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

[Piotr Krysik]

Is there some good candidate that can be asked to do that? When I search
for rtlsdr driver the first page with actual source code is osmocom's site:

sdr.osmocom.org/trac/wiki/rtl-sdr

Maybe they have the maintainer who feels responsible for how this code
works?
I can try to correct this offset in software (especially if it doesn't
change too often) but it doesn't seem as the optimal solution. Frequency
offset estimation might not be perfect either.

--
Piotr

W dniu 25.05.2016 o 21:36, address@hidden pisze:
>
> The AirSpy uses the R820T2 chip for the tuner, but a different
> sampling/DSP "engine".
>
> Yes, making the charge-pump and "dither" mods will help with
> phase-coherence.
>
> Somebody needs to "own" the rtlsdr driver, and merge in the last
> couple of years of field experience and branching that has gone on
> with it.
>
>  
>
>  
>
>  
>
> On 2016-05-25 15:04, Piotr Krysik wrote:
>
>> 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
>> <mailto: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
>>>>>
>>>>> _______________________________________________
>>