160-20m LOG loop-on-ground

[nanZor]

It does look like a lossy reincarnation of a rhombic, but sadly no.

The on-ground loop is so small that no matter what resistance we put in there, it really wants to be an omni-directional blob.

BUT, here's what I'm finally comfortable with: to maintain a nice omni at 160, instead of putting a resistance in the opposing corner, I'm going to use just a small amount in each adjacent corner of the feedpoint instead. A 10-ohm resistor will be put into each adjacent corner. This has much less skew on the low frequencies, and attenuation is much less of course.

I was overjoyed at the 160m SP contest blowing in, but noticed that 80/90 meters took about a 6 db hit - enough so that I didn't prefer to use it with an amp. Just a tad too much attenuation with my first attempt.

Normal people don't need to bother! But for me, with a transmit mindset, somehow calculating and reading a high 100:1 at 160 / 120 meters just wigs me out. The small amount of waste resistance pulls it down to 20:1 or so. Does it *truly* matter for this rx application? Probably not.

There's an endless combination of resistance one could play with to tweak the blob. But unless you model it so you know what to expect, there's truly no need for any resistor here for most people.

 

[nanZor]

HAPPY NEW YEAR!

Ok, now I think I'm done!

Took out the 47 ohm resistor at the opposing corner, and put a 10-ohm resistor into each feedpoint-adjacent corner instead. Sure enough, my pattern is back (based mostly on local qrm squirrely's so far), and the additional attenuation is miniscule enough not to be noticeable on 160/120/90/75 meters.

Recap: 15 foot sided square (60 foot circumference) wire loop, with a 9:1 isolated transformer at the feedpoint. Par EF-swl transformer to be exact, with ground jumper disconnected. MFJ 915 ferrite isolator used right after feedpoint for pattern skew paranoia.

SWR notes: The only reason I put in the 10 ohm resistors at the adjacent corners was to get the swr at 1.8 mhz off the peg. Now reading about 13:1. Does it matter? Doesn't seem to in my installation.

BUT, *perhaps* it would matter for some other transformers that don't like looking into a 60:1 or higher ratio down at 1.8 mhz. I don't have time to test others like most amateur transformers, or others such as the NooElec 9:1 to see if it matters there either. I don't run with a preamp (other than what is in the rig at times), but maybe some preamps might not like a super high swr, and the resistors might help by fooling it with a better match. I'll let others go there and do that kind of testing. So this was just a test and might be helpful for some installations. I just don't know.

See everyone next year - and be ready for the T2FD On Ground!

 

[nanZor]

Meh, ripped out the resistors. And quite frankly, if one is going to do that, just put it across the *feedpoint*, where you won't mess up the pattern either and is obviously more convenient. Don't cut up your loop to do this.

Too much eggnog.

 

[krokus]

Too much eggnog.

Before, or after, the antenna surgery?

Sent using Tapatalk

 

[nanZor]

Heh, the ultimate in surgery: I pulled up the loop and defected to a different design!

https://forums.radioreference.com/threads/non-resonant-feedline-dipole-nrfd.381559/

It isn't that the loop didn't work - it's just that this version has similar performance and was more convenient for my backyard physically with just a straight wire layout. Basically just your classic so-called "end fed" antenna with a 9:1 autotransformer. A coax jumper and common-mode choke finish the design.

Many hang this OCFD in the air, but I chose to put it on ground with the same great results - that is if not exceeding a half-wavelength (wire AND jumper!) for a dipole, you still get the classic "small vertical" loop type of near omni skywave pattern.

 

[nanZor]

160 to 6 meters pattern solution found!

Part of the problem when exceeding a 60 foot loop (15 feet per side for square shape), is that when you go past 14 mhz, or roughly one wavelength, the omni pattern starts to develop some funky lobes. The usual thought here is that if you want to do higher frequencies as well, you need to run with a secondary loop that is smaller to maintain the pattern.

The solution seems simple, but it was counter-intuitive:

Lay down the 60 foot loop.
Now cut through BOTH of the corners adjacent to the feedpoint.

So now you have basically a v-shaped dipole, with another undriven v close-spaced to it. THIS is what seems to maintain the pattern all the way up to 30 mhz, and at 54 mhz resembles a ground mounted vertical pattern!

I found this by accident, thinking I would become the next Moxon with a close-spaced "beam", but no. What it DID do, was help maintain the pattern higher up in frequency!

** NOT TESTED - only modeled so far **

When I get time to rip up my end-fed ocfd version described in another thread, I'll put this one down again, and test. Unfortunately there is not much activity above 15mhz these days, but there are some amateur radio repeaters on 10 and 6m, along with some low-band vhf commercial stuff. But it does seem exciting that a simple solution to the pattern skew for a full frequency pattern problem looks to be do-able. I'd stick to the 9:1 transformer here, and not use anything less. And use good quality low-loss coax as we head up into the higher freqs. RG6 may still be fine for rx-only.

The other note is that modeling shows that this pattern maintenence with the split-V's does not seem to work well if you make the loop bigger - ie, a 120 foot version with the cut corners goes wonky again at high frequencies.

At least with all this testing pushing lawn-staples down, I'm aerating the lawn!

 

[nanZor]

The new loop is down! So far so good. With beverage implications.

The new 60 foot square loop is down. Corners adjacent to the feedpoint cut and separated a few inches making it one v-shaped dipole stacked (horizontally) to another inverted so to speak. 9:1 isolating transformer (Par End-Fed swl with jumper removed) at feedpoint.

What sparked this was noticing that a SINGLE v-shaped dipole on ground was less efficient than a straight one. Some cancellation from the change in direction was taking shape. About 6-10 db or so depending on frequency.

This is the reason I think you never see any radically bent beverages or bogs in the wild. Same problem exists here.

However, based on modeling, the pattern and gain of a bent dipole is restored by stacking an inverted mirror image right next to it. Hence the open corners loop being used here.

The predicted SWR slopes in EZnec, along with confirmation from the AA54 antenna analyzer, make me feel confident.

The big catch-22 here is finding an efficient broadband 9:1 isolated transformer good from 1.8 to 54 mhz! The PAR transformer is doing great, but is rated to 30 mhz tops. But I may test a low end tradeoff by using the Nooelec 9:1 which is reputedly good up to 90mhz since I don't do a lot of 160 meter dxing with a 15 foot dipole.

Beverage - BOG implications!

The discovery here is that this technique *might* be useful to those beverage or bog users cramped for space. Since a radical 90 degree bend in a beverage is never done in the field, I'm wondering if this technique could restore the pattern for them. Example: instead of a long straight bog, it is bent 90 degrees half-way. THEN, another V (or l-shape depending on how you want to look at it), purely passive and not connected to the beverage directly would work. I don't have the space so the beverage guys might want to play with that and see what's up. Bird's eye view it looks like a loop, but is just a pattern correction technique. Pure conjecture since I don't have room for a beverage or long bog.

It isn't intuitive to do this - thinking along the lines that you are making a close-spaced beam, but on ground without any horizontal component, it seems to be a pattern shape restorer...

 

[nanZor]

YES! High frequency pattern improvement

Up at 29.620 FM lives a local 10-meter repeater. What was once a noisy S2-S3 signal strength no matter what former loop shape I had down, this cut-corners version is now a solid S9. This is close to the upper frequency limit for the Par 9:1 transformer. Modeling and listening previously had some squirrely patterns up here, but now it seems solid.

The implication is that this antenna has an improved shape up this high, as predicted by modeling. In fact, modeling shows that the pattern stays relatively stable up to about 6 meters, but the transformer may be an issue now. We'll see.

I know that this is purely anecdotal, but I try my best to be honest about it. Fortunately the antenna is easy to duplicate for anyone so interested ... and as always thanks to KK5JY for the inspiration!

 

[nanZor]

Common-mode skepticism test:

Right now, the only thing I have is the PAR 9:1 *isolated* transformer attached to the feedline. Wires connected to terminal 2 and 3, and the jumper from 1 and 2 has been disconnected. 30 feet of LMR-240 (RG6 would be just as fine, even better actually) making a 3 foot vertical jump into the window connector an on to the rig. This is my baseline.

So the following was added to see if there were any significant improvements or degradation: (fortunely, no major changes):

MFJ 951 CMC choke near feedpoint.
MyAntennas CMC-0510-R also installed after mfj
Radiowavz ISO-X galvanically isolated transformer - installed right at rig.
More large core chokes strewn about the feedline.

Other than the AA54 analyzer detecting the presence of the ISO-X windings tweaking the swr response a bit, no changes. Also ran rig off battery and AC power supply. No changes.

I'm pretty sure I'm done, although I've said that before. An amateur cw contest is on, and that assures me that I'm getting well beyond the backyard (3 - 5K miles with casual listening so far), with 14mhz popping wide open, and now 3.5 and 7 mhz jumping. Later we'll see how well 1.8 mhz does, but I'm going to be realistic about it.

So take heart swl'ers, this is not an amateur-specific antenna. I'm pretty stoked right now. I removed all the unecessary stuff, and am back to just the isolated 9:1 transformer, although perhaps leave one of the CMC chokes on for good measure - but in *my* case, not absolutely necessary.

 

[prcguy]

The Eyring baluns are good from 2 to 65Mhz and I believe they are 9:1. Will have to measure one again but some early patent info mentions 9:1.

Common-mode skepticism test:

Right now, the only thing I have is the PAR 9:1 *isolated* transformer attached to the feedline. Wires connected to terminal 2 and 3, and the jumper from 1 and 2 has been disconnected. 30 feet of RG-240 making a 3 foot vertical jump into the window connector an on to the rig. This is my baseline.

So the following was added to see if there were any significant improvements or degradation: (fortunely, no major changes):

MFJ 951 CMC choke near feedpoint.
MyAntennas CMC-0510-R also installed after mfj
Radiowavz ISO-X galvanically isolated transformer - installed right at rig.
More large core chokes strewn about the feedline.

Other than the AA54 analyzer detecting the presence of the ISO-X windings tweaking the swr response a bit, no changes.

Also ran rig off battery and AC power supply. No changes.

I'm pretty sure I'm done, although I've said that before. An amateur cw contest is on, and that assures me that I'm getting well beyond the backyard (3 - 5K miles with casual listening so far), with 14mhz popping wide open, and now 3.5 and 7 mhz jumping. Later we'll see how well 1.8 mhz does, but I'm going to be realistic about it.

So take heart swl'ers, this is not an amateur-specific antenna. I'm pretty stoked right now.

 

[nanZor]

Sure enough, the isolated balun is the ideal. BUT ...

Could one fudge it and use a 9:1 Un-un instead, perhaps from an efhw antenna they have lying around? Possibly - if you immediately follow it with a separate galvanic 1:1 isolation transformer (line breaker - isolator)? Or maybe instead of / or in addition to a REALLY good CMC common mode choke? The secret being that no antenna is *truly* balanced, especially one that may have changing ground conditions underneath it....

You can lay one of these down and use all the parts you may already have before building or buying a 9:1 isolation transformer .. as long as the skimping on materials isn't too cheap to skew the results...

I recently tested a "cable tv" type isolator - the ones that have the sides labeled "customer / service", and they did pretty darn good, even down low. Kind of expensive, but the model TII 220 worked well enough for dc isolation and rx-only of course.

 

[nanZor]

Low band update:

No problem at 1.8 mhz! Ok, I'll fess up - from 80 to 20 meters, I don't run any preamp. But for 160, where this antenna is really small, the rigs 10db preamp was just enough. And I'll certainly be running it on 15-6 meters if those bands ever open back up.

The Alinco's receiver is just not a contest rig, so I pulled out the Kenwood 590s for the contest. The "split cornerS" loop sounds soooo good on the 590...

 

[nanZor]

Found the real name for this new loop with cut sides: the VK2ABQ square!

Didn't do enough homework to see that this was the predecessor to the venerable Moxon rectangle. Being purely on ground and missing a horizontal response, the pattern has no real F/B ratio to speak of, as one designed for being up in the air does.

So there you go. I've got a multiband, on-ground VK2ABQ square, (well a diamond version) and not a continuous loop now. Too tired to see how the ground will affect a Moxon. At least not today.

 

[nanZor]

Where to go from here? - and additional notes:

Despite all the amateur radio references, be assured that this is still useful for SWL'ers and utility hunters, and the main point being a great rx-only antenna for those who for whatever reason, can't put an antenna up in the air, or those seeking lower noise. It's easy to get sidetracked from an amateur standpoint.

The VK2ABQ square is an early member of the cob-web type of antennas with f/b ratios being the prime feature. HOWEVER, dropping one entirely to the ground makes it lose the f/b, but by accident discovered that it helped preserve the on-ground vertical pattern much higher in frequency than a continuous loop would when going beyond a full wavelength.

That high-frequency (21 to 54 mhz) pattern compared to a smaller dedicated loop is not *perfect* and a bit "sloppy" at higher angles above 45 degrees or so. BUT, there is no ionospheric reflection that high up at those frequencies anyway! Unless you get into weird tropospheric ducting etc. We won't go into that.

Being part of the cobweb type family, my first thought for a continuous loop would be to put a smaller loop (a funky pentagon) inside the larger one at the feedpoint.

But for nearly the same result, why not just simply cut the two corners of a square loop to make a VK2ABQ square and be done with it. Much simpler.

Modeling notes:
Interestingly enough, both the continuous 60 foot loop, and the VK2ABQ version are resonant (minimum reactance or J) around 10-11 mhz or so. No major current was seen in the "reflector", but it did peek it's head out at resonance when viewed through EZnec. That made me feel better knowing that there IS interaction, the one that which preserves the pattern better at high frequencies. Oddly enough, that preservation (although not always pretty at high angles) is seen up to about 150mhz or so!! But try finding a 9:1 isolating transformer that will do 160 - 2 meters.

So in the end, I think the on-ground loop, especially in the VK2ABQ shape, is a great rx-only antenna with controlled patterns, that deserves a try even if you do have the space for all the in-air antennas you could want.

The reason I put one down was not to see how it "competes" with other antennas, but how conveniently it solves a problem with more than adequate performance.

Final note: although the PAR EF-SWL isolated 9:1 transformer is only rated to 30mhz, my local 54 mhz / 6 meter repeater is booming in like it should. Not much of a test - and will never outperform a dedicated antenna up high, but was satisfying that it wasn't a dummy load or a spaghetti mess in direction.

 

[nanZor]

An explanation for the high frequency pattern retention with the VK2ABQ on ground:

Hang in there swl'ers and amateurs, but I had to find what the magic is. I'm no expert, but I *think* this might be a big clue --

In Les Moxon's (G6XN sk) book, "HF Antennas For All Locations" he examines close spaced beams where ends are brought close together. While he is mostly describing an antenna meant to be in the air with a f/b ratio, I'm certain he never thought about them being right on the ground where that f/b is gobbled up completely.

However, page 78, par 3/4, and also figure 5.2 (b) gives a clue where he describes capacitive coupling, current equalization, and phase shifting. I believe that this MAY be the reason for the high frequency pattern retention when used on ground.

I could be interpreting this all wrong, but I'll sleep better tonight.

 

[nanZor]

Field notes on baluns tested here:

One could always build an excellent isolated 9:1 transformer themselves, and KK5JY site does a nice job explaining it.

I tested some off the shelf versions, which may be more appropriate depending on your environment. Specifically bridging the gap between an swl and amateur, where accidentally transmitting into an rx-only transformer could be a problem. There are many options for a 9:1, but most are "autotransformers" and are not galvanically isolated.

I tested three different ISOLATED 9:1 baluns:

RX only: Par / LNR Precision "EF-SWL". To achieve isolation, the antenna wires go to terminals 2 and 3. The jumper between terminals 1 and 2 are removed. Best performance.

RX only: Nooelec 9:1 balun. From factory, it is sharing a ground. To make it isolated, scratch through the single copper board trace on the backside. SMA connector is ok, but be SURE you use quality connectors / adapters, as cheap ones may not make good contact with the sma. Or the cheap jumper you transition to RG6, RG240 feedline cable is junk / shorted. Test your setup! Consider soldering your own beefier antenna connector, rather than relying on the push-in dinky clamps. Provide your own chassis too for protection.

TX capable AND galvanically isolated: RADIOWAVZ B19CI or B19TX. Accidentally pumping power into either of the rx-only baluns above will destroy them. These are capable of handling power, accidental or otherwise. May be applicable to SWL'ers using amateur transceivers and accidentally transmitting. Obviously applicable to amateurs too. My B19TX has side terminals, yet some pics may show pigtails instead.

Performance: The PAR EF-SWL seemed to perform the best. However, both the Nooelec and the RADIOWAVZ only required *very* slight increases in audio volume. Analyzer swr slopes are similar, and all three are still acceptable at 1.8 mhz! So choose accordingly depending on what you are using, and your likelyhood of blowing out an rx-only transformer with power.

Auto-Tuners: Using a rig's autotuner on these loops and VK2ABQ squares does not provide any real improvement at all. If it DID, then you have a problem - most likely massive common mode misconfiguration.

 

[prcguy]

The VK2ABQ loop was purposely designed as a two element resonant beam type antenna and not for use laying on the ground as a broad band receive antenna. If you happened across a similar shape antenna for broad band and especially very low frequency use, and you had no prior knowledge of the VK2ABQ, then I would say you have a new invention.

Found the real name for this new loop with cut sides: the VK2ABQ square!

Didn't do enough homework to see that this was the predecessor to the venerable Moxon rectangle. Being purely on ground and missing a horizontal response, the pattern has no real F/B ratio to speak of, as one designed for being up in the air does.

So there you go. I've got a multiband, on-ground VK2ABQ square, (well a diamond version) and not a continuous loop now. Too tired to see how the ground will affect a Moxon. At least not today.

 

[nanZor]

TOO GOOD TO BE TRUE about higher frequencies! Houston, we have a problem!

prcguy - yeah, when the VK2ABQ version (cutting the corners or the sides of the 60 foot loop), it is a different antenna on the ground pattern wise. The ABQ wants to be up 15-30 feet up in the air to achieve the small f/b. So it is a misnomer I guess with it being totally on the ground. - just the shape is the same.

MY apologies - I just rained on my own parade by being able to get the wires even lower in EZnec by using a smaller diameter wire than what I originally started with. So with that ...

The only *real-world* difference between the continuous 60 foot loop, and the cut-corners (aka VK2ABQ shape) is that the cut-corner version provides a much more stable pattern at 21 mhz, but beyond that, just like the continous loop (which gets funky at 21 mhz), 25-108 mhz gets lopsided and weird. Not that you won't hear anything, but not ideal. My buest guess at this point is that since current is seen in the "reflector" at resonance near 10-11 mhz when on ground, the 2nd harmonic current up near 21 mhz is helping in regards to 15m.

That improvement is worth it to me since I love it when 15 meters opens up. Rare now, but when it does, I want to be there! If that isn't important, then don't cut the corners.

VHF-HI - 108 to 165 mhz. Like the continuous loop, the cut-corners version has a very nice omni pattern. BUT the kicker here is that very high SWR, which unless you run a short feedline, or for some reason are using hardline, then *local* airband and vhf-hi stuff like 2 meters and others would be ok for casual listening. But don't throw away your discone.

Sorry about that discovery gang. This is what happens when you let a non-professional loose on EZnec. At least I caught it fast, and learned some things.

 

[nanZor]

Quick note about using ferrite chokes especially with the on-ground antennas!

The LOG, DOG, and my own end-fed version (actually a center fed non-resonant "RFD" version) all use quality chokes at the feedpoint. Operations *seem* good, but a recent test with all three of these versions and a switching power supply showed that I had a problem that wasn't noticed because I was using a linear Astron supply for rx.

Basically, the great s/n ratio of the on-ground antennas, along with a semi-noisy switching supply used as a test for something else revealed that I need TWO chokes - one at the feedpoint, AND one near the receiver hanging off a small jumper.

http://forums.radioreference.com/th...er-choke-noise-suppressor-rf-isolator.381848/

Being very pattern-conscious about these antennas means that *even if you can't hear a problem*, you still might - even IF you don't immediately hear one!

PHYSICAL ISOLATION? I'm using "galvanic" / physically isolated transformers for the 9:1 / 4:1 baluns. So that by itself isn't a total cure!

IN a nutshell - for these 160-20m versions, I'm using the Myantennas CMC-0510-R at the feedpoint. But even with that, and with a feedline on the ground, I had to use another choke near the receiver to kill the small gremlins heard by the great s/n ratio of the on-ground antennas. I didn't know I had an issue until I pressed a switching supply into service.

The gremlins aren't mind-blowingly bad, and a notch filter could take care of them for the most part. But I want to do it right, so my standard of operations - on ground antenna or not, audible or not, I'm using TWO chokes now minimum. One at the feedpoint and one near the rig.

I tried using another galvanic 1:1 isolated winding transformer at the receiver, but was dismayed that there was only a small reduction of gremlin noise. It took a ferrite choke to do the job.

I got tricked into thinking that if I don't hear any problems, I'm good. Not so if antenna pattern is also a concern. Two chokes for me from now on with ANY antenna project.

 

[Ubbe]

I wonder how much can be trusted on EZnec to really show true results when you go outside of the box of conventional antenna design? The coder of the program have to consider a million things that will have an impact on the end result. The professional version probably use more parameters in the calculations to give a better result but the cost for that program are astronomical.

/Ubbe