@Martin_T - Martin,
There are two methods of performing this:
1.) Use GNU Radio Companion and the applicable LimeSSDR plugins. An excellent write up of this is here —>
https://wiki.myriadrf.org/Gr-limesdr_Plugin_for_GNURadio
All one would need to do is set the carrier frequency to 15.0 MHz and then modulate that carrier (not certain if AM or FM) with 800kHz. All this is capable with PC resources and the LimeSDR. Measuring on the scope just requires that you have the sweep speed at a reasonable setting to see the resulting envelope for the 15 MHz being modulated by an 800kHz source.
2.) Use SDRAngel to achieve the same thing - all the information to make that happen is here —>
You would need to set up the proper environment (Windows or Linux - Linux preferred) and then set up a FM or AM modulating source that is driven by the PC at 800 kHz. Setting up the 15 MHz is kind of tricky but if you choose to go that route with SDRAngel I can set you up with the settings necessary to make that work - just ping me here in the forum.
The choice is yours - choose wisely…
73 de Marty, KN0CK