What else can I do besides using a function generator and an oscilloscope?
To answer your question, I reached out to Sanjiv Dua, the CEO of RFID4U, a leading systems integration and training company. Sanjiv says the easiest way to determine loss, apart from using expensive measuring equipment, is to check the cable and connector types. Most of the cable types are rated with specifications that define cable loss for the UHF frequency. Using these specifications, you should be able to estimate the cable loss.
—Mark Roberti, Founder and Editor, RFID Journal