Narco MK-12D Xmit issue?

[Leo Langston]

Is it possible for an old MK-12D to lose Xmit capability in a certain frequency range? Last week on a IFR training flight we tried to contact Houston Approach on 134.45 several times on both of my MK-12Ds and got crickets. Not even a standby even though we could hear them chatting away with other planes in the area. We had no issues xmitting in the 120-122 frequencies with other towers or CTAF. Maybe they were just ignoring us but that was weird to say the least. So can a Mk-12D lose xmit capability in just the higher 134 bands but not in the lower bands?

 

[wilkersk]

With a transmitter that's perhaps not getting the full transmit power out of the antenna, its possible you found a hole in approach control's radio reception coverage. Its not unusual for one controller to be transmitting and receiving on a couple of different frequencies. And, due to line-of-sight limitations they may just not get a strong enough signal from you to break squelch on their radio.

Sounds like its time to get someone with an antenna analyzer to check the power out on your old Mk12s. It could be some old coax that's no longer up to snuff, a bad antenna, or an internal transmitter problem. But, most of the time I've found its just a coax connector is failing due to age or poor assembly; which causes the signal actually getting radiated from the antenna to be weak.

If the problem is bad enough, a lot of "reflected" RF energy on your antenna line could burn out your transmitter.

 

[Leo Langston]

Thx for the response. We wondered about a reception hole. I just had a comm antenna and coax ending replaced last month. Last month I had no issue talking on 134.45. I will try again this week to see if it’s still an issue. I got new radios coming next year but I want to be able to continue my IFR training but no 134 xmit capability might become a problem.

 

[Mikey52]

Yes it's possible, ours did. A little tune up at the radio shop, and the higher frequencies work again. I forget if the shop replaced a component, or just cleaned up and adjusted a couple pots.

 

[wilkersk]

Thx for the response. We wondered about a reception hole. I just had a comm antenna and coax ending replaced last month. Last month I had no issue talking on 134.45. I will try again this week to see if it’s still an issue. I got new radios coming next year but I want to be able to continue my IFR training but no 134 xmit capability might become a problem.

Between Port Townsend and Portland, along the west/south west side of Seattle's Mode C veil, there's several spots where it can be difficult to get approach to talk to us. A couple of things I've found that helps is to climb a couple hundred feet and also to look up the approach frequency listed for the closest airport to make sure we're on the right one.