve5SuaV@mail.gmail.com>
Date: Sat, 15 Jan 2011 22:40:56 -0000
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Subject: LF: Re: Separate Receiving Antenna?
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Dear Toni, LF Group,

You may find that the big mast works well as a receiving antenna, if it is 
well seperated from sources of QRM from mains power etc. When using the 100m 
mast at the Puckeridge ex-Decca Navigator site some years ago, it was an 
excellent receiving vertical, used with a 40dB attenuator between antenna 
and RX. The inductance of the antenna loading coil will be much smaller than 
for amateur-type verticals, making it less effective as a preselector, so 
additional filtering may be needed at the RX input. Another source of QRM is 
nearby broadcast or utility transmitters, which can induce rather large 
voltages and currents in such a big antenna, and may cause overloading of an 
RX without good preselection. They may also give rise to "rusty bolt" 
external intermods which cannot be eliminated by the receiver, and the big 
antenna can pick up local QRM just like any other antenna. Transmitter sites 
tend to have "industrial" type electrical noise sources. So a small portable 
RX antenna would be a good precaution, together with a long piece of coax to 
connect it to the receiver.

Good luck with your project - it is always fun for amateurs to try a "real" 
LF antenna - especially the luxury of seeing the antenna ammeter needle 
rapidly rising with only a few TX watts!

Cheers, Jim Moritz
73 de M0BMU