Yaesu FT-8900 DTMF mic problems (MH-48)

[SM4XAS]

Hello!

Don't know if this is the correct forum but I give it a try!

I have a strange problem and I wonder if anyone can help me.

I have the MH-48 microphone to my FT-8900 quad band radio

On all bands exept 144-146 (VHF), all DTMF-buttons works fine.
But on VHF band, DTMF 1,2,3 and A (top row) doesn't work!
I can input the frequency with the buttons 1,2,3, but when I
press the PTT and then press buttons 1,2,3,A nothing happens!
As I said, it works on the other bands!

Anyone have any idea?! this is driving me mad! ;P

73 DE SM7XAS (SM4XAS)

[KA4POL]

Just a long shot. Does this happen even with lowest RF power? It could be RF getting into the circuit.

[SM4XAS]

Yes, with lowest power (5W).

[KA4POL]

Have you tried it with a dummy load? Move the microphone into different positions.
Basically your problem seems to come from the row transistor not being triggered. You would have to verify this measuring the voltages inside the microphone.

[SM4XAS]

You were right. I changed antenna (used a small whip first, now I built a dipole) and now it works again

Thank's!

I have a similar problem with my FT-897, the DTMF-mic just sends noise instead of audio when I increase power to more than 10W.
But there I know HF is the problem. I tried putting a ferrite core on the cable but no change. The antenna is a fishing pole, 5m, grounded
in the balcony railing. The antenna works great, except from the HF..

I don't have much space to mount any other antenna, and I cannot ground it any other way either..
There is no grounded power outlet in my appartment (except from in the bathroom ) so that might be the problem..

73 DE SM7XAS

[KA4POL]

So no more:

this is driving me mad! ;P

Great