simple coax homebrews

[cassidy1190]

I was cleaning out my desk earlier this week and found an old radio shack frequency guide that I purchased when I first started scanning. I was browsing through the first couple pages and found instructions on building simple antennas.

One example was making a simple ground plane antenna out of coaxial cable:

They advised to cut the outer rubber shield to a length determined by frequency (I think it was about 6 inches for uhf), and then pull down the aluminum braid around the remaining coax into a sort of skirt below where the rubber was stripped. Has anyone ever tried this before? From the very little I do understand about how antennas work this does make sense, but I want to know if it works before I rip up some perfectly good cable.

[jim202]

I use them all the time. I think the correct name would be a coaxial vertical. I have a commercial
version on a low band channel at 39 MHz. This antenna has a whip at the top with a skirt that
goes over the pipe support. Coax comes out the bottom of the support pipe. The real world
functionality of these antennas is very good. I have a low band ground plane antenna and can
compare their performance by switching antennas back and forth on a radio. The ground plane
antenna either doesn't hear a signal or it is very much in the noise. Going to the coaxial vertical,
the signal is full quieting. Make your own conclusion.

Back to the antenna made just from coax. We have a number of VHF, UHF and 800 MHz radios
that are all using that exact antenna. I hang them above the ceiling with some string tied to the
metal support beams up there. Just tie the other end to the top of the center insulation on the
coax.

I just keep the different radio antennas separated some so they don't cause any inter radio
signal radiation and intermod issues. There are a couple of high powered paging transmitters
within a half mile of me and I don't need those problems.

Jim

Originally Posted by cassidy1190

I was cleaning out my desk earlier this week and found an old radio shack frequency guide that I purchased when I first started scanning. I was browsing through the first couple pages and found instructions on building simple antennas.

One example was making a simple ground plane antenna out of coaxial cable:

They advised to cut the outer rubber shield to a length determined by frequency (I think it was about 6 inches for uhf), and then pull down the aluminum braid around the remaining coax into a sort of skirt below where the rubber was stripped. Has anyone ever tried this before? From the very little I do understand about how antennas work this does make sense, but I want to know if it works before I rip up some perfectly good cable.

[cassidy1190]

so what exactly is the method of skirting the aluminum braid over the cable, this is proving to be alot harder than i thought.

[jim202]

Well first of all the braid your calling aluminum is probably silver plated copper.

Second, the secret is to push the entire shield down towards the remaining jacket. It will expand
some while you do this. While it is pushed down, grab the end of the braided shield and pull it down
and over itself like pealing a banana, but your not splitting it into individual pieces. Just keep pulling
the end of the shield down and over the coax black insulation. You should be able to do this in one
continual motion.

Jim

Originally Posted by cassidy1190

so what exactly is the method of skirting the aluminum braid over the cable, this is proving to be alot harder than i thought.