I am attempting to transmit on a 7.5 MHz center frequency ( fc ). I want 3 MHz bandwidth so the frequency will modulate between 6 MHz and 9 MHz.
The slowest speed for the SXT VCO is 30 MHz. This is above my desired 7.5 frequency. Here is the slowest VCO wave form. It is 33.3ns at 2.0-volt scale.
The NOC (TxTSP FCW) is capable of the 7.5 speed, but its output is mixed with VOC LO in the RF front end. This creates the wave form seen below. It is combination of 30 and 7.5, and the signal has been attenuated to 40-millivolts scale. This is not the form I want.
Dr. Webster tells us to get frequencies below 30 MHz to use interpolation. He states a combination of upsampling and filtering will get my desired results. I have selected upconvert CMIX on the TxTSP tab. I also set the GFIRs as a low-pass filter for 9 MHz on this same tab. I am unsure if upconvert is the same as upsampling .
I started with the example.ini file provided with Lime Suite GUI. I changed the VOC, NOC and GFIRs as stated a above. I have saved the configuration and uploaded for review. Please explain to me how to get the desired FMCW signal that I desire.
Hardware: LimeSDR-USB revision 1.4s.