Homemade CB antenna radials question

[Nationalpatriot]

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.]

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]

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]

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.

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]

 

[W5LZ]

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

 

[Nationalpatriot]

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

 

[W5LZ]

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

 

[W5LZ]

That would sort of complicate getting the radials outside of the pipe, but should work. Or, how about just making a 'sleeve' dipole instead of that groundplane and putting the whole thing inside the PVC? A 'sleeve' dipole benefits from having a choke at the bottom of it.
- 'Doc

 

[Nationalpatriot]

How would I go about building that? (my hardware store closes in 2 hours about, need to know so I can run over there)

 

[W5LZ]

A 'sleeve' dipole is about as simple as it gets. Remove the outer insulation from about 9 feet of coax. Sort of push the braid down and over it's self (turn it inside out) until there's about 9 feet of it down the coax from where the center conductor and insulation extends above it. So you end up with the coax feed line running up through one 'side' of the dipole to the center, where the center conductor and insulation make the other half of that dipole. Sort of like;

---////-======o................ (Great graphics, huh?)

That "---" is the coax, the "////" is the coaxial choke, the "o" the center of the dipole, and the "............" the center conductor.
That 'about 9 feet long' on each side of center is too long, but allows some 'extra' for making a loop to hang the thing from, and you trim the rest to the right length like normal. Keep both sides the same length. A good thing to do is seal that place where the braid turns back from the center conductor, don't want water getting in there. figure about 18 feet of coax as the minimum length required. A PL-259 on the end of it, a double female and then the feed line to where ever it's going. That doesn't include the choke, just wind it in the feed line.
- 'Doc


(Just hang the flag from the PVC containing the antenna.)

 

[Nationalpatriot]

Done. I'll grab some pictures for ya'll tomorrow. It seems my camera decided to NOT work at the most unwelcomed time...

 

[BOOTY MONSTER]

i think this is what doc is talking about .
http://www.iw5edi.com/ham-radio/?the-vertical-bazooka-antenna,18

 

[W5LZ]

Booty',
I have to admit that that 'vertical bazooka' is made like a 'sleeve' dipole, but I'm sure you can see a difference or two.
Never heard of it being called a 'vertical bazooka' before, and since it isn't fed the same way a bazooka antenna is fed, I wonder why? How about an 'OCF Vertical Bazooka', since the two 'parts' to the thing aren't the same length, and it's certainly not a 'balanced' antenna anymore. I think it would still benefit from putting a choke at the bottom of it.
- 'Doc

 

[BOOTY MONSTER]

my bad , thanks for the correction doc.