[Hackrf-dev] HackRF hardware problems

[Karl Koscher]

It sounds like there are many potential issues here.

I do see spurs at multiples of 10 MHz, which are probably harmonics of the
10 MHz reference oscillator. These spurs are far less noticeable with an
external (rooftop) antenna, so I'm wondering if the antenna that ships with
the HackRF is picking up this noise from the HackRF (as opposed to the
noise being picked up somewhere internally). I might get one of the
shielding kits and see what improves.

I do see images of FM radio stations around 1.5 GHz, although it's not
clear where that's coming from. It's possible that the FM stations are
strong enough that even if they are significantly attenuated by the various
bandpass filters, the signals still get amplified before reaching the ADC.

I'm not totally clear on where all the filters are in the HackRF. Looking
at the schematic, it seems like the RX low- and high- pass image reject
filters are between the antenna and mixer? This doesn't make sense to me --
the mixer would be the one creating images. It would make more sense if
those filters were TX filters, but then I'm not sure where the RX filters
are. My guess is that they're in the MAX2837, which converts the 2.3 - 2.7
GHz IF to baseband.

There are also reports of differences between GNU Radio and SDR#.
Unfortunately since the source isn't available for SDR#, it's a little hard
to debug, but I've managed to debug libhackrf in SDR# and it *seems* to be
doing the right thing. However, I rebuilt libusb and libhackrf to make this
work, so it's possible that one of the other prepackaged versions have
other issues. In particular, I do wonder whether the bandpass filter is
being set appropriately for the sampling rate.

Finally, it does sound like some HackRFs are having hardware issues,
especially with the RF amps. Is there a possibility of ESD damage from the
plastic enclosure? The ports themselves seem to be ESD protected, although
a future rev of the HackRF should probably have some additional overload
protection.

Finally, it would be nice if there was some AGC built in to either the
device or libhackrf. I was initially very disappointed with the HackRF
until I realized that I had to futz around with the gain to make it work
well. To make matters worse, there are multiple gain adjustments, and it's
not super-clear what they do or how you should set them.

If there are specific projects I could work on to improve things for
people, I have a complete Windows development environment for the HackRF.

On Wed, Nov 26, 2014 at 7:46 AM, McDonald, J Douglas <jdmcdona at illinois.edu>
wrote:

>
>
> Several people have complained with HackRF problems, worrying if their
>
> unit is defective.
>
>
>
> I have the same worries. Mine clearly is nowhere near as good as
>
> the DVB dongles.  But it clearly works, no quibble. It works both in
>
> SDR#/Windows and Gnuradio/GRC/Ubuntu.
>
>
>
> But it is plagued by spurious spikes of near-CW stuff everywhere, even
>
> up in the upper GHz areas where there should be essentially nothing.
>
> It sees Wi-Fi fine ... but covered by these spurious carriers. And
>
> many of them are DIFFERENT in SDR# and Gnuradio. And using both
>
> they are dependant, both in amplitude and frequency, on the
>
> gain settings at the low gain end as well as the high gain end.
>
> That dependance at the low gain end implies to me that its is
>
> incorrectly dithered or some software problem.
>
>
>
> I bought it for the wide bandwidth for certain special purposes
>
> and it serves those purposes OK even in the presence of the garbage.
>
> But for general use, its a plain, and expensive, joke.
>
>
>
> Doug McDonald
>
>
>
> _______________________________________________
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>
>
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