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Airwave 633 500mW heatsink or not ?


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I too had audio -> video problem,

but only is audio is too strong in level, and/or too hi frequency,

simply fix that and be happy, the square wave from the DZL encoder must be filtered right, and adjusted into right level, what ever that might be, depending on TX and RX side,

the DZl decoder part will accept a wide input range.

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Thomas wrote: "the square wave from the DZL encoder must be filtered right"...

This part has me a little :blink: ... What is the goal of the filter cap? Is it to reduce low frequency noise (high-pass) or to shape the square wave to a triangle (integrator)?

My setup had the best results without any filter cap at all. I reason that whatever circuitry on the receiving end of my Video Transmitter is shaping the square wave to resemble the scope traces I uploaded to the DZL thread. All I had to do on the DZL TX side was adjust my output level to get it to work (100k pot to ground, wiper out).

I made pads/holes on the Beta DZL kits so folks could experiment with a filter cap and I included a .1uf cap to get them started.

Jeff

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-AT-Mr.RC-CAM: I tested with two 623s and a Comtech Receiver and got the noise on all of them, however it's better on the Comtech receiver.

But I can reproduce it also with the Rangevideo TX 1000mW.

I noticed that lots the lawmate sounds pretty popular and as I understand that you and Thomas are using them also. And you seem to be fine with them.

Maybe it's related to temperature, that some part in the TX gets too hot and causes a drift where the receiver's PLL is overextended and can't handle it anymore?!

But it's strange that on the Airwave receivers the noise just starts when a signal is fed into the audio input of the TX, and when I powercycle the TX the noise is gone again, despite the fact that the TX is still hot. And also the audio is nicely quite and fine when no video is fed into the TX.

So I can reproduce the same behaviour with all of the TXs and RXs which I have.

But since I don't believe too much in VooDoo :ph34r: , I will investigate more B)

Did anyone of you happen to measure the video levels or check the TXs frequency stability over temperature? Unfortunately I don't have access to the required instruments.

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But I can reproduce it also with the Rangevideo TX 1000mW. I noticed that lots the lawmate sounds pretty popular and as I understand that you and Thomas are using them also.

I haven't used my Lawmate gear for awhile. Instead, I've moved on to some custom built Airwave systems.

FWIW, I've always noticed that a wireless video system's audio noise increases when the video signal is applied. This includes both Lawmate and Airwave, and even my old X10 hacked system. So I believe there may be some A/V interaction, regardless of brand.

But your problem seemed very unusual. With your latest post, I had a sinking feeling that your OSD was bringing out the worse in the situation. So, I performed an experiment. I believe I can confirm some of what you see.

I used an Airwave AWM633Tx and a AWM625Rx, as well as a AWM634Rx. I don't have time to try this on a Lawmate (but I expect it to be very similar).

Here is a summary:

1. No video (video in terminated with 75 ohms):

Audio very stable, minimal noise.

2. Standard color bar video:

Audio has increased hiss noise (the normal stuff).

3. Video with OSD that uses simple microprocessor derived video (like your OSD):

Noticeable audio clicks. Oscope observes fast rise time spikes synchronized to the vertical frame rate. Mine are not like your sawtooth noise results and what I see is not that bad at all. But the concept is similar to what you have reported.

4. Video with OSD that uses the STV5730A video controller:

Minor increase in audio noise, but not objectionable. Oscope confirms a slight increase in noise on top of video signal. Looks decent though and unlikely to cause any problems with a audio modem.

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Hi Mr.RC-CAM, thanks a lot for your efforts and results! Good to hear that at least something is similar to what I have on my systems, so there might be hope :-)

I think you're right regarding the OSD. I did a few tests yesterday without the OSD and got better results. However, I will investigate more into this direction.

Maybe reducing the video levels and low-pass-filtering the OSD's video signal might help, even though I get noise as well with the video coming from the camera.

Do you maybe have some screenshots of the video signals displayed on an oscilloscope? I'd like to compare my systems to the systems you and the others on this forum are using. For me these measurements are really useful in troubleshooting and improving the quality.

The test patterns I use are mainly Multiburst, white spike, white plane, Ramp and Color bars at 100% level.

I'm very curious on Thomas' OSD. I think that the shade arund the letters will help to reduce the bandwidth also, thus reducing noise in the audio as well.

Thanks a lot for any kind of help!! :rolleyes:

Cheers,

Hartwig

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Maybe reducing the video levels and low-pass-filtering the OSD's video signal might help, even though I get noise as well with the video coming from the camera.

From what I saw in the experiment, you should be able to see some improvement in the audio noise if you tame the OSD pixel levels and their slew rate. All you need is enough improvement to obtain reliable audio modem operation. But even if your reduced video levels and filtering don't help your audio issues, they may offer other improvements that are beneficial in unseen ways.

FWIW, when I developed my microprocessor based OSD, I found that the white saturated pixels that the OSD engine produced were troublemakers. The fast rise times, accompanied by full white levels, produced additional EMI/RFI that would affect the R/C signal. Some of the noise was directly from the OSD and some of it was from the way some video Tx's behaved with the fast pixel generator. It was not a board layout issue or other easy to solve problem. My situation was compounded by the fact that the OSD had direct connections to the R/C system (voltage monitoring and other things), so both conducted and radiated RFI paths were involved. The problem was resolved, but the results involved OSD text that was more transparent than the usual over-driven saturated white levels like I see on other similar OSD design attempts. By the way, my early proto's had a shaded background behind the text, and the problem was worse in some installations.

The reality is that what helps one fellow might not have any benefit to another. Like everything else in our oddball R/C video application, YMMV. So just test/experiment/redesign until it works for you. :)

Do you maybe have some screenshots of the video signals displayed on an oscilloscope?

Sorry, but I don't have any oscope screenshots to post.

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  • 4 weeks later...

I have a couple (or more) questions someone may be able to answer about Airwave modules.

With the Airwave AWM633TX transmitter, has anyone tried a MUCH simpler antenna design. Most of the pictures I have seen here show mounting connectors and duckie antenna's. Is there cheaper and easier ways to do the transmit antenna? What about range reduction, I fly with other flyer's that are using Spektrum transmitters, is there a good way to pad the power down when its not needed or its causing problems.

I noticed someone posting that they used batteries to power the transmitter which started at about 4.8vdc or more. The spec sheet I have for the 633 indicates a supply voltage of 3.3vdc @ 2%, even 3.7vdc sounds a little HOT to me. 3.366vdc should be the high limit, is it not 2% critical?

Maybe even another question about the Airwave AWM635RX. Price, Quality, Availability, etc. The AWM635RX is NOT on the AIRWAVE site that I have found.

Edited by ddwaner
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Yes, that's the Idea... (Thanks for the picture)

Now change the solid copper to 50 ohm small coax, ground the braid and cut the outside shield and ground braid off out from the transmitter, OH about 10 m N m's and leave the insulated center and extend it to about, OH make the antenna length say 1/2 wavelength (may get out better than 1/4) resonant at about 2.44ghz, or SO and just hang it out the bottom of the airplane. That may be less to break off and still do OK for range. Would that work and how many m N m's would you suggest past the insulation/braid cut off for the length of center (at 1/2 wavelength)?

Any suggestions about how important the 2% tol is to the transmitter's 3.3vdc spec?

I read the link you posted before I posted in this thread, which is why I was wandering if anyone had SEEN or USED the 635 yet, OF COURSE... and its price? I understand that they are "All Gone". I kind'a like to DABBLE in building electronic devices, I may be interested in one.

I am also interested in sending 6 or 7 aircraft values (conditions) from the aircraft to the ground over one of the audio channels. Cost is NO object, !!! as long as it costs $25 or less.

Edited by ddwaner
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The 3cm piece of wire on the picture above is what I have on my 10mW TXs and use to more than 1km. Of course you can do better, but is it worth it?

The 3.3V is to be 3.3V. You have to use a voltage regulator between your battery and the TX.

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The 3cm piece of wire on the picture above is what I have on my 10mW TXs and use to more than 1km. Of course you can do better, but is it worth it?

Don't tell Thomas Scherrer, he will be throwing away his test gear in dismay ! :P

Terry

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I learned a long time ago to keep the MAGIC SMOKE inside at all times. The Idea I have has less to do with being better and more to being easier on the circuit board when the equipment is being bounced on takeoff and landing.

I still have not found a price for the 635 and if you have the Aussie version, is it on my transmitter US channels. As I read it, the Australia channels are different freqencys than other country's.

I don't expect my 10mw transmitter signal would look like much at 3000 feet, it wasn't bad at 1500 though. The signal was just dropping off because of range at 1500, what can you expect from a BABY MONITOR! HMMMM

Edited by ddwaner
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Every manufacturer uses its own channels. Sometimes by chance mixing equipment works (check the frequencies, but then it's still not given that the audio will work etc, or video level might be screwed,...)

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In a earlier post in this thread, there was a pic attachment of what looks to be a 633 with the regulator on the back. The regulator looks to be a L7805CV, How's that do on the 633 use after use?

If the reg IS a L7805CV, it may be rated for 5vdc @ 500ma. That doesn't seem to be what a 633 is designed for from what I can tell.

post-6-1181806024_thumb.jpg

Edited by ddwaner
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On that pic it's a 631, which is rated at 5V / 140-180mA.

The 633 however needs 3.3V / 450-600mA. I wouldn't use a linear reg to power one personally. Out of a 2s lipo that would be a 2.5W power dissipation, LOTS of heat.

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Well....................

I couldn't find any 3.3volt switching reg where I shop so I had to make due. As a matter of fact, I couldn't find any 3.3 volt linear regs at the town electronic store that wouldn't take 2 weeks to special order, SO I BUILT A 3.3 VOLT REG CIRCUIT MYSELF.

LM317 and resisters, I got good 3.3333 volt calc values that ended up REAL CLOSE (It stays under 3.366 EASY). My regulator is rated for 1.5 amps and it doesn't get any hotter than the transmitter module to the touch (Corse I used a heat sink). My rig came out a little bigger but it runs from a 2 cell lipo just fine (No switching reg ripple problems, (I didnt use one!)). I will be range testing soon...

I may have to trim a little more shrink wrap from the heat sink side but so far its been ok and the camera plane I am building is open air vented.

post-6-1182070392_thumb.jpg

Edited by ddwaner
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Needed a new message for the back side. I added a 8 position dip switch for selecting the 4 channels, video termination, Left/right audio off(2sw) and Left/Right Combine. Most of the parts came from the Shack...

I found that the picture is fine with the receiver I have but the sound on both channels is noise. I may end up with a 635 down the road.

post-6-1182070519_thumb.jpg

Edited by ddwaner
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Here is a question...

The development diagram for the 633 does NOT show a termination resistor on the video input if the 633. Should one be added and if SO what values could be used other than the normal video termination value (something that might be in my pack of 100 resistors from the Shack)?

Edited by ddwaner
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