[Hackrf-dev] HackRF problems

[Karl Koscher]

It should be noted that the apparent intention of the device (even
reflected by its name, HackRF) is to give people a relatively low-cost way
to experiment (tx and rx) with high-bandwidth RF over a large frequency
range. It is not intended to be the SDR peripheral for the best specs out
there. If it is somehow deficit for your application, all of the hardware
and software is open source and documented, so you are free to modify it
for your own purposes. I suspect adding some additional RF shielding will
help receiving signals, but it wasn't necessary to achieve the goals of the
device.

Now, if there are bugs or design flaws, they should be addressed to the
extent that they can.
On Nov 27, 2014 8:41 AM, "Larry DiGioia" <n8ku at longwire.com> wrote:

>  Thank you! That is the best explanation I have seen in months, and much
> food for thought. I have slowly come to understand that this is not a
> dongle, it is test equipment. Now - could you please give an example/source
> of off-the-shelf "really good bandpass filters?" (For HF/VHF?)
>
> On 11/27/2014 09:58 AM, McDonald, J Douglas wrote:
>
>  I want to emphasize that the RF chain in mine is not defective.
>
> I tested it again last night. The three different gains all
>
> work exactly as expected.
>
>
>
> When connected not to an antenna but to a wired system
>
> the number of spurious signals is greatly reduced but is nowhere near
>
> zero and not as low as the dongles.
>
>
>
> I think that most people for over the air receiving purposes need
>
> to get really good bandpass filters to pick out only the signal of
> interest.
>
>
>
> And remember that 8 bits is a very poor dynamic range for a system
>
> without a really good, designed to purpose,  ANALOG AGC, so you have to,
>
> by hand, get the various gains exactly right. I do it by looking at the
>
> spectrum display. In general when working with weak signals
>
> you want to leave the amp off and slowly raise the two other
>
> gains in parallel from all the way down. At first if your is like mine
>
> you will see big jumps up and down in the level of weak signals,
>
> spurious signals, and noise. The spurious ones come and go
>
> as you raise gain. At some point the apparent noise level
>
> stabilizes and remains the same for a while as the real signal
>
> levels rise up out of the constant noise floor. Then the noise
>
> floor rises up. When it has risen about 5-9 dB you have reached the
>
> best sensitivity and more important dynamic range and
>
> lowest quantization distortion. I am fairly sure that this gizmo
>
> has no built-in dither at the 1-LSB level. If it does there is something
>
> bad going on, perhaps in the DC level area.
>
>
>
> One way to look at it is the HackRF is NOT a receiver: its effectively an
>
> IF strip with no AGC.
>
>
>
> Today I’ll try it as a transmitter feeding my old spectrum analyzer
>
> looking for spurious signals. Currently for most spectrum analysis
>
> I use either it (>2MHZ bandpass) or one of the dongles (better
>
> for narrow band).
>
>
>
> Doug McDonald
>
>
>
>
> _______________________________________________
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>
>
>
> --
> "When people are free to do as they please,
>  they usually imitate each other."
>
>                                      Eric Hoffer
>
>
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>
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