Full Spectrum Switch needed for Tx operation ?
Why does the Full SPectrum checkbox need to be enabled/checked in order for transmission of IQ data? What I have been experiencing over the past two days is that in order to transmit either a previously captured IQ waveform (i.e. File Reader) or a waveform via the IQ Modulator block, I need to have the Full Spectrum checkbox checked. This really does not make any sense given the explaination/description of what this checkbox does, meaning "If activated, the hidden region of the spectrum is also displayed ...".
Any guidance on this would be appreciated.
This requires a little bit of an explanation. The center of the frequency span is zero Hz offset from the main modulator clock, and cannot be generated or received, kind of a blind spot. This blind spot is some kHz wide. Your sample sets the FSK center frequency at 300MHz and the V6 center frequency at 300MHz, so it ends up at this blind spot. If you would set the V6 center at e.g. 310 MHz it would be at a 10MHz offset and significantly stronger.
Now if you set the span to a fraction (as 1/512) in your case, the Rx portion (which uses the same modulator clock) will use only a part of the spectrum and move the blind spot out of the way, thus shifting the center clock without telling so. Unfortunatly the Tx section does not honor this and shifts the center of your signal to a place where you would not expect it (here is clearly room for improvement on our end). Turning on "Full Spectrum" disables the shifting, so this explains the effect this checkbox has on your signal.
So workaround:
1.) Set the center frequency of the V6 some MHz away from the center of the FSK signal
2.) Do not use a Span fraction when using the Tx
3.) You may want to use a larger time offset in the signal generator if your Tx keeps flashing yellow (disable the "Adapt Time Offset" as well)
Hope this helps
Thank you for this detailed reply. I still find it impossible to fully understand the concept here since I do not have a complete understanding of the detailed hardware and software architectures. For instance, "this blind spot is some KHz wide"; how would I ever have known this and how many more "blind spots" may exist?
I'm curious on what is happening in my simple construct of Signal Generator to Spectran, specifically, why do I need to set the FSK Center Frequency as well as the Center Frequency and then the Spectran Center Frequency? This seems like we are not dealing with baseband IQ in the IQ Signal Generator?
Also, why is the Rx1 chain active when I am operating in Tx mode, even though I have it set to Rx Off?
Thank you for this detailed reply. I still find it impossible to fully understand the concept here since I do not have a complete understanding of the detailed hardware and software architectures. For instance, "this blind spot is some KHz wide"; how would I ever have known this and how many more "blind spots" may exist?
There is only one, see https://v6-forum.aaronia.de/forum/topic/peak-in-the-center-of-my-spectrum/
Quote from CorNic East on 27/05/2022, 17:09I'm curious on what is happening in my simple construct of Signal Generator to Spectran, specifically, why do I need to set the FSK Center Frequency as well as the Center Frequency and then the Spectran Center Frequency? This seems like we are not dealing with baseband IQ in the IQ Signal Generator?
Yes, the IQ signal generator does not work in baseband IQ (unless you set the center frequency to zero), but if you set the "Adapt Center Frequency" checkbox, the V6 and the IQ Signal Generator will ensure that the center frequency match. An alternative would be to use an IQ Modulator block between the IQ Signal Generator and the V6.
We have updated the Tx operation.
Please check out the latest missions and documentation here
https://v6-forum.aaronia.de/forum/topic/using-the-tx-example-missions-manual-demodata/
