Carrier Phase Measurement

GNU Radio
1

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.

2

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

3

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 M. [email protected]

4

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

5

One more thing…

The Quadrature Demodulator produces a stream of floats. I used as
previously recommended Keep One in N for sample only 5 times by second.
However, which method can I use to save the Float Stream into a plain
text
file. The File Sink Block outputs a binary file?

Best wishes,

Raydel

---------- Forwarded message ----------
From: Raydel Abreu (CM2ESP) [email protected]
Date: 2013/10/22
Subject: Re: [Discuss-gnuradio] Carrier Phase Measurement
To: Marcus M. [email protected]
Cc: [email protected]

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 M. [email protected]

6

Yes, you are right Marcus.

Well, what other method can I use to compensate a drifting receiver
while conserving the carrier’s phase changes? Someone else wants to
jump in and give any thoughs???

Raydel

2013/10/22, Marcus M. [email protected]: