16Dec22

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NOTES: ADDITIONAL PROJECTS

My eBay Collection: Tektronix 11801A/B Sampling Osciliscopes

About one year ago I acquired both a TEK 11801A and B digital sampling oscilliscopes on eBay. Both worked OK requiring no electronic repair. Initially a SD-22 (12.5GHz) sampling plug-in head was used for providing RF input. The 11801A didn't have a prescalar while "B" did; which seemed to allow triggering up to about 12.5GHz for the 11801B while the 11801A only had a triggering input good up to about 3Ghz; 070-8783-01 11801B User Manual, pg 3-215. "External triggers can be connected to either the DIRECT or PRESCALE* connectors on the 11 801 B front panel. Signals connected to the DIRECT connector are fed directly to the trigger circuitry. The signal is DC coupled and can be up to 3.0 GHz. Signals connected to the PRESCALE connector are divided by eight and then fed to the trigger circuits." To use the 11801A above ~3GHz it became apparent that a prescalar was needed to operate at higher RF frequencies. One option was to find, on eBay, the Tektronix SD-51 prescalar good up to 20GHz which usually goes for a minimum of $670. I decided to check the divide by 8 operation on the 11801A using a "WBSG1 Wideband Signal Generator" having CH1 and CH2 outputs. I set CH2 to be exactly 8X CH1; it worked! Initially I decided to find a /8 prescalar that was good at least up to 20GHz ; my 1st was a lotus-sys "Frequency Divider/Prescaler Divide by 8 (DC to 24 GHz) FD8DC24G" which worked great (see 11801B photo below). A SD-26 sample head was eventually tested up to 20GHz and above Later purchased from RFEXTRA eBay prescaler kits:1st Hittite Frequency Divider HMC36XS8G 12.5GHz which goes well for the SD-22; 2nd 18GHz Hittite Frequency Divider HMC494, and third Divide by 8 and 24GHz Hittite Frequency Divider HMC862ALP3E. The below photos the 11801A and 11801B:

11801A

SD-26

RF signal input two way divider; out 1 to prescalar input , out 2 to SD-26

11801B