On 03/02/2023 12:44, George Edwards
wrote:
Hi Marcus,
I do not have any hardware. I am doing
everything in simulation. I designed the grc to translate a
QPSK modulated signal to a rf freq of 1GHz at a sample rate of
3GHz. Running this signal into QT freq sink or a webgui freq
sink shows the upconverted modulated signal at 1GHz, with a
support base that is miniscule over such a wide freq range +/-
1.5 GHz. So I would like to know if there is a way to instruct
either GUI's such that the display pops up over a range of 1G
+/- 2 MHz or a range of my choosing at the sample rate I am
working at?
Thank you!
George
If it's just in simulation, I guess I don't understand why you need
to "simulate" such high sample rates if your signal is only fairly
narrow. It is usually the case that for actual hardware, signals
are delivered as a complex baseband at whatever your sample
rate is. You might need to shift stuff around a bit sometimes,
which is where the frequency-xlating filters and friends come
into play.
In simulation, you almost never need to simulate the actual radio
hardware *at its operating frequencies and bandwidths*.
In fact, doing that in Gnu Radio *in real time* would be extremely
challenging on ordinary computers the frequencies
you've quoted.
When folks talk about Gnu Radio as a "useful simulation tool",
they're mostly talking about simulating DSP
processing chains *at the rates typically seen in complex baseband
delivered by hardware*, and NOT necessarily
about it being a tool that is useful to simulate actual hardware
-- at least, not in real time.
On 03/02/2023 11:30, George Edwards wrote:
Hi Fabian,
Thanks for your suggestion!
However, it will not help me because I
would like to see the spectrum displayed over the
proper range 1GHz +/- 4MHz.
George
I think we now need more information about your setup. What
type of hardware? I know of no hardware that can deliver
samples at 3Gsps into a host computer that is also
compatible with Gnu Radio.
Processing samples at 3Gsps in an ordinary computer even
with blazing-edge current CPU tech is a "significant
challenge",
and you sure as heck aren't going to do it in Gnu Radio.
My *suspicion* is that you're confused about the difference
between the *desired center frequency*, bandwidth, and
corresponding
sample rate.
Hi
George,
I don't know if the Frequency sink can do that for
you, but I guess it
cannot.
One way is to mix the signal with a complex
oscillation and a multiplier
with the oscillator running at the negative frequency
you wish to
downshift the signal. Then low-pass filter and
downsample the signal.
You can then feed that into the Frequency sink and
also set you
oscillator frequency as offset frequency in the sink's
settings.
Best,
Fabian
Am 03.02.23 um 16:52 schrieb George Edwards:
> Dear GNURadio Community,
>
> Let's say I build a GRC flowgraph operating at a
sample rate of 3 GHz
> and wish to display the spectrum over the fixed
range of 1GHz +/- 4MHz,
> how do I get the QT GUI Frequency sink to plot
over this range?
>
> Thank you!
>
> George