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Airwave 633 500mW heatsink or not ?


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633-spectrum05.jpg

Here is a spectrum from a 633 airwave transmitter I tested today.

CH2 = 2432 Ghz 25.8dBm (about 400mW) video

the audio carriers are on both sides, and they are 27dB lower.

-2dBm (0.6mW) at 2425 and 2438 MHz

if we zoom in a bit, like on this picture, we see TWO audio carriers,

so it is a stereo transmitter, only the right hand side LR carriers:

Left = 2438.053 MHz

Right = 2438.566 MHz

The harmonic at 4.864Ghz is -18dBm

I have acounted for the loss in my test cable, and use calibrated equip.

Edited by ThomasScherrer
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Thomas,

I was overdriving the input side of the modem with RS-232 levels. Once I added a MAX232 and later switched to a TTL level EM-411 the modem works great.

I've been building and testing Eladio Martinez's RCAP v3 and AltHold over at RCGroups so I've been off the modem project. Next week, I'll move back over and match the modem to my Lawmate TX/RX and give it a go. I'm ordering some Airwave modules so I can get on the same page as you guys and get this thing working on the air!

Mark,

I bet that pot is an audio impedance matching pot. That's what it is on the Lawmate RXs. Mine is worn down to a nub as I matched it to the tiny track 3 but it made a big improvement in telemetry (i.e. MILES away - save my ass when I had a unscheduled auto landing 1.5 miles away on a dry lake bed - we would have never found it had it not been for the APRS data).

Jeff

p.s. still trying to figure how to capture screens on my scope... :blink:

Edited by jparisse
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Mark,

Now that you mention it, I can see Thomas reflected in his screenshot! :rolleyes:

You guys are some low tech high teckkies!!! :D

Given my (ultra simple) modem problem, I'm starting to think I ENJOY banging my head against a wall....

Jeff

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Just a question, please forgive me if it's too stupid, though I know it's complicated, and maybe not too realistic, but I'd just like to ask:

Does somebody have already tried transferring data within the vertical blanking interval of the video signal? Just like videotext / teletext / intercast?

What do you think of this idea? I don't have the programming skills for this (yet), but I would just like to to hear your opinions on this idea, since the video signal seems to be much more reliable and more immune to noise than the audio channel, at least on the airwave modules and comtech.

Cheers,

Hartwig

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Mark,

Now that you mention it, I can see Thomas reflected in his screenshot! :rolleyes:

You guys are some low tech high teckkies!!! :D

Given my (ultra simple) modem problem, I'm starting to think I ENJOY banging my head against a wall....

Jeff

Uses quite a few calories to do that :)

I think that the reason that Thomas had a photo of that one is because of the equipment.. http://www.home.agilent.com/agilent/produc...60%3Aepsg%3Apro

Looking at around US$15,000 for one of those second hand! :blink:

Hartwig,

I think that in the blanking period there would not be enough time, it would get really complex stripping the data out and restoring the blanking period to its original state. There might however be some sort of teletext IC that could be used.

I think for our purposes though, its going to be easier to just do it through audio.

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Here is a spectrum from a 633 airwave transmitter I tested today.

CH2 = 2432 Ghz 25.8dBm (about 400mW) video

the audio carriers are on both sides, and they are 27dB lower.

-2dBm (0.6mW) at 2425 and 2438 MHz

if we zoom in a bit, like on this picture, we see TWO audio carriers,

so it is a stereo transmitter, only the right hand side LR carriers:

Left  = 2438.053 MHz

Right = 2438.566 MHz

The harmonic at 4.864Ghz is -18dBm

I have acounted for the loss in my test cable, and use calibrated equip.

Reply from airwave about the 400mW

Dear Mark,

...

You are right. It is only around 26 dBm. For easier to remember, we used to call it 500 mW (27 dBm) module.

Hope this won't cause you too much trouble. And, we do hope we can build fruitful business relationships together.

...

Edited by Mark Harris
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Hi guys,

I'm quite astonished about what you al know about these things. recently I bought an 612TX and 623RX. It took a while before I had designed the PCB but after al it works. Then I did some expiriments to discover the maximum distance between the TX and RX. I was a bit dissapointed because the range whas not what I suspected from a 500mw TX. Now I think that there is a small kind of regulator on top of it coul'd you guys tell me where it's for? Voltage is 5v and the current I measured is 160mA wich means 0,7W this is not much I think?

post-6-1176228075_thumb.jpg

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look here :

http://www.airwave.com.tw/pdf/2.4GHz%20RF%...ules/Awm610.pdf

if your 612 only draw that little, the power stage is dead,

propably killed by running it too hot, or without antenna,

or too much voltage.

all those tx modules use 4 to 5 times the tx power in watt from its powersupply.

bu the way Mark ??

did they say anything about the audio power ?

can we expect the same range with the audio as with the video ?

Edited by ThomasScherrer
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The pdf file you showed tell's nothing about the small whole in the top of the TX someone who knows where it's for?

It's the factory access hole to the PLL oscillator adjustment. It is best to leave it alone.

Are you sure you didn't get a AWM611 by mistake? That might explain the low current drain. Otherwise, I would agree the PA stage is damaged.

Also, your connections to the module's RF output header are very critical. This is were others have ignored the RF rules and were punished by low performance. It might be helpful to see some clear closeup photos of yours. Have you seen this?: http://www.rc-cam.com/forum/index.php?showtopic=1495

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okay the problem is allready a little bit solved. I used batteries to power the TX 4x1,2v wich means 4,8v. but I didn't taught that once the TX is running the voltage woul'd fall that much, it did when working I only had 3,6v! Now I used a powersupply with 5v when I measure the current now I have 240mA but still not the 450mA like they say in the data sheets. how can is see the differens between an 611TX or 612 cause it is possible they sended me the wrong one.

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Your PCB design will not provide the correct impedance match. When using PCB layout on the antenna interface, the copper traces need to be a optimized microstrip design. I suggest you delete the copper traces and mount the SMA connector directly to the sardine can, per the instructions found in the link that was provided earlier.

Regarding the chance of a AWM611 mix-up, you can check the label on the module. If you don't trust the label, or it is missing, then post a clear photo of the module's PCB (top sardine cover removed). That way we can see the RF PA Amp IC, which is different in the 611 versus 612.

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These days I tested DZL's Modem on different TX/RX setups. I think it's quite interesting what I found:

TX: Airwave 612

RX1: Airwave 623

RX2: Comtech FM2400RTIM8B

VideoSource: KX131PALCASED

AltiOSD

AudioSource1: EM-411 GPS with DZL Modem (Modulation: BPSK)

AudioSource2: EM-411 GPS with TinyTrakSMT (Modulation: FSK)

In all setups every way of Audioen-/decoding works fine as long as there no video fed into the TX. As soon as I activate the AltiOSD, or even just the Camera (with one or more bright objects in the picture) the audio signal on the receiver side freaks out, using the Airwave 623. When the video level has high peaks in its signal, the 623 shows up with crossover artefacts in the audio which look like spikes at the times where the video has its peaks. If the picture is merely dark or medium bright, and no AltiOSD active, the audio is clean.

Much better results on the TX612 with Comtech receiver combination. The Comtech inverts the audio phase, and the DZL Modem works much better. The spikes are still there, but much less than with Airwave modules. Also the DZL seems to be more immune to the spikes when the Audio input is inverted?!

However, the audio output level of the Comtech's is much lower than on the Airwave's. So either the DZL feed into the TX needs at least 2.5Vpp or the Comtech's audio output needs a little amplifier stage to be usable by the DZL.

Quite impressive was the FSK encoding of TinyTrak, because it works very nice on both setups, even with all the spikes. On the receiver side I used a homemade Decoder Modem named "AS232" (see AATIS projects) based on the FX614. The only thing to look for in this setup is the audio level matching between receiver and modem input. The modem hast a wide range, ~100mVpp - 2Vpp.

However, the TinyTrak delivers APRS data format, which can't be used in Navigation systems that require straight NMEA from the GPS. For the TT visualization I used an an application called "TrackOn" which works perfectly well, and accepts selfmade maps, PC screenshots from GoogleEarth, GoogleMaps or whatever. Very nice.

Summary:

Transmitting RS232 from GPS down to Laptop or PDA for use with standard navigation software via DZL's Modem performed best when using the Comtech Receiver.

Transmitting GPS data in APRS format works in either TX/RX combination and seems very robust even in noisy RF-environments, but needs an APRS capable Visualization program.

So far my test results :-) BTW, it's real fun to fly FPV in the dark with goggles, and to see the plane's position displayed in realtime on your laptop's map :-)

Needs sufficient light for the KX-131, of course.

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Good info Hartwig, thanks for posting it. I have one question though, have you made or concidered adjusting the video level pot on the Airwave modules ? This may make a difference to the problem you had.

Terry

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Hi Hartwig,

I'm a little surprised with these results. I've been flying UAVs for about 18 months now using the Airwave 612/623 combination, and have yet to experience crosstalk between the Video and Audio channels.

For telemetry I use MSK modulation, using a 12F PIC based modulator, and a MSK demodulator (CMX 369). The link is CRC-checked, and telemetry dropouts are extremely rare.

I'm wondering what would be different about your setup which would produce the different results.

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-AT-Terry: I didn't modify anything on the modules snce I don't know what exactly is adjusted by these pots. Could you send me a small screenshot to see where exactly this video adjustment pot is located? And what exactly does it adjust?

-AT-anthonyrc: Hi Anthony, great to hear from you :-) It's good news that you have such results an I'm very interested to find out how to get my gear working in the same way. Can you give me more details on how you did it? If you want you can also PM me about schematics or whatever. Did you apply certain filtering? Do you use an OSD on the TX side, or just camera?

Cheers,

Hartwig

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  • 4 weeks later...

I attached a screenshot of the video- and the audio waveform at the output of the receiver. The video input signal of the TX gets just a few letters from the OSD and black from the camera, and no signal is fed into the audio input of the TX.

At the peaks in the video signal you can see spikes with a curve similar to a discharge of a capacitor after it.

If I reduce the level of the video signal at the input of the TX, it doesn't affect the spikes in the audio.

Does anyone have an idea what's happening?

Does anyone experience similar effects?

Any help is very much appreciated!

Cheers,

Hartwig

post-6-1178888204_thumb.jpg

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- Which Rx are you using during the shown scope example?

- Are the audio outputs (with the recommended caps) terminated, or are they allowed to freely float? Does the noise go away with a 10K ohm loads on the R/L audio? How about 1K?

- Any chance the board layout of the Rx is allowing coupling between the video and audio? The pixel data is very fast rise time, so coupling can occur if the layout/wiring is not careful.

- Is the module's power sufficiently decoupled/bypassed? This includes the caps proximity to the module.

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- Which Rx are you using during the shown scope example?

=>The RXs are AWM623.

- Are the audio outputs (with the recommended caps) terminated, or are they allowed to freely float? Does the noise go away with a 10K ohm loads on the R/L audio? How about 1K?

=> The audio output (R is used, L is not connected) is AC coupled (22uF) loaded with 10k. Loading with 1k doesn't help either :-(

- Any chance the board layout of the Rx is allowing coupling between the video and audio? The pixel data is very fast rise time, so coupling can occur if the layout/wiring is not careful.

=> Each signal line is surrounded by ground.

- Is the module's power sufficiently decoupled/bypassed? This includes the caps proximity to the module.

=> The TX has its own linear regulator, and the power line looks perfectly clean on the scope.

I also notice that it doesn't start immediately when I power up the TX. For example when I touch the TX's audio input shortly, it starts. (see screenshot) When I short it to ground the distortion is still there.

When I then power cycle the TX, it's gone.

When I then touch the audio input, again the noise appears.

Power cycling again, and the noise is gone.

And so on...

Any idea? :blink:

post-6-1178962001_thumb.jpg

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Most definitely! You can listen to it when attaching the video goggles or my hifi system. Exactly the same behaviour.

Also when I move my hands around near the TX or the RX, the noise varies a lot. Very similar to what some of you might have experienced with old TVs...

You can listen to it in the mp3 file attached.

noise.zip

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If you have more than one Tx and Rx module, does the problem happen on them too? For sure, it would be helpful if you narrowed your problem down to the Tx or Rx. It sort of sounds like the Tx module is defective, but it could be anything.

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