antenna light coming on cobra 29

Pat,

I think the problem was probably moreso with the door not grounding to the tractor . It sounds like the antenna bracket was connected very good to the mirror bracket ; but, remember the only thing conducting a ground to the tractor is that door hinge and /or latch !

 

Pan,
Have you had your radio "tweaked and peaked"?
On 29's the light will start coming on after they've been worked on. Just stop in a shop and have them check the SWR (should be done for free) if nothing is wrong and no work is done. If they check out ok dont worry about it. Or have them disconnect the light.
No big deal...

 

my 29 ant light came on when i went with a longer 18' coax and after checking. A buddy of mine tells me there some times set to sensative. there is a pot inside in the rear of the radio to adjust this. that is if you are not shorted out or it is not grounded. Or as Carolina sez do not rool up coax. We tested the coax on mine it was good ant. was not shorted. so my buddy adjusted this pot to fix it and radio talks great now as it did with it on that was what stumped me. But hope that helps Id have to open my radio to tell you witch one to turn if this is your problem.

 

Your buddy is right; I just posted a long explanation about the Antenna Warning Light on another thread today (if I knew my way around this forum better, I'd link it; sorry!).
*After* you make sure the antenna is matched OK, open the speaker side of the radio. At the rear of the main board, between the power connector and the antenna connector, is a small pot marked VR6. That's the one for the AWL.
My longer thread has more info & background on these; they frequently come on after a radio has been "peaked" because any real shop tunes the radio on a dummy load, which looks to the transmitter like a perfect antenna.
Re: coiling up the spare coax -- a tight ball is bad if the turns are tighter than the minimum radius that the specific cable is designed to withstand. A coil of 6 to 8 turns around a short piece of PVC pipe is used to make an "Ugly Balun" to keep RF off the shield, but typically on balanced base antennas, like beams, quads, and dipoles. CB whips are unbalanced, so there shouldn't be any RF on the outside of the coax anyway.
Unless you've got a special antenna that's made to work with no ground plane, like for Kenworth cabs with the fiberglas roofs, then regular CB antennas are 50 ohms impedance, same as the radio. So if you're running a single CB antenna, the coax has to be just as long as is needed to reach from the radio to the antenna, plus enough slack for doors opening. I always leave an extra foot or so at the radio end so I have room to meter it while it's installed, and to be able to replace connectors if they wear out or get damaged.
The exceptions are the special No Ground Plane antennas, where the coax is part of the tuning network, and twin antennas run as "co-phased". With co-phased antennas, a special harness of 72-ohm coax is made, because they are fed together (paralleled) at the radio end, and they function as a transformer. Those coaxes must remain at their supplied length, or the system will not perform as it should.
So if it's a single antenna, and if it's the correct 50- or 52-ohm coax, cut it as long as you like. And at 27 MHz, there's not enough more loss of signal in 20 feet than there is at 12 feet (you can calculate it, but you'll never notice it) you might as well just loosely tape or ziptie up the slack where you can get to it and stash it up under the seat or the dash. You might want to move your radio mount or antenna one day and will wish you had that extra 6 or 8 feet.
Geez, I was trying not to make a long post....silly me!
Hope that helps.
-- Handlebar in NC --
30-year commercial two-way tech

 

Good job, Pat, and good troubleshooting and suggestions from the other posters. The reply posted about the door-hinge-frame connections nailed it.
As low as CB is in frequency, it's hard to get enough surface area connected to the shield side of the coax to function as the "second half" of the antenna; the "first half" is the whip you install.
If you were using VHF or UHF, you'd be fine without the door bonding.
Something *does* come to mind, though: will the radio power up without the coax being plugged into the back of the radio? If not, then it means your radio is getting its DC ground through the coax and you need to track down your black power lead.
-- Handlebar in NC --
Licensed commercial two-way tech over 30 years

 

The idea that you need 18 feet of coax is just plain bunk. There is no valid rule for coax length. If you can connect the radio to the antenna with enough slack to make a dip in the coax path between the antenna mount and the entry point into the vehicle, you are fine. The dip will allow water to go to the lowest point of the dip thus stopping water from entering your vehicle.
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If you want to save several dollars, use 12 feet of RG 58 coax instead of 18 feet of RG 8 coax. You only lose 0.12% of signal strength going to the antenna. That is just not worth the added expense of RG 8. RG 58 coax will lose 0.34% of signal for each foot of length. RG 8 will lose 0.22% of signal for each foot of length. Obviously, when it comes to coax, shorter is better.
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If you have excess coax length, store it in the shape of a "figure 8" that is approximately 12 inches in length. Secure it with duct tape or something similar. Do not coil it up in an ordinary loop as this increases the resistance of the coax and can cause a SWR mismatch.

 

Xcis,
I'm not sure, but I think you were agreeing with me, at least up til the part about the shape of the coil of the extra coax.
20 ft x 0.22% = 4.4% signal loss
20 ft x 0.34% = 6.8% signal loss

so the smaller coax will only put out 0.18 watts less power at 20 ft than the RG8; hard even to measure, and certainly never hear the difference, unless you're doing moonbounce on 1296 MHz.

My caveat in coiling up the coax was that the manufacturer's minimum bend radius not be exceeded (don't turn tighter than....). Coax that's bent too tightly can crush the insulation between the inner conductor and the braid, which changes the impedance of the cable at that point. Trunk lip mounts are notorious for doing that.
As long as the coax is not bent/curved too sharply, then *all* of the signal is on the inside of the coax. Whether the coax is run straight, or coiled into a 6-inch loop (3-inch radius), or put into a figure-8 (how tight are those turns at the end?), then the shape of the coax run will not affect its performance anymore than the color of the light in the room or what team is playing in the Superbowl.
The other caveat was for some co-phased antennas, because the impedance of the network needs a transformer to go from the transmitter to the two paralleled antennas. In that case the supplied length is essential for that very "co-phasing"; otherwise the feedpoint impedance will be changed, affecting the radio's performance and, if the cables' lengths are changed randomly, the array's radiation pattern.
But I think you were mostly agreeing with me; I just had brunch as am feeling effusive.
Thanks,
-- Handlebar --

 

I have the same problem as panhandlepat. only i have a k40 magnetic mount antenna. i have the same SWR as he had of 1.5. but my ant Light comes on. and the range on my radio is only half what it used to be before the light came on. The radio has been tweaked so i dont know if that caused the problem but it worked when the radio and antenna were both new, i have had it for about half a year now. please help