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Discussion Starter · #1 ·
How do you tune a JMCB2003 for the maximum distance reception?

Is anybody on this list an expert at this? Just put on a new J & M CB unit and its terrific, but am told that the antenna needs to be tuned to get the max distance from it. Funny.... this was not mentioned anywhere in the J & M install instructions? Is this just understood by all who CB?

Who can do this tuning and where? How do I find someone? Am sorta lost about getting this done. Am in Jackson Mississippi

Thanks
WM
 

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the base should have a set screw that you can loosen to move antenna up or down key your mic. and look at meter it if pegs then backs off lower the antenna if it does not pegs raise antenna move antenna up or down until you get highest reading without over peg.

do not key mic. while you have a hold of antenna it will bite you hard

this is the way we do it on our truck cb's
 

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To get the best "tune" you will need a VSWR or Voltage Standing Wave Ratio meter. This meter measures the reflected transmit signal that comes back down the antenna, instead of out to the air waves. The process is the same as Codi mentioned, put it in line and key the mic, then adjust the antenna for the lowest signal. Make small adjustments. It plugs in at the radio between it and the antenna. You can also check local shops to see if anyone does CB tunning. Hope this helps.
 

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As mentioned aboveuse the meter to get your swr and also make sure your bke is not next to any buildings as that efects your signal. Try to do it in a open area.
 

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Discussion Starter · #5 ·
Took the bike to a CB shop which had the SWR meter and seemed to know what they were doing.

Interesting thing was that they did not like the stock J and M antenna set up....

1- said that it needed a nylon washer between the top fitting and the mounting base - which they added.

2- said that the mounting hole needed to be larger.... about 1/2 inch for a 3/8 inch bolt to go thru

3- said that the stock grounding wire was NOT necessary - this one really surprised me.... what do you think?

Thanks for the replies.

Seems to be picking up better now....

wm
 

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So far very good information but sometimes the length of the coaxial cable will need to be shortened or perhaps a different cable installed! Other than that it appears your going the right direction! 8)
 

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VTX Candy Red said:
So far very good information but sometimes the length of the coaxial cable will need to be shortened or perhaps a different cable installed! Other than that it appears your going the right direction! 8)
Exactly right, the length of the coax cable should be cut to match the wave length of the transmitters frequency. This can be done easily by some one with a little experience. The closer you are to matching the wave length, the smaller amount of tuning that will need to be done. If you cut too far out from the wave length, you may not have enough trim in the antenna to tune it well.
 

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Usually the length of the coaxial cable on a decent CB antenna brand
will be very close to the optimum wavelength.
Off hand, I think the wavelength for 27 MHz is
a little less than 15 feet.
It is shorter for a length of wire than it would be in free air.

Ditto on the antenna length.

The antenna would be about 7.5 feet in length except for the
use of loading coils at the base or in the center of the
antenna. The loading coils allow for good distance from a
shorter antenna.

If you spend a lot of time on a channel that is far away from
the center of the band,
like the extreme lower channels or
the extreme upper channels, then you might consider
adjusting the antenna for those channels,
but if most of your time is spent around channels 17 thru 23,
then don't worry about it.
 
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