PLL stands for phase locked loop. It eliminates phase variations.

On 10/22/2013 06:21 PM, Raydel Abreu (CM2ESP) wrote:
Hi Marcus,

Thanks for the tip. In a previous e-mail Marcus D. Leech recommend me to use 
the Quadrature Demodulator Block as something not perfect, but usable to check 
for phase changes.

It works for me, as long as there is a pure carrier without phase changes, and 
without care the amplitude, the Quadrature Demod outputs a float number, quite 
constant, if there is a phase change, the resulting float number changes.

Now, help me with a doubt regarding PLL. Let's assume the carrier is steady 
(zero drift), if there is a phase change (not changing in freq) when passed 
through the PLL, the phase changes are not conserved???

The idea of my small project is to correct any possible frequency drift due to 
poor receiver stability while conserving the incomming phase changes which is 
in part produced by the ionosphere.

So, how can I correct the drift while keeping the incoming changes of phase?

Kind Regards,

Raydel


2013/10/22 Marcus Müller <mar...@hostalia.de <mailto:mar...@hostalia.de>>

    Hi Raydel,
    try Keep N in M (keep 1 in N) for the "sampling".
    However, if you correctly employ a PLL, your phase will be static; if it's 
not, than the PLL is not doing it's job well.

    Greetings,
    Marcus

    On 10/22/2013 05:21 PM, Raydel Abreu (CM2ESP) wrote:
    Hello all,

    I am new to GNU Radio and I am still learning the basic. I have a quick question. 
What blocks and which way can I use in order to "sample" and know the phase of 
a tuned carrier at regular intervals.

    General idea: Let's suppose there is a carrier, after applying proper 
tuning (Freq Xlating FIR Filter, etc), I apply a PLL module (not sure which: 
PLL Carrier Tracking or PLL Ref Out) in order to remove possible drift from the 
receiver and output a steady carrier. How can I sample at regular interval that 
corrected carrier phase. Assuming that intervals are really equals I guess 
every time I should obtain the same phase value.

    I will really appreciate any help in this matter, perhaps someone could 
point me in the right direction.

    My purpose is to observe ionospheric phase scintillation from a 
geostationary satellite beacon, which outputs a steady carrier. Frequency 
drifting should be related to RTL-SDR dongle and part of phase changes related 
to ionospheric irregularities.

    I attempted something similar with SpectrumLab and an analogue receiver but 
due to receiver drifting and sound card poor sampling stability the phase 
result was a phase rotation of several degrees by measured interval. Perhaps 
GNU Radio and the PLL functions it has could help to overcome the frequency 
drift in the measured carrier.

    Thanks in advance,

    Raydel.


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