On Mon, 13 Dec 2010 15:38:20 -0800, nm5k wrote:
On Dec 13, 3:01Â*pm, SĂ©bastien MEDARD wrote:
One thing handy about a small loop is you can turn it to null out the
offending noise.
I should try small loops too.
You get much
better nulls off a ground wave signal, than you do one that is
propagated via skywave. So they tend to work better at nulls in the
daytime vs at night. At night, you get a mix of ground and sky wave, and
the nulls are not as deep. In the day, I can make most ground wave
signals totally vanish by nulling them out.
That's an interesting concept. The difference between ground and sky
waves and the way to use loops. And small loops are easier to make...
Most of mine, I build from PVC tubing for the frames.
A simple, but good idea. PVC tubing is inexpensive and quite rigid...
I have one in this room that is a diamond, 42 inches per side.
One meter... It is approximatively what I wanted to do at the beginning.
It's on a stand
which allows it to rotate, and it stands almost as tall as the ceiling.
Do you tune it, or not? Is there a small loop inside or not?
But they don't have to be that big. I've got another round one that is
about 16 inches across, and it works very well too. Just a tad less
signal than the big one. But the s/n ratio is much the same for the
majority of the stations listened to.
I definitively need to test them.
http://home.comcast.net/~nm5k/loop5.jpg This is my usual favored method
for building a low cost MW loop. The hardest part to come by these days
is the variable cap.
I got one and I am searching for others. It seems that variable caps are
one of the center of a lot of things in radio reception
)
I can see on the loop5.jpg image that you connected one wire to the
ground and one wire to both other connections (double gang capacitor) so
that you add the result of both capacitors. Is that correct?
That way you get a smaller value, and will increase the upper tuning
range, vs just turning all the gangs in parallel to the minimum setting.
So I use switches to do this quickly.
Exact. That sounds good.
But if you can't find any old radios to acquire the variable caps, you
can buy them online from a few places. I wouldn't use one any less than
a dual 365pf BC cap. You can wire the two gangs together for 730 pf.
That's the kind I get.
With careful loop turn design, you can usually cover the whole MW BC
band with one of those. But I prefer the ones out of old stereo
receivers. They are even better, and can give a wider tuning range. I
think the one on my big loop has four or five gangs, some being small
and useful for upper end tuning, if the other larger gangs are switched
out.
I found a 500pF + 500pF one too, with a slow motion drive. Another way to
drive them slowly is to get a 20cm (10 inches) piece of wood, perforate
it on one side to put the capacitor axis into the hole (put some glue,
but a smaller hole is better, and push it hard so that the axis enters
inside the hole), and you get something that can be tune very precisely
with one finger... About the piece of wood, the longer, the higher in
precision tuning.
Sebastien.