The frequency spread between the com and VOR/LOC frequencies is only a
few percent. The frequency spread between the com and glide slope is
about 300%. While transmitting you are generating tens of VOLTS per
meter at the transmit antenna while trying to receive MICRO volts per
meter VOR signals at the nav antenna. To do this at the same time
requires a lot of isolation between the transmitter and the receiver.
You can easily filter out the transmitter signal if it is 1/3 of the
receiver freq however if it is only a few percent away this requires
very precise filters which are large, heavy and cost a lot of money.
Unless you have a airplane as large as a airliner it is difficult to
get the antennas spaced far enough away from each other to get the
necessary isolation. This is one reason that the nav signal is
horizonal polarized and the com is vertical polarized. and spaced as
far apart on the aircraft as possible. Unless you have a strong
nearby nav signal and GOOD shielding on both antenna cables the
transmitter will overload the nav receiver resulting in no signal
during transmit. You did not run the two antenna cables next to each
other did you?

The easy fix is to QUIT RUNNING YOUR MOUTH while making an approach!

On 19 Sep 2003 23:11:56 GMT, (Sircompany) wrote:

This does sound very much like Radio Frequency Interference.
Do you still have a solid ident on the audio?
If yes, then the shielding on the harness between the KX125 and the KI209 is
in question. If no, then we have to think about antenna VSWR, etc.

I finaly disconected both KI-209A and KN-75 from my KX-125, but tracking a VOR
while transmit on COM still resulted "off" flag on KX-125's internal CDI.

I took a test flight to POC which has a VOR and ILS, and I found the following:

Transmitting on Com does not cut off ILS like it does with VOR;

When VOR went "off" while transmitting, there was no ident on Nav audio, the
Nav audio became completely silent; and

Pomona VOR is 110.40 and I transmitted on all fequency from 118 to 136 and each
fequency cuts off the VOR just the same.

Help!

Thanks,

Robin Hou