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Mr.RC-Cam

Airwave SMA Connector Installation Instructions

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The Airwave AWM611TX and 612TX 2.4Ghz RF modules are very popular for wireless video projects. However, since they are bare OEM parts, they do require some "assembly" to use them. The typical user often creates a custom PC board (kitchen-sink etch job) to ease the pain.

My experiments have shown that a good PCB layout {to control the RF path impedance} requires considerable care. Failure to utilize a 50 ohm impedance PC trace layout WILL result in substantial RF power loss {huge RF power reductions are easily earned with *innocent* pcb layouts}. This issue is also true for the receiver module's RF input too. I suspect that poorly optimized PCB layout is the reason some folks do not get long range with their modules.

In a nutshell, if you do not follow the required math to create the 50 ohm micro-strip line that feeds the SMA connector, then do NOT use the module's 3-pin RF header! The problem will occur even if the feedpath trace is short; Microwave wavelengths are short, so short traces that are not optimized for 50 ohms will have dramatic negative affect.

But don't worry -- there's a no-math, non-PCB, solution that eliminates the layout issues. It is a simple matter of installing the SMA connector directly on the RF module. This method has been mentioned elsewhere on the forum by other Airwave users (I think by Terry and VRflyer). So, what I will show you here is not new to the forum. I'm just here to sternly caution everyone to be very careful on how you handle the antenna connector if you care about maximizing range. With microwave RF, everything matters.

The following photos show my version of the RF input hack. It requires some mechanical modifications, but is not hard to do. Just take your time and pay attention to the little details. If you take any liberties on the construction method then be warned that you may end up with some RF loss.

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Start with a Amphenol 901-144-8RFX SMA connector. This is digikey.com part number ARFX1231.

Begin by trimming the center pin length a bit and also reduce its diameter by about 50%. A Dremel tool with abrasive wheel works great and it is a two minute job. Wear eye protection!

See photo.

post-5-1165706625_thumb.jpg

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Next, remove the top and bottom sardine can covers from the Airwave module. Using a fine tipped soldering iron, remove the 3-pin RF connector. Do NOT leave the pins in place! Keep in mind that too much heat will lift the pads off the board. Before moving on, dress the PCB pads so that they look like new.

The four legs of the SMA connector need to mount slightly into the module's chassis. This is done by using the Dremel tool to cut slots for them. Be sure to cover the module's exposed circuitry while you grind, otherwise little bits of metal will sneak in there and eventually ruin your day.

This photo shows the slots cut into the top side.

post-5-1165706809_thumb.jpg

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The SMA connector is soldered to the metal chassis. It is position so that the four corner legs slightly protrude into the chassis (about 0.050"). Use enough solder for a strong mounting.

The center pin is soldered too. Avoid increasing the size of the center pin too much with solder. Even if not shorted, too much solder is not welcome there.

This photo shows the SMA soldered in place.

post-5-1165707214_thumb.jpg

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Before installing the sardine can covers, blow out any debris from the module. Use solder flux remover and clean the soldered areas of the SMA connector. The flux can affect the dielectric properties, so it must be removed. Do NOT omit the cleaning step!

I also recommend that you solder the corners of the metal covers to the chassis. This will prevent video noise that can occur with vibration.

This photo shows the finished module.

post-5-1165707390_thumb.jpg

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My measurements for the hacked module were compared to a custom PCB method that used accurate 50 ohm micro-strip line feedpaths.

In the photo, the top board has the SMA directly mounted on the module. The bottom board is the one with the SMA installed using the stripline layout. Measured RF power was about the same on both versions. So, this suggests that we can be successful without any need to design a PCB that employs controlled impedance PCB signal paths.

Note: Just so there is no confusion, the red colored PC boards, and all the SMD components on them, are not sold by Airwave. These boards are a custom design of mine. They are just shown here to describe how I tested the two methods.

post-5-1165707705_thumb.jpg

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I'm preparing my planes for testing of AeroPix transmiter. The sma connector is not solder to the sardine, Anthony made a PCB layout and solder the connector on the pcb, I'm curious to see if I will get a better range or less then with my own transmiter, mine sma is solder on the sardine can.

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I'm preparing my planes for testing of AeroPix transmiter. The sma connector is not solder to the sardine, Anthony made a PCB layout and solder the connector on the pcb, I'm curious to see if I will get a better range or less then with my own transmiter, mine sma is solder on the sardine can.

I know its a year on, bt how did your test turn out.

How does the Aeropix PCB compare against the direct connection methode.

Am interested as I have started using an Aeropix Tx/Rx

Rob

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Please excuse my ignorance, and starting up a thread that has been dead for a while.

I just wanted to clarify something so I don't stuff up the potential output of my TX.

I'm using an airwaves 633, and mounting it in an enclosure, and instead of using a SMA connector, i'm using one like this: http://www.jaycar.co.nz/productView.asp?ID=PS0674&CATID=35&form=CAT&SUBCATID=433

(sorry can't remember what you call them)

So mounting the connector directly to the Airwaves module is out of the question.

So if I use cable rated at 50ohm, like RG58 or RG174, and solder that directly to the output of the airwaves module, then onto my connector, does that provide the correct line impedance or whatever to maximise the output power of my TX?

FYI the TX is connecting to a +24db Grid attenna with the intention of a long range video link.

Also, would it be wise to use 75ohm for my video input, and correct audio cable for my audio input to make sure a maximise the quality of everything?

Thanks for your help, you guys knowledge is amazing!

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Lug terminations on the N connector is not the best choice for an Airwave 2.4GHhz project. Here is what I would do: Install an SMA directly on the Tx module, then use a N to SMA adapter on your antenna. If you must use coax then keep it short and terminate all connectors with perfection.

Also, would it be wise to use 75ohm for my video input, and correct audio cable for my audio input to make sure a maximise the quality of everything?

If your cable lengths are extremely long then that would be nice. But most installations don't require this since the lengths are within arms reach.

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Mounting the SMA connector onto the module sort of stuffs up my whole layout, but if thats the only option, then it might be what I have to do.

I know you can buy cable especially for those SMA type connects, which I assume would be the right impedance, but I haven't found where I can get it from quiet yet.

So assumming I can find the cable, if I replaced my current N connector with a flush mounted sma, then used say, 2-3cm of that cable to connect to the airwaves module, would that do the trick?

I'm just worried that mounting it straight to the module will

1) Make the layout of the internals of my enclosure very limited, and difficult

2) Put alot of pressure on that connector, and in turn the module, probably causing it to fail at bad time.

Thanks for your help!!

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Generally speaking, all designs involve compromises. So, given that, you should choose the solution that best suits your requirements.

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Yes, that is a fair comment!

Really, the high priority for this project is to get the best range possible out of the units.

In general terms, how much loss am I looking it?

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It would just be a guess on my part. My parting advice: If longest possible range is the goal, then avoid coax feedlines. If ease of installation is the goal, then your proposed plan seems easy to do.

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