Can an SK-4000 be modified to operate below 85 MHz?

Unfortunately, there is no upgrade path to allow the SK-4000 to work on frequencies below 85 MHz or above 4 GHz as it is limited by the hardware.  The best solution is to use our SK-4500-TC (1MHz to 4.5GHz), or our SK-6000-TC (1MHz to 6GHz).