what length coax for cb

[OemUser]

Educational

This thread has explained a lot to me about antenna(s) and cables.....and some unique side effects.

Many years ago, I ran over the road with a KW Aerodyne conventional. Like any other self respecting guy, I wanted a CB that would "talk" a fair distance. The KW had a fiberglass roof and an aluminum body.

The sticks (antenna) were mirror mounts, and I had the CB tuned at one of the outlaw shops. There was always someone who had a bigger, badder radio (so it seemed).

Over a period of time and with available cash, I had installed (ahem) some assistance for the output of the CB.

Not realizing about all of the foregoing information in this thread about ground planes, swr, and the fact that the cables are part of the antenna system....

I was guilty of the mindset that the signal stayed inside the cables until it reached the antenna whereupon it radiated happily away into the ether.

I had made sure that the CB and linear were well and truly electrically grounded...I had no concept of RF grounding. The Radio Shack SWR meter thingy said that all was well.

And yes, the swr meter was between the CB and the linear. (It was a big one.)

Anyway, all the preceding info helps explain why......if I was parked somewhere at night with all of my lights off....and I keyed up....my interior lights and dash lights would glow dimly.....

I had inadvertently turned my interior into a microwave oven....

I should have worn the tinfoil hat...do brain cells regenerate?

Thanx for the info, gentlemen.

 

[jhooten]

do brain cells regenerate?

Relying on recent experiences I'm betting not.

 

[k3cfc]

I drive a big truck and have found that an 18 foot piece of coax works best for me I have tried shorter coax but could get my swr down where I wanted it. My answer to you would be to buy the length of coax you can make work for your set up. Check you swr and if its high add 3 more feet and try again. Don't add 3 feet to the coax, go and buy another piece 3 foot longer and start all over. Better off if you start with either 18 foot or 21 foot of good coax and do the work outside of your favorite CB shop and away from power lines and metal buildings. This way you get a good swr reading. And since your going to mount your antenna on the mirror bracket make sure you check your swr with the doors closed. Hope this helps!

You are exactly right.

K3CFC

 

[robertmac]

self respecting guy

Like any other self respecting guy, I wanted a CB that would "talk" a fair distance. I think not, only if legal.

 

[k3cfc]

Like any other self respecting guy, I wanted a CB that would "talk" a fair distance. I think not, only if legal.

Oh boy

 

[SouthernRoller]

SWR

Ok i get it that you're suppose to check SWR at the antenna, but what is the proper way to check SWR on a NMO mount say such as this Maxrad MBM - $26.95 : The Antenna Farm :: , Your Two Way Radio Source!

 

[majoco]

I'm happy to see that there is someone on this topic who knows what they are talking about. I'll leave it up to you who it is. :roll:

 

[BigIron2]

3' FOOT COAX

I was going to start a thread for this but this one looks like a good place.

I'm thinking of mounting a small mobile unit to the roof (inside) of a pickup that can easily be removed. I want a mag mount on the roof. If I run the cable out the sliding window, I only need a 3 foot cable. The back of radio would face the slider.
Would this be too short of a cable to tune properly? Any other foreseen problems?

 

[k3cfc]

I was going to start a thread for this but this one looks like a good place.

I'm thinking of mounting a small mobile unit to the roof (inside) of a pickup that can easily be removed. I want a mag mount on the roof. If I run the cable out the sliding window, I only need a 3 foot cable. The back of radio would face the slider.
Would this be too short of a cable to tune properly? Any other foreseen problems?

Look on ebay for a cb mobile antenna they most always mention coax length 18 ft this what you use.

 

[NITROTURBO4U]

Antenna analyzers???

So after reading the above posts...Are antenna analyzers any smarter than the swr meter?

 

[LtDoc]

The quick-n-ditry answer to that is, yes. The 'catch' is that the user has to know what that analyzer is telling him. It's not plug-n-play.
- 'Doc

 

[k3cfc]

So after reading the above posts...Are antenna analyzers any smarter than the swr meter?

Well i am probably wrong but i am going to say it anyway yes they can tell you way more then swr's.

you tube has some good video's on them unless your not interested in learning nuttin.

K3CFC

 

[k3cfc]

Ok i get it that you're suppose to check SWR at the antenna, but what is the proper way to check SWR on a NMO mount say such as this Maxrad MBM - $26.95 : The Antenna Farm :: , Your Two Way Radio Source!

Just check it at the radio.

 

[shortride]

CB coax should always be in encroments of 3 feet. General a 6' coax would be long enough depending on were you mount and how far the CB is from the antenna connection.

 

[LtDoc]

"encroments of 3 feet"
Another one of those myths that can be true in particular circumstance but very seldom in all circumstances. That stuff doesn't stretch worth a hoot, so in general, too long is better than too short. Just don't carry that to extremes (in either direction).
- 'Doc

 

[k3cfc]

"encroments of 3 feet"
Another one of those myths that can be true in particular circumstance but very seldom in all circumstances. That stuff doesn't stretch worth a hoot, so in general, too long is better than too short. Just don't carry that to extremes (in either direction).
- 'Doc

I hear ya Doc. this a good one for myth busters. mobile antennas come with 18 ft of coax this is standard as i think you know. over the years i have used various lengths of coax for my cb radidio with no problems.

Have A Good day.

 

[majoco]

Far too many "experts" from what I can see,,,,,

 

[shortride]

Far too many "experts" from what I can see,,,,,

I don't claim to be an expert. I've been an avid CB’er since 1972 and have always been told that the increment of coax has an effect of attenuation and SWR. I have more time than I can remember corrected the length of coaxes to 3' increments and lowered SWR's. If all of that happened to be just a coincidence then so be it. You guys are the one that have the correct answers. That's why we're here.

In 42 years I learned something new. I stand corrected.

 

[LtDoc]

Expert! Me? You've gotta be kidding. Oh wait! Yes, I am! And my prices just doubled.
Thank you thank you!
- 'Doc

 

[jaspence]

CB cable length

If cable length is so critical, then most hams would go nuts with the multiband transceivers and antennas in use. Too much cable will cause signal loss, but on CB frequencies, that is not as bad as VHF/UHF. The quality of the cable and connections is important, especially for connections exposed to the weather.