Owen Duffy wrote:

Tony Giacometti wrote in
:

Owen Duffy wrote:

...
You have already been told there is no such thing as a low noise
antenna. The loop has the advantage of being able to null out signals
from two opposite directions, which can help if the interference is
predominantly from one (or both) of those directions. You can improve
the depth of those nulls, but pattern or directivity is unrelated to
the power transfer problem.

did I misunderstand you, I thought the noise was nullable but at 75
meters the signals were mostly omnidirectional? Or is this one of the
unlearned things?

Keep in mind that noise from very close sources can be much stronger than
the aggregated noise from more distant source. If you live in a street
where everyone has the same noisy plasma TV, the noise from your own one
is likely to be much stronger than the aggregate of the others... think
through the propagation mechanism and especially the effects where the
source is in the near field (say within a quarter wave of your antenna).

You can't do much to null the noise from a hundred TVs spread around the
neighborhood, but you can null the noise from a close by dominant source
like your own, or immediate neighbor's. Of course, in nulling the noise
in that direction you also null signals from the same direction.
Fortunately, lots of signals come via an ionospheric path (a higher
angle), and the null of the loop is normally oriented horizontally so it
doesn't knock the ionospheric signals down as much.

If you try something beside a shielded loop, make sure you use an
effective means of isolating the feed line from the loop so that pickup
on the feedline does not feed the receiver.

Perhaps by solenoid loop you mean a multi turn loop. A multiturn loop is
another way of increasing induced voltage, but it increases the source
impedance and you have to solve the impedance matching issue.

some type of balun maybe?



...
Ok, I want to build a larger loop to get more gain, if possible deep
nulls for reducing local noise, I would like to try wire instead of
coax. I want to mount it on a PVC pipe frame. Can you give me any
ideas as to what shape and size? Whats a solenoid loop?



You started of with a loop that was too insensitive, so you have improved
that with better matching solving that problem. You can increase the gain
by further improvement of the matching... but you don't need more gain
than sufficient to have the band noise swamp the receiver internal noise.

at this point I din't think it does. When I orient the antenna for lowest
noise the S meter never reads above S3, its really quiet.

I guess the question is this, DX signals would be skywave, a loop is omni
directional to skywave signals I believe. Is this correct?


I know you are convinced that matching also degraded the pattern. If the
matching network was entirely inside an effectively shielded box, it
should not affect the nulls. Make sure that you retained the shielded
loop properly.

I didn't use a shielded box, I have a plastic box. The instructions for the
loop I built said either was OK.


Why do you still think that a larger loop has deeper nulls.

If I implied that I didn't intend to do so, what I mean is to "keep" the
deep nulls I now have.


Owen