OK Reg,

You are very patient and your time and expertise is appreciated.

Last night I looked at many web articles on loops, many of which had
preamps. I was a little discouraged. Many were fed with coax, which
seems a little odd, especially since some of these loops had secondary
resonances in the MF or HF bands. It seems like a preamp with a little
non linearity, some big MF signals nearby, and a feed line that isn't
balanced is a bit of a disaster waiting to happen.

I know many of the HF radios in use have preamps that can be turned
off (actually they are 20 db pads).

But, regardless of my receivers susceptibility to out of band signals,
I would want to feed my receiver with balanced line...especially since
it's much cheaper than coax and should help prevent the feed line from
picking up signals.

So............followed everything in your last message and it all
seems so simple (now)....

Getting back to last nights study session. Spent a couple of hours in
my 1987 ARRL Handbook and the remainder on the web looking at real
life loops published there. The web aspect was really disappointingly
devoid of technical jargon, it seems like most of the loop authors
just threw something up and it seemed to work-the end:: Do people
just throw stuff up without understanding what they're doing, or do
they understand and just fail to document the theory??

The Handbook tour was almost as bad. Very little was said about loops
except that which applied to the full wave resonant loop and how it
can serve as a driven element in a 1 lambda 'guad' type radiator.
Other than the theoretical wavelength, the correction factor for wire
diameter, there was not more than 2 paragraphs written with useful
information on short loops such as I am trying to put up.

-------------------------

There was a question I had, perhaps I'm reading between the lines here
tho....

YOU SAID:

And even with an extremely long line any impedance mismatch loss will
be negligible. So forget about 300-ohm balanced line and just use a
simple not-tightly-twisted pair. NO IMPEDANCE MATCHING REQUIRED at
either end. The size of the small coupling loop inside the main loop
matches 50 ohms to a 50-ohm receiver. So ideally the line to the
receiver could be 50-ohm coax. But, as I say, it doesn't matter.

The size and shape of the small coupling loop is not critical. It can
be circular or square. Theoretically, to match the loop to a 50-ohm
receiver, it should have an area about 1/25th of the main loop area.
To simplify construction the coupling loop can be made
self-supporting.


With your statement above in mind, are you telling me (or inferring)
that any loop can be made to match a 50 ohm line by controlling it's
size (area inside the main loop compared to area inside the coupling
loop)??

In rjeloop3, the different sized loops have different feed line
impedances, ranging from about 200 to 4K ohms. I made my final
selection based on the model that matched my existing 300 ohm twin
lead. I know you said my line impedance doesn't matter much, and I
agree, except that it upsets the tuned front end in the receiver a
bit.

If it's possible to control this impedance of the small loop, what are
the parameters I need to know to adjust mine to different values
(other than those given by the software)??

I know you gave me the formula for matching to 50 ohms already. But,
if this value can be controlled to customize the impedance, what do I
need to know in order to make a match for other values?

For my planned 2 meter square loop, my area is 2 X 2 X 4 (2 meters by
2 meters times 4 turns), sm my total loop area is 16 square meters.
From the information you gave me (above), I can feed the receiver
with 50 ohm feed line if my coupling loop is 16/25 (or about .8 square
meters)?

I know the matching isn't critical, but I'd like to have a good match
for the sake of the front end tuned circuit in the receiver.

If you can't say without writing a book, please feel free to decline
to answer. If you can give the answer briefly, I'd appreciate some
comments however.

Hey Reg, was down in the basement where I keep the junk box and found
a couple hundred feet of 4 conductor #24 solid copper cable. It's
used for connecting telephones indoors. It's even cheaper than 300 ohm
twin lead and I was wondering if I could/should use that as a feed
line to the house??

Today I surveyed the loop location in the back yard, I have my solder
and my 5/16" double weave rayon rope spool out and ready to go. My
loop resonating capacitors should be here Wednesday. If all goes well,
I could have a working installation by this time next week! Thing's
are looking up.

Also, Richard suggested a book about loops which I did not find in the
library, or even in the reference section. I didn't price it yet, but
I need to get some additional technical info. Do you have any
suggestions for what to buy for books?? I don't need anything other
than short loop theory (without heavy math).

Thanks to you and Richard and everyone else who commented in this
thread, I learned a great deal.

Regards,

T



At 60 KHz,

4 turns of 2 mm diameter wire, spaced 4 wire diameters apart.
2 meters per side
123 uH, 60,000 pF to resonate
4.7K across the loop.
300 ohm feed impedance at single turn loop feed
Q (unloaded) = 101