[time-nuts] precision frequency/time/amplitude reference

[jimlux]

On 10/9/17 8:00 AM, Mattia Rizzi wrote:
> Hi,
> I did something similar when I had to deliver synchronization over IEEE
> 802.15.4-CSS (Chirp spread spectrum).
> If you have SDR on both ends (TX & RX), you can use complex chirp signals
> and then cross-correlation at RX. Just be sure that the multi-path is not
> killing you (i.e. the cross-correlation peak has a width smaller than
> multi-path echoes delay).
> If you use up & down chirps, you can compensate the time-shift introduced
> by carrier frequency offset (due to RF front-end).
> To estimate clock frequency offset, well, just send a repetitive pattern.
> Amplitude is easy as well.
> 
My application is more like an HF interferometer/radio telescope, so I 
don't have any control over the transmitted signal.

I am willing to transmit a "pilot tone" of some sort to allow me to do 
the interelement cal, but I'd like it to be "real simple". An RTL-SDR is 
receive only, but the beaglebone microcontroller next to it can generate 
pulse trains, for instance.