HackRF

My HackRF SDR arrived on Friday and I had a little time to play with it yesterday. Here's a picture of what the commercial product looks like:

To see what the performance is like I attached my 4-element yagi to a small preamp (to overcome the 15m of cable loss) and fed the output to a MiniCircuits ZFSC-2-1splitter which fed both a HackRF and a RTLSDR dongle. The antenna was pointed in roughly a SW direction (and vertical polarisation). This allows me to pick up both the GB3VHF beacon and the GRAVES signal (via scattering off meteors etc as I've discussed previously) in the same 2MHz passband.

Setting up was easy enough - I'm using my own GNUradio scripts and the gr-osmocom driver (which I compiled from git). I just had to install the udev scripts (to make it accessible to non-root users) and I needed a frequency correction of -11ppm due to the offset of about 1600Hz I found when looking at GB3VHF.

Looking at the stability of the system by looking at the received frequency for GB3VHF shows:

HackRF

RTLSDR

As can be seen from the above plots the HackRF is much more stable than the RTLSDR (which could also double in function as a thermometer!). The SNR for both devices is about the same.

For these tests I'm using gains of RF=0, IF=24 & BB=24. If I used less then I start to see a reduction in the SNR. One thing I have noticed is if I use more gain than 0,24,24 I start to see more spurious signals appearing - i.e. signals which appear strongly in the HackRF spectrum, but not in the RTLSDR spectrum. Even when I turned the gain down to 0,24,24 I still saw the odd signal, for example:

HackRF

RTLSDR

You can see that there is signal breakthrough occurring at about position 2000Hz, 1900 (time 'pixels') - along with a number of meteor detecions later on. I'm not sure what frequency is causing this but presumably it can be reduced by an external filter (I'm assuming its not an 'in-band' signal but a result of the complex RF chain before the ADC). I shall be investigating this further, but at least it does not occur too often - less than once every few hours or so.

Over the next few weeks I'll be looking at other aspects of the HackRF, especially its ability to receive up to 6GHz.

My multichannel RTLSDR has stalled a little of late - I'm having difficulties with the PCB version of the frequency tripler - the veroboard version was causing wideband noise however the PCB version doesn't make enough drive to power 2 RTLSDR dongles. One thing I'll hopefully be trying later this year is using 2 HackRF's with their built in external clock input/output to see how well they perform as a coherent multichannel receiver.