First Impressions - Pixel Loop Diversity Reception

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Stu K6TU recently reported on this Community the success he had in contests using a Pixel Loop with his Flex 6700 for diversity reception.

https://inlogisinc.com/products/amateurham-radio-antennas/ham-amateur-radio-antennas

https://www.youtube.com/watch?feature=player_embedded&v=pkcGIGZ1Cd4

Since they were on sale before New Year’s at HRO @$450, I thought I might give it a try to see how it might work with my SteppIR MonstIR

I must admit to being quite skeptical about small antennas particularly when mounted in the vertical plane when HF is usually horizontally polarized.  Further it’s a magnetic loop so it receives at 90 degrees to the Electrical Field.  The receive lobes are end to end on the loop rather than broadside as you would expect from an electric field antenna.  The loop only weights 3 lbs and is 1meter in Diameter.  The loop has a preamp at its base and uses RG-6Quad to carry both power to the Preamp and signal back to the radio.

I finally had some time today (@Burt I am far to busy experimenting to rag chew) so I built a 5’ antenna base in the backyard out of 1 1⁄2” PVC, installed a small TV rotor and the mounted the loop onto a 5’ piece of 1 1⁄4” EMT galvanized pipe as a temporary test stand.  The loop was 10’ from the ground albeit the backyard hill rises 50’ vertical right near where the stand was installed. 

 

First Impression.. it actually hears things. 

More important it actually hears very different signals than the MonstIR.  Noise spikes that was quite dominant on the MonstIR were absent on the Pixel Loop.  Noise spikes that were heard on the Pixel Loop were not present on the MonstIR.   They are clearly hearing very different things.

Surprise, surprise.. a few signals were actually much louder (10-20 dBm) on the Pixel Loop @10’ than on the 4 Element MonstIR @85’ even when both were oriented for maximum signal. 


Diversity was quite interesting. 

1.       In some cases, it made no difference. 

2.       In some cases it made things much worse as one or the other antenna was not hearing the signal.

3.       However in many cases, the diversity reception was significantly more intelligible than the non-diversity by either antenna.


The 2 SCU's on the 6700 made it very easy to test different configurations for diversity.

I have not spent any time making detailed measurements yet... but I could see in dBm on DDUTIL (I really wish the S Meter in SSDR read out in dBm) that there were significant differences in relative received signals for each of the 3 different cases.

I must admit to being rather surprised that the Pixel loop actually worked and especially since it was only at 10’.


A few months ago we removed the top 30’ of a tree on the backyard hillside.   But we left the bottom 20’ of the tree trunk..

So I now have a perfect natural antenna tower which should not need a building permit for the pixel loop and which once installed on the tree, the loop should clear the hillside.


I will report back once it’s at planned height with proper measurements
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KY6LA - Howard, Elmer

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Posted 4 years ago

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KY6LA - Howard, Elmer

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Photo of KY6LA - Howard

KY6LA - Howard, Elmer

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KY6LA - Howard, Elmer

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View from loop. Fog on the Pacific Ocean.
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KY6LA - Howard, Elmer

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Definitely hears better at height

I sometimes make Q's with the loop and do not hear the station on the beam
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Mark K9BOO

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Thanks much Howard for your reply.  Have you ever tried it mounted horizontally at height?

As you already know, one of the advantages for some are the nulls off the "holes of the doughnut"--with the ability to rotate the antenna for a better signal or to reduce an interfering  signal.

Other applications may require a more 360 degree directional ability to receive.  I read that is possible with horizontal mounting (antenna nulls point up and down).  Just wondering if anyone has tried this and what the resulting experience was like.

Thanks!

Mark
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KY6LA - Howard, Elmer

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Did not try it horizontal and not about to climb the big tree stump again to test it. Once was hairy enough.
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Mark K9BOO

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I don't blame you!  Especially because your existing installation looks very good (and functional).  Maybe someone else will eventually try the Pixel Loop horizontally at height--maybe me one day!

Thanks again.

Mark
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Michael - N5TGL

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I must admit to being quite skeptical about small antennas particularly when mounted in the vertical plane when HF is usually horizontally polarized.
In the near field with a beam, yes.  In the far field, where most HF reception takes place, it is either right or left hand circularly polarized. 

Here's a good spot to get started learning about X and O mode propagation: http://www.pa0sim.nl/XOpropagation.htm
(Edited)
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KY6LA - Howard, Elmer

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You are confusing the difference between the H and E fields

I was definitely a major skeptic too until I put a pixel loop to the test. The loop is about 25' AGL

The Beam is a full size SteppIR MonstIR @85' AGL

There are definitely situations where the loop hears things that the MonstIR does not hear. Had a 40M QSO the other day...The beam was blasted with noise. And dud not hear much of anything but the loop had a number of S9 signals that I worked ok.

On JT 65. I run them in parallel. 80-90% common but definitely uniques on the loop that the beam does not hear.

On The Other Hand. I use the beam to XMT. - 12KW ERP makes up for weak signals heard.
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Michael - N5TGL

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I am not confusing H and E fields, because I'm not talking about them.  I am talking about signal polarization, referencing your comment that you stated that "HF is usually horizontally polarized."  To be clear, I'm assuming your statement refers to the polarization of an incoming HF signal at the station, apologies if I've interpreted that incorrectly.

Once a HF signal has been bent back down toward the earth via ionospheric propagation, it is no longer horizontally or vertically polarized, it is circularly polarized, and likely elliptically polarized because the antenna is probably not dead on aligned with the incoming signal.  Furthermore, it splits into two components, X (counter clockwise) and O mode (clockwise), which are the result of an EM wave bouncing off a magnetized plasma, which is exactly what the ionosphere is.  This is why ionograms specifically call out X and O mode, not H or E. Incoming HF is definitely not horizontally polarized.

Bottom line is that for a RX antenna, vertical or horizontal polarization likely makes little difference in reception.  What would make a big difference would be constructing a circularly polarized turnstile antenna that could be switched for X and O mode reception.
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Reg

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At my QTH the biggest advantage of the Pixel Loop is during convective activity (thunderstorms) which are sometimes active in all directions.  On 40, 80 & 160 meters the receivers will show a noise floor of S8-S9 with other antennas and the Pixel Loop noise floor will be S2-S3.  Obviously, this makes signals "loud and clear" that are buried in the noise when listening on beams or wire antennas.

Howard has the advantage of rare thunderstorms in San Diego but some of us live with the low band noise from April through September.

Reg
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k0eoo

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@Howard,

Howard, I'm hearing lots of good reports on the Pixel loop, but, have there been situations where the Pixel loop has not perform well at your
QTH??
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KY6LA - Howard, Elmer

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Of course, the answer is complex...

When there is a lot of noise (e.g Low Bands) the Pixel loop hears signals that are covered by the noise on the beam.   When both the beam and the pixel loop hear a signal, typically the signal is about 2-3 S units lower on the pixel loop but the background noise is also lower.

Under normal lower noise conditions, about 20% of the signals that the beam hears are NOT heard by the Pixel Loop

The best test for this is to use JT-65 in parallels  80% of the signals are common.  The beam hears typically another 15% uniques which the loop does not hear but the loop hears about 5% uniques which the beam does not hear.

Bottom line:  When the bands are very noisy the loop does very well,  When the bands are quiet the beam totally outperforms the loop.

As Ken Stated.. we rarely if ever have thunderstorms or rain in San Diego... however i am 2,900' from 18 TV transmitters and 23 FM stations. which can produce a cacophony of noise especially when the beam is pointed that way...  When I am working a station from that  direction, i tend to prefer the loop to the beam.. but most other directions the beam is definitely better.
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Walt - KZ1F

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Great assessment Howard...thanks!
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Rob Fissel

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Howard, I have a Pixel Loop coming this weekend. I've heard that the wall wart can get a little warm, and many recommend unplugging it when not in use. I'm like you, and use the shack remotely frequently - hence I'd rather leave it plugged in at all times. Your experience? 
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KY6LA - Howard, Elmer

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It does not get that hot. Mine is 99F. Runs 24/7/365
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Rob Fissel

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Just what I was hoping to hear, thanks!
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k0eoo

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Thank you Howard for the detailed response on Pixel Loop vs. Beam performance.  Its noisy here in MN, especially on the low bands so looks like the Pixel Loop should be useful....
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Ron

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FYI, I tried reducing the preamp voltage from 20VDC to 12VDC to see if performance on the Pixel antenna changed, and it did not!  

I run my radio off batteries and solar power and spent significant effort finding a boost circuit with low noise.  Interestingly with over 100ft of wire to the antenna the Pixel preamp did not show any loss of gain until the source voltage dropped to around 11V.  I presume the developers of the Pixel wanted to make sure that the voltage loss to the antenna did not affect performance, but 20V seems like it was over designed.

Bottom line, it is safe and effective to run the antenna directly off battery voltage and not use the wall wart.

Ron

K2RAS
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Rob Fissel

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This is really excellent news. I was bummed to find out that it ran off 20v. Using a RigRunner bus to power everything in the shack, including replacing many wall warts (HT chargers, shack speakers, LED strip lighting, USB hubs, etc) with direct access to the station's power supply. 
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KY6LA - Howard, Elmer

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My preamp is 20V AC??
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Ron

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Now this is really interesting, I had just presumed that the wall wart put out DC.  I have been running the Pixel using DC for over two years and it works identically to plugging in the wall wart.  I just measured the wall wart and it is indeed putting out 24VAC.  Someone with more expertise than me may be able to add context.

Ron
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Ken - NM9P, Elmer

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Someone else posted a while back that they were told that they could run it from 12 VDC and that it would pass through the rectifier bridge just fine and power the loop. This leads me to think that the Pixel has a built in half or full wave bridge. A good move in that it would protect against reverse polarity damage. Also, a simple 20-24 VAC transformer would be RF noise free, in theory.
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Ron

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I ran into that earlier post and that is what prompted me to try reducing the voltage.  I always wondered how Pixel had sourced such a quiet wall wart, now I know why.  Helps to read the instructions...

Ron
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Dave-N9CHM

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I wondered about using my RigRunner to power the Pixel as well. Good to know, I'm running my Pixel on 13.8V DC now, running fine.