Do I have an antenna issue.

[tceq24443]

Testing and comparing a used CI-122 antenna to one of my older CI-139 style antenna with a Garmin SL40 and another COM. It transmits with the CI-122 at 5w/2.7ish SWR but at 10W/1.2ish SWR over a CI-139 type antenna. I have double checked the ground (antenna base to nonpainted skin, no gasket, metal to metal mount, same cables, different cables, different radios, double checked bnc connectors with no difference. Both radios are transmitting at seemingly half power with the CI-122 while the same cable and connector but the other antenna at full power. Thanks for the help.

 

[Mikey52]

Do a resistance check on both antennas, you may find the answer.

 

[Initial Fix]

The CI-122 is a long wire type of antenna. There is a loading coil in the base. I don’t know if you can open the base, but if you can see if something is corroded in there.

 

[Albany Tom]

Not an a&p. If the antenna is out of tune/damaged, it's going to present an impedance mismatch to the transmitter, that you're going to see as high SWR, and if it's high enough a modern radio is going to reduce the output power so that the reflected power doesn't damage the radio. Best/easiest test is an antenna analyzer. Many hams will have one that will cover aircraft band and be happy to let you borrow it. An ohm meter/DMM isn't going to give you a great result unless there's a problem with the cable or ground.

 

[mondtster]

Not an a&p. If the antenna is out of tune/damaged, it's going to present an impedance mismatch to the transmitter, that you're going to see as high SWR, and if it's high enough a modern radio is going to reduce the output power so that the reflected power doesn't damage the radio. Best/easiest test is an antenna analyzer. Many hams will have one that will cover aircraft band and be happy to let you borrow it. An ohm meter/DMM isn't going to give you a great result unless there's a problem with the cable or ground.

A nano VNA is so cheap there is no reason that it would be out of reach for someone who is concerned with their antenna/radio performance. No need to hunt around for a ham, although finding an Elmer with solid knowledge of antennas and tuning may be helpful. Perhaps the OP already has something, as SWR was mentioned.

On a related note, I’ve constructed and tuned numerous HF and VHF antennas for amateur use but I’ve never bothered to check an aircraft installation. I probably should, just to know how good or bad they typically are.