Receiving Loops and other Limited Space Alternatives?

[Todd, KA1KAQ]

For years I've had really good luck using just a random piece of wire, sometimes strung around the inside of a room, for casual MW/SW listening. I've always wanted to build some kind of a loop or other gimmick to use in a limited space, but never got to it.

I'm curious to know what other folks use and what approach has worked best in your experience. Eventually I'll get a Beverage set up for at least one direction, but having sometime small, even steerable, to use in the house would be cool. I'm mainly looking to null or otherwise block out/minimize unwanted signals and noise to favor a specific station or direction. Not looking for 'tiny', just manageable.

[Steve - K4HX]

I built one similar to the one at the link below. I used PVC pipe as the spreaders and RG6 for the loop.

http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/3805er.htm

[WQ9E]

I tried the shielded loop construction to get rid of a noise source on 75 but I was never happy with the performance.  I ended up rebuilding it with 3 turns of wire around a pair of 4' by 4' spreaders with a 1 transistor preamp/impedance matcher at the feed point.  This setup works very well for me.  With some noise sources the shielded loop might work better but it didn't in my case.

With a small antenna like this on MW or 160/80 it is important to do some sort of impedance matching at the feed point if there is more than a few feet of feed line or the shunt capacitance will kill your signal level.  I guess you might be able to use the old style low capacitance coax that was used in automobiles to avoid the same problem with a short whip for AM.

One of my Drake SPR-4 receivers came with the AL-4 loop that plugs in the top.  I am impressed with how well it works on MW but that antenna input is switched out above the BCB so I have never been able to try it on 160 or 80 to see if it works.

[N8ETQ]

  Hi,

     Got one here, a customer dropped one off he had sold
to a local. customer was here for service work and asked if
his buyer could grab it from me. Doesnt look like the
owner had it up too long and the buyer never showed to get it...

/Dan

[Opcom]

I hung a piece of RG-58 from the ceiling around the perimiter of a 10x15 room. The shield was used as the conductor. This single turn went into a 5:15 (turns) step up transformer on a red core and into a TS-430. It worked OK and I was able to get some halloween SSTV images from 300-800 miles out, but there was still a lot of power line buzzing noise. That is most offensive here. Overall it was never better than the dipole and in most cases much less signal.


Using an analog video distribution amp as a 10dB voltage gain amplifier terminated with 1000 Ohms worked well but the noise was still there. It was also run with a 75 Ohm termination and worked well. I am plagued with power line noise. YMMV if you got no noise it might work well.


BTW this is a good use for those old commercial type video distribution amps. Most are good to 7 or 10 MHz as-is. With some tweeks they can be made to do the whole HF band pretty well and reducing capacitor sizes helps kill off gain below 500Khz. The one in question was a rackmount Dyn-Air having 4 outputs per amplifier channel and each channel is on an assy that can be slid out to swap or work on, hot plug. They are all discrete as well. The commercial ones almost always have a knob on the front to set the gain. In the original application it would set the output to 1V p-p. In this application the desired volts are very low and like any broadband driver amp, can easily make more than 1 volt before clipping and this is even greater with a 1K load instead of the expected 75 Ohms so it's a consideration at the receiver. beware BC interference. It won't overload the video amp but can generate a quite large RF voltage at the output.

[W8UJX]

I have the same question.  There is a 10KW full time AM station on 1290 KHz about 3 miles away from the house.  80 dB over 9 on the BC band.  Strong third harmonic on 3870 KHz where most of the AM stations are.

I live in the city and the usual noise level at night on 80 is S9 to 10 over.

I need a design with an amp that will really minimize stray pickup and provide a sharp null.  I want the antenna to be a small outdoor rotary loop for 75 meters about 5 or 6 feet in diameter that I can mount about 20 feet up and rotate with a small rotor (which I have).

I have looked at a lot of designs but most of them don't appear to be well balanced which I think is necessary to really minimize stray pickup.

Any advice will be appreciated.

Thanks,
Jerry, W8UJX since 1954

   

[VE3LYX]

Maybe this isnt what you want but I use this antenna on my regen. It can hear anything any of my other RXs can hear on any of the other antennas. I have used it for AM work some Sunday mrnings and always use it for my CW stuff.  It just sits here in the window. It is made from a 4 inch wide section of 12 inch Sono tube from Home Depot. I wound 12 turns of #12 stranded wire. (Automotive type wire)around it and tpaed it with masking tape then painted it. It is about 28 inches tall,  the post being 2 inch wooden dowel. I brought the two leads down criss-cross as you can clearly see in the photo even though they are also taped over and painted. At the bottom I added a third wire which does nothing except allow me to braid the wires togther to bring them to the feed point. I used lamp cord (which is 75 ohms)to feed it to the rx  which is incidently a 12sl7 regen running on a 12 volt gel battery for filaments and 12 nine volts clipped together inside a celsetial T box for B plus. The B plus lasts 6 months to a year. The gel battery I recharge occasionally. The antenna works very well. I have had several QSOs using it on the rx. I cant give you a good answer on the sig to noise deal because I use it because this recver really likes it and am hesitant to hook it to anything else. I have used it for the Bruce Kelly deal and all of my AWA group QSOs . I have also used it when talking to Al AGM and Tim 6PG  from time to time on AM on 80m. It just sits here on the desk in the window
Don Ve3LYX

[VE3LYX]

This morning,feeling a bit guilty I hadnt tried it before, I tuned in a QSO on my HR10B using my dual band inverted Vee. Just to see I switched to the loop in the picture. Signal was a bit less. Maybe a S unit but not quite.Some of that could have been just noise but my hearing isnt that good anymore to give an honest appraisal of that.  Still readable in both instances although not strong in either case. For a 12 inch loop sitting on a desk (behind a screen as well.) I am satisfied with it. I did build one from a hoola hoop thinking bigger would be better. I was wrong. This one outperformed it in everyway. Maybe I didnt do the hoola hoop right. Not enuf turns or something but I hit it out of the park with this one so what the hay? With the regen which is a seriously sensitive rx compared to a Superhet it is easy to overload it on the input side. This loop and it work perfectly and the pair will outperform any other Rx & antenna I have here and will run right with my ts830s on a big antenna. Why do I use a regen?
When I operate my 1930s and 1920s style HB sets it seemed only right to me to use the matching RX style . To be running a low count of ancient tubes:ie,   one or two(for AM) and be listening on a R390 or a Racal or something seemed a bit dishonest to my square head so I choose this method but enuf of that. Here is a practical decent working hoop or loop  you can build and use today before the sun goes down. Its performance will be so close to an conventional antenna at height outside for receiving you wont care.
Don VE3LYX

[W1AEX]

Todd,

I played around with indoor tunable loops for the AM BCB, 160, 75, and 40 meters but found them to be kind of disappointing. I finally settled on two broadband outdoor wire loops located away from the house and oriented to give either N-S or E-W coverage. Even without preamps at the feedpoint they performed great but with the preamps installed the results have been even more satisfying. Some cheap RG-6, 85 feet of wire, some rope, and about an hour of time is all you need to put one together. Nothing I built and used indoors ever came close to the outdoor broadband loops.

Rob W1AEX

Some pictures and videos of the loops being used on various bands can be seen here:   http://www.w1aex.com/loop/loop.html

[WU2D]

Rob,

You nailed it - yes you need a transformer for those untuned coax jobs and bigger is better but even a 24 ft circumference loop does OK and smaller loops work with a preamp out there.

Smaller resonant loops work very well outdoors too. For these I typically use 3 feet on a side so about 36 ft of wire and a variable with a motor. The match is a single turn coax Faraday loop with just the center shorted to the ouside of the coax. This guy is a single turn with a diameter of 2 ft.

Mike WU2D

[W8UJX]

Interesting design Don.  I may just try one with my Ocean Hopper 3-tube regen RX.  I could also mount it on a pole outside and use a rotor.  It might pick up a lot of unwanted BC signal on the feedline but a twisted wire feedline may fix that problem.  I have a new toy to play with.  Hi.

I tried the K9AY loop but did not have much luck.  I will try your design Rob and try to come up with a design that allows me to rotate the loop.

Whatever design I try it is important to be able to null out the BC station and try to minize pickup of the third harmonic.

Thanks,
Jerry, W8UJX since 1954   

[Todd, KA1KAQ]

A lot of good thoughts here. I'd wanted to stick with something inside the house that I could manipulate as needed, but Jerry brings up an interesting prospect. If only I hadn't left that lightweight TV rotor behind in VT.

I wanted to avoid anything too big like you described Rob, but thinking about it  - that would actually be a good 'standard' to fall back on. Limited in its utility as far as rotating, but so much better than a piece of wire hung atop the curtain rod.

So maybe I'll get something like that set up and try to build something like Steve showed and mount it outside with some sort of rotor. My biggest problem is a spur coming off a tower a mile or so away that I'll need to be looking right at to see AM 740 out of Toronto. I get a couple strong images or spurs off it already.

The next question is, what is the best compromise length to cover the BCB to maybe 10 mHz or so? Or should I stick to a smaller chunk for best results? I've thought of tailoring a wire or two for specific frequencies to get best results.

[WQ9E]

Todd,

If your receiver is desensing or creating spurs internally a tuned trap may be very helpful.  I have to use one on the input of the SX-101 I use on 160 to keep a Disney station out of Iowa (on the Halli 1650 IF frequency) from creating a hetrodyne on every AM station.

A Drake AL-4 size loop would work very well for the BCB and 160 (probably 75 also) and isn't too big for the inside of your house.  It would be pretty easy to construct a copy.  Mine has a very sharp null on the BCB.  Another good possibility is buy one of cheap marine RDF receivers that show up at garage sales everywhere and use the antenna from it.  Those are designed for coverage from LW through 4 Mhz.  Until I built my external loop to kill the intermittent noise on 75 meters I kept a Bendix marine receiver to pull out weak signals through the noise so the small bar antenna works pretty well.  I am not sure what the impedance is but a manual will probably give you a good idea and it would be easy to match with either a transformer or transistor impedance matching stage.

For the higher frequencies those little active voltage probe antennas work pretty well.  In an early attempt to get rid of my noise on 75 I bought one of the MFJ phase shift boxes.  It didn't help much with the noise but it was fun to play with (I could make WWV on 5 Mhz. go from S-9 down to nothing by adjusting the phase and balance between my main and noise antenna) and used with its internal whip as an active antenna it made a nice compact indoor antenna for the higher SW frequencies.

[VE3LYX]

You mean you havent made it yet? Are ya gonna fish or cut bait? Couldnt take more then an hour.
Don Ve3LYX

[KM1H]

For outdoors a HB T2FD works great 160-10M  for receive with a low VSWR on a 450-600 Ohm line or a balun to coax. There is some loss at the lower frequencies but a simple preamp takes care of that.

Ive been rather pleased with it as a general coverage antenna for boatanchors and old wood cabinet house radios.

[W3FJJ]

I recently moved to an apartment complex, and the noise is terrible on
all bands. Its beyond trying to track down the source. I recently built this loop,  it is 24
inches in diameter loop, made out of 1/2" copper tubing. I originally was going to put multiple
loops of wire inside and resonate it with a capacitor. and put preamp in base.
 But for the heck of it, i just fed one turn
of rg8 mini inside the tube, no capacitor, no preamp.  and see what it would do. Wow, I can null
out the local noise to near nothing and pick up signals now on all bands. They are not real strong, but I can copy
many sigs. Seems my noise is coming from one direction, so that helps..
I will be building a preamp for it, and try a balanced feed, see if it can be improved , but just this simple set up is
impressive to me..

 I going to mount it on a  microphone floor stand so i can move it around the room  and swivel it , 2 feet in either direction,  seems to make
a big difference on signal strengths and noise, depending on band and conditions...

[VE3LYX]

I,like the Mic stand idea. I hadnt thought of it and there is one sitting right beside me about 4 feet from my loop.
This morning on the group with the lads up here I switched off the audio on the HR10B recver and turned on the regen connected to the window loop. Mike 'CMM was txing at the time and for Mike and me,we are not in the best spots for propagation so copy is often marginal at best. To my surprise I could find him easily on the loop with the 1 tuber and while copy was not super it was certainly readable. It kinda surprised me. No better or worse really then with the HR10B and a 80M inverted Vee.
I have been playing with transmitting loops too.(smaller multi-loops)  I threw in the towel once but am back at it. A real challenge but very interesting.
Don Ve3LYX
THis afternoon while playing with different feed methods I wound up disconnecting a link type coupling. I left it in place after changing feed styles although it is now hooked to nothing. Then on a whim decided to put a 150ma flash light bulb accross it to see if I can use it for tune up. I can see the antenna from my shack window. It worked better than I would have thought. Then I took my field strength stuff out along wth a small recvr. I have a variable cap in the loop like a big tank circuit. I tried tuning the cap with the Tx on. The light indicates resonance just like it does on my hb cw one tube rigs. Works very well. Much better then my ears. Nothing to do with RXing for sure but it fascinated me. This antenna is for 40M. Forgive my enthusiasm.

[Todd, KA1KAQ]

You mean you havent made it yet? Are ya gonna fish or cut bait? Couldnt take more then an hour.
Don Ve3LYX

It takes me longer than that to read your daily posts, Don. 

I do appreciate the input and first hand experiences. That's the stuff most helpful when you're looking at a project like this. I'm not looking for 'quick', I have that now with the wire stretched over the drapes. More of a compromise between performance and flexibility. A Beverage would work best at the sacrifice of flexibility. I'm looking for a good compromise.

I recently moved to an apartment complex, and the noise is terrible on
all bands.

Hopefully this is a temporary situation while the storm damage is repaired, Chuck. When I was up north living right on Main street in the village, those damned low pressure sodium street lights were the bane of my existence. There's a lot to be said for living in the sticks.

Noise isn't the issue here, mainly the ability to isolate and hear specific stations that are strong some nights, in the noise others(on the random chunk of indoor wire). I've actually got an old DeForest spider web loop and another Brand X that I've wanted to try. In the end, I will likely go with some sort of steerable loop like Steve posted w/preamp, and a fixed arrangement like Rob uses. That should provide the best of both worlds.

 

[W3FJJ]

Yes Todd, hopefully It's just temporary,...I plan to rebuild.  Apartments in city are nice, but no good
for ham radio!
I agree if you don't have noise problem, the K9AY loop thing or beverages
are preferable to a small loop, in picking out weak signals. However, it be interesting to see how
a small indoor loop will work on pulling signals though  summer time static, as it
has a deep null and more precisely rotatable.. than a wire array..
To me, the more antennas you have in your arsenal, the better. GL and lets us know your findings.

Chuck

[VE3LYX]

you're looking at a project like this. I'm not looking for 'quick', I have that now with the wire stretched over the drapes

This is not a "Quick." This is a very good working antenna that runs in line with my full size inverted Ls and inverted Vees. It works well enuf it is my antenna of choice for this type of operation. This is NOT a stop gap measure. It is a good working RX antenna.
Don VE3LYX