question on command

[alaabadra]

Hello,
i need a question about this command

/home/alarm/librtlsdr-2freq/build/src/rtl_sdr -f <freq_1_hz> -h <freq_2_hz> -n 1.2e6 filename.dat

in which i put freq1 --> 100000000 and freq2 --> 100000000 in which this is as written in code in file sdr_rtl.o
and instead 1.2e6 --> i written as written in this file
but my question on this file --> filename.dat , in which i created empty file .dat after that excute this command but this error : No supported devices found
in which i dont know any thing about this file , must found in it any code ??

please , i need your answer in as soon as please
thank you