Designing a system for controlling the lights at a private airfield

Thread Starter

Rabbit H

Joined Aug 5, 2016
153
Howdy Guys,

Some of you may remember me from a prior circuit design thread that modulated the obstacle light ("ob Light") on a 42ft tower on my property at a residential airport. That project ran on AAC from Aug 2016 to Jun 2017 (https://forum.allaboutcircuits.com/threads/antenna-tower-obstacle-light-flasher-circuit.126328/ ) and I couldn't have done it without the fantastic help from AAC-regulars Crutschow, Doktor Jones, and several others. (THANKS AGAIN GUYS! That circuit is still working perfectly!) The purpose of the modulator was to apply a very slow sinewave to my tower's ob light that would get a pilot's attention but would not distract or blind that pilot like a strobe would. A side benefit of a slow sinewave is that the incandescent bulb's filament would last longer. I'm happy to say that it's been running for almost three years now on the original 2 bulbs!

Anyway, while that circuit activates an ob light on top of a tower, I now need a way for an inbound pilot to turn on/off the spotlights that illuminate our windsock on that tower. This is typically done by the pilot keying his/her microphone (breaking the squelch) 3, 5, or 7 times on a designated aviation frequency. After a preset time (usually 5 to 15 minutes), the ob and windsock lights would automatically shut down. (This is known in FAA-parlance as PCL, or Pilot Controlled Lighting. This kind of lighting control is very common at unattended airports or those with very few night ops.)

Back when we were working on the light modulator design, "hobbyist quality" PCL boxes (squelch-break detectors) were readily available from several sources. (Ramsey Electronics, Wag Aero, and Hamtronics, to name a few.) Unfortunately, now that I'm ready to purchase one, affordable ones have gone away, only to be replaced by "Major Airport-priced" systems! Sooooooo, here I am, back again with hat-in-hand asking for your help! :D

Back before Ramsey Electronics closed its doors, I purchased one of their AR2 Aircraft Receiver Kits and its companion AR2L Runway Lighting Controller Kit. However, I started hearing that Ramsey was in trouble (which would leave my kits unsupported if they folded) so I started looking at the Hamtronics R123 Runway Lights Controller. Unfortunately, Hamtronics has also since gone out of business. And while Wag Aero is still in business, they no longer offer their cheap ($750) lighting controller. Big-Airport, Commercial-grade lighting controllers ARE available but they run many thousands of dollars!!!

Sooooooo,
I figure that an old aircraft receiver can provide the frequency-specific input that I need for a homemade decoder that can count 3, 5, or 7 squelch breaks. The challenge would be designing the decoder to ignore squelch breaks that contain voice modulations.

About me: I was very active in military radar electronics many years ago so I'm not completely clueless. (Ignore what my wife says!!!) But while I still know the basics, I'm not up to date on all the new stuff that's out there. (But I CAN solder!!!)

Also, I'm sure that some well-meaning individual will point out that the FAA will undoubtedly have issues with a homemade lighting controller; however, the truth is that they won't because I live on a private airstrip. It would be different if this was for a Commercial airport but all the FAA cares about on private strips is that we follow accepted norms. In other words, don't use blue lights to mark a runway. (White lights are used to mark runways; whereas, blue lights indicate taxiways.)

Anyone up for a challenge???

Harvey
 
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crutschow

Joined Mar 14, 2008
33,983
Sounds doable but how would a "squelch-break" be detected?
Is there a signal available from the receiver indicating a squelch or do we have to do it from the audio output?
If so, what are the audio characteristics of the squelch-break that can be detected?
Is it that large rush of white noise just before the squelch?
 

Thread Starter

Rabbit H

Joined Aug 5, 2016
153
Well Howdy, Crutschow! I was hoping you'd chime in!!!

By "squelch break", I mean carrier only, no voice or other modulation. I suppose it's the break in the received noise such as when a transmitter is keyed but no mic is connected. Presumably, we'd pick it off right before the speaker amplifier circuit of a dedicated aircraft band receiver.

Harvey
 
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BR-549

Joined Sep 22, 2013
4,928
I would add a buffer stage to the existing squelch(which is a switched output). This output can generate an processor interrupt. This interrupt will measure the time the squelch stays on. If it's beyond the short proper time(several milliseconds).....the squelch is for audio or another signal. And interrupt is reset. No action needed.

If the squelch on time is quick enough.....increment a click memory box. Check count. Reset interrupt.

When click box reaches 7 or your number within a specified time..... Apply your needed function and reset everything.......start a 15 minute timer to turn off lights.
 

crutschow

Joined Mar 14, 2008
33,983
Well, the noise I hear at the end of a transmission for the squelch in the receivers I've used, generates a short burst of white noise before the sound is squelched.
I was thinking that relatively high burst noise could be readily detected.
 

Ylli

Joined Nov 13, 2015
1,083
If you sample the audio stream *before* the receiver squelch circuitry you will find a constant stream of white noise (the same noise you hear from the speaker after a received carrier drops but before the squelch kicks back in). When a carrier is received, that noise level will drop. You can simply 'detect' the noise to create a representative dc level, and that dc level will drop when it sees a carrier. Or just monitor the AGC line, the signal will be quite strong for an aircraft within a few miles. Add a comparator and other circuitry required to count clicks within a time block and a timeout circuit.

BR-549, the R122 is an older Hamtronics model. Current model I see online is the R123. Looks like a nice unit. I see the owner of Hamtronics had an accident but I don't see anything about them going out of business.
 

Thread Starter

Rabbit H

Joined Aug 5, 2016
153
Good Morning guys. It looks like this project is starting to build up some steam. I love it when a new project gets underway!

From what I understand, Ramsey Electronics was shut down by the FCC for selling FM transmitter kits (and factory-built units) that exceeded the output power limitations of US-based hobbyist or college FM radio stations. The way I understand it, in addition to the low-power kits intended for domestic (US) use, Ramsey also produced higher-power units if the buyer promised that they were intended for non-US use only. Of course, the FCC wasn't satisfied with just a promise and ultimately shut Ramsey down for producing "high" power FM radio transmitters with few controls (other than a customer's promise) that they wouldn't be used in the US.

Ylli, the owner of Hamtronics was involved in a serious bicycle accident a couple of years ago and "basically being a one-man operation" (according to a statement by the family) the company was put on hold pending his recovery. However, upon checking Hamtronics' website yesterday, I found an announcement that the owner had passed away from his injuries and his company is now out of business. So sad!

Harvey
 

crutschow

Joined Mar 14, 2008
33,983
One question is, can you go inside the receiver to access the circuit, or do you want only external signals to be used by the squelch-break circuit?
 

Thread Starter

Rabbit H

Joined Aug 5, 2016
153
If at all possible, I'd like to use the headphone output of an aviation receiver. That way, I could use an off-the-shelf receiver without having to open it up and mess up the warranty, etc.

Harvey
 

Thread Starter

Rabbit H

Joined Aug 5, 2016
153
Aviation radios typically have only a low level output for headphones. For those cockpits that are quiet enough for a speaker to be heard (or for use on the ground before starting the engine) a separate audio amp is required.

Harvey
 

BR-549

Joined Sep 22, 2013
4,928
Do you normally hear speakers and headphones at same time? AND do you depend on the headphones for audio communication in noisy ares? All this makes a difference.

I am not a pilot. But for modifying integration....we have to understand your normal operating needs. And the receiver characteristics. Not familiar with your rig or operating procedures.
 

Thread Starter

Rabbit H

Joined Aug 5, 2016
153
Are PMs allowed on AAC? If so, I can scan and send you the circuit descriptions from the Ramsey Aircraft Receiver and Runway Lights Controller kits. I don't want to openly post them for all to see since the info is likely proprietary.

Harvey
 

BR-549

Joined Sep 22, 2013
4,928
You did not want to go internally right?

Let's try this.......can the headphone plug be dedicated the runway lights only?


I believe I shall refrain. Hard for me to grasp.
 

Thread Starter

Rabbit H

Joined Aug 5, 2016
153
Small airplanes (as opposed to luxury planes like corporate jets) typically have very noisy cockpits so we all use headsets. Their foam ear seals make it easier to hear the radio and their mics are noise-cancelling so the receiving party (other aircraft or air traffic control) can understand us. Speakers are sometimes left on after the engine is started but we can't hear it since the engine noise is overpowering.

I would think that a runway lights controller is looking for 3, 5, or 7 (see note below) breaks in the received carrier frequency and ignores all audio on it.

Note: Aviation runway controllers are typically set up to detect one of three available code pairs: Three mic clicks (squelch breaks) within 5 seconds, five within 5 secs, or 7 within 5 secs. Depending on how the ground receiver is set up, these three "functions" can activate the runway lights into low, medium, or high intensity, or in areas with many airports on the same frequency, some airports will be set up to activate on three clicks, some on five, and the others on seven. This way, a pilot doesn't turn on the lights of every airport in a three-state area! (Most airport ground receivers will also have an adjustable squelch so only aircraft within a a couple of miles area can activate the lights.) Recall that the main purpose of these controllers is so the pilot of an aircraft can activate an airport's lights after dark without the airport having to hire round-the-clock staffing.

Harvey
 

Thread Starter

Rabbit H

Joined Aug 5, 2016
153
QUOTE="BR-549, post: 1265806, member: 218447

Let's try this.......can the headphone plug be dedicated the runway lights only?
Hard for me to grasp.[/QUOTE]

I'm sorry, yes, I can easily set up an extra receiver on the ground just for our lights controller. The receiver's output would be low "headphone" level.

I thought you were asking me if it's okay to open up the receiver and pick off the signal at the IF detector or before it goes to the headset amplifier. I'd prefer not to do that.

Harvey
 

Ylli

Joined Nov 13, 2015
1,083
A normal receiver squelch is going to be fast attack, slow release. If the receiver is set so it is squelched with no carrier, it may not recover fast enough to decode 5 or 7 pulses via squelch break. I think you will need to allow the receiver to operate with the squelch open and do all the decoding externally.
 
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