I've bought a pack with 3 temperature senders and 1 receiver. But I want more, and I also want datalogging.
Is there a USB dongle that let's me pick up on a given frequency, lets say '433.92 Hz' and sniff up whatever floats "in the air" as the senders send the temperature every minute or so to the receiver?
300 to 3000 Hz is in the audio range. So you could hook up an appropriate (very very large) antenna, filter, and amplifier to any cheap USB audio or mic line input.
YOu can use any long piece of wire as this will be <<< than the half-wavelength at these frequencies. Then use an active PLL as a Band Pass Filter with a precision VCO and then a demodulator with LPF to match the bandwidth keeping in mind rise time is inverse to BQ or Q of the channel filter.
A DSP is the obvious choice if you want to discriminate all frequencies at the same time using FFT. But Yamaha makes a great chip for this in an LED matrix for music notes.
For now use an audio spectrum analyzer which can be borrowed from a lab to measure down to these rates. In my seismic research days in the early 70's we used mainframes to analyze the FFT of recorded ULF ground waves. We also used VLF receivers to detect WWVB with a simple wire antenna to get Stratum 1 clock time sync on portable recorders.
Alternative you can design a not so simple PLL and quadrature detector to detect these. I have done so and FFT is faster on a spectrum Analyzer. OF course you can use Audacity's free software and Spectrum Analyzer to look at microphone or amplified antenna signals. But you will need a 100 db notch filter at the power line frequency to block the 100V/m electric wave which is high impedance as your antenna is also very high impedance at 0.01% of Lambda. A What do you expect to sniff 433.92MHz?
