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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Jim Bryce W5HFS

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I've been using the Pixel loop for over a year mounted on a ten foot PVC pipe hose clamped to a metal fence post in my back yard. My beam us a Tennadyne T-6 log periodic on a quadrapod on my one story roof. It's up about 30 or so feet. The results are similar to those you describe. It's rather amazing how the loop sometimes does better than the beam, and diversity makes it even better. It is my understand full diversity integrated into the 6700 rather than relying on stereo audio and ears is still being perfected. What's the status on this. BTW I also have a vertical dipole made out of two mobile 20 meter whips I switch in as an alternative for vertical polarization....results are much more mixed than the frequently dramatic improvement with the Pixel.
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KY6LA - Howard, Elmer

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Diversity works fine on my 6700  - Not steerable like in PowerSDR with my old 5000 but definitely easy to use.
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Andrew Russell

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My Pixel loop arrived Monday but came with a USA wall wart 24vac supply, not the 240vac input one I need so haven't had a chance to try it yet on the 6500.

Andrew de VK5CV



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k3Tim

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Thanks for the post about the antenna.  IF you have a chance can you let me know how it does on the SW stations - reduced noise - strong signal etc?  Thanks....

 (I really wish the S Meter in SSDR read out in dBm)

I know you know that  I known you know this...  If you hover the cursor over the s-Meter it will display signal in dBm.

 _..--
k3Tim
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Walt - KZ1F

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Actually, by way of historic relevance, why did the s unit come to pass? It seems to me, as you suggest, dbm is what the signal is not 5 or 7 of 9 or 10 over 9.
(Edited)
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KY6LA - Howard, Elmer

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I believe it was originally an audio measure When S-meters were added to Radios they were totally inaccurate and dependent on the RF Gain settings
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Doug K0DV

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Hi Guys, I also have the Pixel loop, mounted on a tripod with a rotor at a height of about 10'.  I carry it in and out when needed.  I fear that additional height will not improve the signal to noise.  The noise will rise as the height is increased.

By the way, the 6700 (and perhaps the other 6000 units) will read out in dBm.  It's easy to do, just click the signal strength bar with your mouse and then leave your mouse over the readout bar. The signal in dBm will pop up over the bar and will update, if you leave your cursor on the spot.

Doug
K0DV
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WA2SQQ

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I've been using one for two years and I have nothing but praise and amazement for this antenna. Pricey - YES, but it delivers. The first winter season I used it I picked up 6 new countries on 160. Due to my local, relatively high noise level, I was not able to hear the DX before purchasing the loop. Using the loop I can easily copy some of the low power fishing beacons that share 160m. I'm told these are in the N Atlantic and Canada. No other antenna I have can hear them. What you will discover is that height does not make much of a difference.
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Ed - W2RF

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The new SDR-Bridge 1.1.1 DIV SPLIT feature should be useful to diversity users, especially if using CW Skimmer. It is available at http://www.qrv.com/sdrbridge.html.

Brief instructions for DIV SPLIT. To use this feature there is a simple rule:
  • Define splits on the slice pairs, main and split, starting with A: split one on A/B, split two on C/D, etc.
  • After defining split slices, enable DIV on the main slice, where desired: slice A, C, etc.
  • Enable Split by right-clicking the Slice frequency box.
  • "Mute all but active" is enabled by default.
  • An additional option, "Split follows TX slice" is available on the Radio tab.
  • DIV is only supported on the main slices, not the splits.
  • Note that "Mute All But Active" understands DIV splits.
  • Note that "Split Follows TX Slice" also understands DIV splits.
73 ED W2RF

 

(Edited)
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KY6LA - Howard, Elmer

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I am aware of hovering the mouse but it's a PIA. Really wish it would just read out dBm all the time like PowerSDR

My reason for height is to get it clear of the 50' hillside in the backyard that blocks East
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N7AIG

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I have also been using the Pixel Loop for about 6 months now. I have nothing but praise for this little wonder. It definitely needs the preamp, but since using it my home grown QRN is no longer any problem -- even the A/C varispeed motor on the roof, while it still shows up, is no longer the +24 dB killer that it is with my Tx 40m doublet nearby on the roof.

While these things are mildly directional, I didn't bother putting mine on a rotator. It is mounted about 5 ft off the ground in my back yard, about 50 ft from the house, and aimed toward Europe. The lobes are broad enough that I easily pick up South America and Alaska, along with Europe and Japan and Australia / NZ along the main direction. QTH here is Tucson, AZ, in the extreme SW of the USA.

As for diversity vs dual receive (one Rx in each ear), I hardly notice any difference between the dual Rx and true diversity, except sometimes when working CW. I did a test comparing the two approaches the other day, with one antenna being the Pixel Loop and the other antenna being my 40m doublet about 50 ft apart. I tuned to 5 MHz WWV and switched between true diversity (phase locked receivers) and two different receivers, both frequency calibrated to a Rb standard at 29.9 MHz. You really could not distinguish true diversity from dual Rx. Both had the audio image shifting left and right. Phase coherent reception would really seem to be necessary only when trying to accomplish interferometry. Phase coherence should not be confused with frequency coherence - it seems to be more stringent than required for most on the air use.

73 de Dave, N7AIG

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Ed - W2RF

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For diversity vertical polarization I'm currently using a 43' vertical and getting good results. Especially when there is a lot of QSB the signals fade back and forth between the vertical and horizontal antennas, with one or the other sustaining copy.

I gather that noise immunity is a big factor with the Pixel Loop. However I'm in a rather low noise location. Do you think in this situation a Pixel Loop will outperform the 43' vertical, or should I just stay with what I have?

Thanks,
73 ED W2RF
(Edited)
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KY6LA - Howard, Elmer

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Sorry for the late reply
Had the grandkids for "Ski Week" today (We went to the beach)  Exhausting...

HF E-Field is Theoretically circularly polarized exhibiting characteristics of both the vertical and horizontal polarization components.

By contrast the Loop receives the H field which has very different propagation characteristics

Hard to say if it will make that much difference for you as true diversity reception is best achieved by physical separation of more than a wavelength - modified by the different receiving antenna polarization which you seem to be already doing.

They are quite inexpensive (only $500) so it might be worth a try.. if it doesn't work well for you, you likely could recoup most of your investment on the used market.
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MH_Flexer

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Greetings group.

After all the reviews I've read I finally ordered a Pro-1B for myself.  Had a great conversation with Doug at Inlogisinc regarding powering the preamp.  I am full time in my motor home and have been working to get rid of as many wall-wart power supplies.  I asked Doug about powering the preamp with 13.8 volts DC.  As we chatted, Doug recommended just putting the DC input right to the Pre-Amp and let it pass through the bridge rectifier and all the filtering.  I have a very short run of cable so he felt the battery voltage would be plenty.  The original PS is set to provide 20 Vdc to the Pre-Amp to compensate for any voltage drop over long cable runs. 

Great solution and I have been able to meet my goal of using battery power at the radio compartment including a 12Vdc Netgear 1 Gb LAN switch.  My radio is under the seat of my dinette, right by where we like to charge our cell phones and such.  I found a very nice 12Vdc to 5Vdc USB power hub that is totally clean to do our phone and tablet charging. 

All my LAN stuff and personal device use along with the Flex 6500.  Solar panel charging puts me off grid completely.

Looking forward to installing the Pixel.......

dmr

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EA4GLI - 8P9EH - Salvador

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DO you have pictures of your installation anywhere? Looks like a very interesting setup.

As far as the magnetic loop, it is an intriguing antenna to use as a listening antenna if you don ́t have the space to put beverages in several directions. However, being RX only, why the somewhat high price? There are RX and TX loop antennas out there for less, like the Alex Loop for $299. So what is different on this one? What are you getting for your $500? I am just curious, not bashing on this antenna that seems to work great.
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MH_Flexer

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I will take some pictures and post them.  The big thing you get with the Pixel is the $200 Preamp, it makes all the difference.


dmr

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Ken - NM9P, Elmer

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Howard, thanks for your post.

I am interested in the loop's performance primarily on 40-160 meters. You have mentioned some actual signal gain over the StepIR, but how about signal to noise ratio? I have built a simple shielded loop for 160 meters...no preamp, and no matching transformer yet... And I still see S/N improvements of 3-6 dB over my offset fed dipole at 38 ft. The base of my loop is about Six feet off the ground with an "arm-strong" rotator. I plan to add remote varavtor tuning and a 50:5 turn matching transformer before the 160 contest and hope it improves things.

I have considered the Pixel, but for my budget $500 isn't exaclt "inexpensive." Would the improvement over my loop be worth it?
(Edited)
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Dave-N9CHM

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 I've been using the Pixel loop for over a year. Actually I'm using 2 Pixel loops, I picked them up used for ~$375 each. As others have said, height does not matter. I had my 1st loop at 30' and used a rotor with it for a while, but I got tired of turning the loop to see how signals from different directions behaved.  So that's when I got the 2nd loop. Both are on 7' poles about 100' from the house, about 20' apart, one is N/S, and one E/W. They work as well at 7', as they do at 30'  I use a 75ohm switch to instantly switch between them, no more waiting for the rotor!  The ability to completely remove intermittent noises which pop up (I'm in a typical suburban subdivision) by switching between the loops is amazing. These loops really shine on 40M and below (they still work well on 20M and up, but I don't spend much time on the upper bands). I can hear signals on 160M that just can not be heard on my Inverted-L, or my low to the ground 160M RX dipole (S/N ratio is greatly improved). You can see some screens shots of what I'm talking about on my QRZ.com site.  I'm very pleased with both loops, and since the 6500 has 3 separate relay switches, it works great with 2 loops and 1 for the amp. I also have the loops feeding into a front-end-saver before going to the radio (I was already using it with my other 160M RX antennas, but probably not needed since the loops also go to ground when transmitting to protect the LNA in the loops).
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KY6LA - Howard, Elmer

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Here is a photo of my test bed installation



Funny how price pain thresholds are relative to individual circumstances.

Frankly I did no comparative product research whatsoever. I just saw Stu K6TU post about how well his pixel loop worked for him, they had one in stock at Ham Radio Outlet, it was $50 off and most important less than the price of a pair of shoes for the XYL so I did not need to ask for a hall pass.

Had the grandkids yesterday so no time to test. Yuma Hamfest tomorrow but I will try it on low bands when I get back from Yuma.
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N7AIG

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I have never seen a completely satisfactory explanation for the virtues of the magnetic loop antenna, but the best I can come up with is to note that most home grown QRN is from harmonics of fast edge switching, and is near field structure, not far field. So the locally generated electromagnetic field exhibits a mix of EM wave and static field behavior.

We know that static E fields die away as 1/R while static B fields are dipole in nature and fall away as 1/R^2. Couple that with the very small dimensions of the loop compared to the wavelength of the receiving frequency, and you see that the E-field, while stronger than the B field, cannot couple very well to the small antenna. And the local B field is very much smaller than the local E field.

Meanwhile the B field of distant radio waves (far field) is changing very rapidly and the area of the loop is much larger than its linear dimension, so the rapidly changing magnetic flux contained is very much larger than the E field difference between top and bottom of the loop. We know that a loop of wire containing a changing magnetic field generates a voltage where the loop is broken, proportional to the rate of change of the B field and the area of the loop. At MHz frequencies this changing B field has a very large rate of change, despite the field strength being 1/c of the E field strength in the wave.

The end result is that these magnetic loops show much greater immunity to local EM field disturbances and respond quite well to MHz B field changes of the incident radio waves. But the small size, and the relative weakness of the B field compared to the E field of a radio wave (1/c), makes a 30-40 dB preamp a necessity to get comparable voltage levels at the antenna connector.

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N7AIG

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The above explanation should be further specified as for a loop mounted vertically. It's linear counterpart would be a small vertical antenna, also often used as Rx antennas. Both are polarization sensitive for vertical polarization.

I have no idea whether home grown QRN is preferentially polarized, but if it is, or in any event, some of it is vertically polarized, I'd expect the magnetic sensitivity of the loop and the weakness of near B fields to give the loop a better local noise immunity than a small vertical Rx antenna. But this is just a conjecture on my part. I have never directly compared the two options.

If most local noise is horizontally polarized then perhaps a small vertical would perform just as well. Anyone have experience with both kinds of Rx antennas?

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Dave-N9CHM

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I get far more local noises (intermittent static, buzzing, etc.) on my 160M Inverted L (70' vertical, 60" horizontal) and a GAP TITAN all-band vertical, than I ever have on my Pixel loops.  However, I've never experimented with smaller vertical antennas.
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Jim Bryce W5HFS

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I have a Pixel loop and my experience is similar to that described by several others. I also have a vertical dipole for 20 meters. Using the flexibility of my 6700 it is quite easy to switch back and forth between the two receiving antennas and also my 6 element log periodic and a horizontal dipole. While I've not rigorously collected data my general observation is the Pixel is superior in eliminating noise in most situations. The horizontal dipole is the worst followed by the beam. Though the vertical dipole is often better than the beam and horizontal dipole, the loop is superior much more frequently.
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N7AIG

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That's very interesting! Thanks for sharing your experiences.

I have often wondered about this. DX Engineering sells a system of one or several phased short verticals with preamps, similar to the Pixel Loop system, for Rx only. I have wondered about how effective these are. Certainly a phased array can provide directivity that a single loop cannot. But one of the guys here was talking about a pair of loops for similar effect.

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N7AIG

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Yeah, I can't claim that E&M is my strong suit. But I did have Maxwell's Equations from Jackson etched into my brain in the first year of grad school.

Gives me shivers to remember that experience. The only one that aced that course, from a thickly Chinese accented English of Dr. Chang, was Marco Jarich, from Yugoslavia -- he was thumbing madly through a little grey English-Yugoslav dictionary trying to follow along, while Dr. Change filled 3 blackboards with equations. Every one of us always failed the first 1 hour midterm exams, except Marco, who became the class grader. All the rest of us always had to take a 4 hour make up midterm in Dr. Chang's office. .... as I said, it brings back shivers.

I had to live in the library and translate from the French the Theorie  Electrostatique from E. Durand, to make it through the first semester.

I sure wish I had a much better grasp of E&M than I do...

73 de Dave, N7AIG
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WA2SQQ

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The preamp is actually a very highly engineered component of the antenna. I live very close to a 50KW broadcast transmitter. Every other loop I tried (with preamp) suffered from intense intermod and mixing. This antenna / preamp combination works very well, especially with my 6500. With the 5000, I had to use a filter when using on 160m, but that was due to 5000 design, not the antenna. Yes it's more expensive, but it really works better than any other loop I've used or bullt.
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Dave-N9CHM

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I live ~5 miles from the 50KW WSB 750-AM radio tower. The front ends of several newer radios are overloaded by the WSB signal on the lower bands. I also had to use a BCB filter to operate 160M with some radios (other radios were completely wiped out from 75M and lower). I was concerned that the 6500 would be similarly affected due to it's RX sensitivity. I was pleasantly surprised that the RX front end of the 6500 is bullet-proof.  Even with the +30db gain from the Pixel LNA, I can listen too other AM broadcast stations with zero problems. The Pixel + 6500 is a super combo!!!
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Ken - NM9P, Elmer

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Howard, What's the matter with your picture? No snow? I have about 8 inches and we get freezing rain tonight! And it was -8 degrees F. Too cold for antenna experimenting. I may not get the loop modified by next weekend for 160 contest. Would like to, because it will tune 75 as well for my rag chew group.
(Edited)
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KY6LA - Howard, Elmer

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@Ken
The marine layer was in clouding it up....
It was a blistering cold 63F with no sun when I took that picture this morning...

But then I used to live in Canada.. where they would be wearing shorts on a balmy -8F day


Turned it on briefly on 160M a few minutes ago.. very low noise compared to my 160M dipole
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ka7gzr

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I have a 6700 with 2 Pixel Loops. I have them phased 90 degrees apart. One is connected to RxA and the other RxB and I use diversity mode. They are mounted 10 feet above the ground and are separated by ~ 60 feet. They perform very well and exhibit the low noise floor. I find that the audio level is lower with the loops and I must increase the audio gain for comparison purposes to other conventional antennas.
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Larry - W8LLL

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This is my Pixel loop about 10 feet up attached to a fence post. For me this thing is exceptional and usable as a receive antenna on all HF bands as far as noise to signal ratio,  40 meters to 160 meters is the most noticeable. 160 meters was never usable to me before the pixel due to the  noise and the inability to construct a large antenna on my 105' x 40' city lot. I now feel I have the best receive I have ever had due to this loop and my flex 6500.

For the heck of it last week I made a mono band 75 meter magnetic loop out of a 12' piece of LMR-240 ultra flex, some lumber and a trimmer capacitor (Mouser # 659-GME90901) that I can also transmit on. No preamp is required for this loop and just sitting in my living room on my sofa wedged in between the cushions it works exceptionally well on 75 meters, I just turn it in the direction of the lowest noise floor null and signals blast in. This is an easy to build test before you spend the $500 on the real deal.

http://i707.photobucket.com/albums/ww80/llavaseur/loop_zps793d6f11.jpg



http://i707.photobucket.com/albums/ww80/llavaseur/photo_zpsf3c87f44.jpghttp://i707.photobucket.com/albums/ww80/llavaseur/photo_zpsf3c87f44.jpg

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

(Edited)
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ka7gzr

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I do wonder what "diversity" means as implemented in the 6700. It appears that RxA and RxB audio is merely routed to the left and right headset of the 6700. Is there more to it than that? Is this a work in progress?  
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KY6LA - Howard, Elmer

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The 6700 currently has Simple Diversity.. RxA to Left and RxB to the RIght.

By contrast the 5000 had much more sophisticated diversity with the ability to steer the phase and gains of the two signals.  So it would appear that Flex understands some of the possibilities.

I suspect that more sophisticated diversity will likely be a V2.+ feature
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Mark K9BOO

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I also have a Pixel Loop magnetic loop RX antenna, though I am not able to use it again at the present time.  When I did use it in an "RF hostile" concrete-and-steel jungle, it was the only antenna to bring in a usable signal. 

If far enough away from metal sources (and high enough off the ground?), the antenna may be mounted horizontally with the nulls facing straight up and down.  Has anyone tried this orientation and compared it to their experience mounting the loop vertically?

One day I will get an opportunity to redeploy the Pixel Loop, and I could benefit from your experiences.

Thanks!

Mark
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KY6LA - Howard, Elmer

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Pixel loop up in the tree (natural Tower.
(Edited)
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KY6LA - Howard, Elmer

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