This past summer I tested a RF remote control based on the PT2262 remote control transmitter. The PT2262 serially encodes a value presented on input pins. This serial output can be used to on-off key an IR or RF transmitter. This allows a remote control transmitter to be very simple and not require any software.
The remote control I tested used a 315MHz SAW resonator in place of the LC circuit shown in the reference schematic above.
At the time I was renting an Anritsu MS2034B VNA/Spectrum Analyzer. I connected the spectrum analyzer to the remote’s trace antenna and used to the peak hold feature to look at the spectrum of the modulated 315MHz signals.
Here are its harmonics are shown here.
Last week I decided to look at this remote with my Tektronix MDO4000 series mixed-mode scope. The Blue trace is the input line connected to one of the remote control buttons. The yellow trace is the serial data, which starts about 7ms after the input line is asserted. The orange line in the time domain is located at a point when the transmitter is on, so that frequency domain shows the RF activity.
I zoomed in and moved the orange line to a point when the serial output is high and the transmitter is turned on. (I placed the spectrum analyzer’s antenna next to the trace antenna rather than connecting directly to it, so the signal values are weaker.)
If I use the pan knob to inch the orange line over to a point when the serial output is low, I can see the transmitter is off.
All of this makes it clear just how simple this remote control transmitter is-- pure On-Off Keying. I dialed back the power to the point where I thought it would pass under 15.231(a), and it didn't provide the range the project required. They ended up switching to an ISM-band module. I'm interested if anyone has made a simple remote like this work and pass regulatory testing. Based on my testing, I expect ISM standards like Bluetooth Low-Energy (BLE) will take the place of cheap transmitters. The complexity of BLE does not cost that much compared to what is gained in compatibility, power savings, and availability of off-the-shelf modules with regulatory approval.