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Mounting an Airwave module on the back of a GP patch


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#1 LesNewell

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Posted 24 February 2010 - 12:37 AM

Hi,

I am thinking of building a diversity system based on Airwave 625 RX modules and GP patch antennas. To keep RF losses to a minimum I would like to mount each module directly on the back of the antenna. The plan is to glue the module to the back of the antenna and directly wire it without any connectors. Instead of an SMA connector there will simply be a very short wire going from the module PCB, through the hole where the SMA connector should be, to the driven element. The grounds will also be connected directly to the reflector. Looking at the drawings of the Airwave modules there appears to be about a 5mm gap between the pcb and the edge of the module.

Would this adversely affect performance? If so, would it be better to solder a SMA connector directly to the PCB pins? I would rather not do this because I want to keep the units as low profile as possible. I am afraid I don't know a lot about microwave design. My specialty is more audio and digital electronics.

For the video/audio switching my current plan is to hack a cheap automatic video switch. I'll rip out the existing controller and add my own to monitor the RSSI signals and choose the best signal. I could design my own video switch but I couldn't buy the bits for the price of a pre-built switch.

Just as a random thought - how practical would it be to mix the video/audio signals instead of switching? If you have snow on two channels and you mix them together, to a certain extent the random noise should cancel out. Obviously if you have a good signal on one channel and pure snow on another you will get a degraded picture so ideally you would need several channels then mix the best ones. I suppose you could get problems with the video due to delays if the antennas are fairly widely separated.

#2 pseddon

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Posted 24 February 2010 - 02:22 AM

Hi,

I am thinking of building a diversity system based on Airwave 625 RX modules and GP patch antennas. To keep RF losses to a minimum I would like to mount each module directly on the back of the antenna. The plan is to glue the module to the back of the antenna and directly wire it without any connectors. Instead of an SMA connector there will simply be a very short wire going from the module PCB, through the hole where the SMA connector should be, to the driven element. The grounds will also be connected directly to the reflector. Looking at the drawings of the Airwave modules there appears to be about a 5mm gap between the pcb and the edge of the module.

Would this adversely affect performance? If so, would it be better to solder a SMA connector directly to the PCB pins? I would rather not do this because I want to keep the units as low profile as possible. I am afraid I don't know a lot about microwave design. My specialty is more audio and digital electronics.

For the video/audio switching my current plan is to hack a cheap automatic video switch. I'll rip out the existing controller and add my own to monitor the RSSI signals and choose the best signal. I could design my own video switch but I couldn't buy the bits for the price of a pre-built switch.

Just as a random thought - how practical would it be to mix the video/audio signals instead of switching? If you have snow on two channels and you mix them together, to a certain extent the random noise should cancel out. Obviously if you have a good signal on one channel and pure snow on another you will get a degraded picture so ideally you would need several channels then mix the best ones. I suppose you could get problems with the video due to delays if the antennas are fairly widely separated.


I soldered an SMA connector to the airwave (there is a thread about doing this on RC-Cam), built the goof patch again from Rc-Cam which also uses an SMA connector and then used a straight (male/male)coupler to connect the two together.

Peter

Edited by pseddon, 24 February 2010 - 02:22 AM.


#3 LesNewell

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Posted 25 February 2010 - 12:39 AM

I soldered an SMA connector to the airwave (there is a thread about doing this on RC-Cam), built the goof patch again from Rc-Cam which also uses an SMA connector and then used a straight (male/male)coupler to connect the two together.

Peter


Thanks. I would rather not do that because it would be a lot neater to mount the module directly to the patch. Looks like the only way I am going to find out is to try it...

#4 Mr.RC-Cam

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Posted 25 February 2010 - 08:40 AM

The proposed wire connection is mostly an antenna element rather than a passive feedwire. So to minimize its effect, put your efforts into keeping this wire short. Fortunately, the GP patch works well enough that I've seen marginal implementations still provide impressive results.

With microwave RF, everything matters. The closer you follow the GP Patch recipe the more likely you will achieve the optimum results. So, do your best to please the RF gods so that they reward you with the best GP Patch performance.
- Thomas

#5 LesNewell

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Posted 25 February 2010 - 03:06 PM

The proposed wire connection is mostly an antenna element rather than a passive feedwire. So to minimize its effect, put your efforts into keeping this wire short. Fortunately, the GP patch works well enough that I've seen marginal implementations still provide impressive results.

With microwave RF, everything matters. The closer you follow the GP Patch recipe the more likely you will achieve the optimum results. So, do your best to please the RF gods so that they reward you with the best GP Patch performance.


I'll give it a try and see what happens. My modules arrived today and I have the power supply/ adapter PCB designed to fit them. I'll build the PCBs over the weekend. Hopefully the brass will arrive in the next couple of days. I'll post a pic once I have one built.

Edited by LesNewell, 25 February 2010 - 03:13 PM.