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LF: Re: RX Frame Aerial for 136kc/s - still experimenting.....

To: [email protected]
Subject: LF: Re: RX Frame Aerial for 136kc/s - still experimenting.....
From: "James Moritz" <[email protected]>
Date: Tue, 12 Nov 2002 14:24:16 +0000
In-reply-to: <[email protected]>
References: <2D280BB697C7EE4C979C5C89925418EF368F80@TNS-FBU-2E-003.corp.telenor.no>
Reply-to: [email protected]
Sender: <[email protected]>
Dear Jan-Martin, LF Group,

At 12:03 12/11/2002 +0000, you wrote:
Signal strength last night for DCF39 was 80-150µV (-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



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