On Wednesday, November 26, 2014 4:19:24 AM UTC-8, Drifter wrote:
On 11/25/2014 2:18 PM, wrote:
On Tuesday, November 25, 2014 11:05:38 AM UTC-8, Ross Archer wrote:
Hey folks,

Thought I'd share the results of some recent successful indoor
antenna experiments. I wanted something to take on the road and
also use when an outdoor antenna isn't convenient or practical.


I'll preface by saying I've played with various active and passive
antennas over a period of years and discovered that very few
improved the signal to noise ratio of signals and so I've always
given up and gone with an outdoor antenna. This means travel = no
shortwave

But, Success. If I thought there was a way to monetize this I'd
build and sell it, but instead I'll share it with you guys for
free.

Quick summary: it's a loop.

Longer summary: It's a physically big-ish (sort of dominates a
small room) but electrically "larger sized small" indoor loop with
a transformer coupling

Details: 25 feet of copper hookup wire with the ends soldered to
the secondary terminals of a mini-circuits T9-1 transformer (used
because I have them in a junk box. The ratio is probably far from
optimum but it works well -- it was chosen because it's what I
had.) I cut the wire in half and joined the ends electrically at
the center to experiment with both closed-loop and sorta-dipole
configurations. (Short answer: closed loop works better, often
much better, most of the time.) Also, if you travel with it it
WILL get tangled, so being able to separate and untangle the ends
is important.)

The secondary (with the dot) goes to a mono 1/8" plug to the
portable radio's antenna input. It doesn't seem to matter in
theory or practice which terminal goes to tip and which to ground.
I used a twisted pair of regular wire to the radio but in theory a
shielded cable would be more appropriate.)

Hang antenna with two supports to form a big triangle. This part
can require some creativity. I have wooden shelving which serves
brilliantly for this purpose.

Mechanically this antenna is a mess. You'd want to build a box for
the transformer and a plug for the cable to the radio. That's next
and I leave the mechanical details to you.

The point is it's simple, uses no batteries, requires no tuning,
can be packed easily, and seems to outperform an end-fed wire every
single time in the test environment I tried it.

Some notes:

Noise pickup is reduced -- which is the hardest part! Signal
strength is more often than not higher when the antenna is a loop
than when the center wire is disconnected in the same physical
layout. Even when it's not stronger, the noise level is better in
the closed-loop configuration. So far.

WIthout the transformer, many radios I've tried will overload badly
due to broadcast band overload well into the 60 meter band. The
transformer also may help reduce noise transfer, though the results
were so poor without it for other reasons I didn't bother doing any
further testing. I think some kind of magnetic coupling (ratio may
be relatively unimportant) is an essential part of why this works,
but I'm really not sure of the reasons. Point is, the transformer
is apparently an important part of success.

Signal strength does not appear to be particularly affected by
antenna orientation. Probably the mix of horizontal, vertical,
and diagonal wire is helping reduce polarization fading.

You could wind your own transformer with a toroidal core. The
winding ratio is probably not so important although a step-down
configuration may be better if you're trying to match a coaxial
cable. The only thing is you want to be sure the transformer passes
3-30 Mhz range. The mini-circuits part does that, but surely that
isn't a hard thing to accomplish.


If anyone feels like fiddling with this "transformer coupled
medium-sized indoor loop" they are welcome. I can't guarantee
results in the general case but it's the best thing I've tried so
far by a big margin as far as pulling real signals out of the
indoor noise soup.

I finally caught CKZU on 6150 with this which was simply impossible
before in the noise soup of this condominium.

Cheers and hope all are having or planning to have a great Turkey
Day

-- ross

Also, the configuration doesn't seem to matter much. Triangle/delta,
rectangular, whatever. It seems amazingly unaffected, even if some
of the wire is lying on the floor. Use whatever supports you can
find and don't be afraid to experiment. I got great results with a
"delta" shaped loop that almost didn't reach the listening position,
so it was diagonal and took up half the room. Children and pets keep
out!

My working theory is it's responding primarily to the magnetic
component of the incoming signals. At 31 meters, a 25 foot loop is
well above the technical definition of a small loop (1/10th
wavelength) but is still way under the length of a resonant loop, so
that's why I'm calling it a medium-sized loop.


Ross. Sounds like a lot of trouble to me. Myself; about the last 10
or 12 years, I have used a Wellbrooke loop here- inside. When I ordered
my first loop from Andy, I just hung it from a ceiling fan in the small
bedroom I use for my radio storage. And, waiting for the weather to
break, before it would go outside, I had to try it. Well, this loop
is still hanging in that room. A short run of coax to my listening
post here. Works great. 2 other Wellbrooks are out the end of my back
yard, and they work great. But, ya can't beat a good loop inside.
And easy to hide, no wire taped around a window or around the
corner of a room. Yes, i tried all those too. BTW, another good
set-up is a Par- EF-SWL antenna. This is a super short wire, about
45 ft I believe, and fairly quiet inside. I travel with one of these
with my quick set-up. I was told Par sold the operation, so I have
no idea what the antennas are like now. But I recommend Randy, at
Bigapple59 on ebay; he has a few of the real Par antenna.

And, it's 12:00u/ about 7 am here and snowing. So, best of the
Holidays to all you guys. Be careful out there.


Drifter...

Thanks for the tips. I had an AL1530 outdoors and it suffered two deaths. The first is when I selected the wrong antenna with a Kenwood TS-570D connected and transmitted into the Wellbrook and fried the antenna. Apparently it's not designed for 100 watts at 40 meters.... this was a very sad day.

The second was when it was in storage awaiting me getting around to repairing it or getting it repaired, it was stolen along with everything else of value in the unit.

I've already thought about Christmas coming and a new Wellbrook loop, this time to be used only with receive-only gear.

-- ross