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Nationalpatriot · #1 08-27-2009, 07:40 PM

Hi, I just recently got into the "homemade" aspect of radios, bought myself a new CB to replace my 25 year old hand me down, got a new antenna and decided to make myself my own 1/4 wave antenna. I've got everything mounted and ready to boot up except for 1 thing. All the antennae I have been seeing built have unshielded copper wire as grounding radials. I've got the ability to run as many as I need to, but my only question is, am I able to use shielded? I am making a portable antenna and want more durability than just a copper piece of string as it were.

also, side note, would it be bad to create a base out of strong (white) PVC, with two vertical pieces of PVC, one for the antenna and one for a small flag pole? (the flag has plastic grommets and nothing metal on it so I don't think it'd interfere with the transmitting aspect.)

Also, because the antenna will be quite high, is it ok to add an extension onto the coax wire? I've got about 10 feet leading out from the 102-ish-inch antenna already. Thanks

-NP

RickC. · #2 08-28-2009, 05:47 AM

Shielded wire would work OK, but would bring velocity factor of the wire into the mix and would also make it unnecssesarily heavy.

Do you have a pic of the flagpole? I can't visualize what you mean.

Rick

W5LZ · #3 08-28-2009, 06:20 AM

I'm not sure I understand exactly what you mean either. If you are talking about a ground mounted antenna's radials, insulated or not isn't going to make a lot of difference, maybe less than an inch or so. It's one of the qwerks of ground mounted antennas that they require more radials than an elevated antenna. How many? As many as possible until you are tired of the whole thing, sort of.
The PVC and flag pole thing, and the antenna being quite high? That might lead to problems with the radials. That's the part I'm really not sure if I understood correctly.
As for extending the length of the feed line, yes you can do that.
- 'Doc

Nationalpatriot · #4 08-28-2009, 07:51 AM

key:
gray=pvc pipe
pink = coax lead to radio
green = antenna wire
black = two separate pvc (or even if I had to, wooden dowels instead of pvc, I've been reading PVC isn't always the best material to use because of the filler inside of the pvc)
red = flag
blue = radials (in reality they would be the same length as the antenna wire but for 3D sake I needed them to be of different lengths)

I followed this guide line off of Tips and tricks on how to build your own CB Antennas.

Quote:

For a quickie CB antenna, a vertical dipole (1/2) wave can be made right from the coax itself You take your coax and very carefully, without nicking the braided shield, strip 102 inches of the outer insulation jacket off one end. After removing the outer jacket, start bunching the shield down the coax from the end. Now, where the outer jacket and the shield meet, separate the braided shield enough to get the inner conductor out through the hole in the braid. Pull all of the inner conductor through and stretch it and the braid out. Be careful not to skin any of the insulation off the inner conductor. Now attach an antenna insulator to the end of the inner conductor. Measure the braided shield. Cut it off at about 106" and attach an antenna insulator to the end. The total length of the inner and outer conductor should be about 17 feet (1/2 wave). You can haul it up to any height you want with a string or rope attached to the insulator on the center conductor. It's a good idea to coat the end of the coax cable where it separates with some kind of waterproof sealer. This keeps water from seeping into the coax, which could cause a high SWR.

Just attach a coax connector on the end of the coax going to your transceiver and you are on the air. The SWR should be 1.5 or better, if cut to the proper length. It'll get out about as good as a ¼ wave ground plane CB radio antenna if you get it up high and in the clear. Do not hoist this antenna up next to a metal pole, because the metal will interfere with the antenna's operation and cause a high SWR.

BOOTY MONSTER · #5 08-28-2009, 09:05 AM

W5LZ · #6 08-28-2009, 09:05 AM

Looks like it ought'a work after the normal amount of fiddling with this-n-that.
- 'Doc

Nationalpatriot · #7 08-28-2009, 09:39 AM

what do you guys think about routing the antenna wire up the center of the mast? (thinking because the weathering effect and such)

W5LZ · #8 08-28-2009, 03:26 PM

That can work too. Or, just turn that groundplane into a 'sleeve' dipole and run the whole thing up the center of that PVC pipe. A 'sleeve' dipole benefits from having a coaxial choke at the bottom end of it.
- 'Doc

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Homemade CB antenna radials question