Company: E SKY
Type: Esky EK2-0420 single conversion 35MHz PPM
Receiver system: single converting 31136G with LM393 and counter 74ACH164
IF =455kHz, FM decoder: ceramic resonator
IF filter, 455kHz ceramic
RX frequency was accurate within 800Hz using: Yellow label HImodel crystal
RX frequency was accurate within 0Hz using: White label Type 35-12 crystal
Antenna wire desoldered (99cm 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 -117.8dBm (0.3uV) at 10dB SINAD, WOW this is good
with -70dBm input level, the frequency width is measured to = 21.0kHz
with -50dBm input level, the frequency width is measured to = 2MHz!! 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.
Simply avoid other transmitters to be extreamly close to your plane !
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 29dB SINAD
Noise frequency with worst interference = 455KHz due to the IF frequency.
Input noise voltage level when the wanted signal is 19dB SINAD (Demodulated signal drops 10dB SINAD)
Measured to : 9Vpp, so that is close to a new world record !
you will newer see any problems from electric planes even the worst BEC will newer make this much noise
Mirror frequency and other issues:
Since this is a single conversion receiver we will expect to see no mirror rejection
so at 34.1MHz we have -108dBm sensitivity this is compleetly normal.
Even more good news:
It is written on the receiver it is only 6channels, that is NOT true,
the B for battery is in fact the 7th servo channel and it really works, nice.
Need 8 channels ?? the 8th signal is available inside it:
carefully solder a wire to pin 13 of the ACH164 chip !
Jan 6 2008, Thomas Scherrer