KX 155 Nav/Com lost range

[dakota-cowboy]

The dakota has dual KX 155 nav/com radios.
Unit one has been my principle until just recently because the broadcast range has dropped and the Awos reception range is down under 5 nm sometimes less. It use to have Awos reception of 25-30nm just like Unit two does presently.
Question: What can change within an unit to make it loss range broadcasting and receiving?

 

[gismo]

The dakota has dual KX 155 nav/com radios.
Unit one has been my principle until just recently because the broadcast range has dropped and the Awos reception range is down under 5 nm sometimes less. It use to have Awos reception of 25-30nm just like Unit two does presently.
Question: What can change within an unit to make it loss range broadcasting and receiving?

Most likely, it's the antenna, antenna cable, or connections in same. You should try swapping the radios in the trays to see if the problem follow the radio or stays with the tray.

If it does move with the radio, it's likely something has damaged the circuitry attached to the antenna input or the power supply, either of which will require a trip to the avionics shop.

 

[Nadir]

If you've got access to an antenna tester (and the right adapters/cables) that handles the avband, you can save a lot of time diagnosing it. We had an antenna fail on a C172S awhile back. SWR of 13:1 in the avband at the antenna itself, not sure what failed in it, but it failed big!

 

[denverpilot]

Next time you hear of a dead one, ask if they're throwing it out and take it apart. There isn't much going on inside of the fiberglass ones, just some cheap foam or plastic spacers and a piece of wire cut to an appropriate 1/4 wavelength or so.

Better quality ones with all-metal construction usually don't break unless someone snaps them off, but they're not as "pretty" and folks tend to go with the white painted fiberglass ones.

No "magic" stuff in most of them, ADF DF antennas excepted, of course. Those have cool stuff inside 'em. Motors and gears and directional sensors and what-not.

 

[gismo]

Next time you hear of a dead one, ask if they're throwing it out and take it apart. There isn't much going on inside of the fiberglass ones, just some cheap foam or plastic spacers and a piece of wire cut to an appropriate 1/4 wavelength or so.

Better quality ones with all-metal construction usually don't break unless someone snaps them off, but they're not as "pretty" and folks tend to go with the white painted fiberglass ones.

No "magic" stuff in most of them, ADF DF antennas excepted, of course. Those have cool stuff inside 'em. Motors and gears and directional sensors and what-not.

The reason my antennas are plastic covered is for their ability to withstand ice accretion and the significant decrease in drag due to their more aerodynamic shape. As to the robustness, IME a good blade antenna will tolerate more abuse than an "all metal" one, the primary advantage of the metal ones (aside from price) is that any damage is likely to be more obvious.

Also FWIW unless you're talking about the WWII military style mounted in a 5" diameter bullet shape, an ADF antenna doesn't have any motors or gears, just two ferrite loop antennae effectively mounted 90° to each other.

 

[denverpilot]

Good points, all.

Was talking about the ancient stuff, yeah. The cool stuff.

There just isn't much inside an antenna. Lots of folks think they're "magic".