Forum: GNU Radio Inverted spectrum

Cca336c4dc168edf8acb18a5c3410a07?d=identicon&s=25 Andrew Davis (Guest)
on 2013-07-14 02:54
(Received via mailing list)
Hello all,

When using pll_carriertracking_cc, the returned spectrum seems to be
inverted about 0MHz, when looking though the code line 113 of
gr-analog/lib/pll_carriertracking_cc_impl.cc
looked odd:

> optr[i] = iptr[i] * gr_complex(t_real, -t_imag);

could someone explain why the the imaginary component of the NCO is
inverted?

Thank you all,
Andrew
C539637020fd56193dd6daec746c4a84?d=identicon&s=25 Tom Rondeau (Guest)
on 2013-07-22 16:23
(Received via mailing list)
On Sat, Jul 13, 2013 at 8:54 PM, Andrew Davis <glneolistmail@gmail.com>
wrote:
>
> Thank you all,
> Andrew

Andrew,

That block was written so that it would lock to a carrier at a tone
that is then used to downshift the signal. So you have a signal at fc;
the PLL would lock onto that and produce a tone at -fc. This is then
multiplied against the original signal to shift it down to baseband
directly.

Tom
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