HP (Hewlett-Packard) HP 85660B ユーザーズマニュアル

For frequency spans of greater than n 

100 

 up to n x 5 MHz, SW1 is TTL low, routing

the 15 to 30 MHz signal from U3 through 

 

 and 

 to the 

 

 VCO.

When SW1 is high, the circuit provides 90 

 of isolation. R35 and R36 shift the TTL levels

to ECL levels.