KX125 question

[ROBIN FLY]

It has been a few weeks since I added glide slope receiver (KN75) and ILS
indicater (KI209A) to my trusted KX125. All was well, and they track ILS just
fine. But when tracking VOR, com transmission would somehow block off nav
signal and both indicators (KI209A & KN125 built-in) would show "off" flag. It
acts like those old 1&1/2 nav/com radios.

I do not remember if my KX125 acted this way before I added KN75 & KI209A to
it. I tried disconnecting the KI209A from it, but it still show "off" flag on
its built-in indicator when transmitting. I did not try to disconnect the KN75
because it is hard to get to.

Questions:

1. When transmitting from my other com radio, KX125 & KI209A do not lost nav
signal. Does that rule out antenna problem?

2. I also noted that the "comm audio" line is not the shield type. Could this
be the problem?

3. Is it likely the KN75 might be the problem, does it worth the time to
disconnect it from KX125 and see if KN75 is the problem?

Many thanks,

Robin Hou

[ROBIN FLY]

>> 1. When transmitting from my other com radio, KX125 & KI209A do not lost
>> nav signal. Does that rule out antenna problem?
>
>No. The two com radios use different antennas. What are you using for a
>glideslope antenna?

I use a triplexer w/dual VOR & single GS. One of the VOR connector on the
triplexer was left unconnected because I have only one Nav.

[garyPQ]

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.

"ROBIN FLY" > wrote in message
...
> It has been a few weeks since I added glide slope receiver (KN75) and ILS
> indicater (KI209A) to my trusted KX125. All was well, and they track ILS
just
> fine. But when tracking VOR, com transmission would somehow block off nav
> signal and both indicators (KI209A & KN125 built-in) would show "off"
flag. It
> acts like those old 1&1/2 nav/com radios.
>
> I do not remember if my KX125 acted this way before I added KN75 & KI209A
to
> it. I tried disconnecting the KI209A from it, but it still show "off"
flag on
> its built-in indicator when transmitting. I did not try to disconnect the
KN75
> because it is hard to get to.
>
> Questions:
>
> 1. When transmitting from my other com radio, KX125 & KI209A do not lost
nav
> signal. Does that rule out antenna problem?
>
> 2. I also noted that the "comm audio" line is not the shield type. Could
this
> be the problem?
>
> 3. Is it likely the KN75 might be the problem, does it worth the time to
> disconnect it from KX125 and see if KN75 is the problem?
>
> Many thanks,
>
> Robin Hou
>
>

[[email protected]]

On 5-Sep-2003, (ROBIN FLY) wrote:

> I use a triplexer w/dual VOR & single GS. One of the VOR connector on the
> triplexer was left unconnected because I have only one Nav.

Of the two com antennas, is the one connected to the KX125 closer to the nav
antenna?

--
-Elliott Drucker

[ROBIN FLY]

No. Both com ant are about the same distance to nav ant.

[ROBIN FLY]

>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.

I do not know, but I will find out next time I fly. Thanks.

[Sircompany]

>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

[[email protected]]

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
>