CB tuning
- Thread starter BurbanAZ
- Start date
BurbanAZ
Explorer
I was reading around on different sites and it seems to me like one of my main problems is I have no ground plane where I have the antenna mounted especially since the bumper it's mounted too is coated. Maybe I could use one of the NGP antennas and coax cables? I think even with the swr at 3 I could still get use of it on trips talking with other vehicles which is my main goal. Am I going to damage anything using the radio with a SWR over 3? Or can I just use it and deal with not excellent performance?
theksmith
Explorer
double check how you have the antenna mounted, it's important that the center conductor NOT be grounding out, and equally important that the outside of the connector DOES ground. if the paint on your mount is preventing the outside from grounding then that could be your problem, or if you put the little plastic spacer in wrong, then the center conductor or antenna itself could be grounding out.
also, you want to make sure your antenna cable has no loops in it, it should not be coiled if there was excess, instead it should be bunched around loosely in areas you can find to stuff it, but not "coiled".
also, you want to make sure your antenna cable has no loops in it, it should not be coiled if there was excess, instead it should be bunched around loosely in areas you can find to stuff it, but not "coiled".
theksmith
Explorer
off less concern than you might thing. your entire vehicle and that bumper is a ground plane... sure, if you plant the antenna right in the middle of the roof or hood, you have a better plane orientation, but it's not that big of deal. double check the electrical and physical connection stuff i mentioned first. i imagine the part about your mount being painted is the problem. you need to make sure the outside of the connector touches a ground, you can accomplish this by scraping off some paint, or by using a large ring crimp connector and a wire to bare metal.
edit: this page better illustrates what portions MUST be grounded electrically, and what parts must NOT be: http://www.firestik.com/Tech_Docs/Testing_Continuity.htm
if you have a multimeter, you can check all that.
DaveInDenver
Middle Income Semi-Redneck
At CB frequencies the vehicle does not provide a great ground plane, so I wouldn't be overly concerned. You do need a solid RF return path and that is not necessarily intuitive like DC. A #6 wire might seem like good but it's not really any better than a #14 unless it has a very high strand count. The best hasty antenna ground material is the braid from extra coax and a good braided and tinned copper braid is the best ground material for RF.
BTW, talking or not, on CB it's always important to keep your key-ups short while tuning. Even if you do not talk the radio is transmitting a carrier, which is 3/4 of the power in the signal. Even if you never say one word you'll burn up your transmitter if you leave it keyed for long periods. Try and make the measurements in very short bursts, just a second or two and leave a bit of time in between.
If your SWR measurement is higher at 40 than 1, you antenna might just still be electrically too long. Try turning the tuning screw down to its minimum length and see if the SWR changes a lot. This will tell you if you're looking at a tuning problem or a more fundamental problem of a short or bad coax or something.
One thing that's easy to check is that the PL-259 connector has good conductivity between the center pin and the antenna center, which is the inside threaded part on your mount. Check that it does /not/ have DC conductivity between the center pin and the vehicle body, indicating a short in the connector, coax or mount. Then check that the outside of the connector has good conductivity to the vehicle.
Also, you might have to scrape away a little paint from under the antenna mount to make sure you have a good path there. You want it touching bare metal.
BTW, talking or not, on CB it's always important to keep your key-ups short while tuning. Even if you do not talk the radio is transmitting a carrier, which is 3/4 of the power in the signal. Even if you never say one word you'll burn up your transmitter if you leave it keyed for long periods. Try and make the measurements in very short bursts, just a second or two and leave a bit of time in between.
If your SWR measurement is higher at 40 than 1, you antenna might just still be electrically too long. Try turning the tuning screw down to its minimum length and see if the SWR changes a lot. This will tell you if you're looking at a tuning problem or a more fundamental problem of a short or bad coax or something.
One thing that's easy to check is that the PL-259 connector has good conductivity between the center pin and the antenna center, which is the inside threaded part on your mount. Check that it does /not/ have DC conductivity between the center pin and the vehicle body, indicating a short in the connector, coax or mount. Then check that the outside of the connector has good conductivity to the vehicle.
Also, you might have to scrape away a little paint from under the antenna mount to make sure you have a good path there. You want it touching bare metal.
Finlay
Triarius
That kind of antenna doesn't require a good ground plane, it uses a wound coil to compensate. In fact, the coil on it is variable, hence the ability to tune it without actually cutting the wire.
Having it down on the bumper is sub-optimal because of that wall of metal (the grill, etc.) right next to it, but that will only serve to distort the radiation pattern and reduce gain somewhat. You should be able to tune the reflection out.
All that to say that while there are "better" locations, any mobile antenna is a compromise. You should be able to get it to work, it's just matter of sorting the bugs out.
BurbanAZ
Explorer
Ok I'll just keep messing with it then and hope I get get it working a little better. Will I damage it just using it how it is now?
BurbanAZ
Explorer
well i moved the ground closer and onto the body, then started messing with random arrangements of how i had the antenna mounted. I had taken out those little plastic washers to get stuff to fit so i shaved those a little thinner so i could get one on the top and it seemed to work. Now im getting SWR of about 1.2 on channel 1, 1.1 on channel 19, and about 1 on channel 40 so im happy with that. Thanks for the help everyone. Hopefully this thread of me having troubles will help someone else if they have the same issues lol.
BurbanAZ
Explorer
Yea I'm definitely glad I got one especially cause their so cheap, I never would have know it was so far off