Do I need 18' coax cable for my radio?

GreenZR

GreenZR

Joined
Sep 26, 2011
Messages
757
Location
Springville, Indiana
Bike
2000 ST1100
2024 Miles
001743
STOC #
8497
I just replaced my broken CB antenna with the Firestik II 3' one. It recommends using 18' coax with it. My ST1100 has a coax cable just long enough to reach from the front where the radio box is located, along the frame to the antenna. Since it is probably closer to 7' or 8', and I have had some issues with a very short range with this radio. My question is, should I replace the shorter cable with one that is 18', and just loop the extra cable around the frame? I have the "made for Honda" Honda CB/intercom system.

Thanks, Gary.
 
Is it a no ground plane antenna? Usually firestik puts a yellow band on the antenna to designate that. If so, you'll need at least an 18' NGP type coax setup. I don't think it matters with a non-NGP antenna but not sure.
 
It was not marked as a NGP type, and I have it grounded with a heavy ground cable, actually the ground cable I have on the mount is the starter cable from the 91.
 
If they specifically call for it in the instructions, use it.

Antennas at CB frequencies (27 MHz) need to be physically large to work well because the wavelength is very long (a quarter wave, which is used in a lot of antenna designes is about nine feet). To build one that's smaller requires making compromises, such as winding the radiating element helically around a mast. The 18-foot length of Coax is probably being used as a counterpoise, which provides the ground plane of the antenna. The ideal for one of these is a conductive plane, such as the roof of a car. Since bikes don't have roofs, the extra coax has to serve that purpose.

--Mark
 
Anything you do on a bike is going to be a compromise on a compromise. Make as much of it straight as you can get away with.

--Mark
 
coil it up and zip tie it in 2 locations so that it no longer has a round coil shape. Basically flattening out the shape
 
I've bought a few NGP Firesticks, and they always came with the cable, as a unit. I just coiled it around the rear of the seat and it worked well.
 
I checked the SWR last night, and it was high on ch 1 & 40. Both had the same reading on the scale. Adjustments at the top of the antenna made no difference at all in the readings. I am going to get the 18' cable and check again.

Gary.
 
18' cable, coiled and zip tied flat under the seat. SWR readings are still way too high. STumped, and just going to put it back together and ride it. I'll look and listen for more options and try to find out what to do. Thanks everyone for the input.

Gary.
 
I recently put a GP 3' Firestik with a tuneable tip and a 9' coax on my ST1100. I tried tuning the antenna and had a high SWR. I was about to give up, but for some reason I removed the screw tip of the antenna completely, the SWR came way down to less than 1.5
 
mcthorogood said:
I recently put a GP 3' Firestik with a tuneable tip and a 9' coax on my ST1100. I tried tuning the antenna and had a high SWR. I was about to give up, but for some reason I removed the screw tip of the antenna completely, the SWR came way down to less than 1.5
Click to expand...

Thanks, I'll try that before I go back into moving or changing the cable again.
 
Where are you connecting the SWR meter where the antenna cable connects to the antenna or were the antenna cable connects to the CB radio. Normally it is recommended you connect it near the radio. Also this may seem like an obvious thing but are you re calibrating the meter before each test?
 
If you have or can borrow a dummy load, check your swr into that . if the swr is still high, you may have a blown out-put match inside the radio.
 
Ridingfl said:
Where are you connecting the SWR meter where the antenna cable connects to the antenna or were the antenna cable connects to the CB radio. Normally it is recommended you connect it near the radio. Also this may seem like an obvious thing but are you re calibrating the meter before each test?
Click to expand...

I'm connecting at the closest point to the radio that I can. For each test I turn the adjustment knob down all the way. (Left) Switch meter to calibrate, then key the mike. Then bring the knob adjustment to the right until the needle is on the calibrate mark on the scale. While still on the mike, I switch the meter to test, and the needle drops down slightly, but stays above 3. I started with ch 1, then 40, then 20. Same reading for all 3 tests, no difference.
 
v8-7 said:
If you have or can borrow a dummy load, check your swr into that . if the swr is still high, you may have a blown out-put match inside the radio.
Click to expand...

I don't have anything like that, not sure where I could access one close to home. I will check around and see if I can find a place that will be able to check it for me.

Thanks everyone for the input.

Gary.
 
One thing I found was that the coax that I took off had continuity between the center post and the outer connector. I think it must have been smashed and is shorted somewhere in the cable. Would this have ruined the radio? The intercom and the aux input still function properly.
 
It sounds like you tested it correctly. The fact that you are in the red zone on three channels suggest that the you have an electrical short in your coax connectors or the center transmitting core of your mouting bolt is grounding, (shorting) against the mounting bracket. The first place I would check is your antenna mount make sure the insulating washer is in the right place. If you changed cables it could be out of sequence or have shifted. J&M Corp. has a good instructional video on how to mount and tune an antenna. Even thought you don't have a J&M radio or antenna the basic instructions will still be helpful for mounting the antenna using the SWR meter and checking the cable continuity. I will try to post the link below.

http://www.youtube.com/watch?v=mp0kWX_Dx-A

Since you have a new cable and antenna it is unlikley they are the problem although it is easy to do a continuity check on them with a multimeter. I recently had an antenna go bad on me after a few years. It looked fine but when I checked the continuity from the bottom to the top there was no continuity. The wire had broken somewhere in the atenna probably from repeated flexing while riding. If everything, the mount etc. checks out try swapping out the antenna with a friends, if one is available and re-ckecking the SWR. Some antenna's just don't tune as well as others. I replaced mine with a K40 3ft flex antenna I purchased for $25.00 from a local CB shop in south Florida called Bells CB Radio. They also have a web site you can order from and may give you some advise if you call them.

http://www.bellscb.com/

The K40 was plug and play. Very low SWR readings on all channels. I didn't really have to tune it but if it does need tuning it comes with a tuning screw at the top. Finally I'm not sure you really need 18' of cable that sounds like a lot. I'm still using the cable that came with my original J&M antenna I don't think it is that long and it works well with the K40.

Good luck. Hopefully it will be an easy fix like double checking the installation of the mounting bolt.
 
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