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
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