During recent development project on FCC certified remote control transmitter and relay receiver kit, we have found our PT4302 superheterodyne receiver module becomes unstable or impossible to decode transmitter data when data rate is set to more than 5kbps, after hooked up undecoded data stream from receiver module on oscilloscope, we have found the reason is that high bits are too long while low bits are too short, which changes the default high / low ratio from 2:2 to 3:1, thus causes the following decoder software can’t read data correctly.
After searching for solution in PT4302 receiver chip’s datasheet, we have found it has something to do with PT4302 receiver chip’s data filter settings, first we need to know what is data filter in receiver module? according to datasheet, data filter is utilized to remove unwanted spurious signals after the OOK / ASK demodulator, usually it uses capacitors low-pass filter to smooth OOK signal, thus is helpful to decode the real data that we want other than data noise.
You may wonder, why data filter has something to do with data rate settings? because high data rate usually means shorter shortest-pulse-width, take Microchip HCS301 encoder for example, when set to default 2.5kbps data rate, the shortest pulse width value is 400us, while when set to 5kbps data rate, the shortest pulse width value is 200us, so if data filter setting is inappropriate, then data filter may over-smooth the data stream, thus causes data stream to be broken.
Usually on PT4302 superheterodyne receiver module, data filter bandwidth should be set as 0.65 / shortest pulse width, which means if our shortest pulse width is 200us as discussed above, the correct data filter bandwidth setting should be around 3250 Hz.
After we set correct value on PT4302 superheterodyne receiver module, it starts to decode remote control transmitter data correctly, so we would recommend everyone to try check data filter setting first if you have similar issues.