Antenna Warning, COBRA 50th Aniv

I have checked the SWR meters in my cobra radios against two external meters and the readings were exactally the same. The meter is there to tell you that the ANTENNAS need to be adjusted. Simple as that.

As far as the OPs issue. Yeap sounds like an antenna issue. Set screws could have been slightly loose after adjusting the antenna and the whip moved.

If it is low (around 1.5 or so) on 1 and high (2.5 or 3.0 or higher) on 40 then it is an antenna issue. If it was 3 or higher on 1-20-40 then it is a coax issue or ground issue.

Low on 1 and higher on the upper channels usually means the antenna is too long or needs to be shortened, if my memory is correct.

 

Plug a dry load in and that would prove that synopsis to s**!

 

I had the same problem.

An adjustable $20 antenna (thick black with a thinner antenna at the top that slides in and out) did the trick mounted to a mirror mount.

 

I am not sure how to post a PDF File on here but if you send me a PM I can send you the file that Cobra sent me to fix this issue.

 

cable may be bad. this will also cause this issue. bad connection. poor ground

 

"if your radio has been "peaked & tuned" as they say, the swr/ant warning light has to be removed from the circuit".

no it doesn't.

"Radios that have has power mods done, or clipped, or anything that changes the factory alignment for rf power output will set off the ant light, this is a major issue in the cobra 29 radios" (all of them).

well yeah. if the power output increases then the swr mismatch calibration point controlled by vr6 changes too. it's only a major problem for people who don't know what they're doing.

"You can solve this issue by adjusting vr6 full off until the ant light does not come on, there's no harm in the radio, once you've modified the radio, the need for the internal swr meter is shot to hell and useless anyway at this point."

yeah, let's trash one of the features that you paid for in the first place.

no, here's how you solve the problem. you fabricate or purchase an rf load that simulates a 3:1 swr and attach it to the antenna output connector. you activate the transmitter, flip the front panel switch to cal and adjust the cal control for a set meter reading as usual. then switch to swr and you will see a 3:1 swr. now adjust vr6 down from full on until the light just goes out and no further. now, under normal operation if the swr rises above 3:1 the ant warning indicator will light normally, as it should, indicating an antenna problem.

if you want to know if someone really has any business inside that radio here's how you can tell. they should be able to fabricate their own simulated loads for 2:1 or 3:1 mismatches from their scrap resistor drawer from common values. if they can't do that then they're out of their league.

"Once you change the circuitry of the radio you have make other adjustment to compensate for the modifications, the ant warning light is one of those things some techs out here fail to correct",

they don't "fail" to like they're lazy or something, they don't have a clue as to how to correct it because they don't understand the operation of the circuit in the first place. in the second place they don't possess the required simulated mismatched rf loads to re-calibrate the ant. warning indicator either.

"and this is also the number one reason to own an external swr meter, the internal meters can not be trusted."

no, it's the number one reason why the antenna warning indicator can't be trusted. the operation of the swr meter is not compromised.

the swr metering circuit is accurate enough that it will allow you to look at the actual swr that would be seen if you made your measurement at the feedpoint of the antenna without actually doing so when fed with a tuned halfwave line, not because the swr meter is anything special but because that's one of the properties of that particular length of line.

destroy the ant warning indicator and sell 'em an swr meter. lmao.

it's no wonder people call it a "hack job". the term is well deserved.

 

EPIC FAIL!

Internal/Onboard SWR Calibration "feature" on some chassis
ONLY ZERO'S THE RADIO,if you were as smart as Bruce you would know that . . . .

 

in reference to the swr meter function in Cobra 29LTD, the "calibration control is used to provide a "set" reference based on transmitter power output and the match looking into the feedline so that the meter provides an accurate swr reading", much like the "calibration" or "set" control on most garden variety swr meters.

the only "epic failure" that exists is the lack of understanding on your part as well as bruces as to exactly how an swr (resistance) bridge operates. the design of the swr meter in the 29 as well as the majority of inexpensive external devices revolves around a circuit that has been around for decades called the wheatstone bridge, (hence the term swr bridge) composed of four circuit legs in which three are represented by the characteristic resistive impedance called for in this type of equipment (50 ohms) and a fourth leg which is connected to the load (antenna) under test. the closer the antenna load impedance matches the other three legs in the bridge circuit the lower the standing wave ratio.

 

1ST.......

This is not my fight it is between you and YUP .......

2ND .......

Many SWR meters have nothing to due with a wheatstone bridge And after more than 45 years I do understand how to MEASURE VSWR and how the meters work .....

Now you can return to your fight with YUP .......