Multiplex RX6 Synth Light single conversion 35MHz PPM
Receiver system: Sigle converting 31136G
IF = 455kHz, dual ceramic filter
FM decoder: ceramic resonator
RX frequency was accurate within 0Hz quite typcal for Synth receivers
Microcontroller = MSP430F111, PLL IC = LE145170, both running at 8MHz
Antenna wire desoldered (88cm long) and 50 Ohm RF test generator attached.
modulation: 1kHz sine and 2.5kHz deviation.
The demodulated audio signal was found on a test point.
Sensitivity -93.3dBm (4.8uV) at 10dB SINAD with -70dBm input level, the IF frequency width is measured to = 12.5kHz
with -50dBm input level, the IF frequency width is measured to = 16.4kHz
Sensitivity to injected noise on the power line
I inject a sine wave signal 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 or servo wires
35MHz RF input signal level at -90dBm this gives us 15dB SINAD
Noise frequency with worst interference = 455KHz due to the IF frequency.
Input noise voltage level when the wanted signal is 5dB SINAD (Demodulated signal drops 10dB SINAD)
Measured to : 650mVpp
Mirror frequency and other issues:
Since this is a SINGLE conversion receiver we will expect to see almost no mirror rejection
so at 34MHz -85.6dBm sensitivity this is 7.7dB rejection, this is normal
March 2008, Thomas Scherrer