Re: [Discuss-gnuradio] Multi-rtl - making multi-channel receiver out of multiple RTL-SDR dongles

[Piotr Krysik]

Hi Marcus,

I don't know much about AirSpy.

Does it use the same demodulator chip as current RTL-SDR dongles?
And does it mean that change to low level part of rtlsdr driver might
help to get rid of that frequency offset?

--
Piotr

W dniu 25.05.2016 o 16:35, address@hidden pisze:
>
> There are a couple of issues with the rtlsdr driver used by gr-osmocom
> in this regard:
>
>  
>
>   (A) The charge-pump loop current is too constrained for the higher
> frequencies
>
>   (B) The "dither" option appears to have a bias that causes a (small)
> frequency offset.
>
>  
>
> The driver that AirSpy uses fixes both of these, although without
> "dither", the tuning granularity is worse.  Not sure this matters.
>
>  
>
>  
>
>  
>
> On 2016-05-25 09:28, Marcus Müller wrote:
>
>> That, or simply, the output clock VCO changes its reaction to the
>> control voltage under certain circumstances (temperature, frequency) so
>> much that the control loop loses the ability to reach stationary
>> exactness (e.g. due to natural limits on the magnitude of the VCO
>> voltage). These devices definitely were made with cost in mind – not
>> with maximum reliability, and hence I can believe that for example with
>> the Elonics E4000 tuner, the charge pump used to generate the VCO
>> voltage simply might deteriorate with temperature.
>>
>> Cheers,
>> Marcus
>>
>> On 25.05.2016 14:25, Sylvain Munaut wrote:
>>> Hi,
>>>
>>>> of the drift remains a mistery (probably due to the implementation
>>>> of the PLL,
>>>> but I cannot understand why Phase Locked Loops would drift in Phase !).
>>> If the phase comparator is digital ( i.e. a XOR ) and the input clock
>>> is somewhat analog, the gate thresholds might vary depending on
>>> temperature, thus shifting the cycle a bit.
>>>
>>> Just a thought.
>>>
>>> Cheers,
>>>
>>>     Sylvain
>>>
>>> _______________________________________________