antenna impedance

[N787R]

I am getting extremely weak transmission on one of my comm. Even on the ground with another aircraft 50 feet away.
I have comant belly antenna. This antenna has no insulation. I checked the impedance right at the antenna female connector input to antenna itself. And I see an open connection.
So I am curious how this works. I expected to see zero ohms between the antenna and its input. Is it a bad antenna or this behavior is expected?

Thanks

Ben

 

[topgun260]

Measuring Antenna Impedance

Antenna impedance cannot be measured with a volt/ohm meter.
I would check coaxial feedlines for a short first by checking resistance between the center conductor and the shield of the coax. A SWR meter would be helpful for checking your antenna/feedline installation if you have access to one. Reflected power should be less than 2 to 1. 1.5 to 1 is better. The lower the better. Someone in your local EAA chapter may have one or if you know or can find a local ham radio operator they will likely have one that will cover VHF frequencies.

Brian
KF7TG

 

[Bob Axsom]

You say on one of your Comm...

You say on one of your comm units you have weak transmission. This suggests that you have some trouble shooting possibilities available right there. If you have two comm units how is the transmission out of the other one? There is no way to know your comm system design or its operational history. How is the receive signal on the weak transmission antenna? If you have a second antenna you might consider making up a trouble shooting coax to connect to the problem comm to the other antenna. There is no way to know what Commant has in the base of the antenna so a DC resistance check is just collecting information (all knowledge is good). Sure the antenna can be bad (open or shorted). The system cross check to the degree that your system enables it is a path I would take. If the coaxs were home made (probably) there sure is a possibility of fabrication problems. they should be continuity and discontinuity checked. I have Commant antennas on the belly of my RV-6A and there have been no problems after approximately 500 hours of operation but I am reluctant to pull my seat pans out to give you a comparitive resistance check. Maybe some one that hasn't closed everything up could provide the information from their antennas. Just some thoughts.

Bob Axsom