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 |
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 |
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.