[Hackrf-dev] HackRF problems

[Larry DiGioia]

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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