Survivalism & Self Sufficiency Topics > Amateur Radio How-To's

UnderGround HF Antenna ,40 meter Loop

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Medicineball:
This is just amazing! Is this solely for NVIS?

backwoods_engineer:

--- Quote from: Carl on August 21, 2014, 03:46:58 PM ---Maybe a GRASSWIRE ANTENNA is in your future.
http://f5ad.free.fr/Liens_coupes_ANT/G/K3MT%20Antenne%20gazon.htm

--- End quote ---

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?

Carl:

--- Quote from: backwoods_engineer on August 21, 2014, 10:20:44 PM ---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?



--- End quote ---

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.

Medicineball:
This is truly amazing. Learn something new every day. Makes me want to just throw my antenna on the ground and see what happens.

Carl:

--- Quote from: Medicineball 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.

--- End quote ---

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.

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