A Communications service monitor is a tool for servicing radios. Until recently, most large organizations used VHF/UHF FM radio for communications on dedicated channels. A service monitor is a tool that can usually absorb the full output power of these radios while measuring power, frequency, distortion, etc. They can also generate a variety of signals for aligning receivers.

Most of the older, affordable models go from almost DC to 1 Ghz. I've got an IFR 2947a, which goes up to 1.05 Ghz.

Here's an example from ebay.

https://www.ebay.com/itm/168770412399

Here's a specification sheet for the one I have, a pdf

https://www.testmart.com/webdata/mfr_pdfs/aerofl/2947a.pdf