HackRF One wont go below 4mhz

[Ronald Festa]

OS is Ubuntu Mate 15.04 64bit. On Windows using SDR# I can use the full range 1Mhz to 6Ghz, but on Ubuntu with GQRX I can't go below 4Mhz. I've tried both the official Ubuntu repo version of GQRX and building from the latest Git source, but the results are the same regardless. I'm also using the latest Git source for the HackRF driver. Any insights what could be the problem?

[Alexandru Csete]

Hi Ronald,

The gr-osmosdr source block returns a frequency range starting at
sample_rate / 2 and ending at 7.25 GHz:
http://git.osmocom.org/gr-osmosdr/tree/lib/hackrf/hackrf_source_c.cc#n510

This means that if you are using 8 MHz sample rate, the lowest
possible center frequency in gqrx will be 4 MHz. But you can still see
the full spectrum down to DC and pick out signals using the software
tuning feature.

Note that if you are tuning down to 1 MHz and are using 8 MHz sample
rate, you will waste almost half of your sample rate since you will
get a repetition of the signals from 1 to 4 MHz mirrored to -3 to 0
MHz. So settings the center frequency down to 1 MHz makes sense with 2
MHz sample rate and it should also be possible in gqrx.

If you have a special use case where you must set the center frequency
below 4 MHz you can either use the lower sample rates or modify the
gr-osmosdr source code I linked to above.

Alex

[bevan.sm...@gmail.com]

Hi and happy new year!

I just started playing around with a HackRF One and now I have the same issue. The given explanation makes absolutely sense but I can't get the gqrx to tune into frequencies below the lowest hardware rf frequency. It seems like the lower bound is applied to the received frequency instead of the center (hardware rf) frequency.

Here is what happens starting with a tuned frequency of 4 MHz and a receiver offset of 0Hz:

- Lowering the receiver offset the hardware frequency is increased by the same amount so that the received freq. is still 4 MHz.

- Increasing the receiver offset the received frequency (large frequency dial) increases. Lowering it again to 4MHz the hardware freq. actually drops below 4MHz, which should not happen due to the hardware freq bounds.

- Klicking into the spectrum to select a receiver frequency below 4MHz sets a negative receiver offset but the hardware frequency increases by the same amount (as described above)

May this be a bug in that the frequency bounds are applied to the wrong frequencies here? I'm using gqrx 2.4.

Michael

[Alexandru Csete]

Yeah, it sounds like a bug but I don't have any time to work on this
anytime soon. A patch would be welcome though.

Have you tried enabling "Ignore limits"?

Alex

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[bevan.sm...@gmail.com]

Am Freitag, 1. Januar 2016 17:54:50 UTC+1 schrieb Alexandru Csete:

Yeah, it sounds like a bug but I don't have any time to work on this
anytime soon. A patch would be welcome though.

Have you tried enabling "Ignore limits"?

This in fact helps as a workaround. I will see if I can provide a patch. Otherwise I will open a bug report on github to keep track of this.

Thanks for the quick response!

Michael 

[Alexandru Csete]

To have it fixed completely, one should probably also update the range
returned by gr-osmosdr. I don't know what the lower limit should be
though.

Alex