materialpigeonfibre
New Member
- Reaction score
- 6
- Points
- 130
My opinion:
AS-2259/GR NVIS antenna is not used correctly.
(To be clear, I consider NVIS a type of operating. Not a type of antenna. NVIS operating means you are directing the majority of your RF energy skywards.)
Problems with the 2259:
It is resonant (AFAIK) on two frequencies aprx 7 and 10MHz. (A good choice during Vietnam)
[Image How It Was Good Ol Days]
You might say “HOLD ON, I’VE READ THE MANUAL. THE ANTENNA IS GOOD 1-30MHZ!”.
Sorry, that’s a dirty dirty lie. Double check the manual. It says that it works “with a tuner”.
Yes, your tuner will tell you (and the radio) everything is fine at 1:1 SWR. But it will also say that with a screwdriver jammed in the socket. And you know that a screwdriver won’t make the comms.
Great advertising, and it sold the antenna.
We may be going through a new prolonged sunspot minimum. Meaning the frequencies we must use for effective NVIS are much lower than the frequencies the antenna was designed/ cut for.
I ran a simulation for frequencies that would work with a prc-160 for NVIS in Canada during July 2020.
[ManPack Canada July 2020 Simulation NVIS]
Making it work:
I hear there is an NVIS extension kit. If you can get one. USE IT. The frequencies we have to use are much lower. The antenna must be longer.
Almost every time it doesn’t work in the field, you will see the 2259 set up, then 100feet of coax to the radio.
THIS DOES NOT WORK. THIS DOES NOT WORK. THIS WILL NEVER WORK well.
The 2259 is a fan dipole with a solid low loss coax (as the support) to the feed point. A very cool design.
It may be useful in six years but it’s not great right now.
To give it the best chance of working, you MUST have the tuner as close as possible to the base of the antenna.
If you have a long line of crappy RG-58, it will bounce back and forth to the tuner. That length of coax will be heated. Heat is radiation that is wasted (it didn’t go in the air). No comms.
THE TUNER MUST BE AS CLOSE AS POSSIBLE TO THE FEED POINT.
The 138 has that external tuner? Place it RIGHT AT THE FEED POINT. VERY short run of coax to the antenna from the tuner.
Using a prc160?
Have that radio RIGHT CLOSE to the antenna. Short length of coax.
Use external tuners. PLACE THE REMOTE TUNER RIGHT NEXT TO THE ANTENNA. Run the coax to the operating location from the tuner.
Mixing antennas. If you have one antenna set up as NVIS and the other antenna nearby (Under 10km) set up as a vertical, THEY WILL NOT TALK TO EACH OTHER.
DO:
NVIS TO NVIS.
NVIS is good for links 20KM+ to 300KM
OR:
VERTICAL TO VERTICAL
LineOfSight LOCAL DATA/VOICE and Long Distance Shots
For success the officer must figure out what frequencies will work. This can be done with propagation programs (I know they are provided).
Give the operators multiple working frequencies.
A better solution is to build dipoles/ fan dipoles for the correct frequency and suspend them off the ground 7 to 15 feet. It will always be that high off the ground for the NVIS.
[FAN DIPOLE.gif)
Bonus points:
Have a CST(LCSS TECH) check the tuning (with a flipper kit).
AS-2259/GR NVIS antenna is not used correctly.
(To be clear, I consider NVIS a type of operating. Not a type of antenna. NVIS operating means you are directing the majority of your RF energy skywards.)
Problems with the 2259:
It is resonant (AFAIK) on two frequencies aprx 7 and 10MHz. (A good choice during Vietnam)
[Image How It Was Good Ol Days]
You might say “HOLD ON, I’VE READ THE MANUAL. THE ANTENNA IS GOOD 1-30MHZ!”.
Sorry, that’s a dirty dirty lie. Double check the manual. It says that it works “with a tuner”.
Yes, your tuner will tell you (and the radio) everything is fine at 1:1 SWR. But it will also say that with a screwdriver jammed in the socket. And you know that a screwdriver won’t make the comms.
Great advertising, and it sold the antenna.
We may be going through a new prolonged sunspot minimum. Meaning the frequencies we must use for effective NVIS are much lower than the frequencies the antenna was designed/ cut for.
I ran a simulation for frequencies that would work with a prc-160 for NVIS in Canada during July 2020.
[ManPack Canada July 2020 Simulation NVIS]
Making it work:
I hear there is an NVIS extension kit. If you can get one. USE IT. The frequencies we have to use are much lower. The antenna must be longer.
Almost every time it doesn’t work in the field, you will see the 2259 set up, then 100feet of coax to the radio.
THIS DOES NOT WORK. THIS DOES NOT WORK. THIS WILL NEVER WORK well.
The 2259 is a fan dipole with a solid low loss coax (as the support) to the feed point. A very cool design.
It may be useful in six years but it’s not great right now.
To give it the best chance of working, you MUST have the tuner as close as possible to the base of the antenna.
If you have a long line of crappy RG-58, it will bounce back and forth to the tuner. That length of coax will be heated. Heat is radiation that is wasted (it didn’t go in the air). No comms.
THE TUNER MUST BE AS CLOSE AS POSSIBLE TO THE FEED POINT.
The 138 has that external tuner? Place it RIGHT AT THE FEED POINT. VERY short run of coax to the antenna from the tuner.
Using a prc160?
Have that radio RIGHT CLOSE to the antenna. Short length of coax.
Use external tuners. PLACE THE REMOTE TUNER RIGHT NEXT TO THE ANTENNA. Run the coax to the operating location from the tuner.
Mixing antennas. If you have one antenna set up as NVIS and the other antenna nearby (Under 10km) set up as a vertical, THEY WILL NOT TALK TO EACH OTHER.
DO:
NVIS TO NVIS.
NVIS is good for links 20KM+ to 300KM
OR:
VERTICAL TO VERTICAL
LineOfSight LOCAL DATA/VOICE and Long Distance Shots
For success the officer must figure out what frequencies will work. This can be done with propagation programs (I know they are provided).
Give the operators multiple working frequencies.
A better solution is to build dipoles/ fan dipoles for the correct frequency and suspend them off the ground 7 to 15 feet. It will always be that high off the ground for the NVIS.
[FAN DIPOLE.gif)
Bonus points:
Have a CST(LCSS TECH) check the tuning (with a flipper kit).
