Today I made a standalone Adjustable TTL Trigger generator box. Following are some features:

• The rising edge of output can be used to trigger all TTL compliant external trigger enabled equipment (oscilloscopes, HP4395A, SR785 etc.)
• Uses AD620 at very high gain (G=5k) to create a comparator. Positive input is the signal and negative input is controlled with a 100 kOhm potentiometer.
• The threshold can be set anywhere between +18V and -18V.
• Powered internally with four 9V Alkaline batteries and has a switch to turn ON/OFF. Should last really long.
• The output is through a 4.7 V Zener Diode which activates in reverse bias when the signal becomes 140 uV higher than the set threshold.
• Input impedance equivalent to AD620.
• The trigger is not latched and output goes to -0.7 as soon as the signal falls below the threshold.
• Has a window port for checking the threshold.
• The practical way of operating would be to see the signal and output of the box together in an oscilloscope first and fine tune the potentiometer to see triggers at the right point.