Graupner R700 (BACK)
Type: R700 Single Conversion.
Pulse decoder=4017 and LM339, Receiver system= Single converting 4116
IF=455kHz, IF filter=455kHz ceramic, FM decoder=Coil resonator,
RX frequency was accurate within 10Hz using original crystal.
Antenna wire de-soldered (100cm length), and 50 Ohm RF test generator attached.
1kHz sine and 2.5kHz deviation.
On the PCB I found a via/pad with demodulated audio signal,
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 -110dBm (0.7uV) super good.
with -70dBm input level, the frequency width is measured to = 23.5kHz
with -50dBm input level, the frequency width is measured to = 67.3kHz WARNING
The AGC (Automatic Gain Control) can not handle strong signals. some blocking can occur.
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 : 630mVpp Verry good, can be used in electric planes, or with noisy digital servos
Mirror frequency and other issues:
This Receiver uses single conversion so it recieves two frequencies,
the wanted and the mirror, both with same sensitivity, normal for all single conversion types.
29th of April 2006, Thomas Scherrer