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Re: [Discuss-gnuradio] How to reset the phase for subsequent sweeps from

From: Martin Braun
Subject: Re: [Discuss-gnuradio] How to reset the phase for subsequent sweeps from VCO?
Date: Thu, 10 Jul 2014 20:25:43 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0

On 07/10/2014 07:27 PM, khalid.el-darymli wrote:
> Hi,
> I am using the VCO block in GRC to generate complex-valued sweeps with
> BW of 50 KHz and a sweep time of 1 second. The VCO is driven by the 
> sawtooth signal generator in GRC.
> The problem I am facing is that subsequent sweeps do not start at the
> same time. Each new sweep seems to have a random phase shift relevant to
> the other. Please see the attached figure which demonstrates the case
> for seven subsequent sweeps. This figure was generated in Matlab after
> saving the output of VCO to a binary file in GRC. Then, for the sampling
> frequency of 50 KHz, individual sweeps were resolved and superimposed on
> each other.
> My question is, how do I reset the phase of the VCO at the beginning of
> each new sweep?

The block doesn't let you do that, and it probably shouldn't -- a "VCO"
has, by definition, a continuous phase.
If you want full control, you could use the phase_modulator block; but
remember you need to calculate what the phase is for a sweep beforehand
(you know integrate and that math stuff).


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