I have been using this transponder for about three years when the tower now says they cannot see it. I have had it benched checked and the power adjusted to 200 watts. It outputted all the mode a codes on the bench along with a couple of mode c codes. I have changed the antenna, the rf coax, and the short coax and rf connector on the tray. I have borrowed the neighbors kt76a and the tower still cannot see me. I had the avionics shop start a vfr transponder check and his power meter showed 100 watts out of the antenna on the plane. Before we could see why the power was down his meter quit. He thought even at 100 watts they should still see me within 10 miles. I have tried a different tower also. I have visually checked the power and encoder connector and it looks ok. I have not done anything with the encoder. The interrogation light flashes 3 times for every sweep with my transponder. Only once with the neighbors older model. He says he has never had any trouble with his. Anyone have any ideas?
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