Antenna warning

I disagree a little with cobras down and dirty antenna light adjustment. It says to turn the pot just until the light comes on. The problem with that is, the light is dim when it first comes on. To me it should be bright, especially with no antenna hooked up. So I tweek the pot a litter more till the LED is bright. Not very scientific I know, but hey its just a cobra.

 

Consumer Response Group

February 25, 2008
Page 1 of 1
TECHNICAL SERVICE BULLETIN
10057
MODEL(S):
CB model 29 (all versions with the ANT light)

DESCRIPTION:
The ANT light is coming on even though the SWR is below 3.

The specification for the ANT light is as follows:

•The ANT light should not illuminate if the SWR is below 3.

•The ANT light should illuminate by the time the SWR reaches 6.

ACTION:
Trimmer potentiometer VR6 will adjust the antenna light.

VR6 is located in the back of the radio, between the antenna jack and the power jack.

Equipment required:
25 ohm non-inductive load capable of dissipating 4 watts

1KHz audio source

Modulation meter

ADJUSTMENTS:
Adjust as follows:

1. Connect the 25 ohm load to the antenna jack.

2. Turn VR6 fully counter-clockwise.

3. Key the microphone and apply enough audio for full modulation.

4. Slowly turn VR6 clockwise just until the antenna light turns off.


There is another bulletin that has images, that one is bullsh**, it doesn't set the threshold right and looks like it was created by a drunk woodbutcher.

AND yes telling anyone to key the mic up to set the swr threshold can damage the radio, that's why that bulletin is bullsh**.

 

From another thread:
↑
To the OP try this, http://downloads.cobra.com/CB/Models/MiscInfo/29antlight.pdf , I had the same thing happen to me. Know problem with Cobra straight from factory. Hope this helps.


Actually DID do that. Ended up calling them and they put me on the phone with a nerd. He emailed me those exact instructions and also had me add a ground wire to the back. Problems are all gone.

GoldDot40,


I guess radios are NOT being burned up without using The special Equipment Required:

25 ohm non-inductive load capable of dissipating 4 watts

1KHz audio source

Modulation meter

I personally have not seen a radio burned out for having a swr out of wack. Not saying it can't happen. I believe most radios are not tuned correctly, and they are not burning out transistors, not operating at peak maybe. By keying a mike for a couple of seconds without a antenna is not going to burn your radio out. If you think otherwise maybe write to Cobra and tell those idiots that put the instructions, on THEIR COBRA OFFICIAL website, that YOU think they are wrong and people are burning up radios left and right.

 

I’ve seen radios burned out by SWR over 3.0, a stock radio at that. I’ve also seen a system running 1600 watts with 2.3:1 and do it all day long. Put an analyzer on the system, do it right. It will save a lot of heartache.

 

I don't know how long you've been doing this but I've been around with CB things for a long time and have seen a lot of finals burn up with just 2:1 swr, just wanted to make sure the OP gets it fixed RIGHT.

By the way, I would like to meet the idiot who wrote that SB and break his fingers so he can't type up any more bullsh**.

 

Oh I agree with you on fixing it right. I’m not happy if my equipment is reading anything over 1.3

Just my own preference.

 

While radios with problems can fail unexpectedly for just about any reason, an SWR of 2:1 is unusual not considered harmful for legal factory equipment. A 2.0 SWR level would indicate about a 10% signal loss/return, which is not typically considered dangerous for standard equipment. Regardless, it is advisable to seek a lower SWR for best signal performance.

On the other hand, if the equipment is producing signals at significantly bigger power levels, all bets are off since such equipment has a lot more signal to return at any given SWR value, and a 2:1 level is more likely to be a problem. The more wattage produced, the more wattage returned at any SWR level and the more heat introduced into the equipment. Those with the big juice need to be a lot more picky in regards to SWRs when approaching the 2.0 level.

 

I have a Cobra 29 lx and instead of ant warning light the words " antenna warning" flash on screen despite the fact that swr is 1.2 ( external meter) and when doing radio diagnostic tests is says pass for antenna, it doesnt display all the time but I just ignore it.

 

Thats why i keep tellin people that swr doesnt have any real affect on performance of an ant unless your puttin out big power...Only then is swr important....
Resonance,resistance and impedences can be sky high and still have a good swr..
A ohm meter and analyzer solves most issues..

 

I've been around CBs since the 23 channel days, but I have never delved into how they work as long as they were working.

Today I took my work truck in for service and they managed to break the antenna, probably when it was on the lift. Apologies for picture quality. View attachment 240339

No big deal, just go get a new antenna.
I don't remember the brand of my previous antenna, but it was a relatively short fiberglass antenna mounted on the headache rack. It worked well with low swr according to radio meter ( cobra 29), and no antenna warning light.

I bought a 31" Francis, installed it, and now the in-radio meter reads about 1.8, pretty consistent between 40, 1, and 20, and the antenna warning light is on when keying up. I checked ground at the mount, continuity of antenna wire and shielding, isolator washer, all good.

Questions:
Are Francis antennas decent, can you trim them, any guess why the antenna light now comes on?

After reading this thread I guess I'll pick up an external meter and check the swr before any else. I need to use the radio tomorrow (wife will drive it and pilot me with an OSOW load). I gather from this thread that damage is unlikely.

Thanks for any input!