Please feel free to explain why you say this is.

I have never had a problem with 102-108" whips and irregular lengths of coax.

 

Fred said SOME antennas need 18' to properly tune, not all antennas. The "experts" say if you cannot get the antenna tuned try switching the coax to 18' and that should help.

I think the issue is 1/4 wave is 108", so if an antenna is shorter than 108", like a 4' firestick, it is because it is "loaded" to make it look the full 108". So between the load created at the antenna, poor ground, and location, the 18' could help. Many factors in getting the antenna right on a mobile set up.

 

Some yes.... as in an antenna system with an impedance mis-match, but a properly mount resonant 50ohm antenna..no.

Using coax to "tune" your antenna isn't tuning your antenna at all, just hiding it from you and your radio.

 

Straight from Fire Stick as well.

"Q Is the length of the coax cable important?

A We find that it is very important ... especially with high performance top-loaded antennas. Your safest bet is to use 18 feet (5.5 meters) coaxial leads on all of your CB installations."

"Q I only needed 9 feet of coax to go from my radio to my antenna. How should I handle the excess?

A What ever you do, do not roll it into a small convenient coil. It will become an RF choke. If you cannot let it lie loose under a seat or in a headliner, wrap it into a yarn-like skein of about 12 to 16 inches, put a wire tie in the center and tuck it under your dash, seat, etc."

I've used all kinds of CB radios and all kinds of antenna over the years, some I've never even tried to tune and they work fine, etc. You just never know, you can always get lucky.

On this install I'm trying to do everything by the "book" so to speak so I can try to eliminate the annoying engine noise I'm getting. Some people don't care about the noise, for what they use the radio for, some people don't bother to tune their antennas either. For the most part, people just using them on the trail for club use, etc, just install it and make sure it works somewhat.

 

Certainly with a 102" SS whip with spring that coax length is needed to make a 1/4 wave length on the CB band or with a tuner on 10m amateur band so they will tune. If they need tuning you cut a little of the SS whip off at the bottom with a cutoff wheel or bolt cutters the stainless can be tough to cut.


This is explained in any ARRL manual or good CB setup manual that covers antennas at least the older one's for CB's did and all Amateur Radio manuals explain it.


On a fiberglass antenna they use wire wrapped around them inside the rubber and you trim the end of the wire at the top where the cap is till the require match is reached.


Mikesignal was correct in his post and did check a few of the facts, I like that.


I don't want to inject too much here but I do hold an Extra Class license and teach classed for those wanting to get an Amateur license. In addition I'm an FCC Licensed examiner for testing all class's of license and have 2 other Extras who help me with the exams we give every month.

 

So you are using the coax as the counterpoise?

 

Jeepy... Also from Firestiks website.

"20. If your ground plane is good, your mount grounded and, your antenna favorably located, coax length rarely becomes an issue. But, if one or more mismatches occur, you may find high SWR. This can often be corrected by using 18 feet lengths of high quality coax. "
http://www.firestik.com/Tech_Docs/63Things.htm

Also from the Firestik website...

"They say that if your system is set-up properly that the length of the coax is irrelevant. We agree!"

They also go on to say that using 18' of coax is a good way to hide poorly mounted antennas so take the easy way out and just use 18' of coax... but they say it prettier so people think it's the right thing to do. And since society as a whole is lazy... it easier to tell someone not familiar with CB to use 18' coax because it's the right way to do it, than to explain how to properly mount an antenna or offer support when they contact you because they can't get their SWRs down as they installed their ground plane dependent antenna on the mirror mount of a truck with a fiberglass cab.

http://www.firestik.com/Tech_Docs/coaxtalk.htm

And for your reading pleasure...


http://www.bellscb.com/cb_radio_hobb...x_cable_be.htm

 

Well, I know my antenna mount is grounded good, I made sure of that by removing the powder coating from the mount where it bolts up, cleaning the bolts and then testing the ground with a multi meter when done. I'm also tuned at 1.3 swr at ch 1 and ch 40. So I think mine is done right. Not my first CB install by any means. However, this is the worst case of engine noise I've had on a CB with this 2001 XJ. Antenna unplugged or plugged in, same noise. The fuel pump makes noise through the CB when you first turn the key on, then the engine add to it once started. Going to meets around with adding a ground to the hood like mentioned above, ground the exhaust and see what happens. My noise when the engine running makes the thing almost unusable, it's that bad.

In my '92 XJ, I had a tuned up General Lee 10 meter, all I had from that was a little alternator whine.

Of course, maybe part of it could be the "cheaper" Uniden pro520xl radio I'm using. I've never ran a Uniden before

 

NO, In effect it is a part of the antenna. I use a counterpoise with the vertical I have mounted to the hitch of the XJ for HF Radio 10-160m use a 33' wire and 31' of antenna fine wire on a push up pole I use it mostly for 20-40m on hill tops for QRP operation.


I do have a Hi Gain Hy Tower at the house here that when first installed had only a 150' of coax laid on top of the ground with no radials yet that day. Came into the house about dark and using only a 100 watts worked Australia on 80m and the coax was the counterpoise very surprised. But it did have 6 8' ground rods driven for it.


I said on antennas like the fiberglass one length of coax usually wasn't a large factor, but some antennas it is a factor ALL is a big term.

 

I just noticed that Wal-Mart online has the remote Cobra CB like mine (shown in earlier post) on sale for $102.00 only a few left and a good price, if anyone is interested.

 

I love to sub to threads like this because there is so much to learn.
I feel my SWRs are adequate, but I went ahead a sought out an inexpensive handheld. Found one for $30 on C.L. I find that it comes in very handy.

 

So you are using a 108" antenna with an adequate counterpoise.... how is the coax a part of the antenna? It's not radiating anything, if it is you need to fix your antenna install. You have an antenna and a ground plane, the coax is just a feed line, nothing more. There isn't (or shouldn't be) an impedance mismatch to try and correct.

I would have thought an Extra class ham would know this.

 

Did I say ALL? No.. he said a 102" whip... I said a 102" whip. which don't require 18' of coax if properly mounted. An antenna system with an impedance mismatch such as dual antennas or a No Ground Plane antenna require 18' of coax.... a properly mounted 50ohm antenna does not.

This exactly right... if you can't mount an antenna with an adequate ground plane you can fake it by using 18' of coax, sure it will make your SWR at the radio look good but the antenna is no more efficient than it was if you saw a 3:1+ reading. If an antenna is properly mounted with adequate ground plane any length of coax will work. Exactly what I said on post #25...

 

Where you get a ground plane with a whip of that size, a roof or hood mount? In the real world there is no ground plane other than a man made one that works and that is only with a lot of radials with a vertical.


I would love to see your 102" whip on any car with 6' of coax work "properly" unless you have laid out radials from it and use the length of coax required.


But do it your way I could care less I only try to pass along info that works in theory as well as real world.

 

What you want to do is, go to the nearest cb shop and grab your ankles.