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vonkal

Help on audio

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I have a couple of sets of the Airwave 2.4Ghz units that I got from Active-Robots. Two 612 500mw Tx’s, and two 620 Rx’s.

I can’t get the audio working. I have connected it to both a DVD player and have built the circuit described at http://www.delemarre.ciscon.nl. I have the 33u/10v capacitors connected properly on the receiver.

All I get is static with every configuration I try. Can someone tell me where my problem might be? Also, can anyone advise me on how I might be able to test the Tx portion of the audio? (All I have is a volt/ohm meter though)

Thanks!

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All I get is static with every configuration I try.

Try these experiments:

1. Remove mic and preamp and gnd the mic input with a 1K resistor. Turn up the volume on the Rx. It should be very quiet. What do you hear?

2. Next, turn off the Video Tx, but keep the Rx turned on. The audio should no longer be quiet. Instead, it should be white noise. What do you hear?

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Test 1) Remove pre-amp and connect Tx pin 4 to 1k resistor then ground. White noise!

Test 2) Only Rx on. White noise!

Hope this points you to something. I have also rolled both Tx and Rx as I have two sets and built the boards so they could be plugged in.

Thanks,

vonkal

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Well, you've just demonstrated that the audio subcarrier is missing. All is not lost (yet). Connect your speaker system to the other Rx audio output (there's a left and right audio output) and repeat the tests. What do you find?

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Thanks for the help!

I have tried both left and right already. I have three RCA’s connected to the receiver. Video, plus left and right audio. The audio RCA’s are wired to the board and connected to pins 4 and 5 of the Rx.

As I mentioned before, I have two Rx’s and two Tx’s. I have built one board for the Tx and one for the Rx in accordance with the info on http://www.delemarre.ciscon.nl. I can switch the units themselves and I get the same results. I have also installed dip switches on both boards to select each of the four channels available, and no audio on any of them.

I have also tried both the pre-amp with the mic and going directly into pin 4 on the Tx with an RCA coming out of a DVD player. The picture is fine with all these combinations but only white noise for the audio.

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Well, then my best conclusion is that your mono audio Tx is not compatible with the stereo audio Rx. The audio subcarriers are probably different. I do not have any other words of wisdom other than that. I hope I am wrong and you find an easy cure to the problem.

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If I remember correctly there is a trimmer inside the TX to adjust audio subcarrier frequency. It's the one that is on RF (antenna) side. Try adjusting that one while listening to the received sound.

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Kilrah

That did it!! The audio is working on both of my Tx’s now, but only on one channel. I will try to fine tune them to see if I can get both working, even though I only need one.

I had posted a question a few weeks ago, asking if anyone knew what this pot was used for, but no one responded and I didn’t want to adjust them until I knew what they were used for.

Anyway, thanks for your help.

von

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Hehe, you're welcome :)

You won't get the second channel as the TX only sends one (there's only one input). No use to try ;)

Edited by Kilrah

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Thanks Kilrah,

I would have kept trying to get that second chanel. I never did understand why there is only one audio source on the Tx, and two, left and right, on the Rx. I assumed it was just some simulated stereo that put exactly the same audio on both left and right chanel.

I'm sure I will have more questions as I go, but thanks to both you and Mr. RC-Cam for all your help.

von

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never did understand why there is only one audio source on the Tx, and two, left and right, on the Rx.

The Active-Robots site sells a matching Tx with stereo audio (Airwave 609).

I have a feeling that if you bought the 609 Tx you would have to restore the Rx pot tweaks you performed back to their original position. My guess is that the mfg adjusts the Rx to work with the stereo Tx's audio subcarriers.

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