Australia, QLD, Brisbane
Joined Nov 2011
Turnigy 9x8Cv2 sensitivity mods
I was surfing in another thread regarding RSSI levels and OSD stuff on the 9x8Cv2 receiver.
Was having a look at the performance of the receiver and it looked pretty poorly matched on the input, with a return loss of around -2.2dB.
( Meaning more than half of the power coming into the receiver from the antenna is reflected back out )
... I got bored and re-matched the receiver on the board. ( sad I know )
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 a little better.
Return loss at 2.4GHz = -13.2dB, 2.5Ghz = -6.3dB
Sweeping RSSI levels with a pulsed signal generator on the input :
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 around 4dB better receive sensitivity.
Hope it helps! --
Quick info on the RSSI signal from the receiver below:
The screengrab below is a receiver receiving a transmitter that has been already bound.
The high part at around 2.07V is where the A7105 RX 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.
*disclaimer - I haven't tested these in the field yet - If someone get's a chance it'd be cool to see how it goes.
Also the parts are not that easy to solder without good irons.
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