[G0HZU_JMR]

Actually, because it's FM you probably only need to do adjacent channel IMD testing, so the spacing can be a bit wider. Realistically, the tones and the IMD would need to be close enough to go through the (1MHz wide?) tracking preselector to get to the mixer.

Your Siglent analyser can still achieve quite a good SFDR in a 10Hz RBW even when phase noise is factored in. It's probably going to be fine for testing each of the various input stages of a VHF FM receiver assuming that you are going to be using something like a level 7 diode ring mixer or a MOSFET mixer.