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Mr.RC-Cam and Vrflyer, Thanks for the help.

I went to an electronics shop and tested my transmitter on one of the recievers that they sell. The performance was identical to the reciever I made which meant that the reciever I made is fine but the problem is in the transmitter. I've concluded that the problem must be a fault in the transmitter's Airwave module.

I can't get the transmitter's range to improve so I will use the reciever but I'll buy a 500mW transmitter from: http://www.rangevideo.com/500mw.html

I also moved the connector but there was no performance increase:

cimg32981cr2.jpg

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Matt,

The problem that you are having with bad reception sounds very familiar..

Check that the RSSI pin on the receiver isn't shorted to ground. Due to the fine-pitch of these connectors its quite common. When this happens the receiver performs much as you you explain.

I've found these transmitters and receivers to work very well, infact I designed some PCBs for them and have been selling kits for a few weeks now. (www.aeropix.ch/store).

For the SMA to module connection (both for Tx and Rx), I wouldn't worry about too much. The track length is so short that it doesn't have much of an impact on the transmitted/received signal. Of course if you were running it a few inches around a board, I would start to think about 50ohm traces.

Hope this helps

-- Anthony

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I have one of those sets too (ordered from Felsweb a couple of years ago for a much higher price though), and I too have had sensitivity problems with the receiver. I ended up using another one I had which would already show a noticeable difference at a few hundred meters.

Anyway I nearly don't use it anymore because of repeated R/C interference issues. Anyway, I'd never need 500mW... other than for that 4km test on skydivers :)

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Guys,

This might help you. See this page for info on what the PCB trace should be for 50 ohms. The file must be saved and renamed to *.pdf before opening since I can't upload a PDF.

Best, T.I.

SMA_Edge_Johnson__Mouser__.txt

Edited by Temporary Insanity

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Thats a useful resource. Another is this site: http://www.emclab.umr.edu/pcbtlc/microstrip.html

Using this site, for FR4, double-sided with ground plane, track thickness of 35u, permittivity of 4.7, PCB thickness of 1.6mm, and target impedence of 50 ohms...

the track width should be 68.21mils, or 1.73mm.

Practically though, if the SMA is mounted very close to the module, with a track length of a few mm, the width doesn't really matter.

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Matt,

The problem that you are having with bad reception sounds very familiar..

Check that the RSSI pin on the receiver isn't shorted to ground. Due to the fine-pitch of these connectors its quite common. When this happens the receiver performs much as you you explain.

I've found these transmitters and receivers to work very well, infact I designed some PCBs for them and have been selling kits for a few weeks now. (www.aeropix.ch/store).

For the SMA to module connection (both for Tx and Rx), I wouldn't worry about too much. The track length is so short that it doesn't have much of an impact on the transmitted/received signal. Of course if you were running it a few inches around a board, I would start to think about 50ohm traces.

Hope this helps

-- Anthony

Thanks for the replies,

I haven't had much free time lately to work on the problem.

The problem is the transmitter. The reciever is fine and I've used other recievers also.

I've worked out that the circuit is fine.

Also in my last post you can see how close the SMA is to the module pin: ~2mm so that shouldn't be a problem.

The only possibility left is:

The module could be faulty???

My other option is to buy a new transmitter. I need around 500m of clear video. If I do buy a new transmitter what power would you recommend for this kind of range? I'm very tempted to buy this 500mW transmitter: http://www.rangevideo.com/500mw.html But do I really need all of that power?

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I'm reasonably sure that those transmitters do not transmit on the same frequencies as your Airwave receiver is tuned to*. To my knowledge, only Airwave transmitters are truly compatible.

*The exception is channel #3 which is the same f for both Airwave and Lawmate (that sold be rangevideo and many others).

Airwave:

2.414

2.432

2.450

2.468

Lawmate:

2.410

2.430

2.450

2.470

Best,

T.I.

Edited by Temporary Insanity

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I just came across an ongoing thread of yours on RCgroups where you discussed your Airwave board troubles. Over at that site you included a photo that was not posted here. The photo shows that you have installed the tantalum caps backwards. This will cause instability with the regulators and may explain some of your bad luck. These caps can also explode if they are reversed. Do not re-use them; remove and replace with new parts.

The photo below shows the areas that I can see that are backwards.

post-5-1161532254_thumb.jpg

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Yes, you are right. When I first tested and connected up the reciever to power, the capacitors all exploded! I replaced them and installed them the right way around.

The Range Video TX arrived but I can't test it because its raining.

There are photos of my downlink setup here: http://www.rcgroups.com/forums/showthread....=10#post6332767

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