Author Topic: UnderGround HF Antenna ,40 meter Loop  (Read 14026 times)

Offline Carl

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UnderGround HF Antenna ,40 meter Loop
« on: August 20, 2014, 06:42:02 PM »
I really did not consider it worthy of a separate thread as it is so easy to do... it is a loop of wire buried with an edger or in my case a cable "plow" /ditch digger ...you know...looks like a big chainsaw/digger. Place the wire beneath grass level and INSULATED WIRE does work a bit better. My loop was cut for 40 meters or about 154 feet long (longer than above ground loop)with a dry feed point (buried bucket with a lid) as the feed point has a 4 to 1 balun ,though a 9 to 1 may be better.

My loop shows about 1.8 to 1 SWR on 7.250 before I engage the LDG auto-tuner and that makes it match all bands ...except for 10 MHZ for some reason.The wire is left over electrical /copper  10 gauge though wire size is not too important...I have even used galvanized electric fence wire (1/4 mile for $12) but nature tends to be hard on un-protected metal.

In use the antenna loses about 2 to 3 "S" units compared to a dipole at 25 feet or my end fed half wave antenna at 8 feet above ground...but those "S" units are just NOISE ...so unless you  like full scale meter readings , this LOW KEY antenna is a winner. Though I note the GROUND MOISTURE does effect it a lot after a rain,though even when wet I was able to talk to several Canadians and Northern US while running 100 watts out with little trouble ...just low "S" meter readings.

Worms...night crawlers also tend to surface after I transmit a while when soil is wet from rain.

A bit more about it and how it is working here :

http://thesurvivalpodcast.com/forum/index.php?topic=50979.0

Offline Alan Georges

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Re: UnderGround HF Antenna ,40 meter Loop
« Reply #1 on: August 20, 2014, 08:11:28 PM »
I must say it does work, and work well at that.  Losing 2–3 S-units is quite a hit, but with anything more than a QRP rig it can still reach out several hundred miles.  For an ultra low-profile antenna this one is awfully hard to beat.

I can think of all kinds of evil uses: an unfindable pirate shortwave site, "borrow" part of your neighbor's yard for that ginormous 160m antenna (install when they're on vacation), and of course, fish bait.  3;)

Offline Carl

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Re: UnderGround HF Antenna ,40 meter Loop
« Reply #2 on: August 21, 2014, 07:30:11 AM »
I must say it does work, and work well at that.  Losing 2–3 S-units is quite a hit, but with anything more than a QRP rig it can still reach out several hundred miles.  For an ultra low-profile antenna this one is awfully hard to beat.

I can think of all kinds of evil uses: an unfindable pirate shortwave site, "borrow" part of your neighbor's yard for that ginormous 160m antenna (install when they're on vacation), and of course, fish bait.  3;)

You know how low key the peppermint mine location is,even though I did find a way to put a half wave end fed antenna in the grape arbor to pass all but the closest inspection.Did you know that a TREE can also be used as an antenna, Look for TREES as ANTENNAS file in my end fed half wave folder...anyone can view and download.

https://drive.google.com/folderview?id=0B5ZIZLZV4AwIX3ZwckFUeGpEOXc&usp=sharing

Offline backwoods_engineer

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Re: UnderGround HF Antenna ,40 meter Loop
« Reply #3 on: August 21, 2014, 03:29:30 PM »
Thanks for posting this, Carl.  I might have to give this a try, in my present rental-house situation.  I wouldn't bury the wire, you understand, just put it right on the surface.

Offline Carl

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Re: UnderGround HF Antenna ,40 meter Loop
« Reply #4 on: August 21, 2014, 03:46:58 PM »
Thanks for posting this, Carl.  I might have to give this a try, in my present rental-house situation.  I wouldn't bury the wire, you understand, just put it right on the surface.

It will surprise you at how well a wire on the ground will work,too many people just KNOW it won't work.
Maybe a GRASSWIRE ANTENNA is in your future.Or my  loop will surprise you at how well it works. I can hear BETTER
with the current LOW antennas I use now, including the end fed half wave at 8 feet.

http://f5ad.free.fr/Liens_coupes_ANT/G/K3MT%20Antenne%20gazon.htm


Offline Medicineball

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Re: UnderGround HF Antenna ,40 meter Loop
« Reply #5 on: August 21, 2014, 08:10:44 PM »
This is just amazing! Is this solely for NVIS?

Offline backwoods_engineer

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Re: UnderGround HF Antenna ,40 meter Loop
« Reply #6 on: August 21, 2014, 10:20:44 PM »
Maybe a GRASSWIRE ANTENNA is in your future.
http://f5ad.free.fr/Liens_coupes_ANT/G/K3MT%20Antenne%20gazon.htm

The low takeoff angle of the GRASSWIRE end-fed antenna would seem to make it better for DX than NVIS... but that hasn't been your experience with your worm-burner, has it, Carl?


Offline Carl

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Re: UnderGround HF Antenna ,40 meter Loop
« Reply #7 on: August 22, 2014, 05:41:34 AM »
The low takeoff angle of the GRASSWIRE end-fed antenna would seem to make it better for DX than NVIS... but that hasn't been your experience with your worm-burner, has it, Carl?



When the band is open,it is open and DX is easy,though a couple "S" units lower than my ,at height,full size dipole. This actually helps me to work DX as there is much less noise and signals are easier to hear...especially weak ones. Though not at optimum take -off angle an antenna still radiates and DX still happens.

  Think of the times you hear mobile stations or QRP (low power) stations from all over the country and often all over the world...not to slight them but a 100 watt mobile rarely RADIATES MORE THAN 5% OF THAT POWER...OR 5 WATTS..and with the ground level(or below) you are at no more handicap than a mobile station with it's inefficient antenna and ground system.

  In fact ,you get a combined ground and antenna in one.. My reason for a low antenna is to keep that operation as low a visual impact as possible and for the NVIS properties. While NVIS works better with an above ground antenna (6 to 8 feet above ground) even a buried antenna appears to do the job as true earth ground with conductivity is well below the surface at least until the rain adds to ground conductivity.It probably has something to do with the water table and I am glad I'm not in the swamps trying to do this.

I have had only one sign to show where the antenna is placed and that is the fact that worms tend to surface when transmitting with damp soil and I could see the path of the antenna with worms and night crawlers attempting to spell out CQ DX or LOOK HERE , something like that.

  What the heck,wire is cheap and I have time to play. in the future I might make a sub-surface BEAM to see how directional properties are effected by a little soil on the antenna.

Offline Medicineball

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Re: UnderGround HF Antenna ,40 meter Loop
« Reply #8 on: August 23, 2014, 09:36:15 PM »
This is truly amazing. Learn something new every day. Makes me want to just throw my antenna on the ground and see what happens.

Offline Carl

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Re: UnderGround HF Antenna ,40 meter Loop
« Reply #9 on: August 24, 2014, 07:16:05 AM »
This is truly amazing. Learn something new every day. Makes me want to just throw my antenna on the ground and see what happens.

Well ,being near or on (or UNDER) the ground greatly changes the tuning and I would not do it without at least an SWR meter and knowing how to use it...But automatic antenna tuners make it east for us now...I just allow 25% or so MORE wire than 'standard ' cut lengths suggest and work for there. It is to different an idea to have enough data for cut length data that I know of to be available. The tuner matches the impedance that your radio expects .

  To make my loop ,I used an MFJ 259B analyzer to ballpark the length as the wire was laid out on the ground...when I was close to resonance , I simply quit cutting and buried the wire....with the feed point/balun in a bucket in a hole with hole in the bottom for water to escape.and the balun and coax feed supported near the to of the bucket and all wires were sealed with silicon bathroom sealer.

  You see the entire antenna is below the surface to preserve the facility from being found as anything more than an old bit of un-used farmland/woods. I have used barb wire fences as antennas...even farm implements....if it conducts electricity , it can be an antenna.

Offline exSun

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Re: UnderGround HF Antenna ,40 meter Loop
« Reply #10 on: August 24, 2014, 05:29:26 PM »
Shallow, buried antennas were studied by (IIRC) Eyring Research Institute in the early '80s. They were of interest to the Air Force, since they offered survivablity against blasts that above ground antennas don't. The idea was backup HF links for missile sites. I haven't heard of ERI for a decade or two - either they went out of business, or what they found worked so well it went black. Your guess as to which.

Offline Carl

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Re: UnderGround HF Antenna ,40 meter Loop
« Reply #11 on: August 24, 2014, 06:02:10 PM »
Shallow, buried antennas were studied by (IIRC) Eyring Research Institute in the early '80s. They were of interest to the Air Force, since they offered survivablity against blasts that above ground antennas don't. The idea was backup HF links for missile sites. I haven't heard of ERI for a decade or two - either they went out of business, or what they found worked so well it went black. Your guess as to which.

My first one was a buried loop for CB radio to try to maintain contact with spelunkers in Virginia( late 70's). It worked OK ,but it was found that UHF did penetrate ground better ( as far as 3 miles as best I remember) and the same antenna was pressed into service without so much as an SWR check...those were the good old days.

Offline Carl

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Re: UnderGround HF Antenna ,40 meter Loop
« Reply #12 on: December 28, 2014, 03:43:25 PM »
Antennas even work underground...

Offline armymars

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Re: UnderGround HF Antenna ,40 meter Loop
« Reply #13 on: January 09, 2015, 07:09:27 PM »
  The best on the ground or under ground antennas are CCD antennas. The current has a much low peak so less loss. They are 1 wave length long for a dipole and a pain to build. Each segment of wire and a capacitor make up a resonant circuit then you have to add a resistor across the cap.  to bleed off static. This has to be water tight, but it does work well. 73

Offline merlin

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Re: UnderGround HF Antenna ,40 meter Loop
« Reply #14 on: March 18, 2019, 12:16:36 AM »
Hi, we have a group on Facebook about buried antennas

https://www.facebook.com/groups/earthprobes/

73's
John