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Eggfinder RP-SMA Antenna and Metal Interference?

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mccordmw

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The documentation on the Eggfinder says to avoid metal like the rods in an avionics bay since it will interfere with the signal. When reading about replacing the whip antenna with an RP-SMA antenna, I can across a discussion with this picture:



Is an RP-SMA antenna ok to use in an avionics bay around those metal rods? Or does that kill its range? I have lots of free room in my bay and would love to mount my GPS unit in there instead of cutting up my nosecone.

The forum discussing this image is at: http://www.ausrocketry.com/forum/viewtopic.php?f=32&t=4406&start=30

Thoughts?
 

thomas

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It depends of course on the range you need and what antenna you have on the ground.
I had some problems with the Telemetrum range when I had the antenna completely in the bay beside 4 metal rods.
I do not really get the point, why a whip antenna directly solder should be anyhow different from one connected with an RP-SMA?

I now run my antenna through the bulkhead in a clear plastic tube (should be clear so one can see if the antenna is placed right)
ebay.jpg
 

smapdiage9

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I avoid this problem entirely by putting my external antenna on a 6-8" RP-SMA extension cable. These are cheap and available on amazon/ebay/etc, and you can put the entire antenna outside of potential influence without much effort.
 

cerving

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cerving

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The documentation on the Eggfinder says to avoid metal like the rods in an avionics bay since it will interfere with the signal. When reading about replacing the whip antenna with an RP-SMA antenna, I can across a discussion with this picture:



Is an RP-SMA antenna ok to use in an avionics bay around those metal rods? Or does that kill its range? I have lots of free room in my bay and would love to mount my GPS unit in there instead of cutting up my nosecone.

The forum discussing this image is at: http://www.ausrocketry.com/forum/viewtopic.php?f=32&t=4406&start=30

Thoughts?
There's no question that having the antenna close to metal allthreads will cause some signal degradation. The issue is, How much? That's difficult to say. What happens is that the signal gets blocked by the allthreads, so you get kind of a flattened figure-8 signal pattern. This means that if you're looking dead-on with the allthreads the signal may not be so strong. Also, the signal bounces back, so there are "nulls" created where the reflected signal cancels out the transmitted signal, although they're most likely fairly close to the transmitter.

I don't know if anyone has done any kind of empirical testing to see what the effect on the range might be, that would be an interesting test, although it would have to be done several times to yield any reliable data. You'd have to have two Eggfinders in the rocket on different frequencies, one inside the AV bay and one in the NC. I do know that I've heard of several people using an Eggtimer TRS (which is basically an Eggfinder TX transmitter and Eggtimer altimeter combo) in their AV bays with allthreads and they've reported reasonable range. I've done it too, and haven't had any issues with the flights I've flown to about 7,000'.
 

ksaves2

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It depends of course on the range you need and what antenna you have on the ground.
I had some problems with the Telemetrum range when I had the antenna completely in the bay beside 4 metal rods.
I do not really get the point, why a whip antenna directly solder should be anyhow different from one connected with an RP-SMA?

I now run my antenna through the bulkhead in a clear plastic tube (should be clear so one can see if the antenna is placed right)
View attachment 298793
Thomas is doing it the right way. One wants to put a plastic or cardboard stent over the wire antenna to make sure it doesn't get squished by the recovery laundry like shown here.
Another strategy would be to have an aft SMA connector on the bulkhead and an interconnect to the transmitter. Might as well have the aft facing antenna out in free air at apogee rather
than have it take the blast of the ejection charge in the forward bay. I've used Thomas' strategy myself successfully many times.

Avoid metallic paints as that may attenuate the signal. Again ground test for the range. If you can live with your ground test as compared to antenna out in free air then you can take a shot at it.

Nothing worse than going outta sight and not receive any packets.

What's the purpose of the Aerogel capacitor? Kurt
 
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