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From: | Juha Vierinen |
Subject: | Re: [Discuss-gnuradio] Multi-rtl - making multi-channel receiver out of multiple RTL-SDR dongles |
Date: | Thu, 26 May 2016 11:47:56 -0400 |
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,If the phase comparator is digital ( i.e. a XOR ) and the input clock
but I cannot understand why Phase Locked Loops would drift in Phase !).
is somewhat analog, the gate thresholds might vary depending on
temperature, thus shifting the cycle a bit.
Just a thought.
Cheers,
Sylvain
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