The 141T is typically used with an 8552 series IF plug-in and an RF Plug-in, of which there are different frequency ranges. The 141T in the photo has the 8554B & 8552B Spectrum Analyzer Sections, but are NOT included.

You can find the 8500 series plug-ins below

The 141T mainframe features an easy-to-read 8x10cm variable persistence CRT with a writing rate from 0.2 sec to 15sec. Maximum storage time is over 2 hours at reduced brightness. The 141T Spectrum Analyzer System IF and IR sections feature a tuning range from 20 MHz to 18 GHz (40 GHz with external mixers), with a scan width maximum of 200 MHz/div. Amplitude range is from -127 to +10 dBm. Bandwidths are adjustable from 100 Hz to 300 kHz.