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Old 05-15-2015, 05:24   #31
glebo
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Quote:
Originally Posted by PTF Guy View Post
I think "it depends". I would not consider 1800 miles on HF to be NVIS - it's more like one or two hop F Layer skip, depending upon the freq/time. If you are confined to one freq, I'd go with a half-wave dipole, one half wave above "ground" to get the low takeoff angle you need for that shot. You might have to cut several dipole legs depending upon your freq plan. As noted above, use insulated wire - and clear away any nearby wet foliage - if you can. String the dipole at right-angles to your target azimuth of course. If you have some "lift" to help with weight, here is the portable kit I use for field expedient antennas. You should find what you would need in a pile like this! VOACAP is really pretty good too, if that's all you can get. Given your path and freq, it will tell you the optimum time, etc.
http://www.n6cc.com/field-antenna-kit
AR
Guys...ever heard of "skin effect"...

http://en.wikipedia.org/wiki/Skin_effect


There's a false sense of security using insulated wire. It works great for electricity, but not radio frequency EM energy. EM energy flows along the outside or very close of the wire. How would an antenna radiate if the energy was "insulated" in the wire???


Anyway, HF in the jungle, challenging at least. How much room you have, freq, required take off angle etc, etc.

That's a pretty long shot, and as stated will probably be multi-hop. Propagate for that.


Good luck....oh, and for antenna suggestions....use the one that works...

Oh, not to stir up stuff with commo guys, but we could debate/dicuss/argue for a looong time over this stufff...lolol
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Last edited by glebo; 05-15-2015 at 05:27.
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Old 05-15-2015, 13:19   #32
PTF Guy
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Hi glebo - Yep, a challenging problem - getting "out" from a jungle location, especially at low takeoff angles. That close-in wet stuff absorbs a lot of energy. The antenna you can get going is mostly limited by the amount of time and energy you have available!
On insulated wire - I think it doesn't matter with antennas. Yep, skin effect keeps most of the current flow on the outside surface of the wire conductor but "insulation" is essentially transparent to radio waves (think plastic radomes, fiberglass vehicle whips etc.) . But it does keep wet leaves off the conductor - which helps with immediate power loss and random detuning. Insulation has a slight effect on the length calculation, however I think that can be ignored for practical purposes.
Yep - you're right: The best antenna is the one that works! No BS GI !! LOL
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Old 05-16-2015, 04:53   #33
glebo
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/\ /\ /\ I can concur with that.

That's what makes commo "interesting"...try to get that damn signal out...lol
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Old 05-16-2015, 09:13   #34
mark46th
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I used to tell the 11B's to climb up a couple of trees hold the ends of the antenna and gut out the RF...
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