Setting SWR and antenna question

[djh3]

I was cleaning my bike the other day and bumped the CB antenna. It made a funny sort of sound besides the "boing boing" Kind of a click as it was setteling down. As I pulled on the top part of the antenna it came out of the lower black piece. YIKES So I slipped it back in as far as it would go and then pulled it up maybe 1/8" and locked down the set screws. I dont have a SWR meter anymore and way to like OHM it out or something?

[Freebird]

Nope...the only way to adjust it is with an SWR meter. If you don't know anybody who has one, you can probably find a local truck stop with a CB shop nearby that could help you out with it. To be honest, I don't think that the SWR is ever set on these things from the factory and certainly not at the dealer. It was probably never correct to begin with so is as good as it was before it came out.

[RedRider]

My CB antenna seems to be messed up. Haven't taken it apart yet, but will soon. Are there any good aftermarket antennas to replace this with?

 

Sorry, too lazy to do the search as I'm sure the info is already in here somewhere.

 

Thanks, RR

[CaptainJoe]

I was told by a guy that sells CB's for a living that it's the length of the cable that dictates reception as a lot of CB antennas are not adjustable.

 

The 18 wheelers antenna are tuneable by losening a small allen head screw and raising or lowering the antenna.

 

Not sure if our bikes antennas can be raised/lowered to improve recption/transmission using a SWR meter...

Edited August 14, 2013 by CaptainJoe
ment 18 not 10..

[Flyinfool]

I was told by a guy that sells CB's for a living that it's the length of the cable that dictates reception as a lot of CB antennas are not adjustable.

 

The 10 wheelers antenna are tuneable by losening a small allen head screw and raising or lowering the antenna.

 

Not sure if our bikes antennas can be raised/lowered to improve recption/transmission using a SWR meter...

 

Our bikes do have an adjustable antenna.

Having the SWR correct will not have a much effect on reception, But a high SWR can let the magic blue smoke out of the CB while transmitting.

[Guest tx2sturgis]

I was told by a guy that sells CB's for a living that it's the length of the cable that dictates reception as a lot of CB antennas are not adjustable.

 

The 18 wheelers antenna are tuneable by losening a small allen head screw and raising or lowering the antenna.

 

 

There a lot of falsehoods that get perpetuated by CB shops. They always want to sell you something, or do less work, or show you things are 'working' and let you drive off happy but ill-informed. You cannot properly explain this stuff in a 2 minute conversation with a customer. And if you do, it will conflict with the info the customer got from the last five CB shops he visited. Some CB 'techs' have no idea about how this all works, they just know what works for them.

 

Here is the way it actually works: If the SWR at the antenna feedpoint is correct, (less than 1.5 and 50 ohms impedance) then coaxial feedline length does not matter. But, an 18 foot coax, which is 1/2 wavelengh at the CB frequencies, can mask a mismatch and make the SWR meter AND the radio happy with the match.

 

So nearly all CB shops will tell you, you HAVE to have an 18 foot (sometimes 9 foot, 1/4 wavelength) for the SWR to match. They are WRONG. (unless we are talking about dual antennas, in that case, you DO need TWO 18 foot pieces of 75 ohm coax, called a co-phase harness, and the antennas must be spaced about 9 feet apart)

 

There are several articles I have posted on how to measure and set SWR.

 

 

Here is one: http://www.venturerider.org/forum/showpost.php?p=740831&postcount=31

Edited August 14, 2013 by tx2sturgis

[CaptainJoe]

There a lot of falsehoods that get perpetuated by CB shops. They always want to sell you something, or do less work, or show you things are 'working' and let you drive off happy but ill-informed. You cannot properly explain this stuff in a 2 minute conversation with a customer. And if you do, it will conflict with the info the customer got from the last five CB shops he visited. Some CB 'techs' have no idea about how this all works, they just know what works for them.

 

Here is the way it actually works: If the SWR at the antenna feedpoint is correct, (less than 1.5 and 50 ohms impedance) then coaxial feedline length does not matter. But, an 18 foot coax, which is 1/2 wavelengh at the CB frequencies, can mask a mismatch and make the SWR meter AND the radio happy with the match.

 

So nearly all CB shops will tell you, you HAVE to have an 18 foot (sometimes 9 foot, 1/4 wavelength) for the SWR to match. They are WRONG. (unless we are talking about dual antennas, in that case, you DO need TWO 18 foot pieces of 75 ohm coax, called a co-phase harness, and the antennas must be spaced about 9 feet apart)

 

There are several articles I have posted on how to measure and set SWR.

 

 

Here is one: http://www.venturerider.org/forum/showpost.php?p=740831&postcount=31

 

So basically if you have a (non-adjustable single CB antenna) it must have a 18' coax, but if you have an (adjustable single antenna) provided you can adjust within range with a SWR meter, the coax can be any length?

[Guest tx2sturgis]

So basically if you have a (non-adjustable single CB antenna) it must have a 18' coax, but if you have an (adjustable single antenna) provided you can adjust within range with a SWR meter, the coax can be any length?

 

The antenna might be non-adjustable, but that does not mean it is non-tunable. I can tune any normal CB antenna made. And I can make it work with ANY length of coax. (Things like glass mounted, marine, or rubber or telescoping antennas on walkie talkies or power AM/FM/CB antennas dont count)

 

Regular metal and fiberglass whip antennas can be trimmed, but obviously its hard to add material back if you cut too much.

 

If the antenna is close to resonance, (low SWR) and trimming it, which occasionally does take 15 minutes or so, will make it work well, then why would you go to the trouble to disable or remove the factory harness and replace it with one thats 10 feet too long?

 

Of course, a CB shop will sell you the $20 cable and send you on your way. Its much faster, and most customers wont pay someone by the hour to mess with a CB antenna on a bike. BTW....the CB setup on most motorcycles was never designed to be a long haul communication solution. You're gonna be lucky to get a mile or so between bikes. More likely a half mile or so is about what will be expected. There is no range guarantee in the manual.

 

 

 

Edited August 14, 2013 by tx2sturgis

[Guest tx2sturgis]

I should probably add that I own a couple of antenna analyzers, and have several years of CB and RF work experience early in my adult life. Plus I have built, installed, and maintained amateur and commercial VHF and UHF repeaters for over 25 years as a sideline/hobby.

 

Antenna analyzers cost a lot more, and do a lot more, than the simple SWR meter that the CB shop will bring out to the vehicle to test the antenna.

 

So I'm not trying to say that the CB shops are all bad...but some of them operate like a fast-food place. Get-em-in, get their money, and get-em-out. And a high quality commerical radio shop will rarely be bothered to mess with consumer level, non-licensed, 4 watt CB equipment.

 

 

 

[CaptainJoe]

I should probably add that I own a couple of antenna analyzers, and have several years of CB and RF work experience early in my adult life. Plus I have built, installed, and maintained amateur and commercial VHF and UHF repeaters for over 25 years as a sideline/hobby.

 

Antenna analyzers cost a lot more, and do a lot more, than the simple SWR meter that the CB shop will bring out to the vehicle to test the antenna.

 

So I'm not trying to say that the CB shops are all bad...but some of them operate like a fast-food place. Get-em-in, get their money, and get-em-out. And a high quality commerical radio shop will rarely be bothered to mess with consumer level, non-licensed, 4 watt CB equipment.

 

 

 

 

From the sounds of it, you'd be a real popular guy if you brought your Antenna analyzers along to a MD?

 

I would definately get you to look at mine as it's doubtful that it's tuned right.

[RandyR]

I don't think this part of a question was answered.

 

Most people that replace their stock antenna use a Firestick (brand) cb antenna.

[Cougar]

Just did this myself. and yes the CB ant is tunable.

I had to raise mine about a 1/8 inch and man it really picks

up now.

I had added a new wire and then went to radio shack and paid $29

for the SWR meter or maybe it was $39

Anyways it is very simple to use. even my Chihuahua can do it.

 

That old boy tx2sturgis helped me out a bit as well

 

From what I understand firesticks are tunable as I looked into them

as well last year.

[Galapagos]

Try this.

 

http://www.rightchannelradios.com/tuning-cb-antenna-adjusting-swr

[dacheedah]

Ez mod, all my parts were at a loves truck stop.

 

 

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