On May 9, 11:35 am, "no spam" wrote:
I'm looking for plans for a simple AM antenna to connect to my stereo to
replace the little loop antenna that came with it. In the past I have used
long wires but they are not very directional.

I have found some fairly good plans online for what looks like wire wound
around a box but all of them seem to have potentiometer in the mix
somewhere. It would be very little problem to build an aimable 18 to even
48 inch frame.

I only have two AM stations I'd like to come in clearer (690 KHz and 1440
KHz). Would it be possible to make a 'box' with one 'tap' for 690 and one
for 1440 then just connect one or the other the radio? How long would be
wires need to be and how would I feed it into the connections on the radio
(coax)?


Like Richard says, it's easier to find an old cap, and build the loop
around the cap. The old analog dial stereo receivers have some of
the best variables for this purpose. Most are multi gang caps, which
often can approach 1000 pf or more if you tie all the gangs together.
This can be handy for wide freq use as you can use switches and
switch gangs in or out of the circuit to change freq coverage.
Most stereo caps also had a few small gangs with low pf values,
which are good for extending the coverage higher in frequency.
Most old AM radios used dual 365pf caps, which would total 730 pf
tied together. This will work ok, but not as switchable as using a
several gang cap.
The cap on my 44 inch per side loop is 5 gangs total, and I have a
switch.
You can also "tack" fixed caps in parallel with the variable to drop
in frequency. For that matter, once you determined the amount of
capacitance for the two frequencies, you could switch between two
fixed caps, but who wants to be limited to two freqs? Once you
start playing with a good loop, you'll probably want to dial around
a bit..
Also, using your present loop as the coupling loop to the bigger
loop would be the easiest route. No actual connection is made.
You just hold the present small loop within, or closely in front of
the bigger loop, and vary distance for max signal. You will notice
the sensitivity vary greatly as you move the loop around. Just
find the "hot spot" and nail it down...
Here is one PVC design I've used.. It's about as simple as I could
conjur up, and all parts can be found at any hardware, home depot,
etc..
http://web.wt.net/~nm5k/loop5.jpg
My big loop is even more simple.. It's just a mast of about 2 inch
PVC, and the cross arm is regular 3/4 inch PVC which I drove
through a drilled hole on the 2 inch PVC. I drilled wire holes
directly in the 2 inch PVC at the top and bottom, and used "T's
on the ends of the 3/4 inch PVC. Same as the one in the jpg...
It sit's on a stand in the room here, and rotates.
If you can't find any old variable caps, they can be bought on the
web...Maybe not real cheap, but they can be had.
Myself, I butcher them out of old analog dial stereos...
BTW, I feed my loops with coax, and have a single wire coupling
loop within the bigger main loop, but I built one of the "jpg" loops
for a guy on the shortwave group, and he used his antenna in the
radio as the coupling loop. He just found the hot spot, and
rigged a mount so he could place the radio in that location
on a little stand or whatever..
MK