DME Antenna replacement
Hi,
Hope some of you with experience in avionics can help me. My DME's performance began to degrade over the last year. It checked out good at a local avionics shop. As a additional test I connected the transponders antenna to the DME and it was like night and day. It really worked well. So it is either cable or antenna. I cleaned both ends with non oily contact cleaner but no difference.
I shorted one end of the coax and read the other end with a vom., It showed about .2 ohms which is what I would expect. I can't determine the capacitance though.
So, now I am trying to find a replacement for the existing antenna and here is my problem. The existing shark blade style antenna looks like the KA-60 from Bendix, or a Comant CI105 BUT mine does not have studs as they do. It has 2 phillips screws that recess into the molded plastic from the outside at each edge of the antenna. These screws are 4 inches apart. It also has a PL259 style screw antenna connector which requires an adapter. The KA-60 and others have studs that are 1.75 inches apart.
I looked on line for a replacement but I have not seen one picture or description of the style I have. It says Bendix King on the antenna.
If a direct replacement cannot be found, would it be better to just leave the existing antenna in place and install another one. This leads to another question. It seems that if I add another one it would be easier and cheaper to install a stub style antenna. Is there any difference in their performance?
It is on a 1975 Piper Archer.
Thanks for any help!
Hope some of you with experience in avionics can help me. My DME's performance began to degrade over the last year. It checked out good at a local avionics shop. As a additional test I connected the transponders antenna to the DME and it was like night and day. It really worked well. So it is either cable or antenna. I cleaned both ends with non oily contact cleaner but no difference.
I shorted one end of the coax and read the other end with a vom., It showed about .2 ohms which is what I would expect. I can't determine the capacitance though.
So, now I am trying to find a replacement for the existing antenna and here is my problem. The existing shark blade style antenna looks like the KA-60 from Bendix, or a Comant CI105 BUT mine does not have studs as they do. It has 2 phillips screws that recess into the molded plastic from the outside at each edge of the antenna. These screws are 4 inches apart. It also has a PL259 style screw antenna connector which requires an adapter. The KA-60 and others have studs that are 1.75 inches apart.
I looked on line for a replacement but I have not seen one picture or description of the style I have. It says Bendix King on the antenna.
If a direct replacement cannot be found, would it be better to just leave the existing antenna in place and install another one. This leads to another question. It seems that if I add another one it would be easier and cheaper to install a stub style antenna. Is there any difference in their performance?
It is on a 1975 Piper Archer.
Thanks for any help!
Comments
Two things first! If your transponder antenna cable is the black RG-58, replace it. If your antenna is as old as you suggest, this is likely the cable you have. (see my article in the June issue of "Piper Owners" on Avionics maintenance). This cable losses it's Dielectric properties and, in short, stops doing it's job. Secondly, the spike transponder antennas do not provide good performance for DME applications. The Transponder antenna you have has a "C" connector, not to be confused with a PL-259. This is not the same connector. The good news is that Comant/Cobham makes a CI-105 with a "C" connector. From my experience, this CI-105 is the best value in a transponder/DME antenna. You'll probably pay a bit more with the C connector but this is a better concept than an adapter. When you put a connection on a connection on a connection, you lose something. You want a "clean signal between your transponder and your antenna. That includes cable and connections. Check with your local avionics provider for a CI-105-X (looks like the CI-105-7 has a "C" connector) If you need help, contact Ron at APG Rotables @ (941) 637-8585 Good Luck! Bob Hart www.AvionixHelp.com