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Rezarf
04-15-2008, 03:01 PM
Howdy-

I know this isn't HAM per'se but I bet you folks are in the know! :D

I want to move my antenna to my tire carrier, to get it up a little higher than the roof. I have a spring and quick disconnect mount. Isn't there something I need to do with the groud to make it work correctly? This will be on the swing out. I will get about 3' of clearance above the roof if I go this route.

Right now it is located on the lower bumper and doesn't reach above the roof line even an inch.:blah:

FWIW, it is a Cobra CB with the weather stations wx-18 or somethin' like that:hill: And a Wilson 1500 antenna... maybe:confused:

Any help would be great, thanks!

Groucho
04-15-2008, 04:22 PM
I couldn't find a Wilson 1500 antenna.

However, there are a couple of things to keep in mind when installing an antenna on a vehicle.

1. (And I know Dave will disagree) NEVER, EVER, USE A MAG MOUNT. They are bullets waiting to fly off and kill someone.

2. Keep the feedline (coax) clean and short. No big loops of extra coax bundled up anywhere. These become loading coils that will mess with the resonant effects of your antenna. Don't kink the coax. It too will mess with the impedance.

3. Unless your antenna is a shorted-to-ground like the homebrew antennas we made for 2M, keep the two conductors from shorting out. That means that your antenna needs one of those fancy little plastic washers with the shoulder. This keeps the center conductor and the shielded conductor (ground) from coming in contact with each other before the electromagnetic waves get a chance to be resonated on the antenna.

4. Mount the antenna securely. Mount it as high and over as much metal as possible. If your feedline is not shorted like :perry:, and you follow these simple guidelines, you should be able to use your CB as a trail radio no problem.

Any questions?

Rezarf
04-15-2008, 06:10 PM
Nathaniel, you my friend are a wealth of information! :D

Should I still ground this little wire? Here is a pic of what I have. Also I think it is the Wilson 1000, 4 ft, with adjustable tip. :thumb:

How high above the roof line will this start to become a problem? I am seeing myself putting it on and off for trail riding only.

One more question, where does the little nylon washer go? Between the antenna mount and the antenna itself? In terms of the pic, does it go above or below the mount? I am assuming it is some sort of insulator?

Thanks! :cheers:

Groucho
04-16-2008, 08:22 AM
Most folks have no idea what the insulating washer is supposed to do. Hopefully this .pdf can illustrate it better.

If you notice the cross section of coax, the thing to remember is that the inner copper wire (inner conductor) and the outer shielding are important for keeping SWR consistent. The distance between the inner and the outer must be a specific value for the impedance of the coax. If you have 50Ω coax, the distance will be different than 75Ω coax. Any fluctuation in that distance will change the impedance, and thustly change the SWR. That is why coax should never be smashed.

The way to "coil" up any excess coax is to loop it and then tie iit together in the center of the loop to form a kind of figure "8". That way, you minimize the effect the coil will have on the antenna. (Basically the coil would aid in "matching" the feedline to the antenna, so the impedance is the same at the feed point of the antenna and the coax.) Without knowing what your impedance is at those two locations, you don't want to coil up your wire.

DaveInDenver
04-16-2008, 09:06 AM
Most folks have no idea what the insulating washer is supposed to do. Hopefully this .pdf can illustrate it better.
Great diagram. I do think the little plastic shouldered washer in your sketch is shown on the wrong side of the mounting bracket, though. It does depend on how the whip-side connector is designed.

Here's the Firestik style:
http://firestik.com/Tech_Docs/mkfr-instl_nohook.htm

http://firestik.com/Instl-Art/MK-FR002.jpg

Groucho
04-16-2008, 09:31 AM
That is what I get for trying to draw a sketch without much sleep.:bawl::ranger:

Rezarf
04-16-2008, 09:37 AM
Thanks Fellas!

I am going to get on it tonight and get the CB/antenna installed and finished.

Rezarf <><

Groucho
04-16-2008, 10:01 AM
I should have looked at my mount. Now THAT'S an antenna mount!


Great diagram. I do think the little plastic shouldered washer in your sketch is shown on the wrong side of the mounting bracket, though. It does depend on how the whip-side connector is designed.

Here's the Firestik style:
http://firestik.com/Tech_Docs/mkfr-instl_nohook.htm

http://firestik.com/Instl-Art/MK-FR002.jpg

Red_Chili
04-16-2008, 10:17 AM
TIG-O-licious.
Wish I could lay down microscopic stack-O-dimes like that.

subzali
04-16-2008, 10:18 AM
That's ridiculous. Ridiculous crazy cool fool :cool:

Rezarf
04-16-2008, 10:26 AM
TIG-O-licious.
Wish I could lay down microscopic stack-O-dimes like that.

I saw that too, unreal, thanks for the pics Nathaniel! Gonna try to get that done tonight.

Beater
04-16-2008, 10:51 AM
if you made that mount, tell the class just how long it took, and how much gas was used... TIG and I have a love hate relationship

Groucho
04-16-2008, 11:13 AM
Yeah, I drew it up. I did not operate the laser when it was cut, but I did form it on the press brake. I did not weld it. The machined items (round pieces for the quick disconnect, and the insulating washers) came with the antenna mount.

One of my welders did the welding. He is a champion welder. Took him about 30 minutes to weld four of them. A little slow for him. They should have taken him 24 minutes.

Beater
04-16-2008, 01:19 PM
ok - the drawing got it for me... I didn't even think of origami. duh.

single pieces with tack and jig would have been a nightmare on that

Rezarf
04-16-2008, 09:29 PM
Nathaniel, you have to be one of the coolest people I know, with one of the coolest jobs! :D :thumb:

Rezarf
04-18-2008, 07:40 AM
So back to my pic, do I need to run that wire all the way back to the body of the cruiser or can I just ground it through the swing arm of the tire carrier? I am imagining that the swing arm wouldn't ground that well when the pivot is working well?:confused:

I have seen guys attach ground straps from the bumper to the vehicle body, do I need to mess with that?

:thumb::cheers:

Drew

Red_Chili
04-18-2008, 08:09 AM
It would be a good idea. Your ground is as important as the antenna itself.

DaveInDenver
04-18-2008, 08:46 AM
It would be a good idea. Your ground is as important as the antenna itself.
Yup, Bill's right on. It's really best to cross hinges, bolted/painted/coated interfaces and other places where continuity will be poor with a ground strap.

Mendocino
04-18-2008, 08:58 AM
Here is my CB antenna install. I did not want something under the roof line and went to Summit Radio by Ige's and got the Francis 4.5" antenna and a "folding mount."

the images kind of speak for themselves. The last one shows where in the cab the backing plate for the antenna was located. Its behind the junction block and was a major PITA to install (I really mean major). :( I had to lean around my cage and seat for an extended period of time to get this together. I am happy with the result but would not look forward to this install again. I still need to get the antenna tuned but plan on doing that next Saturday.

Groucho
04-18-2008, 10:10 AM
So back to my pic, do I need to run that wire all the way back to the body of the cruiser or can I just ground it through the swing arm of the tire carrier? I am imagining that the swing arm wouldn't ground that well when the pivot is working well?:confused:

I have seen guys attach ground straps from the bumper to the vehicle body, do I need to mess with that?

:thumb::cheers:

Drew


Drew, as Dave mentioned, anything that doesn' have a good path of signal would be canidate for a jumper or "bonding". While a small braided piece of copper wire is better than nothing, it is just slightly better than nothing. Proper bonding needs to have a thin piece of copper strap or copper clad steel braid (like in the pictures) to be most effective.

See a really good article here (http://www.k0bg.com/) and select the Bonding category on the left hand side. Allan is a good friend of Bruce's, and he's wicked smart.

If you don't look at the page here are a couple of things to ponder:
1."The best mobile antenna money can buy, isn't any better than the ground plane it is mounted over. Maximizing the available ground plane is what bonding is all about."

2."Here is a money saving tip. If you don't intend to properly bond your vehicle, you can save a lot of money by buying a cheap antenna. The basis behind this is simple. If ground losses are high, it doesn't make much difference how good the antenna is, because ground losses will be the largest factor in determining efficiency. If ground losses are low, the difference in efficiency between a cheap antenna, and a good one become very apparent."

3. "One method of bonding is to use braided wire. Not just any braided wire mind you, but one which is flat and wide. RF flows at the surface rather than through the wire, and flat braid has more surface area for any given current carrying capacity. Thus it provides less resistance to RF than an equivalent round wire. It also has more capacitive reactance which increases the self resonant point. Flat braid is also much more flexible and less likely to fail due to repeated flexing."

If nothing else, take those ideas and remember them. They will help you get the most out of any mobile station setup you use, CB or HAM.

The first picture is a picture of the copper shielding tape that I laid over each of the spark plug wires in Bruce's Gasser 80 with the big HF antenna on the back. The rest are shots of the different pieces of the vehicle where I bonded with the copper clad braided strapping.

nakman
04-18-2008, 10:15 AM
Hey so my HAM antenna is currenly a lip mount on the hood.. if I added a bonding strap to the firewall like you show in the pic above, would I improve my ground plane and thus improve performance? :confused:

subzali
04-18-2008, 10:41 AM
Where did you get the copper tape for the spark plug wires?

Groucho
04-18-2008, 12:11 PM
Hey so my HAM antenna is currenly a lip mount on the hood.. if I added a bonding strap to the firewall like you show in the pic above, would I improve my ground plane and thus improve performance? :confused:

In theory, yes. Overall performance might be subject to your ability to discern slight differences in receive and transmit quality.

Where did you get the copper tape for the spark plug wires?

Here ya go, Matt! (http://tinyurl.com/5zm8du)

DaveInDenver
04-18-2008, 12:28 PM
Here ya go, Matt! (http://tinyurl.com/5zm8du)
To which someone may ask, "Where do I actually send my money and how much?"

Mouser Electronics P/N 517-1181-1/2, page 2072, 3M #1181, 1/2" wide, 18 yard roll is $21.50/ea.

Same in 3/8" wide is $14.54 and 1/4" wide is $10.80

http://www.mouser.com/catalog/633/2072.pdf

Did not comparison shop, but Digikey, Newark, Allied, Waytek also all carry 3M products.

corsair23
04-18-2008, 03:32 PM
So, I've got to ask the experts...

What about the "No Ground Plane" Antennas like a Firestik? That is what I went with on my LX last year because on where I was mounting the antenna (tire carrier) and the issues with grounding.

Now, I'll confess that I had, and probably still do, a high SWR when I measured it after installation. Firestik figured it was due to the 6' of additional coax (Radio Shack) I had to add to reach the dash (the 18' Firestik lead wouldn't quite reach :eek: - I was about a foot short). They state to use lengths of 9' extensions. I don't know...I think maybe it might have to do with the loop I created in the excess coax in the PS kick panel area after Nathaniel explained at the antenna building party what to do with the excess coax.

But, back on point, can a person like Drew use a no ground plane antenna and be ok?

DaveInDenver
04-18-2008, 04:13 PM
That magical 9' length thing is hogwash. There is no exact right length for the coax unless it's acting as part of the antenna and you definitely don't want that to happen. If you trim to the length for a clean run and the connections on each end are solid, it will not matter practically how long the coax is. Remember from the class, you have a source (the radio), a feedline and an antenna. Ideally the feedline just passes all the energy from the source output to the antenna feedpoint without any loss.

Your loop of coax would be one thing to suspect (but it would not be my first guess). I would expect to find a bad connector or corrosion, whip mount issues (like shorted to ground) or tuning. I dunno why Firestik pushes that 9/18/27 foot thing, I really don't. Only thing I can think is that they say that to cover their rear ends so that badly tuned or shorted antennas don't get high SWRs and then they have a ton of people calling and asking why they peg their SWR meters. If you short the antenna with a perfect 1/4 wavelength long piece of coax, it will act like an antenna and your SWR would actually be low even though you are not radiating much energy into space.

A no-ground plane antenna is a misnomer. a NGP antenna can utilize a ground plane, it's just that it does not need a ground plane to achieve a low SWR. NGP does not mean you can ignore your ground connections, you still need to ground the mount and radio right and have to make sure not to short anything. They are talking about the ground plane relative to the radiated energy and not physical grounds.

Wanna know more about anything or is that sufficient?

Edit: Just had a duh moment. :doh: If the antenna is a 1/2 wavelength long, then you need a matching network to achieve the 50 ohms impedance presented to the radio. If you are using a no ground plane antenna, it is 1/2 wavelength long (this is important to the reason why you don't need a ground plane). Most manufacturers that build 1/2 wavelength antennas have a matching network in the base of the antenna, which is a 1/4 wavelength (electrically) short to ground. Wonder if that's why the 9' thing. Have to mull that over some more.

Rezarf
04-18-2008, 04:13 PM
Thanks guys, I continue to learn from each of you! :thumb:

Where are places to source that strap stuff locally? I really don't know where to begin. thanks! :D

Rezarf
04-20-2008, 10:39 PM
Well, I got this far today repositioning my antenna. I reroute the cable and wired up the CB on a new fuse panel.

:thumb: