Tower J-pole

[kc5uta]

For the last five or so years, I have used the tower (65 feet guy wires insulated from the tower) as part of a 20 meter J-pole. I have been getting good results, with plenty of psk contacts, from the US, and even a few from France, Asiatic Russia, and even Japan, on just 10-50 watts. Has anybody else done this? Also I am wondering if it would work differently to feed the stub like Arrow 2m open stub antenna, instead of shorted like a "standard" J-pole. Thanks. Dave

 

[dksac2]

Were it me, I'd buy antennas with gain to put on a tower, forget the J Pole antennas. They are just a so-so antenna.

The one thing you need to think about on a tall tower is the amount of loss in the cable, especially at 2 meters, it's a lot. If you figure that using LMR-400 cable, which is one of the best, you will lose half of the power by the time the signal reaches the antenna in coax loss.
It's for this reason you want an antenna with as much gain as possible. Even a beam and rotor if you want max gain.
By going to a high gain antenna, you can not only make up for the loss of power in the coax, but may even put out more power than the transceiver has originally. A J Pole has a maximum of 1.5 dbi of gain, with DBI, it's really negative gain when it's only 1.5 dbi. An antenna with 8.3 dbi gain will at least make up for all the signal lost in your coax. Be sure to use LMR-400 or a better cable, none of the 8X types at all.
J poles also require a balun at the antenna, they put a great deal of signal on the outside of the coax, which hurts even more.

73's John

 

[kc5uta]

Thanks for the reply. I think you might have misinterpreted my question a bit. The top 50 feet (or so) of my 65 foot tower IS the half wave part of the 20 meter J -pole. the feed point is at shoulder hight standing on my roof. I fed 1/4 wave section with the center conductor. MY question was has anybody out there did the same with their tower, and curious if so how they fed it? The 2 meter reference was more of an example of alternative feeding methods. Feed the 1/2 wave or the 1/4 wave?

 

[LtDoc]

Feed the 1/2 wave of the 1/4 wave? Think about that for a second. RF is AC, right? So, every half cycle that center conductor is the 'ground' and the braid is the 'hot' part, right? So there's actually not much difference how you do it. There is a slight 'shift' in the radiation pattern, but there are so many 'bulges'/'dips' in a radiation pattern anyway that it isn't gonna make a huge difference.
Or, just swap the connections to see for your self what would happen.
There are a lot of people who 'load' a tower as an antenna. Maybe not in exactly the same way, but it isn't uncommon at all.
- 'Doc

(How about a 'High Tower'/18HT, I think it is?)

 

[kc5uta]

***slaps own forehead with hand**** Well duhhhhh dave!

forgot about the AC aspect. I think I will try to re-do the feed like you would a steel whip, to make it more weather proof. Thanks for the "schooling" there doc. lol