Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Building an Aircraft Communications Receiver

Status
Not open for further replies.

katzelect

New Member
HI,

I am somewhat new to all of this, & had a few questions for the pros on here. :)

I am thinking of building this Aircraft Communications Receiver, it looks simple enough that I could do it. :D

Questions;

1. What is the "range" on something like this? I don't actually live near any airports. Actually, I am pretty far out in the country (woods).

2. I don't understand what the purpose of "L1" in the circuit. Is that for a "fine tune" or calibration adjustment & then you let it alone?

3.What type of antenna would you use for this?

Also, I came across **broken link removed** site that modifies an existing am/fm radio to receive these signals? Would that work?

It all looks like it should be fun, but I don't want to put alot of time/effort into it if it wouldn't work for my particular application/location.

Thanks to all for the replies & trying to help a noob out!
 
Aircraft "MAINLY" use the frequency range of 108Mhz to 136 Mhz with 108 - 118 mainly used for data, therefore the main frequency range you would need is 118 - 136Mhz

If you want the full breakdown of spectrum look here: https://www.jneuhaus.com/fccindex/aviation.html

The frequency range they mention for that receiver is actually used for Military communications

The receiver is a regenerative type so would be reasonably sensitive but not exceptional and i would suggest you have to live pretty close for the ting to work, but bearing in mind it will pick up only Military aircraft then your not actually going to hear much!

Ideally to understand how far away you can hear the signals, you should read some of the MANY pages relating to radio waves and VHF/UHF transmission and reception.


If you live in an area with flat terrain (no mountains between you and the airport) it is "possible" to hear the tower from around 20 miles or so away on a good day.

Bear in mind ALL communications originating from the ground are relatively LOW power and will only have a short range where you can hear them.

Transmissions FROM the aircraft to the tower is different due to the height of the plane.
These can be heard from Many miles away, sometimes in the range of 40 - 50 miles or even more, and they can hear and respond to the weak ground transmissions from the tower the aircraft is so high the signal travels WAY further than it does on the ground.

I suggest you do some research on how radio waves travel if you wish to understand this
however for now, just take a look at the enclosed picture which hopefully explains it extremely simply
By the way, its easier to pick up a cheap scanner for a few $ than try and build something these days
Code:
108 - 137 MHz 
•  Aviation [FCC RULE Part 87]
•  136-137 MHz: Space operations (space-to-Earth), meteorological-satellite service (space-to-Earth), and the space research service (space-to-Earth). Stations licensed prior to January 2, 1990 may continue to use this band on a secondary basis to aeronautical mobile service. 
137 - 138 MHz 
•  Space operation (space-to-Earth) 
•  NOAA Meterological satellite (space-to-Earth) 
•  Space research (space-to-Earth) 
•  Mobile-satellite (space-to-Earth) 137.025-137.175 MHz, 137.333-137.4125 MHz, 137.475-137.525 MHz, 137.595-137.645 MHz, 137.753- 137.787 MHz and 137.825-138 MHz 

225 - 243.00 MHz 
•  Military 
243.00 MHz 
•  Survival craft stations, ELTs  
243.00 - 328.6 MHz 
•  Military] 


328.6 - 335.4 MHz 
•  Aeronautical glide path stations 
335.4 - 399.9 MHz 
•  Military 
399.9 - 400.05 MHz
•  Radionavigation 
•  Mobile-satellite, Earth-to-space
 

Attachments

  • Example.GIF
    Example.GIF
    2.4 KB · Views: 528
Last edited:
Hi karenhornby,

you forgot to mention the international VHF-emergency frequency which is 121.5MHz, just half of the military. Btw, ships use 500KHz for SOSing.

Boncuk
 
Aviation receiver

Hi katzelect,

almost everything has been covered already by karenhornby. The question of a suitable antenna is more a financial question. For omnidirectional reception I would use two crossed dipoles either for the VHF or for the UHF band (or both).

For extended range use yagi-antennas on a high mast. VHF already follows line-of-sight which restricts reception considerably. A 30m high mast with the antenna array on top will extend the range to approx. 40miles. (since the antennas on control towers are also mounted at the highest spot).

Using yagi-antennnas also means you need four of them for omnidirectional reception. Don't use too many directors (maximum of seven) for them since the reception angle might narrow to two degrees using too many of them and under windy conditions reception might fade.

Dipoles can be homemade easily using a 1/4" water pipe with holes every lambda/4. Stick the directors, strong wires (3 to 4mm dia, shortening factor from the longest to the shortest 0.98 each) directly into the water pipe and fix them with a screw or glue them. The dipole should be a closed loop with 240Ohms TV-cable connected. Its length is lambda/2. The reflectors should be lambda/2+(lambda/2*0.1). This design should work good for your purpose. The numbers are rough estimates.

Boncuk
 
Last edited:
As already touched on, aircraft use the VHF frequencies and these are generally line-of-sight bands. This means that the signals don't travel very far over the curve of the earth nor thru mountains or hills - there are exceptions but this general explanation is good for this discussion. If you can look up from where you live and see aircraft - even if on the distant horizon - you will probably be able to receive them with a modest antenna. Keep in mind that many commercial aircraft fly at altitudes that make line-of-sight possible for very long distances. Only way to know is try it and see.

What might be useful is to borrow a scanner with aircraft capability to see what you can hear from your location. Transmissions are typically very short so tuning around with your home-brew receiver could produce results that are disappointing. You might be over a common flight path. The aircraft change channels or frequencies at various phases of flight. There are ground control channels where you might hear "clear for takeoff" then after takeoff you'll hear "contact departure on 118.3" - and if you wanted to follow that flight you'd switch to 118.3. There is similar chatter when an aircraft is 50 or more miles out - and it will call the airport for instructions. Once you figure these channels out you'll have more fun.

The problem I see - the circuit you might use may not be stable enough for long term listening. You might tune it but after a few minutes it might drift far enough that you are off channel. Still - no harm in trying and it's good experience. There are construction techniques that you can use to improve the stability and reduce drift. Mechanical stability and a relative constant temp can help.

Aircraft also use channels in the 6 mHz and 8 mHz regions for long haul stuff. They also use other channels - I just happen to listen in on 6 and 8 mHz. Where I live I'll often hear aircraft going to/from Europe - usually contacting Gander on the east coast.

Any, have fun.
 
Thanks guys, all good info.; what are your thoughts on "modding" an existing am/fm radio to do this with, as in my second link? Is that workable to change the freq. range like that, just by bending a component & retuning?
 
Modifying an existing normal FM radio is actually usually quite simple, provided it is one of the old designs and not controlled by a processor or anything complicated
sorry cant get on your 2nd link, it says "restricted" for some reason

HOWEVER:
Aircraft transmissions are AM(amplitute modulated), and fm transmissions are FM (frequency modulated) the proper name for your fm radio should in fact be VHF radio as thats the range of frequencies it covers.

Anyway before I get into a massive long story of the differences between the various am's and fm's there are and then go into bandwidth and filtering the easiest way to try what your suggesting is
If you open up an old "fm" radio, you will find the tuning capacitator, the but that changes the radio stations you listen to, look on the circuit board so you can identify this component, the inside vanes will turn as you turn the dial.
Next to or very close to it will be a wire coil very short and probably less than 10 turns, if you cut snip out the centre section of this coil and resolder it (so you have a coil with half the amount of turns you originally had! you'll basically be changing the frequency range the radio receives from the original 88-108 Mhz, to HOPEFULLY a minimum of 100Mhz to maybe 120 maybe 130Mhz if your lucky

This is all trial and error and there is no guarantee it will actually work at all
its a very crude and simple way to try it out.
I'm sure others will come up with other suggestions, like calculating the actual reasonant frequency range with the coil/tuning capacitor values and how to change the capacitator instead of the coil, but I chose the simplest to try.

Oh Boncuk I didn't "forget" to mention the international distress frequency, I just didnt see any point in complicating things, I could have mentioned the HF distress frequency too but no point

One thing that MAY interest someone is that quite often there are various VOICE transmissions from the international space station and NASA just above the normal air band, but these use narrowband FM
 
Not sure how much you might want to spend, but I built one of Ramsey's aircraft receivers several years ago.

**broken link removed**

It was easy to assemble and it worked pretty good...but I live near an airport. It uses voltage controlled tuning (potentiometer), so not a lot of coil/capacitor tweaking to get it to work. In fact, I fed a sawtooth voltage to the the tuning voltage input and to the horizontal input of an oscilloscope, and the audio to the vertical input...Vwa La!...an aircraft band spectrum analyzer. By switching between the pot and the sawtooth, I was actually able to calibrate the dial to MSP (Minneapolis) Airport Com frequencies. :D

Ken
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top