Tunable loop antenna help needed

[jimbofish]

Some time ago I set out to build an AM loop antenna from a 14" embroidery hoop. Using one of the formulas available somewhere, I put 17 turns of #28 enameled wire side by side, then set out to find an old radio to salvage a variable tuning capacitor, as it didn't appear to have much effect when connected directly to the ant terminals on a CCRadio.

Fast forward about 2 yrs and many detours later, I finally got a nice VC from a Grundig radio. Connected the loop to it, experimented with an old transistor radio and was able to get some stations to come in more clearly, but not as much improvement as I expected. I haven't tried adding a second pick-up coil as most of the radios I want to use it with don't have ant terminals.

So, I'm wondering if there's a problem with the way I wrapped the loop or the type of wire I used. I placed the wraps of wire side-by-side, closely packed. Should I have spaced them apart a bit? Or used heavier wire with insulation?

[jr_tech]

I suspect that the calculation is correct if you are indeed using a variable cap designed for the broadcast band. I have one small commercial loop that has a 9" coil and is wound with 28 turns of something like #26 enamel coated wire, closely spaced.... Pix 1.

I have constructed several loops, such as the 2 foot (diagonal) loop in Pix 2.
It has 18 turns of # 22 wire, spaced about one wire diameter. It has a 1 turn coil in the the in the center, between the other turns, for pickup. The pickup coil is helpful, as connecting a radio directly to the tuned loop reduces its "Q" and causes the tuning to become rather broad and reduces the improvement provided by the loop.

It may be that your environment is noisy from computers, lamp dimmers tv sets, battery chargers and other common household items that produce interference, and pretty much render the loop useless, as it picks up more noise as well as additional signal. Get away from the house and see if the loop works better. For most AM DXing, I use an outdoor loop (about 4 1/2 foot diag. 8 turns #14 wire) located about 75 feet from the house. It can barely be seen from the "radio room"... hint: the cross arm is directly behind a hummingbird feeder in the "woods". Pix 3.... Unfortunately, there are a couple of "solar dryers" located very close to the loop, which mess up the sharpness of the directionality somewhat, but it still beats using something indoors.

I added a close up pix of the outdoor loop... the 1 turn pick up loop can almost be seen at about 2/3 the diagonal of the main loop. I experimented with several different sizes for the pick-up coil and chose a configuration that yielded decent signal strength without reducing the "Q" too much. Many times, mostly in the summer, I will park my Icom on the small table in front of the loop, and operate it from a 12V lawnmower battery, to further reduce interference from sources in the house. I have an additional capacitor mounted in a box below the loop, to tune below the broadcast band. Last winter, I nailed several Long wave stations from Russia! These were on 153,189 and 279 kHz.
jr

[jimbofish]

Hmmm... we do have a lot of noise from the AC lines in our house, most of it coming from our neighbor. I'll give it a try out side. At least that might tell me if the loop works... or not.

I'm still unclear about the spacing of the wires in the loop... should they be spaced apart? Or does that not have an effect?

Thanks.

[jr_tech]

Originally Posted by jimbofish

I'm still unclear about the spacing of the wires in the loop... should they be spaced apart? Or does that not have an effect?

Thanks.

As A DXer, I prefer spacing the turns, as IMHO, this configuration produces higher "Q" which yields sharper tuning and better nulls. Much of the time, when DXing, the loop is aimed to "null out" an interfering station rather than maximize the gain on the desired station.

A suburban listener, desiring to improve reception of semi-local stations, might be well served by a broader tuning, less critical loop, that may provide a bit of improvement on several stations, perhaps without re-tuning when the station is changed.

Note: Many larger portable radios, such as the CC radio, GE "Super Radio", Sony 2010, Panasonic RF-2200, Grundig S350, and similar larger portables contain a fairly large "loopstick" antenna, and show little, or no improvement when used with a smaller loop, like the one in my first picture.
jr

[dieseljeep]

Greetings: I bought a Select-a-tenna at a thrift shop for a buck in like brand condition.They asked me what it was. I replied that it was a passive antenna for an AM radio. You are right that it doesn't do a thing for the GE Superadio.

[Reece]

Dieseljeep wrote: They asked me what it was. I replied that it was a passive antenna for an AM radio.
(Their response, no doubt: blank open-mouthed stares! )

[jimbofish]

Originally Posted by dieseljeep

it doesn't do a thing for the GE Superadio.

I'd guess it probably won't do much for a CCRadio either then...

[jimbofish]

Originally Posted by jr_tech

As A DXer, I prefer spacing the turns, as IMHO, this configuration produces higher "Q" which yields sharper tuning and better nulls. Much of the time, when DXing, the loop is aimed to "null out" an interfering station rather than maximize the gain on the desired station.

A suburban listener, desiring to improve reception of semi-local stations, might be well served by a broader tuning, less critical loop, that may provide a bit of improvement on several stations, perhaps without re-tuning when the station is changed.

Well, I'm 20-75 miles from any local stations and 150 or more from the ones I want to hear, so would spacing the turns slightly work better for me?

[Sandy G]

Try looking for a Kiwa MW Loop...Tiltable, steerable, tunable...I'd about give my guns up before I would my Kiwa...(grin)

[jr_tech]

Originally Posted by jimbofish

Well, I'm 20-75 miles from any local stations and 150 or more from the ones I want to hear, so would spacing the turns slightly work better for me?

I think that in that situation, I would use a fairly large loop (2-4 feet) with spaced turns. One nice thing about this hobby is that wood, pvc pipe, and wire are inexpensive, so you can build several different designs and determine which is best for your application.
This builder even makes his own capacitor:
http://www.youtube.com/watch?v=VPALB-ZZGbY

nice 4 footer here:
http://www.youtube.com/watch?v=HXQeZxeCJ2c

2 footer here:
http://www.youtube.com/watch?v=QpGXE...eature=related

Another:
http://www.youtube.com/watch?v=l_keF...eature=related

The ability to tilt the loop like the Kiwa is a desirable feature. Sometimes I end up with one of my home-made loops propped up at an odd angle to better null out an offending station.
jr

[Sandy G]

The R-389, the R-390s & EK-07 all LOVE the Kiwa...Took it over to a friend's house one Sunday afternoon in the winter-He has a late Thirties cathedral style radio that would barely pick up anything at his location...He thought his radio was sick, even tho he'd recapped it & checked the tubes...It "Came Alive" once we hooked up the Kiwa...Little 1KW daytimers up in Virginia & Kentucky popped out of the woodwork..Ratshak had a very good tunable loop several years back, & at $20, IIRC, it was better than one you could make yrself...Took some "Shade-tree" mechanic-ing, but it made a good showing of itself against the Kiwa...Naturally, when I went to grab a couple more, they'd been discontinued, so typical of RatShak...Excuse me, CELL-FONE Shak...(grin)

[jr_tech]

Is the Kiwa loop still available? I just checked Universal Radio and did not find it.

jr

[Sandy G]

Naw, it got axed several years back, too...IIRC, I gave $350-400 for mine brand-new...But its almost MAGIC in how well it works, especially w/ a super-sensitive receiver like a 390A...But they DO have a "Pocket Loop" which will fold up & fit in yr pocket-Call 'em at 507-634-6134, & it works all the way up to 23 mHz, so you get most of the shortwave spectrum, too...

[Dave A]

I have a TERK passive loop and it works well on my Radiola 60. It's called the Advantage. Two wire connection and inductive if you wrap the radio with the wires. $35-$40 or so.

[jimbofish]

When I tune the cap, the radio sounds average most of the cap range, then it suddenly changes and blocks out the station I'm trying to listen to. I'm guessing it's tuned to the station freq.

So what do I do to get the station I want if that's what it's doing?