On Fri, 10 Dec 2004 17:27:54 -0500, GeorgeB wrote:

On Fri, 10 Dec 2004 14:17:27 -0800, "Jerry J. Wass"
wrote:

john smith wrote:

That and he has instructions for building one on his website.

jls wrote:
Give Jim Weir time to reply; I believe he sells a kit for an outside
aerial.

That copper tube "J" Pole works nice, Be on lookout for 58 ohm co-ax
cable. Not The TV stuff. it's 75 ohm.

You may be thinking of RG58 ... thin 50 ohm coax.


Purchase an SO-239 chassis connector. Get one that has 4 small screw
holes (one in each corner. I've forgotten the length of a quarter
wave on 122.8, (I'd have to look it up some where around here)

Cut a piece of thin brass brazing rod, or brass, or copper to a
quarter wave length. Solder that into the chassis side of the SO239
connector. This is the radiator/antenna. Cut 4 more pieces of the
brass (or what ever) rod about 10% longer than the radiator. Solder
one end of each into one of the corner holes. Bend these out at about
45 degrees so the thing can stand on them. You now have a good
antenna. It will stand on a flat roof, or straddle the peak. Use a
bit of Silastic RTV (TM) to hold the feet to the roof.

I used to use one of these at work with over a 100 feet of RG-58 and
it worked fine.

Don't worry about loss in the RG-58 unless you have a run of a 100
feet or more. The height of the antenna will more than make up for
the loss and you are using a receiver that is probably far more
sensitive than the average aviation receiver.

You can go to RG-8X which is slightly larger than RG-58, but a lot
smaller than standard RG-8 and more flexible.

Put a PL259 (male connector) on the end of the coax that goes to the
antenna. Put what ever is required for the end that goes to the
radio. I use PL-259s on each end with an adapter to fit the radio.

Hook up each end and you are in business.

J-pole antennas are very good, but not the best for aviation ,,, they
are fairly narrow band, and just the comm portion is around 15% wide
... likely better off with somehting with better wideband

I'm using a co-linear 144/440 MHz dual band antenna that isn't even
cut for the aviation frequencies and it works very well. The base is
at 25 feet and at the far end of about 120 feet of LMR-400 (RG-8
equivalent, but better) The reason for the large coax in this case is
the amount of power I run on those two bands.

I have another co-linear at 50 feet on the main tower with 144 and 440
beams at 130 feet (at the end of 228 feet of LMR-400. They also hear
ATC and aircraft just fine even though the signals are well outside
the range of the antennas.


Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com
characteristics. A cheap vertical whip cut for band center would do
fine. Consider usinb larger caox, RG8 or similar, not for power
handling, but for loss. Find a local ham and have him help you come
up with a matching bridge and use low loss twin lead ...