Espritmodel.com Telemetry Radio
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Old Jan 12, 2012, 07:17 PM
Power-line attraction pilot
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Can you please provide more info and a link? I cannot find anything useful...
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Old Jan 12, 2012, 07:33 PM
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Quote:
Originally Posted by caall99 View Post
Can you please provide more info and a link? I cannot find anything useful...
sorry but i dont have time to read all that long thread and do the search.
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Old Jan 13, 2012, 12:29 PM
Power-line attraction pilot
United States, MA, Natick
Joined Jun 2011
517 Posts
can you remember if you had to use a capacitor and/or resistor when you did RSSI on the turnigy 9x receiver?????
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Old Jan 13, 2012, 02:37 PM
Power-line attraction pilot
United States, MA, Natick
Joined Jun 2011
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great now i am getting nothing for a reading from the receiver. this is highly frustrating. yesterday was great. turned everything off. and today all dead. even my OSD is spazzing
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Old Jan 13, 2012, 05:54 PM
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sorry about all that, like i said this mod is way behind me, i have upgraded all my gear and no longer use this, this was a blog with information and i have little time to troubleshoot this with you, i will delete this blog entry.

Sorry again
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Old Jan 13, 2012, 05:57 PM
Power-line attraction pilot
United States, MA, Natick
Joined Jun 2011
517 Posts
Why would you delete it??? Can you just tell me if the mod ever worked for you?
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Old Jan 13, 2012, 05:59 PM
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Quote:
Originally Posted by caall99 View Post
Why would you delete it??? Can you just tell me if the mod ever worked for you?
it did not have the correct output to work with my stock remzibi OSD back in 2010, so i bought a chainlink long range system and never use this rx, check the "various rssi pin" thread under video piloting section.

Maybe some1 there can help you out.

Thanks
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Old Jan 18, 2012, 10:45 PM
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Just did this same mod, I get the same readings he does. I'll report my OSD results when it arrives.
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Old Jan 25, 2012, 11:20 AM
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Hi, I had a look at the RSSI signal on an oscilloscope and rf siggen to see what is happening. - It is hopping between channels and once it locks to a new channel the RSSI pin goes low to what ever the signal level is.
If I put it into bind mode and inject a signal at 2.4005 GHz pulsed, I can characterise the RSSI pin range. With no signal the RSSI signal is steady at about 840mv.

Giving it a pulsed signal and reading RSSI level on each pulse. I get:
-100dBm = 740mV
-90dBm = 616mV
-80dBm = 472mV
-70dBm = 340mV
-60dBm = 196mV
-50dBm = 68mV
-40dBm = 20mV

The screengrab below is the same receiver receiving a transmitter that has been already bound.
The high part at around 2.07V is where the receiver IC is being programmed with channel information (can see on data lines), the rough bit around ~750mV is where the receiver is waiting for the transmitter to show up (has no signal), the low part between the two vertical dashed lines is the rf level of the transmitter according to the table above. If I walk across the room and shield the TX antenna, I can see the part between the vertical lines go up, meaning less signal, which makes sense.


Just from a quick look at the signals through the RX, it seems as though the interfacing to an OSD may be a bit more involved than a simple buffer amplifier. Maybe a negative peak hold circuit would be the way to go - since the lowest portion of the waveform represents the RF signal level...

Out of interest I had a look at the default antenna, the return loss looks OK (less than -10dB), but the receiver input return loss looks a bit average, around -2.2dB across the whole band ? (that means it reflects a lot of the power going into the receiver).. When I get bored one night I will look if matching the receiver makes it any better

I hope it helps some one !...
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Old Jan 25, 2012, 11:23 AM
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just curious, on some of the OSD's, what are the typical voltage ranges used for analog inputs, for RSSI and the like. 0 to 3V or so???
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Old Jan 25, 2012, 11:47 AM
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Interesting research you did there, i know that the chainlink LRS system has rssi range 0-2.0v and that RVOSD G5 works fine with that, when you do the wizard it ask you to switch the TX off and then back on, thats how it calibrates the RSSI voltage from off to 100%, so if its reverse the OSD makes the correct calculation for you.
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Old Jan 25, 2012, 11:53 AM
Power-line attraction pilot
United States, MA, Natick
Joined Jun 2011
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when i first tried grabbing RSSI from the Rx i got a high signal strength at 1.05v and a low signal strength at 1.25v when measuring with multimeter and OSD.... now, everything is different:

i can no longer read the voltage with a multimeter, but my osd reads 1.5 volts as high signal strength and 3.0 volts as low signal strength. I have no idea why this happened.
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Old Jan 25, 2012, 12:10 PM
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... I got bored and re-matched the receiver on the board.

Looking from the antenna, the first part in series I changed to an 0402 0.47pF capacitor, the second part, a shunt to ground I changed to 0402 1.8nH inductor.
The receive looks OK, not perfect but better.
Return loss at 2.4GHz = -13.2dB, 2.5Ghz = -6.3dB

Sweeping RSSI levels:
Input level (dBm), Original RSSI (mV), New RSSI (mV)
-100, 740, 700
-90, 616, 580
-80, 472, 420
-70, 340, 290
-60, 196, 130
-50, 68, 30
-40, 20, 20

Lower voltage levels on RSSI for a given signal input level are better.
Working it out, the mods above should give 4dB more receive sensitivity !
... at 2.405 GHz at least.
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Old Jan 25, 2012, 01:19 PM
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Do I understand correctly, so you changed a capacitor and some other part on the receiver circuit and doing so the sensitivity was increased..

What about the complex rssi signal...so we would need some sort of circuit between the receiver and osd to correctly show the value? Are you going to design that kind of circuit?
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Old Jan 25, 2012, 01:58 PM
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Yes, thats correct - changing those 2 parts gave improved sensitivity on the bench.

Looking at the RSSI signal, and imagining how an OSD might work ( I have never used one ), I would think a negative peak detect circuit would be the way to go. A bit of googling around gives a couple of circuit examples which maybe a good start?

I have no plans to design a circuit at the moment, but I may get bored again - who knows ...
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