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Type: Corona RD820 Double Super 35MHz PPM
Microcontroller decoder (Atmel ATMEGA48 resonator)
Receiver system: double converting
1. IF =10.7MHz, 2.IF=455kHz
FM decoder: ceramic resonator
IF filter, 10.7MHz ceramic SAW filter and 455kHz ceramic x 2
RX frequency was accurate within 400Hz using original crystal supplied.

Antenna wire de soldered, and 50 Ohm RF test generator attached.
1kHz sine and 2.5kHz deviation.

The demodulated audio signal was found on a test point.
so it is easy to see with a scope how the receiver perform, when wanted signal is equal to noise,
the RF input signal level is recorded.

Center frequency with best sensitivity -106dBm (1.1uV) so it is better than the 2uV stated on the parcel, nice.

with -70dBm input level, the frequency width is measured to = 19.2kHz
with -50dBm input level, the frequency width is measured to = 242.1kHz  !!! due to blocking
but OK, -50dBm is also a really strong signal, you need to be under 5 meters away from tx to get that strong signals,
so in real life I don't think you will experience any problems with this.

Sensitivity to injected noise on the power line
I inject sine wave signals via a 400uH coil and transfer capacitor 100nF,
directly into the power supply connector of the receiver board.
This simulates a bad motor regulator BEC or Servo current pulse, or noise picked up on long power and servo wires
35MHz RF input signal level at -90dBm
Demodulated signal observes as with the sensitivity test.
Noise frequency with best interference = 455KHz,
Input Voltage level when the wanted signal is jammed to 50% signal to noise.
Measured to : 700mVpp, so that is fine for electric planes.

Mirror frequency and other issues:
Since this is a double conversion receiver we will not expect to see any mirror reception frequency's,
but I found out one quite critical issue, at 38.1000 is has a sensitivity of -80dBm !!
not really nice since I would expect it to only receive 35.1000.
Again in real life situations we never know if 38.1 is free ? or a powerful local radio station there ??
I had only one RX crystal for 35.1 so I don't know if it is always 3.000 MHz higher than RX frequency ??

I like to add that the DSP software seems to be working really good.
on a PPM receiver it made me happy to see this perform so smooth and good,
I dont see any servo pulse flips even when TX is turned on/off while RX is running, nice !

 17. March 2007, Thomas Scherrer