AM receiver convert to ATC receiver

Hi all

If I change the tank circuit components (reduce the capacitance and inductance) and change the transistors to appropriate VHF ones, will I be able to pick up ATC (Air Traffic Conversations) using this circuit ?

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Thanks Shelton.

Reply to
Archimedes
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Yes I didn't read the article, but the coil and cap of that receiver look like broadcast band. When you build it, keep all the wires short in the RF portion of the receiver.

Do you have the means to calculate the needed L and C to cover about 118MHz to 136 MHZ?

Reply to
Don Bowey

Not likely. I doubt you'd ever get that circuit to work at VHF frequencies no matter what you did with the resonant circuit portion. There are many problems including wrong impedances for the various parasitic capacitances.

Secondly air traffic stuff is FM I believe.

Reply to
Bob Eld

Military may use FM, I don't know, but airplane related communication is unique in that it does use actual AM.

A project that saw publication a number of times in the old days took advantage of that, a "crystal radio" that tuned VHF. It was nothing more than a tuned circuit and a diode detector feeding an earphone, not sensitive but useful near airports and since it didn't radiate anything, even useable (though maybe not legally) on an actual airplane.

The description of the circuit says it's a regen receiver, and those were never popular at VHF, I'm assuming instability came into play. You did see superregen receivers there. Either type will radiate, and that's not a good thing in the aircraft band.

Michael

Reply to
Michael Black

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Hi

Thanks for all the reponses - yes i can calcualte the required parameters to get this into the ATC band - but im now confused - some say it will work some say it wont? So will it or will it not ?

Reply to
Archimedes

"Archimedes"

" Thanks for all the reponses - yes i can calcualte the required parameters to get this into the ATC band - but im now confused - some say it will work some say it wont? So will it or will it not ? "

** IMO - very poorly, if at all.

You will need to be very close to an airport to hear anything and then you will regularly hear several voices together as TRF sets have poor selectivity.

VHF communications listening really requires the receiver to be a superhet - preferably a double conversion one.

A small " scanner " receiver is ideal.

...... Phil

Reply to
Phil Allison

Thanks Phil - very informative answer - and thanks to the others who also responded!

Reply to
Archimedes

My guess is that it might work -- sorta -- but never at any useful level. I see a whole lot of problems with that approach.

One idea that's relatively simple to accomplish, and will teach you a whole lot, is a tunable converter that you place between a suitable VHF antenna, such as a groundplane vertical, and a standard AM broadcast receiver.

I fiddled with one of those as a kid and was able to achieve surprisingly good performance, after some fiddling. I used a couple of vacuum tubes. A tunable converter should be a lot easier to build using toroids and modern ICs. (Look as the SA612 data sheet. You'll probably get a few good ideas for a converter when you read that.)

Have fun!

Tom

Reply to
Tom2000

My guess is that with enough fooling around, you might get something that will tune a few of the very strongest signals occasionally, but never very well. You'll never get any selectivity out of it, and it will be unstable as all get out. All in all, I think you'll be quite frustrated, if you can ever get the fool thing working at all.

But your desire for a simple air band receiver reminds me of a project from the old vacuum tube days -- a tunable air band converter that you connect between the antenna and a standard AM broadcast band receiver.

The converter mixes the air band signals between 108 and 136 MHz to a fixed IF frequency somewhere in the AM broadcast band. Just tune your AM receiver to that frequency and tune air band signals by changing the converter oscillator's frequency.

These days, folks would probably want to build something like that all fancy and complicated, with PLL tuning and a tracking front end, but that primitive vacuum tube converter worked pretty well with some very simple circuitry. It might be funto blow the dust off that old design and give it a new life.

You could bring that converter design into the 21st century easily and cheaply using an SA612 chip. The SA612 contains both an oscillator and a mixer, and is even available as a through-hole part. You could tune its oscillator with a varactor diode driven by a cheap 10-turn pot you might scrounge through the surplus channels.

That might provide all the gain you'd need. But if you wanted a bit more pop, you could use a couple of J310s in cascode as an RF amp. Shooting from the hip, I don't think an RF amp would be necesssary, though. I wouldn't use it for my initial design.

You can find the SA612 data sheet here:

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You should get quite a few ideas for a converter design just from reading the data sheet.

SA612s, J310s, toroidal cores for coils, varactor diodes, voltage regulators, and all sorts of other good stuff is available from Kits and Parts:

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The idea would be to keep the design really, really simple. Don't add anything that you don't absolutely need. Feed the antenna directly to the mixer (through a toroidal transformer, perhaps) and the output of the mixer directly to the AM broadcast receiver. Let the radio do all the post-mixer filtering for you.

You might find, through test and experimentation, that your converter needs something more. If so, figure out what's causing the problem, sort it out, and fix it.

But I think that a simple SA612 design won't need much debugging. It's a "high probability of success" project, right out of the can.

Have fun!

Tom

Reply to
Tom2000

Here are the facts

Military ground troups and close air support

30 Mhz to 87.975 FM only

Air traffic control

117.975 to 156.000Mhz, AM only

Maritime

156.000 to 173.975 ( with some reserved for Sonobuoy operations) FM only

Military

225 Mhz to 399.975 Mhz AM or FM ( they can actually choose wich one for any freq in this band) Not interesting in this band as there is a lot of encryption, freq hopping and other hush hush stuff.

Claude

Reply to
Claude

Typo here: ^136.000

Reply to
Don Bowey

Yes, and then you'd quickly have visitors coming with vehicles bearing government license plates. A regen-receiver is most definitely not a good idea in the aircraft band.

--
Regards, Joerg

http://www.analogconsultants.com/
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Reply to
Joerg

Quite correct, it is most likely jail time where you will have hours and hours of fun designing electronics such as movement alarms that will detect the proximity of "fellow inmates" . Just swearing on an ATC frequency will net you a $2,500 fine in Canada, I can't even imagine what they would do to you if you jammed one of their frequencies.

Claude Montreal

Reply to
Claude

One of you naysayers should estimate the amount of radiated energy from a typical regen receiver.

Also, what is the distance from the intended regen location to the airport, and what would you imagine the comparative strengths would be of the regen signal and air traffic signals at air traffic receivers?

The regen receiver radiated signal would be lost in the noise.

Reply to
Don Bowey

The other party to air traffic communication are aircraft. Those happen to roam about quite a bit :-)

Seriously, disregarding the airstrip that's almost next to the office here we are also roughly in the flight path for Mather Field. Altitude above our building maybe 1500ft, give or take. If Fedex, DHL and other pilots would report some weird shhhhht noise everytime they pass a certain spot, guess what would happen?

--
Regards, Joerg

http://www.analogconsultants.com/
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Reply to
Joerg

I doubt that at 1500 feet the signal from a regen receiver would break the squelch.

Reply to
Don Bowey

One of the nice things about AM, and the reason they use it for aviation, is that power wins. If two signals are colliding, the more powerful one will always be heard.

There are various "unicom" frequencies around the US, which are used by pilots at uncontrolled airports for announcing positions in the traffic pattern. Since the frequency space is not all that big, they tend to overlap. You can often hear folks announcing at airports up to 100 miles away. However, there is never any problem, since the near transmitters just blast over the far ones.

I'm guessing the regen receiver outputs less than one mW through its power wires. That isn't going to be a problem for anybody unless the OP decides to start messing with the design, and somehow manages to build a far more effective transmitter. If he puts it into a metal box, he'll be safe.

OTOH, he'll never get it working in the AM aircraft band, since the circuit itself really sucks.

He should instead buy something like this:

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For 35 bucks buy-it-now, not a bad deal. It also does weather, AM broadcast band, FM broadcast band, and shortwave, and even works from a crank so you can work out while listening to the ATC folks vector jets around.

If the OP really wants to hack at something, I'd suggest an old Cessna transceiver. Just don't plug in the microphone, and power it from 24V. Should be fun to play with. This actually will get you arrested if you mess up and jam a frequency, though. There is one on sale at eBay now for $10, but it'll go for more.

I landed at Mather once when it first went GA. Very creepy. The runway is so wide that it feels like you are much lower than you really are. A 172 feels like a gnat on a surfboard.

Regards, Bob Monsen

Reply to
Bob Monsen

"Bob Monsen"

** That is how FM behaves - ie the "capture effect".

AM does no such thing - " colliding " signals simply combine in the receiver and are heard together.

Weak signals are heard in the background of strong ones.

...... Phil

Reply to
Phil Allison

Thanks for the clarification. However, I'm curious about this.

An FM signal is really just a frequency shift on the carrier. As I understand it, the transmitted signal is the carrier frequency shifted in proportion to the amplitude of the sound that will get transmitted (for mono).

So, given two transmitters on the same frequency, you end up with two varying carriers. If your receiver is just receiving both signals, mixing them down to a lower frequency, detecting the shift, and converting that into an amplitude, the detector must be doing this locking on. Do you know how it works? How does it lock on rather than just outputting a mess?

Thanks, Bob Monsen

Reply to
Bob Monsen

"Bob Monsen"

** Firstly - I am very impressed that you accepted my comments in the spirit they were intended.

A rarity on usenet - my congrats.

** Capture effect is almost entirly due to the " limiting " that occurs in the IF amplifier stages.

Unlike AM, the IF stages of an FM receiver are normally operated very heavily into overload ( ie gross amplitude clipping ) so the weaker of two ( IF frequency FM signals ) is completely over-whelmed by the stronger ne - which them becomes the only signal present at the FM detector.

There is even a Wiki about it:

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This feature was seen as a BAD idea for aircraft radio comms - it being preferable to have something more like a telephone party line, so the weaker voice could still be heard and even if not read clearly, the pilot or ground controller could ask for a repeat of the message.

This got screwed up once at Tenerife and two jumbo collided as a result.

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...... Phil

Reply to
Phil Allison

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