Attic Loop and Antenna Tuners

(1/3) > >>

A. Chris Fristad:
I am planning to put a loop inside of my attic that will run along the peak, down both sides to the eave and then along the eave.  Approx dimensions of loop will be 35’ by 10’ (90'approx).

I asked ICOM if the AH-4 tuner would work for this configuration by connecting one end of the loop to the antenna connection on the tuner and the other end of the loop on the ground connection on the tuner.  Their response was, “That application of the AH-4 is not supported by Icom, but there is information available of successful installations similar to yours. Check the Internet, ARRL and other publications for information.”

I was wondering if any of the forum members has tried using the AH-4 in this manner?  If not in this manner, could I connect the loop as a random wire instead of a loop?

If the AH-4 does not work for this, what kinds of tuners are other amateurs using?  Do they have a remote?  If a different kind of tuner, will it work with the ICOM self tuning?

I have an ICOM 756 PRO II which is why I would prefer using the AH-4 to have the tuner as close to the antenna as possible.

Bill Savage:
There was an article in QST a while back where the author used an autotuner similar to yours to feed a delta loop. Keep in mind that your feedline will become part of the antenna, since the ground lug on the tuner is at the same RF potential as the coax shield. As a result, you may have an "RF in the shack" problem, at least on some bands.

A loop that's just 90 feet in overall circumference will have a very low impedance on 80 and 40, and the Icom may not be able to match it. And unfortunately, a horizontal loop that size will radiate much of the 30, 20 and 17 Meter energy straight up and straight down. There will be some low angle radiation on 15, 12 and 10, but you know how often those bands are open these days!

But give it a try. If you get consistently lousy signal reports and/or or a lot of your calls go unanswered, then you may want to try a different configuration with the AH-4, such as a "zig-zag" doublet (dipole).

Can you put the AH-4 outside? Install it by the house (maybe behind a bush) at ground level, and run some insulated 26 ga "stealth" wire up to the roof and across it. Zig-zag it if necessary. A 70 foot wire will get out fairly well on 40 and up when worked against a ground rod and just a few radials.

Jon M. Pollock:

Rather than connect the AH-4 directly to the antenna, I would suggest trying a good quality 1:1 CURRENT Balun between the  AH-4 and the loop. A loop is a BALANCED antenna, whereas, the AH-4 output is basically UNbalanced. You could put a SHORT piece of coax between the AH-4 and the Balun and then connect the loop to the two Balun BALANCED output terminals.(You would connect the center conductor of the coax to the "hot" output terminal of the AH-4 and the Braid of the coax to the Ground terminal with the other end of the coax terminated in a male coax connector to plug into the balun.) You could also connect the balun right at the AH-4. This would help keep RF off the feedline to the AH-4. You could also put several ferrites on the line to the AH-4 and/or put a choke of coax (typically 10 turns about 10" in diameter) between the AH-4 and your rig.

Make sure your rig has a GOOD ground with a short lead to the ground.

You proposed loop WILL work... the unknown question is HOW WELL...which you won't know until you try it.

"Give it a try!"  Experimenting is what Ham radio is all about!

73,  K0ZN

I have a lousy little loop going around my place, it's not that great, but my Yaesu FC-901 tuner will tune it.

As far as actually getting out, that's another question!

You can always switch capacitances, coils, in and out to change bands or optimize it for your choice of bands.

Do not contact:
Loops are terrible when operated below their fundamental frequency, which is a full wavelength loop. 1005 divided by the frequency in Mhz equals the length of wire needed in feet. A random wire would work better. If you're stuck with attic only antennas you might consider a small Magloop antenna. This link will get you started on researching them.
Capacitors for Magloop antennas can get expensive! Here is an article on home brewing your own capacitor that works very well.


[0] Message Index

[#] Next page