The AM Forum

I'm having a devil of a time finding this. I tried one at ham-com 2012 and it was wonderful at killing noise.

This guy makes them and sells off a small site on the internet.

1 meter diameter, of aluminum? tubing. For HF.

At the top is a "T" mainly as a support for it as a pipe extends top to bottom, and at the bottom there is a box with a 30dB amp inside and a antenna pole mount. It gets DC off an injector near the RX.

Santa can only bring it if I can find it!

The Pixel RF-1?

http://www.pixelsatradio.com/product/shortwave-magnetic-loop-antenna/

That's it, thanks!

That antenna is worth the money. I have one and with careful rotating, can null out unwanted signals and it is noticeably quieter, cuz of the Magnetic Loop.......
Fred

If you do set up one of these ants, please give us a report of your experience.
Thanks!  

Save a ton of money and build your own. It's just a Mobius strip loop with a preamp from Clifton Laboratories.

I have been using one for several months. Although signal levels are lower than from a "normal" antenna there is a 2 to 3 S-Unit improvement in s/n with loop at about 30 ft. Where my loop is located the null/peak effect is useful, but not very pronounced, maybe a couple of S-Units.

In case you are interested, an article I wrote for my club newsletter is attached.

There are a number of user reviews on eham at:
http://www.eham.net/reviews/detail/9441?page=2

That's what I was thinking. When I couldn't find a price in the first 2-3 pages, I figured there was a reason. But for the folks who either can't figure it out or don't have the time and don't mind throwing money at the problem, it's probably a good alternative.

After setting the SX-62B back up recently and hooking a temporary chunk-o-wire to it, I was just about to make a post to solicit loop comments. There's a thought....

I don't have the time as we are aware! The money has been thrown.

I have some time to take off after the holy days already intended to work on the Tucker TX, so a simple test can be made of the loop on a 10 FT or 20 FT pole, such as one or two TV set poles. I can orient the loop so it's the same direction as the dipole, and go from there. This week I'll get some guy cord to temporarily hold the poles in place. A stake in the ground should be temporarily OK for the bottom.

I need an up to date SWL frequency listing. Mine's at least 10 years old.

I have no 'percise' SDR DB meter.. any judgements will be how listenable a signal is in an a/b comparison and I'll note whatever 'db' the s-meter may indicate. The easiest thing to use is a TS-430.

Like anything else, I might examine it and add making a bigger one to the end of the list of experimental things to do. I believe I know the preamp IC used, it's a wideband line driver perhaps for DSL but I don't remember the part number which the salesman told me at hamcom.

+ or - $450 for it.

Time=money=time.

73DG

Let us know how well it works. If you can make some SNR comparisons (measurements) comparing the loop with another antenna (wire, dipole, etc), that would be great.

Someone wanted a recording. Here's one.

I have been using a Wellbrook 1530 (which is similar to the Pixel loop) and a home brew diamond shaped tuned loop for years. The difference between those and the dipole can be dramatic.

In this recording I'm fooling around switching between the loops and the dipole. The dipole is the noisy signal. You can probably figure out when the phasing is adding and when it's cancelling:

Very impressive results Jon!  Big difference for sure.  Sounded like Gary in the recording.

Joe, W3GMS

"  Time=money=time. "

Yes, first Cliff, N6ZU, then Gary, K6GLH.

If the result is like the recording there will be no complaints.

Baum's original article describes the benefit of additional Moebious loops connected inside the shield tube, so it might not be necessary to make the loop larger to get better results -- just more loops inside. Clifton Labs uses a pair of matched grounded-base 2N5109s for the input stage of their Norton preamp. Cocnern mentioned earlier about interference from a high power broadcast station is addressed by Pixel, which offers a BCB rejection filter in the preamp as an option.

Jon gets terrific results with his loop. Mine has not shown that degree of noise rejection although noise here is extremely wide band compared to what seems to be power line or other recurrent pulse-type noise at K6JEK.

Bob - NE

That's two loops phased with the DX Engineering phaser, the NCC-1. That could account for some of the difference. And it depends on the noise. Sometimes the loops don't help. Sometimes they are worse than the dipole.

I dream of a quiet QTH. People talk about S3 noise levels. Mine is often S9, sometimes 20 over on 75 meters.

I went back and read your post more carefully Jon, and now understand what you have there.

As for S9 noise, that's the usual situation here on 75M. I feel blessed on the few occasions when it is down to S5. It's almost enough to drive a man to CW, where narrow bandwidth comes to the rescue!

The loop showed up a week ago and I finally had time to open the box.

For a quick test I set it up in the dining room where a R390/ hi-fi system is and hung it from a screw I ran into in the ceiling. (got to love that, XYL never complains!).

If how I am now receiving KAAM is any indication, this may solve many noise issues. For whatever reason, the lower the frequency of interest, the worse the noise is. KAAM goes to 1KW at night. It's unlistenable at night normally, but now I hear it clearly with no buzzing, and not only that, between the songs, I can hear the various other AM BC stations that are on the same frequency beating. Not with great clarity, but no more racket.

Don't get me wrong, there is racket up and down the bands. The R-390A is sensitive enough to pick it all up and the loop is after all 4FT above the floor, in the house.

I have an excuse to go out tomorrow because the knob on the old GE washing machine broke. I thought it was the switch, but no, the little plastic teeth at the back of the knob have finally been shorn off after 15 years of service. You know, push in, crank around to desired cycle, and pull out to start. Now it's push in and spin the knob freely. While the switch is out, I already cleaned and lubed the little ratchet clutch. It all turns much easier now.

While I am out, I can pick up two of those 8 or 10FT TV masts. That with a set of guys is enough to put the loop and a lightweight TV rotor up.

It is very directional, as advertised. In the BC DXing it's most useful to null out the undesired station. I wonder if that will work on a noisy SSB station that fires up.

Tomorrow, Dennis W5FRS is coming over, and he's going to help me with that Tucker transmitter. He says it will be working before evening. I'm not always optimistic about how much can be done in a day but I'll go with the flow.

The performance vs the single 160 Ft turn lying on the ground is much better, but that has no amplifier and it necessarily runs beside metal posts, a metal building, and over a 240V 100A circuit. bah.

I'll report later after the new loop gets put up right and used with the radios in the 'shack'.

I should also mention KAAM does not transmit that HD stuff any more. No more hash coming out of the hi-fi. Better now for good wideband analog listeners.

Now,  Imagine that loop on a 5 ft horizontal mast with a second loop made of coax mounted sideways to it for the back door. Mount the center of the mast on the TV rotor and turn the whole thing around.   The plans for this are in an old antenna book I have. 

C

I think I saw something like that on top of a robot's head once. Or maybe it was a dish and a horizontal loop. That article would be interesting if you could find the book, who knows I might have a copy somewhere too.

I will look for it. But the concept was very simple. It just had a second loop slightly larger in diameter behind the first loop.  The loops formed a T.   A capactitor tuned the back loop.  The rest is all my idea.

Good news,  I talked to Jay at Array solutions.  Jay has the rights to the Shared apex loop antenna and has been testing it and fine tuning the design now for many months.  They are on the third preamp design and now have 6 to 7 SU of directionality.  The PCB board is now being made. 

I think for me a wideband shared apex loop setup that you can steer around from the shack is ideal.

C

And what do the two loop do?

Two loops enable use of a "phaser" like Jon's DXE NCC-1 to combine their outputs. RF from the loops can then be manipulated in phase and amplitude to enhance rejection or maximize desired signal.

Oddly, there is a lengthy article by a local boy on loops for DF in August 1940 QST.

Phasing can be done with any two antennas. I've done that with the MFJ 1026 phaser unit. It wasn't clear what Clark was doing or why the physical arrangement was important. Same for the purpose of the capacitor.

There was a good article in the October 2010 QST by Tony Preedy, G3LNP, "An Orthogonally Steered Antenna That Reduces Interference" wherein a K9AY loop is modified so that the rear side null elevation angle can be steered. The entire loop could be rotated in the azimuth plane, so a null could be placed almost anywhere. Some pretty amazing QRM reduction was possible. This system was designed to reduce more distant QRM. No evaluation was done on local QRN. My K9AY might be modified this way soon.