The method I use is to measure the frequency offset that provides the Costas Loop Block of GNURADIO. But it needs proper scailing in order to measure Hz. I can measure at the same time the 750 QPSK beacon and if I want I can Tx at a free frequency and measure also mine. I Tx also BPSK similar to 750 signal but with random data. The values are compared to Doppler calculations. In previous tests Doppler calculations was outside GNURADIO. Now can included in it if desired.