View Full Version : HF Antennas in Jungle Environment
I am training for a JCET and I am would like some insight on HF antennas in thick jungle vegetation. The antenna will be employed on the team level and the distance will be around 1800 miles. Suggestions?
rocketjok
01-28-2013, 06:15
I used a simple dipole antenna but had to get it really high into the air like 60 or 70 feet to be effective. Its a NVIS shot which you would think needs to be closer to the ground but my partner force showed me the erros in my ways. Its also easy to teach and easy to build and you can get all the parts you need almost any where. If your partner force uses HF they can probably show you what works best you would be supprised the things you learn.
mark46th
01-28-2013, 08:59
As above.
I have used and do carry today a wire reel, small.
I too use a dipole, but I feed it form the end and not use coax.
Look up end feed antenna. Has the same effect as a dipole feed in the middle, the closer to the ground you go the higher the RF off the wire goes up. The more NIVS you get.
inches off the ground ... Google NIVS
AL
any questions ? i will share... ask a Ham .
Sinister
01-28-2013, 16:19
I saw a couple of awesome Sky Wire Loops in Haiti for NVIS shots clear back to MARS stations back in the States.
Badger52
01-28-2013, 17:07
I like albeham's idea. Mid-summer I began playing with an end-fed solution that was originally envisioned as a sloper. The RF will tend to predominately come off the high-end, headed toward the low end (where it's fed). You'll get sky-wave and quite a bit of distance (depending on height, driven by freq & how far the shot is, etc.). It can be quite effective in getting somewhere on the first hop or two. Sometimes a bit of directionality can be a good thing too.
A plus to an end-fed is you really only need 1 support. (In theory, sloping low-to-high, you could pivot your operating position about the high-end and serve more than one target for the shot.)
But as albeham says, what really gets interesting is if you go ahead and flat-top the thing as if it were a dipole, if you have a couple of supports. You'll still get a good bit of signal headed back "over the shoulder" so to speak toward the fed end, but it plays VERY well broadside to the wire as well.
Note: If for some reason you need to feed the thing with coax, make or get a little 9:1 UNUN for your "don't leave home without it" bag & run a counterpoise off one side of that, maybe 1/4 of the wire you have up in the air, along the ground tossed under the wire above.
Be interested to hear how things work out.
Thanks for the insight. Ill do some additional experimentation.
Yesterday I spent several hours testing dipoles, longwires, a raised up-and-down fling wire, and an off center fed dipole. The area I was working in was not optimal; low swampy ground and shooting straight into power lines. However, mission dictates location. Needless to say I had no luck hitting the base station.
Today, I was able to move locations. I had an open area in the jungle and a 30ish foot tree to work with. I used a sloping V antenna. No grounds, no resistors, and a coax transmission line off a balun from a SORAK. First shot out of the box I hit the base station and data was sent in a couple minutes.
If I have time tomorrow, I will go to the same location and test out the previous antennas and see how they compare in the new location.
I do have one question. What is the difference between radio waves propagated over land and over water? Say if you shoot over an ocean, will the waves propagate more efficiently?
Thanks for the insight. Ill use this to build up my HF comms bag.
I used a simple dipole antenna but had to get it really high into the air like 60 or 70 feet to be effective. Its a NVIS shot which you would think needs to be closer to the ground but my partner force showed me the erros in my ways. Its also easy to teach and easy to build and you can get all the parts you need almost any where. If your partner force uses HF they can probably show you what works best you would be supprised the things you learn.
What kind of distances were you shooting with a dipole that high?
Appreciate the info. I feel comfortable with NVIS vs long range shots.
69harley
01-29-2013, 09:03
An excellent tool for HF is VOACAP. You can download it here, newest version was updated in 2012. VOACAP (http://www.voacap.com/)
This has some very usefull tools to predict propogaton, signal to noise and antenna modeling.
Although the freqs are sort of preset with the 137, this software can be used to predict where the link will be made and the take off-angle required. It also has program to design an dipole antenna to a user spec'd freq and take off angle.
Try inputing the locations for the two stations, transmit power, solar flux, etc and run the prop. then look at the time of day for when you want to communicate. It will give you the muf, luf and fot. Will also give you the take off angle and the number of hops required.
Take the freq and the take off angle and use them in the antenna modeling program. Design and build an antenna on the computer before ever cutting a piece of wire.
I used this software (older version) for many years to successfully plan HF networks that relied on PRC-104s and DMDGs. Had very good success.
mark46th
01-29-2013, 09:21
I know you are just on a JCET but when in indian country, never transmit from the same location twice. You probably know this but , jus' sayin'...
"Say if you shoot over an ocean, will the waves propagate more efficiently?"
Salt water is excellent -- and fresh water very bad -- for ground wave propagation.
I know you are just on a JCET but when in indian country, never transmit from the same location twice. You probably know this but , jus' sayin'...
Will do. Too easy to get comfortable in a low threat area.
Make sure you have a good machete to clean up the wire front the plants. Have a few fishing weights as you will lose some. Insulated wire is a must......
I bet Billy Bob has a bunch of stuff left over from panama.
Concur on insulated wire. Today I set up a 30' vertical fling insulated wire with a grounding stake off the radio. Basically a large whip antenna. Terrain was dense jungle and no clear view of the sky.
Again first shot out of the box hit the base station with strong signals. Interestingly enough I tried the same antenna without the grounding rod and had no luck
Badger52
01-31-2013, 04:32
Concur on insulated wire. Today I set up a 30' vertical fling insulated wire with a grounding stake off the radio. Basically a large whip antenna. Terrain was dense jungle and no clear view of the sky.
Again first shot out of the box hit the base station with strong signals. Interestingly enough I tried the same antenna without the grounding rod and had no luckNeat. Signal needs something to work against, ergo, why a ground works or, in case of end-fed slopers, a counterpoise of some kind.
"vertical fling" - I like it. :D
rocketjok
02-15-2013, 00:02
My partner force was shooting only about 600-800 miles to there base. The terrain was high mountain jungle with lots of vegetation but not triple canopy type stuff just lots of green. My partner force at the time was using HF for every thing short of squad communication. Alot of the shots where valley to valley or valley to a ridge line for retrans. I taught them during our class portion that its supposed to be low to the ground for NVIS shots but under real world condition for that region it worked up high. I suspect it had some thing to do with the soil and water tables.
yup, sounds likely. Water table is apt to be higher in that environment...
Just remember..."what's the best antenna???"...the one that works...
Get it 1/4 wave up electrically (or possibly a bit lower)...viola...(that's "waalaaa") for the grunts...:p
Good NVIS that way, higher take off angles..but...freq's, freq's freq's....good prop'll do ya. :D
69 harley is on to some good stuff...:lifter
Yes I 100% agree...hell we always had a water table in the desert...but it was about 1000 feet below .... :D
glebo... when you go to open a school to tech this shit let me know...
AL
Yes I 100% agree...hell we always had a water table in the desert...but it was about 1000 feet below .... :D
glebo... when you go to open a school to tech this shit let me know...
AL
haa, I'd love to. My best job was on the 18E committee as a green suiter (87-91) and a civilian (03-06), my favorite class to teach was theory and antennas....amongst the others I had..
Shoulda stayed there, and not moved up to DOT-D...oh well...
I feel your pain!!!!!
Maryland sucks...:boohoo
Have you tried using a second wire staked out in a mirror of your current antenna as an artificial ground plane? I haven't done any HF work in the jungle but it seems to me that if the water table is the issue, take it out of the equation as best you can. I would imagine there are many things that you could try that would work but I didn't see this suggestion anywhere so I thought I would put it up. Good luck.
Quick update
The elevated fling wire worked great the entire duration of the exercise. For the latter half of the training, a new basestation was brought in and we were only working 40ish km away. I was a little concerned at first because of the close NVIS shot. I ended up using the elevated fling again in lengths of 10-20ft. Again I had no issues sending data.
And just for fun we attempted to shoot back to the states at Norfolk, VA. We set up a Sloping Vee of approx 30ft height and 40ft feet lengths spread at approx 60 degrees. We used a 10 watt radio with no power amplifier. We shot from Thailand to Virginia, a distance of approx 9000 miles and were able to send data with this antenna. I was pretty impressed.
I have few questions,
Can a gauge of a speaker wire used for antenna design prevent RF output, say not enough power?
For sloping "vee" used for ALE on 137/150, you would suggest cutting an antenna to expected freq (time of day, etc) or using a set length (117ft wire)?
Also, would you say it makes any sense to use 100 ft slant wire for the same platforms during the day for a midrange shot?
Questions are in general, not necessary for jungle environment.
Thank you, back to PT.
TOMAHAWK9521
11-17-2013, 10:43
An excellent tool for HF is VOACAP. You can download it here, newest version was updated in 2012. VOACAP (http://www.voacap.com/)
This has some very usefull tools to predict propogaton, signal to noise and antenna modeling.
Although the freqs are sort of preset with the 137, this software can be used to predict where the link will be made and the take off-angle required. It also has program to design an dipole antenna to a user spec'd freq and take off angle.
Try inputing the locations for the two stations, transmit power, solar flux, etc and run the prop. then look at the time of day for when you want to communicate. It will give you the muf, luf and fot. Will also give you the take off angle and the number of hops required.
Take the freq and the take off angle and use them in the antenna modeling program. Design and build an antenna on the computer before ever cutting a piece of wire.
I used this software (older version) for many years to successfully plan HF networks that relied on PRC-104s and DMDGs. Had very good success.
I could have used that site back in '99 while in Vannuatu. Group gave me prop charts and freqs for some Latin American mariachi radio station. :(
Monsoon65
12-05-2013, 21:57
Just remember..."what's the best antenna???"...the one that works...
That sounds familiar.
I took an antenna theory class when I was with Third Herd at Tinker. Seemed we always used a 500 foot long wire and were trying to find some other alternatives to use.
We did just about any HF antenna you could think of; long wire, sloping V, you name it.
Figured out the 500 foot long wire was the best. ;) It was good training, tho.
One thing we always made sure we had plenty of was "bug nuts". Seemed like we were always needing them.
And Ardmore, OK was an RF black hole. We'd get great comms during the day, but at night it was a bear trying to keep the link up and running.
I have few questions,
Questions are in general, not necessary for jungle environment.
Thank you, back to PT.
Can a gauge of a speaker wire used for antenna design prevent RF output, say not enough power?
..No. I have used 28 ga wire to make my shoots.
For sloping "vee" used for ALE on 137/150, you would suggest cutting an antenna to expected freq (time of day, etc) or using a set length (117ft wire)?..
..Google sloping vee. Learn..Do. When you run an ALE station there is always that lowest freq that is will try to use. So when you have an antenna that has at least several quarter wave cut to that freq, and when you start to go up in freq you now get an antenna that will give you many more quarter wave lengths, this gives you more gain, low angel antenna pattern, etc. This is a good thing. You could, depending on the freqs get a 500 foot sloper. But 117ft wire, is can work, you just need to try it. Let the magic work.
Also, would you say it makes any sense to use 100 ft slant wire for the same platforms during the day for a midrange shot?
Remember a midrange shoot you would like to have a more higher angle antenna pattern, more to the 90 degree as possible. NIVIS google it. So when you shorten a long wire, (the legs of a Vee), you antenna starts to react to the ground and your antenna pattern moves into this NIVIS type pattern. (frequency dependent )
I have use 100ft wire for low band VHF and HF, works.
AL :munchin
sneakypete314
05-14-2015, 09:29
we are looking at trying to talk long hual HF. Command is expecting us to talk back states side. the fling wire will work to hit the local base station at around 700 miles. and retrans over email from that point. like previously stated they cant get away from the G2W of sat com. does anybody have any ideas for around 7800 miles?
69harley
05-14-2015, 11:29
we are looking at trying to talk long hual HF. Command is expecting us to talk back states side. the fling wire will work to hit the local base station at around 700 miles. and retrans over email from that point. like previously stated they cant get away from the G2W of sat com. does anybody have any ideas for around 7800 miles?
The prop chart is the key to making this work. Run a prop between the two ends of the HF circuit and look at the predicted take off angle. That angle will drive antenna selection.
The prop chart is the key to making this work. Run a prop between the two ends of the HF circuit and look at the predicted take off angle. That angle will drive antenna selection.
Do not forget the terrain and climate (jungle vs Desert vs wooded terrain) Those are also factors.
We would use a portable tower, log periodic or other tower mounted antenna for FID missions since we would be static. 7800 miles living out of your ruck is going to be hard. I once did a shot from NE alps in Italy back to Bragg with 3 rolls of foil, 2 long wires and got through but I had a great focused reflector and I was not hiding while setting up.
just my 2cents
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
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...:D
Oh, not to stir up stuff with commo guys, but we could debate/dicuss/argue for a looong time over this stufff...lolol
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
/\ /\ /\ I can concur with that.
That's what makes commo "interesting"...try to get that damn signal out...lol
mark46th
05-16-2015, 09:13
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...