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oxxyfx

RSSI again

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Hello,

I did some tests with an Airwave (623) receiver and the RSSI signal level last night - thanks to Thomas who sent me the dummy loads (thank you Thomas).

I just have to ask you guys about these signal levels:

- With the transmitter beside the receiver (with the dummy load or without) the RSSI signal never goes below 0.4V. That seem to be the max. level I could get - the two units being side by side.

- With the transmitter very far apart - confirmed on the TV screen - almost no signal at all - The RSSI was as high as 3.3-3.5V but never higher than that.

Are these values correct? Did you guys get higher values than this? If I want to bring in the RSSI signal into an A/D converter, since the A/D converter's reference is 5V, I would probably need an opamp to amplify the signal to 5V max. I do not want to input anything higher than the reference voltage, so that's why I am asking if you've seen higher values than 3.5V.

Thanks.

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The levels sound about right, you only need an op-amp if you need max res, for most jobs it will be fine to connect directly.

Terry

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just input this voltage directly into the ADC

and do the rest in software.

if your CPU is running at 5V it is perfect.

if your CPU is running at 3.3V

just attenuate the RSSI analog down to 3V for max

so the rest is simple in software,

you want to make a PIC or AVR power signal meter indicator ?

or what have you in mind ?

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Thanks Terry and Thomas,

Well, two projects. The first one is a receiver with a servo underneath - streching the pulses to rotate 170-180 degrees. Based on the RSSI it will (should) keep track of the plane - rotate the receiver/GP-Patch assembly such to search for the strongest signal.

The second project - more complicated - a modular board in which you can plug in 1, 2, 3 or 4 receivers positioned at 90 degrees horizontal to each other and about 25-30 degrees up. This will be plug and play - it will look for how many receivers you have plugged in and will start with that. The circuit will switch based on the RSSI signal strength during the vertical pulse, so no visible lines on the screen. Also it will have 2 outputs, one for goggles and another one for the camera.

So far that is all I can talk about, I am writing the program for the first one, and trying to determine the design, parts, and way to best do the second one. My main problem is that I only speak the "hobby electronic english" while you guys are all speaking the "professional electronic english"... This sometimes creates discrepancies... :)

The CPU will run at 5V.

Thanks guys, I keep you both posted...

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Hello,

my RSSI signal will go into an ADC. Since the RSSI is not a very constant voltage even at close range I see little variations, I thought I will take a number of measurements and calculate an average before I start working with the value.

How many measurements would you guys suggest? 3? 5? more?

Thanks, Ox.

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I don't average as such I sample 256 keeping the highest signal as the reading I use. I figure that the peak is the correct level and the rest are just invalid as they must be reduced due to a turn or something. I also sample over a 1 second period to reduce the chances of a wrong low reading as this will cause the aerial to turn the wrong way. You may want to filter out a few of the highest samples as well but it's not made much difference in my tests and complicates the process.

Terry

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