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Message-ID: <B9CA887310D3469FAD6C4F446AB298B6@JimPC>
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
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Date: Mon, 2 Jan 2012 23:53:05 -0000
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Subject: Re: LF: LF ferrite RX antennas
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Dear Doug, LF Group,

>I wonder.....if someone were to make a large enough ferrite core antenna
>(not for portable use), would it even need amplification? The cost and/or
>size would probably be prohibitive.

Some calculations and experiments were done a few months ago on this 
topic... The point of the experiments was to see if it were possible to make 
a portable ferrite rod antenna of 300mm length or less that would give 
reception limited only by the external noise, i.e. where on a quiet band, 
the band noise would still dominate the internal noise due to the rod 
antenna/preamp/RX. It turned out to be fairly easy to achieve this using 
appropriate preamp designs, and at that time both DK7FC and myself came up 
with satisfactory working antennas. My conclusion was that, although there 
is quite a bit of variation between ferrite rod antennas of different 
thickness, material, shape, windings etc, you can say that a ferrite rod 
antenna  and an air-cored loop will yield very roughly the same signal level 
if the diameter of the loop is the same as the length of the rod.

The signal output of a 300mm rod or loop antenna is very small, and a preamp 
is definitely needed for commercially available receivers, which have much 
too high a noise figure to use such an antenna directly. The output can be 
increased by scaling up the area of the loop, or length of the rod. Quite a 
few LF amateurs have made tuned loops a few metres in diameter that provide 
enough signal to drive a decent receiver directly. For portable use, a 300mm 
long rod antenna is certainly a more convenient thing to carry around than a 
300mm diameter loop. No doubt you could scale up the rod antenna for fixed 
use, but a suitable chunk of ferrite a few metres long would be very 
expensive, very heavy, and not really have any advantage compared to the 
air-cored loop. I'm not sure if there is much practical advantage in 
eliminating the preamp, but if you wish to do so, a large air-cored loop is 
probably the most practical solution.

KB4OER wrote:
>Mal, you lost me on this one. Are you suggesting I (or we.....here in North 
>America) erect large verticals, inv L systems, >Rhombics, and V beams in 
>order to receive EU LF signals?
>I thought I was doing pretty well with my micro RX antenna!

I think everyone apart from G3KEV thinks so too! Don't take too much notice 
of Mal's opinions - however often he repeats them, they remain nonsense ;-)

Cheers, Jim Moritz
73 de M0BMU