0.1 to 5 MHz Span Switch @
For frequency spans of greater than n x 100 kHz up to n x 5 MHz, SW1 is TTL low, routing the 15 to 30 MHz signal from U3 through U6D, U7D, and Tl to the AlOAl PLLl VCO. When SW1 is high, the circuit provides 90 dB of isolation. R35 and R36 shift the TTL levels to ECL levels.