160-20m LOG loop-on-ground

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nanZor

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Comparing the LOG to the small-vertical-loop, aka a Wellbrook, LVP, MFJ broadband preamplified antenna:

Just some quick comparisons that might help on "visualize" what is going on: If one is familiar with the patterns of a small vertical loop already, the log will be nearly the same, even though the wires are flat on the ground.

Both have a similar directional pattern. That is, when seen from above, at skywave angles, it is mostly omni, but in reality is an oval shape. So there is some skywave directionality, but it is not huge. Down low, there are nulls that can aid in reducing noise.

The small vertical loop can easily be rotated to finely tune out a low-angle point noise source. With the log, your only option is to move the feedpoint around, so finely tuning a null is kinda' hard - so you do the best you can.

If one wants, you can envision both the log and the small vertical loop as verticals with no overhead null, and slightly oval patterns rather than a pure circle. Close, but not quite - a little squished.

Both the log and the small vertical loop have size limitations in regards to the classic pattern. Exceed these dimensions, and the classic patterns will distort into something you may not want.

That means the LOG should not exceed a full wavelength in circumference. For the small vertical loop that means not exceeding 1/10th of a wavelength. The example here is that if you go beyond a 15-foot sided square for the log, then frequencies higher than about 14 mhz will start to go squirrely. If you try to use the typical 3-foot diameter small vertical loop as a scanner antenna (disregarding any preamp limitations), then that pattern too will distort.

A log can be easily matched to the lossy ground resistance using a transformer, typically 9:1. Other ratios can still work depending on your needs. The small vertical loop needs a bit of help with a preamp typically. The log doesn't absolutely need a preamp, but depending on your gear, size and frequency of your listening needs, one may be helpful here too.

In the end, if you have a LOG in your backyard, you might close your eyes and envision a stationary small vertical loop just above the ground.

So choose what works for you. Each has their pros and cons, but they are in the same family even though they surely don't look like they are. :)
 

nanZor

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I think I'm done with the on-ground loop study. (crowd cheers)

Due to a need for backyard replanting, I ran with a loop-jr. That is, I pulled the far side of the square back towards the feedpoint - in essence making a "folded vee" out of it. Seems to have lost about 6-10db overall compared to the fully open loop, but the pattern was still reasonably omni.

The point here is that unless you exceed a wavelength in circumference for a loop, or exceed a half-wavelength for a dipole (or variant like a folded one), one always ends up with that "oval gumdrop" pattern. Provided of course you have taken measures to not make your feedline part of the antenna.

The only thing that happens when you play around like this, is changing the direction that the oval / null points to. But the skywave gumdrop pattern overall is still useful - even if it is heavily attenuated by ground loss.

I have used them successfully on VHF low, up into the VHF airband just for fun as folded-dipole versions. Yep - preamps on! But it just proved that for an unusual situation where NO antenna can be mounted or visible, (or perhaps being too close to a noise source) the on-ground option is viable within reason if it passes all your own listening environment variables.

In the end, the LOG makes a great general purpose HF antenna for both portables with hyperactive front-ends, as well as more advanced receivers that may or may not actually need to use the typical on-board preamp. The same goes for scanners with hyperactive front-ends. Remember this: "A full length dipole on the ground outside, will beat the pants off your duck indoors." :rolleyes:

I'd like to thank the mods and users of RR for putting up with this long-winded study. And especially to KK5JY who pointed out that an on-ground antenna that isn't a bog or beverage can actually be useful, albeit with a totally different objective.

I'm done with the study, but I'm definitely keeping my log firmly planted!
 
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ka3jjz

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Hertz, we could turn this into a wiki article, if you would gather up all your reference materials, links and observations. If you were to write it up in Word, then private mail me, I can change your Word doc into a wiki doc. That way your work won't eventually be lost.

Mike
 

nanZor

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Thanks guys - I'll think about writing something, but quite frankly, KK5JY's loop site says it in much less words than I do. Maybe I can come up with something later...

Re the small vertical loops like the LVP et al. I've been there and while fun and useful, others express things much better than I do. *Electrically*, I do have a small vertical loop with the log. It just looks funny and is a ***** to rotate. :)
 

g4jnw

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Been interesting following this, so you dont have to scroll back pages, I started using the LoG due to having S9+ noise on my 3 favourite bands. 80/60/40m and went from 15ft square to my max garden size, 50ftx25ft i did see an improvement but not massive. My wellbrook ALA-1530LN was as almost as noisy (2S points down) on my 3 favourite bands, I could not null out the noise. After 4 months of messing about it seems the noise (white noise) is VDSL (internet over the telephone wires) lots of wires run over the property on each side of the house via 4 poles (Im in a housing development and in a square of houses) I now have sold my Wellbrook loop and done some work on my longwire. I have moved the 9-1 balun feed 70ft away from the house and put grounding rods on to the earth side of the balun, no improvement on noise, im now considering putting a 1-1 balun at the feedpoint and at the receiver plus making my 50ftx25ft LoG wires into a counterpoise. Then making a new LoG of 15ft square. So the experiment goes on!
 

prcguy

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I think you will find an effective 1:1 choke balun will calm down some of the noise pickup, possibly from the feedline. I would use one near the antenna and another near the radio end.



Been interesting following this, so you dont have to scroll back pages, I started using the LoG due to having S9+ noise on my 3 favourite bands. 80/60/40m and went from 15ft square to my max garden size, 50ftx25ft i did see an improvement but not massive. My wellbrook ALA-1530LN was as almost as noisy (2S points down) on my 3 favourite bands, I could not null out the noise. After 4 months of messing about it seems the noise (white noise) is VDSL (internet over the telephone wires) lots of wires run over the property on each side of the house via 4 poles (Im in a housing development and in a square of houses) I now have sold my Wellbrook loop and done some work on my longwire. I have moved the 9-1 balun feed 70ft away from the house and put grounding rods on to the earth side of the balun, no improvement on noise, im now considering putting a 1-1 balun at the feedpoint and at the receiver plus making my 50ftx25ft LoG wires into a counterpoise. Then making a new LoG of 15ft square. So the experiment goes on!
 

ka3jjz

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Thanks guys - I'll think about writing something, but quite frankly, KK5JY's loop site says it in much less words than I do. Maybe I can come up with something later...

Hertz, what we could use, I think, are links to the various chokes and other things you've added to the loop that were effective. It would be easy to link to the original site and this thread, but all the various things you've used would be just as valuable. Just wrap it around the thread and the website, and you've got it. Mike
 

nanZor

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Thanks Mike - I guess I'm still not done, but very close. :) The danger is over-engineering this thing. Much like over-engineering the scanner vertical OCFD antenna.

I'm a little less paranoid about common mode pattern skewing now. In theory, just having the coax on the ground should attenuate the common mode, but I wanted to CYA it, and used a very nice choke that would cover down to 1mhz or so. But I'm not using this for BCB dx'ing, and I feel the simple MFJ 915 can rot in the sun for awhile instead. I'll save the awesome CMC from myantennas for a different project.

I might add that my claim that the LOG is electrically the same reception pattern as a small vertical loop stands, but with one important addition for clarity - that small vertical loop would also be positioned very close to the ground.

Which brings me to more testing - the mini 8-foot sided version. My heart still goes out to apartment / condo owners etc. Follows all the same rules, although sure enough at low frequencies, a preamp is certainly a must for most.

But the realization of going smaller is that we're reaching the point of merely putting an LVP, Wellbrook etc simply on the ground. The reception patterns are similar. All we're dealing with now is amplification, and the pain of not being able to rotate it easily. :)

I still have to test the 50 ohm resistor on the opposing corner. Maybe I can whip something up after the start of the new year.
 

nanZor

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G4JNW - I feel for you man - almost the same situation here with multiple neighbors running BPL in the homes. Fortunately, the stupid ac line routers in the US have brick-wall amateur band filtering, leaving me to be mostly amateur-swl and utility listener to about +/- 100 khz on each side of the amateur bands. I'm amazed that the UK didn't mandate similar.

BUT - how about this: what I've used as a "field expedient" so-called shielded coax loop. Due to it's design, it already incorporates it's own common-mode choke opposite the split in the braid. (common mode currents on the transmission line braid split and are opposite and equal in the arms - self cancelling). See the very middle diagram for the "shielded coupling loop" about half-way down here:

http://webclass.org/k5ijb/antennas/Small-magnetic-loop-coupling-loops.htm

Although the author claims that nobody does this for the main loop, I've used it for years this way for rx-only. *Maybe* you might be able to obtain a better null. Worth a try anyway.

Quick construction tips - let's use a 20-foot length of coax, to make a 16-foot circumference loop (4 feet per side for a square / diamond), with 4 feet left over as a length to couple the main transmission line to:

4 steps:

1) Create a shorted pigtail at the end of a length of coax. Cut back the outer dielectric for a few inches. Temporarily push it back on the cable to expose the center conductor covering. Cut away the center conductor covering, and fold the braid back on the center conductor to short them together. Solder together.

2) Measure 4 feet from where you started to cut back the outermost covering of the pigtail and mark the coax. A half-inch on each side of the mark, cut away the coax covering. Now, using sharp dikes, *carefully* cut away the braid, but don't go so deep as to weaken the center conductor covering. Leave no frog-hairs across this gap. Perhaps shrink-wrap or tightly tape this exposed gap for a little strength and weather protection. Braid loves to suck in moisture as you know.

3) Measure 4 feet from the *center* of the newly created gap, and cut away 1 inch of coax *covering only* further down the line.

4) Wrap the shorted pigtail around the exposed braid from the step above. *Lightly solder* or provide some other snug connection. Again, braid is exposed, so tightly tape it.

Of course this needs a frame / support of some sort. And some feedline back to the shack. Try to keep that a bit short. Optionally use a tuner (manual - NO transmit !!!) to hunt and find a spot where you can reduce some of the overall "system" reactance. We aren't tuning the loop per se.

Don't worry too much about the "pigtail short" center conductor connecting back to the braid at this point. This is a zero-current point. All the action for out-of-phase signaling coupling back inside the transmission line is happening at the gap - the real feedpoint if you will. So best to keep the gap at the top, not inverted.

OR yeah, you could use a preamp I suppose.
 
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nanZor

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Oops - change those dimensions in step 2 and 3 to EIGHT feet for a 16-foot circumference loop. You get the idea - just keep your cuts nice and even on both sides of the gap depending on what size loop you desire...
 

nanZor

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"Fascinating, Captain"

On my 15 foot sided square log, I lost the high end at 20 meters with an experiment. It was there, but the pattern was toast.

Waiting for my test resistors to arrive so I can pop one into the corner directly opposite the feedpoint, I wondered what would happen if lightning or massive static took out my resistor in the loop. So I cut open the opposing corner.

Guess what - no longer a 1 wavelength loop at 20 meters, but now a symetrical dipole, shaped like a loop with an open.

Even though it looks like a loop, it is now an open-loop-shaped dipole, and on 20m exceeds a HALF wavelength, leading to a very skewed pattern. The pattern on the lower bands stayed normal - because the wire is not exceeding a half-wavelength for the DIPOLE family.

Fired up EZnec, and sure enough, there it is with the bad pattern. Geez, I don't want to have to babysit that resistor when it goes in to make sure my loop stays contiguous...
 

pastian

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I built this exactly according to KK5JY's very easy to follow directions, I took it a step further than Hertz, and built a 2nd loop exactly as KK5JY suggested 15 feet apart. I oriented them exactly identical.

I haven't had time to build a phasing line for them because I hooked it up to my MFJ-1026 and as you all know this did they "Phasing" for me.

I can steer this Array any way I want. 160 through 20

I have 2 words for this....Incredible

When you're done listening to more than you could possible take in let me know how it works for you.

HP
 

nanZor

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WOW - nice job on the dual loop phasing with the 1026! I can see this on a dx-pedition on an island with a hostile environment or no vertical supports available....

Observations about Chris' 350-foot loop: I kind of harp on how exceeding a full wavelength makes the pattern go screwy. However, that does not mean the loop that large won't work when squirrely.

All it means is that with such a large amount of wire out there, at some "non-optimal" angles on the 350 foot loop, it would be about equal in signal strength for my smaller 60 foot loop at it's optimal angle! Fun stuff.

I've often wondered about putting two loops together, ie a smaller one inside a larger one, with some sort of transmission line connecting the two to see if that might provide a larger range of the classic pattern. Gosh, the projects never stop!
 

nanZor

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Thank you Canada! Perfect time to test the resistor - listening to all the provinces going nuts in the RAC contest.

The 47 ohm resistor has been placed in the corner opposite the feedpoint, and it basically agrees with what EZnec says it should do when measured on my RigExperts AA-54 analyzer.

That additional bit of resistance made for a much better match on the low end of about 20:1 down to about 8:1 on 120 meters. (450 ohm feedpoint to a badly wired 47 ohm remote resistor <grin>) As we go higher in frequency, the improvement lessens, but is still there until the improvement would be considered negligeable from an rx-only systems standpoint.

Most importantly, while there is a slight amount of pattern lean of about 3 - 6db or so back towards the feedpoint on the low frequencies, the higher frequencies above 5 mhz don't seem to be affected much - at least not anything I could tell from a practical standpoint. BCB signals still blowing in - but I should have been more scientific about it taking readings first to detect the skew. Oh well.

But is this just a mere technical exercise playing with additional loss to make a match from a *systems standpoint* better? Perhaps any improvement or degradation will be hidden by natural band noise changes? We'll see later tonight when I hit the low bands.

Thanks again to all the Canadian amateurs in the winter RAC contest prove that I didn't kill my loop with the resistor! Hope I can hear some activity on 160.
 
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nanZor

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Getting ahead of myself with resistors ...

I'm a bit excited about what the next few nights might bring with the resistor inline. However, I'm keeping notes about W8JI's advice about resistors for beverages in mind :

Beverage Antenna Construction

That is, they can change value by being zapped (or destroyed worst case like my 1/2 watt 47 ohm). Since the log is non-resonant, perhaps a little inductance wouldn't hurt - especially on the low bands, so maybe a power-resistor or such would actually be ok. Maybe we'll test that once I get some quality time in with the dinky carbon resistor out there now...
 

nanZor

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SP (Stew Perry W1BB sk) 160 meter contest!

What luck! Tested the log + resistor with the 160m contest right after listening to the RAC contest. Still works great, although I haven't hear anything beyond the midwest.

Resistor Analysis: In all honesty, I can't tell any more if it *truly* improved things, or if I have just padded the whole system by 3db or so. It would take someone much more experienced than I to know the difference.

Did I lower the noise floor, or did I just attenuate the whole thing a bit? Is the 9:1 binocular core in the Par End-Fed-SWL transformer happier with a 10:1 swr at 1.8 mhz, than the initial 20:1 ratio without the resistor? I just don't know.

I'll leave the inline for awhile and try to study up, but in the end, I have receiver gain to burn (Alinco R8T receiver needed no 10db preamp for comfortable 160m cw copy, but I normally do use it once in awhile)

I don't think the resistor is a must, unless I can find some concrete evidence of it truly helping.
 

pastian

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"Fascinating, Captain"

On my 15 foot sided square log, I lost the high end at 20 meters with an experiment. It was there, but the pattern was toast.

Waiting for my test resistors to arrive so I can pop one into the corner directly opposite the feedpoint, I wondered what would happen if lightning or massive static took out my resistor in the loop. So I cut open the opposing corner.

Guess what - no longer a 1 wavelength loop at 20 meters, but now a symetrical dipole, shaped like a loop with an open.

Even though it looks like a loop, it is now an open-loop-shaped dipole, and on 20m exceeds a HALF wavelength, leading to a very skewed pattern. The pattern on the lower bands stayed normal - because the wire is not exceeding a half-wavelength for the DIPOLE family.

Fired up EZnec, and sure enough, there it is with the bad pattern. Geez, I don't want to have to babysit that resistor when it goes in to make sure my loop stays contiguous...

Congratulations you have made a Rhombic On The Ground
 
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