HFU HF Underground
Technical Topics => Equipment => Topic started by: Josh on May 26, 2017, 1859 UTC
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Just ran across this page that describes a small loop on the ground for hf reception;
http://www.kk5jy.net/LoG/
I have plans for workable hf underground antennas (apropos for this website) as the results from emp testing and have considered building same, but this antenna lying directly on the surface would be a lot easier to pull off; for the underground types one must remove the outer shield from coax and use the center conductor and dielectric for the antennae as well as burying the antenna - much more work than I want to do.
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I would guess if it's buried it needs to have a waterproof dielectric?
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I've used them on and off for the better part of two decades or more. You generally need to crank the gain on your receiver a bit for best results, or even uncouple the ground side for weak sigs. During a bad static season they can make the difference between hearing something and hearing nothing.
Before KIPM went to high power, I used to listen to Max via a LOG in the summer months on those marathons. It went from,"What is that weak weird sh!t?" on the dipole to "Ah-ha!"
Some people advise running them on top of moderately high grass and brush, at about a foot, but don't believe it. I've heard marked differences in static levels from near quiet, flat on the ground, to high levels of static as little as 6 or 8 inches above the ground using them at various sites. If you feel like you need more "oomph" uncouple the ground side or add more wire.
I prefer a BOG, Beverage on the ground, after years of messing w/ both as wavelength isn't as big of a deal on HF and there is more directivity, but antennas both are prime static eliminators. The plus with both is you can always straighten the loop out if you've got clue which direction the broadcast is coming from and use it as a BOG, or turn your BOG into a LOG in seconds. It's basically two simple, low cost, effective noise reducing antennas in one.
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"I would guess if it's buried it needs to have a waterproof dielectric?"
Yes, so foamed dielectric is a poor choice for this use.
http://www.rexresearch.com/rogers/1rogers.htm
http://www.dtic.mil/dtic/tr/fulltext/u2/783274.pdf
http://ke7hr.com/caveradio/80meterhfunderground.pdf
http://www.antentop.org/016/files/underground_016.pdf
As to loops over Beverages and etc, I was thinking more along the lines of a rhombic but am not sure how the directivity will approximate that of a full size rhombic - wich is the goal.
If you're interested in antennae and radio at all you need to read this at least once;
Interviewees:
Dr. Harold H. Beverage and H.O. Peterson Interviewer:
Norval Dwyer
Dates: July 1, 1968 and July 1973
http://www.hard-core-dx.com/nordicdx/antenna/wire/beverage/interview1.html
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If you're going to leave it out for a long while, scalp the grass short before you lay it down, let the grass grow to about eight inches and use pegs to hold it the wire secure and tight to the ground while mowing. When your done mowing that section, stow the pegs until next time you mow over top of the thing. By the end of summer it should have buried itself in the yard. BTW, the technique works for radials,too, if you live in lands with a minimum of soil on rock, clay, or good ol' hardpan. It beats trying to dig slits for them in that kind of country.
Give it a try, Josh. They're about an easy of receiving antenna as there is to build and they work well once you learn the little tweaks you need to make it shine with your preferred receiver. There were several summers when my main back porch late night listening antenna was a LOG. I still use them at the beach for SW. They absolutely shine close to the coast in performance and ease of set up. Lay it out, do some listening, roll it up and do it again the next day. It takes all of thirty seconds to roll out or roll up.
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Plus it'll keep those damn kids of my lawn!
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And penguins. They're waddlers and shufflers. The wire will snag them. When you get a few, I'll forward you a certain address to send them to. Punch holes in the side of the box and write "From Belinda" on the label, the poor ol' fella who lives there will be thrilled.
Just think, if you ever need bait, you can simply feed your ham rig and amp into the thing, key it down, and pick up all the nightcrawlers and red wigglers you need off the surface. There's nothing a LOG can't do.
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"Red Wigglers! The Cadillac of Worms!"
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Also cheap "pegs" that can be left in the ground indefinitely or at least till they rust away is to cut up a coat hanger (NO MORE WIRE HANGERS!) into sections and make them into U shapes, press them into the dirt over the wire and the wire will keep in place even when mowed over.
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It's amazing how great minds think alike.
My first and only foray into FM pirating involved a homemade 1/4 wave vertical made of coat hangers. It worked surprisingly well.
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My first 2m 1/4 wave vert was made with coat hangers and a uhf socket, worked fine. People underestimate the ubiquitous coat hanger.
https://www.eham.net/articles/7005
http://www.hamuniverse.com/2metergp.html
http://www.arrl.org/files/file/Technology/tis/info/pdf/ab18-16.pdf
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Here are the basic details for my 148' "shielded" coaxial loop-on-ground antenna:
https://www.hfunderground.com/board/index.php/topic,29940.msg114696.html#msg114696
I actually built it for mostly regional listening of lower HF, but it worked decently enough for general purpose reception to take over as my primary receiving antenna from longwave through mid HF.