Airband carrier detect circuit

[perryc]

Hi All,

New guy here trying to dust off some old skills that I've let atrophy away. I'm looking for some direction to build a modern version of circuit that's been around a while. In the aviation world a lot of small airports have a lighting system that can be turn on by a pilot by tuning a specific frequency in the air band (118-137Mhz am 25kHz spacing) and transmitting 3 one second bursts of carrier. Some of the old stuff I've looked at used relays and cascading charging of capacitors to so this (yeah really old). I'd like to do a 21st century version of this using a PIC based controller but am looking for some direction on the RF part of this. I was thinking a programmable oscillator running at the desired freq feeding a mixer with some notch filter and threshold detector circuit on the output of mixer that the PIC will monitor. Is this still the way it's still done (my rf knowledge is from the 80's) or is there some one chip wonder that simplifies all this?

 

[MikeMl]

If you started with a full-up superhet, dual-conversion AM receiver, then your task is simple. Such receivers have an Automatic Gain Control, which detects the "average" signal level at the AM detector, amplifies it, and applies it as a gain-reducing control voltage to the RF amplifier, and first IF gain stages. The voltage on the AGC line in such a receiver is proportional to the signal level at the antenna terminals. In some receivers, the AGC line is connected to the S-Meter, if there is one...

For your purpose, simply sampling the AGC line from the receiver using a PIC's A/D converter would give you both the signal level, and the timing of any pulses sent by keying the aircraft's transmitter.

A suitable receiver would be a retired aircraft COM receiver, or a kit like this one, or put a 120MHz to 27MHz RF converter ahead of an old CB the receiver of which is use as the IF/detector..

btw, my aircraft are based at an airport that has Pilot Controlled Lighting.

 

[perryc]

Thanks for the reply Mike, yeah I agree there are simpler ways to coble something together like using the AGC from an existing radio but I'm trying for a clean little one pcb solution. The longer story is I hit a deer while landing last week and really don't want to do that again so I want to trigger a couple of propane scare cannons from the plane so am working on something semi-portable and possible battery/solar powered.

Perry

 

[4pyros]

In that case you can use you own equpment and freq. Thare are many one peace trans/recv modules and use a tone insted of 3 burstes. Andy

 

[perryc]

The reason to use airband is so any aircraft landing that knows the frequency/procedure can trigger the scare cannons.

 

[MikeMl]

You might try **broken link removed** for the receiver. Looks like it is low cost and has low power consumption. You may have to modify the Local Oscillator to be crystal controlled.

 

[perryc]

Thanks very much for that link! My numerous Googles somehow missing find that kit. I've ordered a couple kits and should be well on my way to keep the critters off the strip for next year.

Perry RV-10 C-FMHP