Message-ID: <5.1.0.14.0.20021112133603.00a927d8@gemini.herts.ac.uk>
Date: Tue, 12 Nov 2002 14:24:16 +0000
To: rsgb_lf_group@blacksheep.org
From: "James Moritz" <j.r.moritz@herts.ac.uk>
In-reply-to: <001201c28a43$90d64a80$0504210a@c.scope>
References: <2D280BB697C7EE4C979C5C89925418EF368F80@TNS-FBU-2E-003.corp.telenor.no>
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Subject: LF: Re: RX Frame Aerial for 136kc/s - still experimenting.....
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Dear Jan-Martin, LF Group,

At 12:03 12/11/2002 +0000, you wrote:
>Signal strength last night for DCF39 was 80-150猩 (-75...-80dBU)

At your distance, the field strength of DCF39 should be roughly +60 dBuV/m 
- so if under quiet band conditions the band noise is around 0dBuV/m in a 
bandwidth of a few hundred Hz, the receiver will have to have a noise level 
below about -135 or -140dBu to achieve optimum sensitivity. So you might 
need a preamp!

>Not sure if it is still a point to ground the center of the tuned loop.


I have used several loops here for LF reception, and have never found any 
advantage in grounding the loop centre tap, allthough in theory it ought to 
improve rejection of E-field signals. That might just be because of the 
nature of the QRM at my location, though. I have to say I am skeptical 
about the idea of E-field rejection being an important benefit in reducing 
noise pick up at LF. In fact, I find a small, screened, LF loop to be quite 
a good mains cable detector. The big advantage of a small loop RX antenna 
over TX type antennas is that is easy to move the loop around until you 
find a position where the noise level is low - but you can do the same 
thing with a whip antenna. The other benefit of the loop is the directional 
nulls, of course.

Cheers, Jim Moritz
73 de M0BMU