SparkFun Forums

[bburan]

I need to find a 318 MHz receiver so I can record the signal generated by a 318 MHz transmitter (SAW based, Manchester Coding @ 75mS for 9 bits of data). However, I have only been able to find a 315 MHz receiver (both on Sparkfun and other websites). There are some 318 MHz receivers (e.g. RWS-438-4 from Wenshing); however, I cannot find a place to purchase these receivers. Does anyone have any advice on how I could find a 318 MHz receiver that can be used to record the signal sent by the transmitter (using an PC, Arduino or similar)? I'm also open to suggestions for spectrum analyzers, but those are a bit pricey.

[stevech]

spectrum analyzer won't tell you about the signal changing rapidly in time.
Try one of the receivers at
http://www.anarduino.com/details.jsp?pid=145
in the "ASK" mode

[bburan]

Thanks for the suggestion. I looked at those receivers and they look promising, but the technical documentation is a bit confusing. I'll have to read through it to make sure that I can figure out how to program the device to operate at 318 MHz.

[stevech]

Easy part is programming frequency. Hard part is to put it into a mode where packets are disabled, FSK is disabled and raw FM demodulated is passed to an output pin. Rarely used.
This is becuase you said you wanted to inspect the 318MHz signal and you don't know if it's AM, FSK, etc. Reverse engineering the protocol is too hard for a novice.

[Valen]

I suggest you search for RTLSDR, SDR#, GNURadio (in Google)

Or just start here: http://www.rtl-sdr.com/about-rtl-sdr/

You can use a cheap EU Digitial TV receiver usb module (around $20 or even cheaper if bought from the land of the wall), with modified firmware to read pretty much the entire spectrum from 25 Mhz to 1.8 Ghz. Al you need extra is a good antenna for the signal of interest. Then software like SDR#, or GNUradio if you need to build special or customized decoding algorithms, to demodulate the signal on a pc (realtime).

[stevech]

If you have the transmitter, another approach is to use a 'scope and find the serial bit stream at the logic voltage level, and reverse-engineer with that. The transmitter is mostly likely on/off keying (OOK). That's a crude form of amplitude modulation (AM)- crude because it's just on/off, no analog.