QT Freq Sink Display not centering correctly?

So, I first noticed this problem with my main GNURadio install (3.7.5 on
Debian Jessie) but I’ve reproduced it on a brand new 3.7.7.1 live USB.

Basically I’m looking at two frequency sinks. One of them centered at 0
and
one centered at 16kHz. I have a single signal source input to both
sinks,
starting at 4kHz but adjustable up to 32kHz. My expectation is that the
initial 4kHz signal will display at the far left of the 16kHz-centered
sink…but it doesn’t. It displays as a 20kHz signal instead, to right
of
center.

I’m pretty sure that’s not WAD…and if it is, can someone explain why?

On May 15, 2015, at 12:07, Jason N. [email protected] wrote:

So, I first noticed this problem with my main GNURadio install (3.7.5 on Debian
Jessie) but I’ve reproduced it on a brand new 3.7.7.1 live USB.

Basically I’m looking at two frequency sinks. One of them centered at 0 and one
centered at 16kHz. I have a single signal source input to both sinks, starting at
4kHz but adjustable up to 32kHz. My expectation is that the initial 4kHz signal
will display at the far left of the 16kHz-centered sink…but it doesn’t. It
displays as a 20kHz signal instead, to right of center.

I’m pretty sure that’s not WAD…and if it is, can someone explain why?

The sink always displays the content of the signal you give it. The
purpose of the center frequency setting is to adjust the frequency scale
displayed in the widget to match the original frequencies of a
downconverted signal.

The simplest use of this is to set it to the same frequency as your
receiving hardware is tuned to, so that the frequency scale displays
true RF-spectrum frequencies rather than 0 bandwidth.

If you want to actually shift the way the frequency content of the
signal is displayed, you could use the rotator_cc block before the sink.


Kevin R. http://switchb.org/kpreid/

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