[Hackrf-dev] HackRF (FM) carrier frequency sweep rate

[Michael Ossmann]

Stephen,

If you can restrict your hopping to a 20 MHz range, then you can use a
sample rate of 20 Msps and hop instantly (well, within a 50 ns sample
period) in software.

If you need to hop over more than 20 MHz and must control the hopping
from a host computer over USB, then your tuning time will be dominated
by USB latency.  I'm not sure how quickly you would be able to tune, but
I guess something like 2 ms.

If you can tune in firmware, then you can reduce the tuning time
considerably.  I've measured tuning times between 145 us and 750 us from
firmware.  I haven't done much work to optimize this, but it is probably
possible to achieve consistent sub-200 us tuning time for most
applications.

Tuning doesn't take much CPU time.  The reasons it takes time (roughly
in order) are:

1. USB latency (if controlled by host computer)
2. inter-chip serial communication
3. PLL settling

You might find this talk interesting:

https://www.youtube.com/watch?v=3AZgQzrevjo

Mike


On Wed, Jul 06, 2016 at 03:48:39AM +0000, Yen, Stephen wrote:
>
> Hello,
> 
> I have a HackRF One that's been running  various transmitter modulation schemes and would like to know how quickly one could hop around in carrier frequency.  For example, how much time is required to sweep a 1MHz BW data message on an FM modulated carrier starting from 600MHz to 700MHz in 1MHz intervals (around 100 channels)?  Is the time needed to switch carrier frequencies mainly dependent on the internal CPU execution time?  
> 
> Thanks,
> -Stephen