>>Loops receive propagated waves omni-directionally, so once the loop is set
>>for maximum local noise nulling, further rotation will not significantly
>>benefit propagated wave reception.
Steve wrote:
>That is what I had been led to believe as well before building and using a
>number of shielded and air-core tuned loops for LF and NDB work. Although I
>haven't measured the null depths, I have noted significant nulls on many
>skywave signals, especially the further ones.
I agree with you Steve, I use a 3 turn co-ax loop using RG58 as my MAIN rx
antenna all the time.And I have to turn the loop to hear/work between EU
and the USA and the East from my location in South Africa.Definite nulls on
skywaves 90% of the time.Maybe not so strong in the mornings with greyline
enhancement to the USA.(Higher angle signals?)
I have tried various flag antennas and always receive something that sounds
like a TV lines transformer.I would then look for common mode trouble and
could never find it and would go back to the loop. Now, Dough Waller and Tom
wrote the following:
Dough:
> The loop shield is a shield of sorts, providing equal
> magnetic coupling to surrounding objects, provided the
> shield gap and ground wire connection are substantially
> opposite each other. The shield "is" the antenna, with
> the received signal's RF current flowing around the ends
> of the gap, inducting signal to the internal loop wire by
> transmission line action.
Tom's answer:
I agree. The shield, if properly constructed, makes the
system better balanced than simply having a wire loop with
all coupling at the feedpoint and one side grounded
(unbalanced feed). A properly constructed system with
balanced coupling directly to the shield (no inner loop)
would have identical performance to a properly constructed
shielded loop in any environment.
Could it be that my co-ax loop is rejecting something in its very near
field,(the TV of my neighbour that I suspect is about 10 meters away from my
RX antennas!)or is it a case of unbalance in the Flag antennas,(that would
make sense)I do not have to rotate the loop to get rid of the offending
noise, it simply is not there!I also tried K9AY (various ones) with the same
problem as the flags.
73
Raoul Coetzee
ZS1REC
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