Notch Filters?

The installation manual for my GNC 300XL calls for a notch filter in the com antenna line.

Have people found this neccessary? Where could I find one? (Googling the Garmin suggested part number only hits Garmin GPS installation manuals)

Pat

I added one...

4kilo said:

The installation manual for my GNC 300XL calls for a notch filter in the com antenna line.

Have people found this neccessary? Where could I find one? (Googling the Garmin suggested part number only hits Garmin GPS installation manuals)

Pat

Click to expand...

I got one from my local avionics shop.... about $40 IIRC

In my case, I upgraded an Apollo Loran to a slide-in replacement GX-55.

The installation instruction gave a set of Comm frequencies to transmit on... if any of these frequencies caused a loss of GPS signal, the installation needed to be tweaked. I had a comm. antenna too close (since moved) and a notch filter in that co-ax solved the problem.

Since it's a "plug-in" device, it's somewhat easy to add later as long as you can get to the coax. behind the panel. In my case I had a straight coupler in line, so I just replaced it with the notch filter.

Do your installation instructions give you the specific comm. frequencies to test?

gil in Tucson

It's been a while ago and I may be mistaken, but I'm pretty sure that one was included with my GNC-250XL.

When I ordered my GNC300XL from Stark, I asked about the notch filter. He said he didn't think it was really necessary. He said he would throw one in with it, but I think it came with the unit anyway.

Mel,

You were right again. There is a gizmo in the GNC 300XL materials which must be a notch filter. I didn't recognize it as such because it was labled something else in German.

Thanks all,

Pat

Looks like a "T"

4kilo said:

Mel,

You were right again. There is a gizmo in the GNC 300XL materials which must be a notch filter. I didn't recognize it as such because it was labled something else in German.

Thanks all,

Pat

Click to expand...

It should look like a BNC "T" connector, with the long leg not having a connector on it...

gil in Tucson

Gil,

That describes it exactly.

Thanks again,

Pat

In the Comm coax...

Pat... glad you found it...

Just to be clear, the notch filter goes in line with the Comm. antenna cable. You might need 2 filters if you have 2 comms. Put in in line first with the comm. that has it's antenna closest to the GPS antenna.

Some details here...

http://www.avionics.com/Avionics OnLine/kitplane.htm#GPS: Com Interference

It's usually not needed in you label your GPS "VFR USE ONLY"....

gil in Tucson