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Thomas,

finally I desided to hook up the Tiny-Mic I got from you quite some time ago.

I supply it with +5V, GND and I connect the white cable directly to one of Airwave's audio in pins.

The test revealed.... nothing - just static. Adjusted carefully the small pot with a juweller's screwdriver does not make a difference either. Tested and double tested all (3) connections for continuity - OK.

This 633 module has been tested earlier with sound without problems.

Do you have anything else to suggest?

Regards,

Dimitris

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Does it work if you connect the Tiny-Mic directly to the TV/DVR/sound system? {Omit the wireless Tx/Rx}. If it is still dead with the direct connection then please contact me privately to arrange getting you fixed up.

BTW, the mic will not tolerate reversed power, or shorting the audio out (to pwr or gnd). So be very careful to not let that happen during the tests.

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Ok tried it straight on the TV - it works.

I am trying it again through the Tx/Rx and it works too!

I don't know what happened earlier - maybe I did something stupid, like didn't turn up the volume on TV...

Thank you for the help!

Dimitris

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That is great to hear. If you have any more problems then just let me know.

BTW, it's not a problem to assist on the forum, but for fast response to technical problems with dpcav.com products you can also use the formal contact method: Contact dpcav

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Well.. I got excited too soon...

The mic IS working because when connected directly I could hear my voice through the TV's speakers. But when I tested the mic through the Tx/Rx I just tapped with my finger and blew with my mouth on it. These were picked up by it but unfortunately not all the other regular sounds like my voice, music, etc.

Message sent via support form too!

Dimitris

Edited by Dimitris76

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Blowing on a mic is not recommended. Moisture from your breath can cause a degradation in performance if the mic is not moisture resistant. Better to just always tap it lightly with a finger.

Edited by W3FJW-Ron

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The mic IS working because when connected directly I could hear my voice through the TV's speakers.

If the Mic works fine when directly connected to the TV, but is not satisfactory when connected through the Airwave A/V modules, then the problem is most likely in the Airwave Tx or Rx area. That is because the Airwave modules essentially emulate a direct audio connection. In other words, because the direct TV connection works, the wireless Airwave connection should sound the same, or nearly so.

Message sent via support form too!

Thanks, I was given your tech support message. A response was sent with details on getting a replacement Tiny-Mic to try (if you would like to do that).

I blew from a 15 cm distance a couple of times... did I break it? Are they so sensitive?

Not a problem. I do worse things to the Tiny-Mics I use and we're still friends. :)

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If the Mic works fine when directly connected to the TV, but is not satisfactory when connected through the Airwave A/V modules, then the problem is most likely in the Airwave Tx or Rx area. That is because the Airwave modules essentially emulate a direct audio connection. In other words, because the direct TV connection works, the wireless Airwave connection should sound the same, or nearly so.

Since we concluded that the Tiny-Mic is functioning satisfactory, I will continue here in public my sound troubleshooting:

I did one more test during which I talked a little louder than usually at ca. 15cm from the mic. My voice was picked up only when the mic's pot was turned all the way clockwise and then only very faint. Another think that I should mention is that I have too much background noise on both channels of my audio. I had this noise from the start but didn't bother because I didn't have a mic and I was wathcing the recorded videos muted. Now when I turn up the TV's volume in order to hear the mic the noise get's louder too and is very annoying.

In contrast on the video I have crystal clear picture - no noise at all.

Could it be due to the 40 cm long ribbon cable I am using between the camera/mic/power supply and Tx?

P1010444.jpg

P1010445.jpg

P1010443.jpg

Why don't I have noise on the video too then?

Dimitris

Edited by Dimitris76

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Audio noise on many video RF modules is usually dependent on the video content. So, if you connect only a camera (no OSD or other accessory on the video signal), and leave the lens cap on the camera so that it sees no image (black video), does the audio noise become less offensive?

What supply voltage are you using to operate the AWM633TX? It's a 3.3V part, so don't use 5V or it will be damaged.

Which Airwave Receiver module are you using? Did you follow the data sheet precisely? For example, are the audio coupling caps the correct value and installed with correct polarity?

Lastly, if you compare the wireless audio levels to the direct hard-wired levels, how different is the loudness?

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Audio noise on many video RF modules is usually dependent on the video content. So, if you connect only a camera (no OSD or other accessory on the video signal), and leave the lens cap on the camera so that it sees no image (black video), does the audio noise become less offensive?

What supply voltage are you using to operate the AWM633TX? It's a 3.3V part, so don't use 5V or it will be damaged.

Which Airwave Receiver module are you using? Did you follow the data sheet precisely? For example, are the audio coupling caps the correct value and installed with correct polarity?

Lastly, if you compare the wireless audio levels to the direct hard-wired levels, how different is the loudness?

The noise is exactly the same with or without the lens cap. I do use an OSD that produces bolt white fonts all over the screen, hooked up the control channel, turned off the OSD and BINGO! - the noise immediately disappeared and I can hear my voice clearly now!

So it's the OSD. What are we doing now???

Dimitris

Edited by Dimitris76

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I don't have any specific solutions for reducing the Bob-4 induced audio noise. If it is a custom project then you can experiment with character placement and character attributes (color/size/etc). The noise is usually related to the text's white levels, especially when adjacent to darker luminance. So maybe use mostly gray color text (instead of white), disable (or minimize) any shadow/backgrounds, reduce the amount of text, and perhaps consider the variable OSD's transparency feature (a bit of circuitry is needed, per the OSD data sheet).

But really, It is hard to say if a satisfactory solution can be realized. But, now that you know where the nasty noise is coming from, you can at least experiment to to see if you can find a satisfactory solution.

If you are like most folks that have a mic on the model, the main interest is hearing the motor. That is a useful bit of feedback that helps during piloting. So, if that is the goal, maybe the noisy setup will work out as-is. Or, as a last resort, don't fly with the OSD turned on all the time; Enjoy the scenery instead. :)

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I don't have any specific solutions for reducing the Bob-4 induced audio noise. If it is a custom project then you can experiment with character placement and character attributes (color/size/etc). The noise is usually related to the text's whites, especially when adjacent to darker luminance. So maybe use mostly gray color text (instead of white), disable (or minimize) any shadow/backgrounds, and perhaps consider the variable OSD's transparency feature (a messy bit of circuitry is needed, per the OSD data sheet).

But really, It is hard to say if a satisfactory solution can be realized. But, now that you know where the nasty noise is coming from, you can at least experiment to to see if you can find a satisfactory solution.

If you are like most folks that have a mic on the model, the main interest is hearing the motor. That is a useful bit of feedback that helps during piloting. So, if that is the goal, maybe the noisy setup will work out as-is. Or, as a last resort, don't fly with the OSD turned on all the time; Enjoy the scenery instead. :)

Thomas,

I remember reading some test done by some german folks about the 633 modules. They said that the video signal levels measured were out of whack - tested 3-4 different 633 modules - and none of them were the same. Sander also said something about Airwave modified these modules to work better - if I recall he said something about the imput inpedance being closer to 50 ohm than 75. Can that cause these problems?

I suggested Dimitris to try some other modules the 630 and 631 apperently does not suffer from the same defect...

Zoltan.

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Good point, but in this situation the lower than expected video input impedance of the AWM633 is not the reason for the noisy audio. Instead, the OSD issue is related to RF module's video bandwidth and frequency response. The text/graphics from some OSD's often pushes the module's performance.

Other RF modules will have different behavior, so trying other types will result in better or worse outcomes. Plus, keep in mind that the OSD issue can occur from the wireless Tx or the Rx. All in all, swapping modules can be a whack-a-mole sort of troubleshooting experience. But worth a try if changes to the OSD text/graphics does not help much. :)

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Ok guys!

I sat down, looked at the whole setup and gave it a little more thought.

My camera/OSD/mic/power/Tx harness is built this way, so that the audio is nowhere close to the video (on the same PCB or adjacent cables) - not until they hit the 633 module. So I could safely assume that it's not some kind of weird RF interferance between the video-audio channels, but simply the "video signal is way too high" and is introducing distortions on the audio. Zoltan said that's exactly the opposite from what is usually happening - usually the high audio levels are ruining the video quality.

Anyway, I remembered reading long ago here on this forum some threads about video signal level adjustment, so after Zoltan's approval I soldered a 220ohm micro pot directly on the 633, between video in and Gnd. Then with the OSD on, I slowly turned the pot from around the middle towards lower resistance levels and at a certain point: BINGO second time (and hopefully for good)! The audio noise disappered without noticable loss in video's luminance and I can hear my voice clearly. I don't even have to turn the mic's pot all the way up!

P1010500.jpg

P1010499.jpg

P1010501.jpg

For the record, I measured the pot's resistance after the adjustment and it's 15ohm but I don't know how accurate that is because I didn't bother to unsolder it from the Tx module.

EDIT: I looked at the pot again and it's wiper is ca. 45 degrees from the one end. This 220ohm pot has a total travel of 270 degrees between the two end points, so at 1/6th of travel it's resistance is calculated around 37ohms.

Thank you for all the help!

Dimitris

:)

Edited by Dimitris76

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Glad to hear you found a easy solution. Be sure to check everything you plan to use with the wireless video system to see that they all still work as expected. For example, some DVR's, video displays/glasses, and things like Oracle diversity, do not always work well with non-standard video levels. Better yet, measure the video level at the output of the Rx. You never know, with the added pot, it may now be exactly to spec.

Zoltan said that's exactly the opposite from what is usually happening - usually the high audio levels are ruining the video quality.

On some systems high audio levels will indeed mess up the video. But, video content will sometimes mess up the audio. These little odd-ball gotcha's make things interesting for us. :)

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It tested ok on my livingroom's flat TV. I'll test with my Icuiti goggles and the EasyCAP that I am using for recording just to make sure.

Dimitris

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Better yet, measure the video level at the output of the Rx.

Thomas,

on the ground am using that Pyle PLV2 4-way video splitter that I got from you. Can I use the pots on it to adjust the video levels individualy for a playback/recording device? That's the same thing right?

Dimitris

Edited by Dimitris76

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Yes, you can use the video buffer to correct the levels and that should fix you up just fine. However, if the video level from the wireless Rx is too low (going into the Pyle buffer) then the vertical sync quality may be affected (especially with the OSD in use). So hopefully your native video level is not too out of whack.

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What supply voltage are you using to operate the AWM633TX? It's a 3.3V part, so don't use 5V or it will be damaged.

By the way, I am now using two 1N4007 diodes in series in order to drop the voltage (you can not see them - they are hidden under the blue shrink wrap).

According to this: http://www.tnw.utwente.nl/onderwijs_overig...nten/1n4007.pdf

each of these diodes has a forward voltage drop of around 0.8 volts at this current. So 5 - 1.6= 3.4volts.

I had a proper LM3940 regulator on a small PCB that I replaced with the diodes for simplicity.

Is this a proper way of doing it?

Dimitris

Edited by Dimitris76

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Diode V-drop solutions are fine for things that you don't care about. In this case I would recommend using a 3.3VDC LDO Vreg IC (like the LM3940) instead of diodes. That way you have deliberate regulation and improved noise immunity from the shared 5V power supply.

The Tx module is going to run hot, especially wrapped up in heat shrink. Might be a good idea to add a finned heat sink to its metal tin case. Don't forget to allow air flow too. My rule of thumb is that if it is too hot for me to comfortably hold on a warm day, then it will be too hot for the electronics.

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Yeah, it's getting hot on the bench - but not like you can't touch it hot!

On the EasyGlider it gets plenty of air flow as it is mounted with a little tape on top of the fuselage.

I am worried about that thing you said though - "Diode V-drop solutions are fine for things that you don't care about"

I do care about my Tx and since I am flying FPV through it, I care about loosing my model too!

I don't have any noise problems right now with the diodes - didn't have earlier with the regulator either. Is the diode solution a potential reliabilty issue? I mean is there any chance that I might see white smoke all of a sudden?

According to the data sheet these 1N400x series diodes are rated for 1A continuously.

Dimitris

Edited by Dimitris76

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It's not that the diodes will fail. Basically, the diodes are a cheap and dirty solution when you don't care about the quality of the voltage. I have used that trick many times, but in this particular application I would use a LDO Vreg IC that is rated for the task. The RF module needs clean power that is 3.3V, so you don't want to skimp. Just my personal opinion.

I'd also install a 22uH choke on the input to the VReg, and perhaps another on the input to the RF module, and include low ESR .1uF ceramic caps on the Vreg's and RF module's power. Again, these are things I would do on mine, which may not be the same thing someone else would do.

Keep in mind that when you use these modules, you become the application engineer for the device. How you implement them is up to your requirements. Like most data sheets, Airwave's documents provide the absolute minimum details that are needed to use the part in a very basic way (the rest is up to the designer).

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