transistor garage door opener

Let me start by saying I have NO experience with RF. However, I have a great interrest.

Recently, I came upon a project that I thought would interrest me. Basically, I would like to duplicate a "gate opener" that I use to get into my apartment complex. Sure, I could go and buy one for S20, but I would really like to get some RF experience.

Here is what I know:
Brand: Linear
Model: ACT-31B

From what I understand, the system allows a total of 1million possible "codes" that are programmed at the factory. The code, when transmitted, is static...not some constantly changing code, etc. The transmission frequency is 318Mhz.

The question is, how do I go about this? Basically, I want to be able to generate the identical "signal". I know nothing about how the signal is modulated (FSK?).

Just a general point in the right direction would be tremendously helpful.

Thanks
Tomas

This is not an easy project for a beginner. Especially one with no test equipment. It will be somewhat like trying to make an automobile engine starting with a block of iron and a file and saw.

The transmitter is probably a one transistor oscillator. The modulation is probably on-off keying.

Actually, I have plenty of good equipment. A 500Mhz Digital Phospher OScope and a 2Ghz Spectrum Analyzer.

Also, please keep in mind that I'm not a beginner to electronics. I have a pretty vast background in 8-bit embedded design (analog, digital, etc).

I've never heard of on-off keying. Is this a frequently used modulation scheme in this sort of application?

Thanks for the info,
Tomas

You may well be able to do it then. First make a one transistor oscillator and get it working in continuous operation. Then for your exiting remote controller measure the digital waveform that the digital chip sends to the RF oscillator. This will be your code number. See if this waveform turns the oscillator on and off. This is on-off keying. Then as a test wire it to your oscillator and make sure it opens the gate. Then make your own digital word generator for your new remote control.

Very good info. I think that gives me a really good direction to go in. I'll give this a shot this weekend.

Thanks
Tomas

Added after 1 hours 31 minutes:

In the process of reverse engineering the circuit. Everything seems pretty straight forward so far. I have one question about a part.

One of the parts looks like an oscillator, but I've never seen one in that package. It's a 4 pin device and designated as FR1 The markings are:

108
0221H07

Picture of the PCB:
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The part in question is the second rectangle package from the right of the PCB edge.

I'm guessing it's a 108Mhz oscillator? I guess the circuit must multiply this by 3x since I know for a fact that the carrier is 318Mhz.

Is there a name for that package?

Anyway, so far, this is looking very straightforward. I think I'll have no problem tackling this project. Very interresting.

Tomas[/url]

Any ideas on that oscillator looking package?

Tomas

You can try looking for a ready made module or if you want to learn there is a post on this site https://www.edaboard.com/viewtopic.p...highlight=ming that has a circuit you can copy.