Then it is enough to redirect the signal using Virtual Audio Cable from HDSDR to RDS Spy (in the VAC settings you also need to specify the bitrate of 192KHz).
It can be connected via HDSDR if you select FM modulation, a signal width of 120KHz and a bitrate of 192KHz, as shown in the figure.
You can receive RDS data of local stations using the RDS Spy program. Further, after bit-by-bit decoding, data packets of quite a few types are decrypted - in addition to text, for example, alternative broadcasting frequencies of a radio station can be transmitted, and when entering another area, the receiver can automatically tune to a new frequency. Using phase modulation, a low-frequency signal with a frequency of 1187.5 Hz is encoded here (by the way, the frequency of 1187.5 Hz is also not chosen by chance - this is the 19-kHz pilot-tone frequency divided by 16). On the waveform, if you output both signals together, it looks something like this: The spectrum of the FM station signal after demodulation looks like this:Ī pilot tone is located at a frequency of 19KHz, and an RDS signal is transmitted at its tripled frequency of 57KHz. The presence of RDS (Radio Data System) provides the transfer of digital data “inside” the FM signal. The FM radio itself is unlikely to surprise anyone, but we will be interested in RDS in it. As in the first part, the signals will be considered in increasing frequency. Such a receiver covers the range up to 1.7 GHz, all the signals described below are received precisely on it. Therefore, those who want to repeat the experiments described below will have to get their own receiver, of the cheapest you can note the RTL SDR V3, which can be purchased for $ 30.
Unfortunately, there are no similar services on VHF - the frequency range is too large. In the first part, we used the Dutch online receiver to receive long and short waves. Who cares how it works, continued under the cut. As in the first part, we will consider those signals that can be independently decoded using a computer.
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