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mike_s

Futaba T6xA receiver / p.c. interface

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After failing to get the Q&D "antenna interface" [url=http://www.rc-cam.com/forum/index.php?showtopic=2718] working, I'm starting to try to design /research the basics of a 72.990 receiver front end /interface for my Futaba T6xAs to connect to the soundcard (mic or linein) inputs for use with a software oscillocope

So far, I've found information on calculating the values for a resonant circuit, and have wound a coil and put a trim cap on a breadboard.

For the coil I wound 12 turns of #26, which should be ~ 1uh according to this calculator

I have a 2-30 pf trimcap.

So I guess the next thing would be ~70mhz capable amplifier, to bring the signal up to ~1v for the soundcard?

If so, I can probably find a circuit for it using an LM386, 2904 or 741, all of which I have, but if someone already has such a circuit, I'd love to see it.

Assuming I'm on the right track, I think I'd need a cap (preferably for ease of construction) or a transformer to connect the coil/trim cap tank-circuit output to the amplifier input ? ... Or can I connect the "tank" directly to the amplifier input? ...

Ok, I have no idea how to connect the tank to the amp, info /answers greatly appreciated.

Also, a simple antenna would probably help , ~3 feet of #26 wire or some such ? What would I need to connect that to the "tank circuit"?

Ok, with those two components connected,, a first step would be to have an LED blink in response to the received signal. What resistance / other components would I need to connect the amp output to the LED? (I know I need at least a current limiting resistor for the LED, but I don't know what is required to "generally" connect (if there is such a thing) to the output of the amp.

Assuming that all works, at ~72 mHZ, the LED probably won't blink but will just stay on I'd guess . A "side project" would be frequency convert the amp output down to something visible, but that's a second priority. (Feel free to post info though if you're interested

Now to the soundcard. I think I have to limit the voltage (current ?) output from the amp to soundcard. Is a two resistor voltage divider => ~1volt output sufficient?

If I can get all this working, the next step will be start demodulating / decoding the signals. A whole 'nother project in itself.

thx in advance for any info / tips.

Mike

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So far, I've found information on calculating the values for a resonant circuit, and have wound a coil and put a trim cap on a breadboard.

For the coil I wound 12 turns of #26, which should be ~ 1uh according to this calculator

I have a 2-30 pf trimcap.

So I guess the next thing would be ~70mhz capable amplifier, to bring the signal up to ~1v for the soundcard?

Will not work. Don't waste your time unless you like learning from mistakes.....

Assuming that all works, at ~72 mHZ, the LED probably won't blink but will just stay on I'd guess . A "side project" would be frequency convert the amp output down to something visible, but that's a second priority. (Feel free to post info though if you're interested

You would need a count down or divide by counter that only has an output of 2, maybe 4 times per second.

Now to the soundcard. I think I have to limit the voltage (current ?) output from the amp to soundcard. Is a two resistor voltage divider => ~1volt output sufficient?

At DC, or audio frequencies, yes.

next step will be start demodulating

A diode with an RF bypass cap will do this.

Edited by W3FJW-Ron

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