[Hackrf-dev] hackrf_transfer receives 1kB (at most) of valid data

[Dominic Spill]

On 12 February 2016 at 06:43, Brent Thorne <brentathorne at gmail.com> wrote:
>
> Got to lesson 5 in the tutorial and I think I broke something after
> upgrading to hackrf-2015.07.2 (firmware and cpld images) .  I can only
> capture 1kB using 'hackrf_transfer -r'.  Help me understand if I'm
> doing something wrong.
>
> $ hackrf_info
> Found HackRF board 0:
> Board ID Number: 2 (HackRF One)
> Firmware Version: 2015.07.2

Looks good.  You could also upgrade the CPLD too but if you're coming
from the 2014.08.1 release there's no need because there was no
change.

> 19.9 MiB / 1.000 sec = 19.9 MiB/second
> 19.9 MiB / 1.000 sec = 19.9 MiB/second
> 19.9 MiB / 1.000 sec = 19.9 MiB/second
> ^CCaught signal 2
>  4.7 MiB / 0.224 sec = 21.1 MiB/second

This looks like it transferred much more than 1kB.  How big is the
rx.raw output file?

> $ hexdump rx.raw | head -10
> 0000000 ff00 ffff ff00 ff00 ff00 ff00 0000 ff00
> 0000010 ff00 ff00 ff00 ff00 0000 ffff ff00 ffff
> 0000020 fe00 ff00 ff00 ff00 ff00 ff00 ffff ff00
> 0000030 ffff ff00 ff00 ff00 ff00 0000 ff00 0000
> 0000040 ff00 ff00 fe00 ff00 ff00 ff00 ff00 ff00
> 0000050 ff00 ff00 ff00 ff00 fe00 ff00 ff00 fe00
> 0000060 0000 ff00 ff00 ff00 ff00 ff00 ff00 ff00
> 0000070 ff00 ff00 ff00 ff00 ff00 fe00 ff00 ff00
> 0000080 ff00 ff00 ff00 0000 ff00 ff00 ff00 ff00
> 0000090 ffff ff00 ff00 ff00 ffff ff00 ff00 ff00

These values are signed int8s, which means what you're seeing here are
very low values, fluctuating around zero.  This looks like valid data
to me.

This brings us back to the command that you're using to capture the data:

> $ hackrf_transfer -r rx.raw

You will probably see more interesting data if you set some gain
levels and perhaps start out by tuning to a local FM station
frequency.  -l -g set gain levels, -a enables the amplifier (although
I usually leave it off unless I need it) and -f will let you set the
frequency.  I would expect you to see much more interesting data if
you set these.

Please let me know how you get on with this.

Thanks,
  Dominic