ant. warning light help

[donnievon]

I just bought a 29ltd chrome and set the swr's to well below 1.5, thirty minutes later ant. light comes on and swr's are over 3. I changed ant., coax, mounts and studs and no improvement. Does anybody got any ideas. I've noticed the new chases are only 8 volt, do I need to unground the chase from the truck? I found this out when i tried to ground my echo board to it. Any help would be greatly appreciated.

 

[loosecannon]

lets see if we can get to the bottom of this.

need more details first.
dont leave anything out.
how and where is the radio mounted?
where do the power and ground wires go to exactly?
where and how is the antenna mounted?
how is the cable routed to the radio from the antenna?


please tell us more about the echo box, and ungrounding the chassis.
the more detailed you can be, the better we can help.

LC

 

[donnievon]

I have the radio mounted above the mirror to the sheetmetal of the cab in a ford f350. The coax (wilson coax)is ran inside the headliner, then down the back of the inside of the cab to a rubber grommet, then outside the cab,then through the bed of the pickup through another rubber grommet to the mount (wilson mount and gumdrop stud), that is bolted to the side of the bed, with the paint scaped of for a better ground.I'm useing a wilson 3foot silverload antenna. The radio is grounded to the metal frame behind the dash and the positive is hooked up to the fuse box. This is the same setup I've used for three other pickups. On another note,when I hooked up my echo board I notice the case wasn't grounded fully. What I mean is if the antenna isn't hooked up and I have it on my work bench, when I checked for a ground on the chassis and case it would start out at 12.4 volts , sometimes 8 volts and then it would just drop to zero in 5 or 6 seconds. It acted like it was charging up and then it was bleeding off when I hooked up the volt meter.

 

[loosecannon]

check the connections on the coax at the radio end and the antenna end.

sounds to me like you have an intermittent connection in the coax.
did you install the connector yourself?
key the mic with the meter set to SWR mode, and wiggle the coax connector and coax going into the radio.
if the needle moves around, you have found your bad connection.

do the same thing at the antenna end.

having the chassis of the radio connected to the frame should not hurt things.

sounds like you definitely had that echo board wired wrong.

usually, when you see an SWR of over 3 across all 40 channels, it indicates a bad ground connection somewhere.

good luck,
LC

 

[donnievon]

Thanks for your help loosecannon. It's cold and dark here so I'll check those two connections in the morning. Besides, it's the wifes b-day so I better not pay anymore attention to the radio tonight, or I may not get any attention for myself for a couple of nights. I'll post tommorrow to let you know if that is the problem.

 

[donnievon]

Well I checked the coax and the connectors and that doesn't seem to be the problem. Is it possible the swr meter and ant.warning light are bad in the radio? Or could there be something else wrong in the radio?

 

[mrgumby]

how close to the back of the cab is the antenna also does the antenna clear the top of the cab..?? that 3 foot seems a little short

 

[Robb]

Well I checked the coax and the connectors and that doesn't seem to be the problem. Is it possible the swr meter and ant.warning light are bad in the radio? Or could there be something else wrong in the radio?

There might be a service bulletin for it - you might go to the Cobra tech support site and ask a question.

You can always take 4 - 400 ohm 2 watt resistors and solder them in parallel to an old pl-239 connector. That should make a 100 ohm dummy load. That should see a 2:1 SWR on that radio. If the AWI light comes on; you will know that it is out of adjustment -and it is warning incorrectly.
Just a thought...

Other than that, I would put a 4 ft Wilson Silver load on the setup. Shorter antennas -like a 3 ft job- are more susceptible to minor changes in antenna height and are a bit more inconsistent with SWR. But that is me...

 

[loosecannon]

im assuming you have the manual for this radio already, but if not, here is a link:

http://www.cbtricks.com/radios/cobra/29ltd_chr/graphics/cobra_29ltd_chr_om.pdf

just to make sure you are checking the SWR correctly.
i understand that you actually do have some sort of antenna problem because the AWI is coming on.

try unplugging the coax from the antenna mount.
now check the antenna using a multimeter by using the continuity function or the resistance function and touching one lead to the antenna whip and the other lead to the vehicle body.

there should be no connection between the two, otherwise known as an open connection.

now check the coax that you just removed from the antenna mount the same way.
again, there should be no connection. (the other end of the coax should still be screwed into the back of the radio)

if you find shorted connections on either of these tests, you have an antenna mounting problem or your coax is bad. could also be a bad connection on the PL-259 connector that plugs into the radio.

did you use a soldered connector here or one of those non-soldered connectors from radio shack?

remember that large metal objects within a foot or two of that antenna can cause problems.

good luck,
LC

 

[donnievon]

After just playing with the radio again I suspect it's the radio. I've got a 2.9:1 ratio on channel 40 and no red light. 2:1 ratio on channel 1 and I get a red light. Channel 20 gives me 1.5:1 ratio with no red light. I've tripled check antenna,coax, mount and stud for proper continuance. I have three of these antennas and they all do the same readings. I even tried my cheap 2foot magnet mount on top of the cab and same readings. I'm going to try my wilson 5000 antenna on it sometime this week (if I can remember where I put it) and see what I get with it. We'll figure this out and pass a beer around to everybody.

 

[loosecannon]

and just to be sure, you are calibrating the SWR on each channel right?

and you understand how to use the SWR CAL knob correctly right?

i mean no offense, but not knowing your experience level with these things, they are valid questions.

maybe you could describe your SWR checking technique so we can be sure we are all on the same page.

you see, im getting the impression that your SWR meter is not telling you the correct story, and your AWI light IS telling you the correct story.

please be as detailed as you can when describing how you check your SWR.

LC

 

[fodendaf]

I don't like to sound like an idiot, but when nobody else said it why don't you try another radio and then you'll know if the antenna's are wrong.

 

[donnievon]

Well I found the problem, I borrowed a swr meter from a friend and everything checked out so I guess the light is set to sensative or it's just screwed-up. I got the swr set to 1.7:1 on channels 1 and 40 and shows 1.3:1 on channels 19 and 20. I guess it goes to show you can never trust the built in swr meter on the radio. Thanks for everybodies help and input. I'd put the smily faces cheering beers to everyone but they don't have that one here, so thanks again guys.