I had to do a little Dremel work to make it fit, but it wasn't that hard.
Just use a sanding wheel and grind a 3.5cm-4cm collar on the bottom that will just fit into the antenna recess on the SDSD100.
Grind a little, check it, grind a little more.
Go slow, you don't want to grind off too much.
I then used some alumi-black to spiff it up a bit.
150-159 is VHF high btw. I'm curious - how far away is the transmit site you are trying to receive, and / or are you trying to monitor simplex mobiles or handhelds? I ask because VHF high reception for me is acceptable, except for marine band portables which are typically 1W. Disclaimer is the VHF I listen to is typically half duplex repeated systems (and the analog audio is scratchy.)
I'm trying to improve my reception on the VA STARS system. I'm within range of about 5 or 6 sites, but none real solid. By changing from the stock antenna to a RH77CA BNC w/adapter, I can improve from about -100db to about -90db, which gives me some reception, but choppy.
I assume there's some loss from the BNC > SMA adapter, so trying to find a direct fit.
The BNC adapter likely has negligible loss. In fact, it will provide a more solid mechanical connection to the top of the radio especially with a longer and less flexible antenna like the RH77CA. Perhaps it is time to consider an outside antenna.