Ok thanks for the info. Is the Diamond good antenna over the stock one thats on the 396XT?
I have used the Diamond RH77CA (BNC) and the Diamond SRH77CA (SMA).
I prefer using the BNC version simply because the SMA version doesn't hit bottom when you screw it on, so it leaves a slight gap. Purely cosmetic, but OCD kicks in, and it has to be correct.
Both Diamond models perform exceptionally well for my usage (VHF / UHF / 800mhz) scanning.
[Edit] I realized I didn't really answer your question: Over the stock antenna, there is a significant gain in performance.