The Fluke 190 rs232 interface is suitable for tryouts but the closes one is from the Fluke 279/289.
Found this DIY rich in info as part of my own answer :DIY optical link cable for the Fluke Scopemeter 190 series
http://omapalvelin.homedns.org/fluke/After assembly and testing on HyperTerminal at 19200bps I was able to send a few commands and had response for GD (Get Down), SO (Switch ON) and RI (Reset Instrument). ID (instrument ID) , IS (Instrument status) and RT,RD and others returned nothing. Down to 9600 bps minimum for FSH3 and checking the RX signal on oscilloscope shows a lot of noise and missing data at the output of the IR comparator.
The info and pictures of the 189 interface in this blog motivated to keep me going :
http://kimboricha.blogspot.com/2013/12/build-usb-to-fluke-189-irinfrared.html even though none of the suggestions and mods worked
The two transistor darlington configuration was the solution for the high speed required :
https://electronics.stackexchange.com/questions/391266/high-speed-infrared-uart-link-with-photodiodeConfirmed optical Rs232 interface working by Hyperterminal, any command sent replied using mirror( a spoon is better) and when connected to FSH3 I sent ID enter returned all R&S info and firmware version. Observed a nice square wave modulated when tested with a TV remote. Tested the home made Rs232 interface with both instruments and FSH viewer connected a 19200bps.
Firmware updated fix the FSH3 Frequency range anomaly.
Have found version 13 of FSH viewer here:
http://www.korearental.co.kr/cData/CDATA_PDS_VIEW.ASPX?IDX=250&Cate=1&bbscode=7,2,0, .
And Version 14.2 is here:
https://uloz.to/file/B41l7yCShG9O/fshview-v14-20-setup-exe?showDialog=1 .
The new firmware update ver. 14 is a self extracting file and is suitable for all old FSH 3 ,6,18 but requires FSH Viewer 14 and up Installed .
IF administrator have a way to let me upload somewhere the two 10MB FSH Viewer installers I will be happy to do it before the links disappear
I got some progress on the option keys from my serial 102121.
2918745366 - K5 - GSM/EDGE Application Firmware (Option Key error)
0659588824 - K7 - AM/FM/PM Measurement Demodulator (Enabled) DEMO MODE ENABLED FOR 1000Hrs
1048859114 - B17 - IQ Online (Option Key error)
3837700883 - None (Option Key error)
0840658593 - K84 - 1xEV-DO BTS Application Firmware Remote Control Enabled
2135204116 - K84 - 1xEV-DO MS Application Firmware Receiver Meas. Enabled
1863906345 - None (Option Key error)
0204267013 - FSP-B15 FSP-B70 FS-K7 (Option Key error)
2684356591 - K72 prior K74 (Option Key error)
0371030575 - None (Option Key error)
0679722459 - K9 - Power Meter (Option Key error)
3208052079 - FSP-B15 FS-K7 (Option Key error)
3516151515 - None (Option Key error)
3712172277 - None (Option Key error)
1067738526 - K76 - 3GPP TD-SCDMA BTS Application Firmware (Option Key error)
4183377164 - K77 - 3GPP TD-SCDMA MS Application Firmware (Option Key error)
0890457939 - K30 - Noise Figure Measurament (Option Key error)
3488976067 - K82 - CDMA2000 BTS Application Firmware (Option Key error)
4253200286 - K83 - CDMA2000 MS Application Firmware (Option Key error)
2499311400 - K8 - Bluetooth Application Firmware (Option Key error)
0071209860 - K40 - Phase Noise Measurament (Option Key error)
2187555649 - None (Option Key error)
1044162665 - None (Option Key error)
1586385696 - None (Option Key error)
1960780550 - None (Option Key error)
2793864759 - 31 days trial period (Option Key error)
0212545182 - 78 days trial period (Option Key error)
3895538962 - None (Option Key error)
1099830336 - None (Option Key error)
0581656715 - Frequency Extension (Option Key error)
1434950248 - None Accepted None
1662463819 - Trasducer Set Accepted None
Patty