HF Antennas in Jungle Environment

[k-rub]

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]

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]

As above.

[albeham]

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]

I saw a couple of awesome Sky Wire Loops in Haiti for NVIS shots clear back to MARS stations back in the States.

[Badger52]

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.

[k-rub]

Originally Posted by rocketjok

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]

An excellent tool for HF is VOACAP. You can download it here, newest version was updated in 2012. VOACAP

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]

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'...

[Hammock]

"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.

[k-rub]

Originally Posted by mark46th

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.

[TOMAHAWK9521]

Originally Posted by 69harley

An excellent tool for HF is VOACAP. You can download it here, newest version was updated in 2012. VOACAP

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.