If you're building a loop don't forget that a lot off turns side-by-side
constitutes electrically another loop at right angles to the main one, much
smaller perhaps but quite enough to knock the notch down from a possible 50
dB to only 15-20 dB. For this reason flat "pancake" loops are better.
Provided you are not too bothered about the deep nulls loop antennas
with side-by-side windings are good for DX if they are over a metre
in diameter. This construction (see the PA0SE design in the RSGB
Communication Handbook and the G3LNP design in Radcom July 1999)
allows the individual wires of the windings to be spaced to reduce
the loop internal capacity and increase the Q.
In the early days of experimenting with 73kHz, G3XDV and I used
ferrite loopsticks from transistor radios for with mobile receivers.
While these antennas, even with an FET amplifier, are no good for DX
they do have very sharp nulls.
Ferrite loop antennas can be used for DX. See the 160m design, using
lots of ferrite, by Richard Q, Marris, G2BZQ, in the ARRL Antenna
Compendium, Vol 6. Could this be modified for 136kHz?
Has any one seen, or even posses, one of the large flat slab ferrite
DF loop antennas used in the RAF (circa 1960)?
I can confirm that a 1.5m LF loop antenna made from computer multi
colour ribbon performed badly.
--
Regards, Peter, G3LDO
<[email protected]>
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