[Hackrf-dev] FW: deaf HackRF

[Paul Connolly]

As the sample rate increases, so does the the noise floor. Or with more
bandwidth comes more noise. So giving the numbers without the sample
rates used is not useful. In SDR# for the HackRF you can type in a
sample rate in the sample rate pull down box, try using 2 MSPS. And for
the RTL2832 try dropping the sample rate to 0.25MHz. And repeat your
experiment again.

On 19/01/2015 20:25, Stephen wrote:
> Hi Tom,
>
>  
>
> Thanks for the reply.
>
>  
>
> The RX sensitivity figure I quoted is dBm – ‘Decibels above a MilliWatt’. -95dBm is 95 db below a MilliWatt, wheras -127dBm is 127 db below a MilliWatt.
>
> This test was conducted with an RF signal generator.
>
>  
>
> Regarding the test, to register minimum scale on the SDR# spectrum, the HackRF required -95dBm , the RTL2832 required only -127dBm.
>
>  
>
> Expressing this as microvolts instead of dBm, the equivalent level in microvolts (to register the same scale on SDR#) are:
>
>  
>
> 0.1uV  for the RTL2832 
>
> 3.5uV for the hack RF
>
>  
>
> Accordingly, The HackRF requires considerably more signal to register the same scale on SDR#.
>
>  
>
> I discovered this performance limitation when  I attempted to try to receive NOAA weather satellites, I found HackRF barely registered, wheras the RTL2832 registered a strong signal for the same satellite pass  on the same antenna.
>
>  
>
> I appreciate you are trying to help & I don’t mean to be rude by contradicting you,  but the HackRF I have is definitely ‘deaf’.
>
>  
>
> Regards,
>
> Stephen
>
>  
>
>  
>
> From: Tom Buelens [mailto:tom.buelens at gmail.com] 
> Sent: Monday, 19 January 2015 8:23 PM
> To: Stephen
> Subject: Re: [Hackrf-dev] deaf HackRF
>
>  
>
> Hi Stephen,
>
>  
>
>  
>
> I might be mistaken but I actually think the numbers you mention show that the HackRF is better at receiving the signal.
>
> You see, an attenuation of -105 dBm is resulting in a smaller signal then -69dBm. Please also see here:
>
> http://en.wikipedia.org/wiki/DBm
>
>  
>
>  
>
> Cheers,
>
> Tom
>
>  
>
> On Mon, Jan 19, 2015 at 2:36 AM, Stephen <refsmmat at gmail.com> wrote:
>
> Hi,
>
> Ive just bought a HackRF, but I have found  RF performance is poor. Compared to a $12 USB RTL2832 SDR, it is deaf by about 32-36dB.
>
>  
>
> The tests were done with an HP 8922 test set & an unmodulated carrier at 137.5MHz. The test was the generated RF signal required for both devices to achieve the same scale level in SDR#.
>
>  
>
> RTL SDR                  HackRF     Difference
>
> Scale1   -127dBm              -95dBm               32dB
>
> Scale2   -115dBm              -79dBm               36dB
>
> Scale3  -105dBm               -69dBm                36dB
>
>  
>
>  
>
> The tests were done with max gain on both devices, but with the HackRF AMP off.
>
>  
>
> I have seen from posts that others have had this problem – related soldering of RF switches in the manufacturing process.
>
> Can anyone provide further details on the fix  or suggest a resolution please?
>
>  
>
>  
>
> Thanks,
>
>  
>
> Stephen
>
>  
>
>  
>
>  
>
>
> _______________________________________________
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>
>  
>
>
>
>
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