The DLRs have 18 hop sets of 50 frequencies each. This is up from the DTRs having only 10 hop sets to work with. The first 10 hop sets in the DLRs match the 10 hop sets in the DTRs. Hop set #1 is the default frequency hop set in the DTRs and DLRs.
Digital modulation on a given hopping frequency is according to an 8-level FSK scheme. The vocoder used is VSELP.
I looked up the FCC test reports in the FCC's Equipment Authorization database for one of the DTR models a while back and happened to find the info you are looking for. It should be in the reports for the DLRs. For each hop set, the information is listed as a base frequency in the 902MHz range and follows a formula with a step size to calculate the 50 frequencies in the hop set. A frequency hopping spread spectrum (FHSS) device operating in the 902-928MHz band is required by FCC15.247 to use a minimum hop set of 50 frequencies. The DTRs and the DLRs spend no more than 90ms within a 400ms period on any given frequency in the hop set. The entire 902-928MHz band is used when these radios transmit.
DTR410 FCC ID = AZ489FT5842
DTR550/650 FCC ID = AZ489FT5852
DLR1020/1060 FCC ID = AZ489FT5870, AZ489FT5871
In case anyone is wondering, forget about trying to monitor these on any consumer grade receiver (scanner) because you can't.
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