[NLRS] HackRF One SDR Xcvrnsmit

[Glen Overby]

I sent this directly to Doug, but thought that more of NLRS might be
interested.

On Mon, May 30, 2016 at 12:41 AM, Doug Reed <n0nas at amsat.org> wrote:

>
>
> I'm wondering if anyone in the group has tried using a HackRF One as a
> poor-man's microwave radio? It is spec'ed from 5MHz to 6GHz receive
>

Yeah, I think "tried" is a good way to put it.

If you look at the block diagram for the HackRF One, you'll find that it's
a 2.3ghz - 2.7ghz receiver (wifi) with a mixer in front of it.

The GNU Radio support for hackrf is half-duplex, in that you can either
transmit or receive.  To switch from one to the other, the GNU Radio chain
has to be stopped, the device closed, and reopened.  This is not a fast
operation (hundreds of milliseconds).

I've modified the hackrf_transfer utility to be a transceiver that can pass
data to GNU Radio and switch RX/TX without closing the device.  It needs
some work to really be usable.  I have a GNU Radio chain that uses a filter
to downsample from 10mhz to 48khz and upsample (rational resampler they
call it) from 48khz to 10mhz (8mhz is the minimum bandwidth of the hackrf
due to certain chip specs; below that you get images).  The code for this
is on http://www.github.com/glenoverby in the libhackrf and dttsp-sdr repos.

Someone who knows C++ better than I could look at how the BladeRF works and
modify

The next thing you'll find about the hackrf is that it is deaf.  I think a
softrock using a 24 bit sound card hears better, although I haven't done a
side-by-side comparison.  As you said, it has 50dB of dynamic range -- and
that range doesn't start at -130dbm.  All of my Yaesu radios hear better
than the hackrf.  This is because the hackrf doesn't have a front-end: a
good LNA and a bandpass filter.  The hackrf isn't unique in this area;
there is an article in the January 2015 QST on building a front-end for on
of the Ettus Research (read: expensive) SDR boards.  The author has info
and a copy of that article here:

https://sivantoledotech.wordpress.com/2015/01/27/a-selective-and-robust-uhf-front-end/

that article also talks about why a bandpass filter is needed.

You'll also need a filter on transmit.  The hackrf has some harmonic output
that should be easy to filter most places, except 432 mhz.  There is a
birdie on 432 that's too close to filter; I suspect this is the oscillator
driving the mixer and that it can be gotten rid of by  changing the tuning
equation, but I haven't tried it yet.

I took a look at the lime SDR.  Their software appears to support only GNU
Radio -- there is no simple library like HackRF has. I could not find any
Lime SDR code in the upstream GNU Radio project source, so it appears to be
supported only by the GNU Radio packages released with Ubuntu.  I expect it
to also need a front-end.

If you're looking for something packaged such that you buy the hardware,
install the free software and get on the air, this isn't it.  If you're
looking for a project, this could be it.  I bought a hackrf hoping to use
it as an IF for a 24ghz system.

73,
Glen, kc0iyt