On Nov 25, 12:46 am, Tony Giacometti wrote:


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?

A solenoid loop is like this..
http://home.comcast.net/~nm5k/loop5.jpg
A pancake loop is about the same, except
that the wires are stacked in the same plane
like an electric range burner, vs being side by
side like the solenoid loop.
All the PVC loops I make are diamonds,
fed at the bottom corner.
The depth of the nulls is due to balance, not
the size of the loop.
But... In some cases it's easier to get good
balance on a larger loop as it's easier to
ensure a symmetrical loop as related to the
mounting hardware, feed devices, etc..
But in my case, even my smallest 16 inch
loop is very symmetrical and has just as
good of balance as my larger loops.
So size doesn't mean much. Care in symmetrical
construction means much more.
I've never had common mode problems to be a
big deal. I may have a little, but when I tune
the loop, the greatly increased "tuned" level
swamps any small common mode signal I may
have.
So in effect, it's usually not an issue.
I do try to keep the feedlines only as long as
needed to reach the antenna, and I keep
them on the floor.
Another thing that I think helps a bit is to
use a separate coupling loop to feed the
loop. But this may help with balance more
than common mode reduction. But I still
recommend it none the less.
One thing.. make sure there is not metal
around the antenna. This can whack things
out fairly fast. IE: metal frame chairs, file
cabinets, etc...
On my loops, I've use no baluns at all so far,
but as my recordings prove, I have no lack
of nulls, or signal level for that matter.
When I null a single point ground wave signal,
say bye bye.. It's gone. :/
BTW, you will never have good luck at nulling
general "band noise". When you say "band noise",
I will assume you mean all the noise received from
all directions at once. As has been repeated
many times, if the noise source is not from a
single source, the loop will not be able to provide
a decent null. You will never be able to null random
noise. But if say a power line device starts making
noise from a single source, you can null almost
all of it, and still hear most of the skywave signal
you are trying to receive.
It's quite possible you are in a location with multiple
noise sources, and the small loops may not do the
job you want them to. In general, a loop is a loop is
a loop.. If the one you have is working properly, and
you are having trouble nulling the noise sources,
going to a bigger loop may not help much at all.
MK