Gatwick Director on 118.950 MHz...

[Piggly]

Morning all,

In scanning around airband I think I have noticed something wrong...Gatwick Director is listed on 118.950 MHz but appears to be transmitting on an actual frequency of 118.955 MHz as close as I can measure it.

Is anyone else seeing this and have I misread the listings?

Regards

Piggly

[milly]

Two transmitter sites to improve coverage / remove dead spots. One will be +5kHz and one -5kHz. Aircraft will use the listed frequency and hear the stronger transmission.
For some ATC Sector freqs three transmitter sites can be used (on 25kHz channels) and these use the centre frequency as well as +/-7.5 offsets

In both cases it's less common now than it was prior to 8.33kHz channelisation

[Piggly]

You are quite right and I learned something new here!
I’ve been an RF engineer for 30+ years and I’ve never come across this technique used in aero radio. Every day is a school day!

Tra.
Piggly

[Piggly]

So, having now realised I didn't know something rather interesting and useful, I'm now back at the start of the process which led me here...

I tripped over this issue because I heard hetrodyne tones on airband, specifically a 5 kHz tone on my R30. Now I understand where this comes from I'm back to the point of wondering why the R30 has such a wide AF bandwidth and no selectable filter like the R6 has. Have I missed a hiden setting somewhere?

Regards

Jason