These files just contain raw samples.

The fact that the signal then isn't around 0 Hz is simply because it

1. (optionally/depends on example you're referring to) was mixed, in the generating GNU Radio script, onto a carrier frequency within the first Nyquist zone and 2. on the fact that DACs introduce *images* in spectrum at multiples of the sampling rate, and you exploit these to have a copy of your signal, shifted by a multiple of the sampling rate. You should filter out all the other copies.

Terms to google for: reconstruction filter, band-pass undersampling

Best regards, Marcus

On Sat, 2018-06-09 at 00:47 +0100, Fred Neich wrote:

Hello,

I have a question about osmo-fl2k, the generated binary file using the fl2k grc transmission flow graphs, contains the carrier frequency, the fl2k_file stream the file to the device, so how the device can transmit these data in that frequency. I mean how it recognize the frequency to transmit on.

Thank you.