The Diamond RH951S is described on the Universal Radio site as "... a triband antenna for 2 meters (144), 70 centimeters (440) and 23 centimeters (1200). It terminates in a male BNC plug. 50 ohms. It is a slim, black flexible antenna that is 15 inches long."
It's too long for me; I have a Diamond on the VX-6, and in the car it is a PIA. W2GLD suggested a Watson W-801 (from ScannerMaster, a sponsor of this site). I don't have the tools to measure its performance over the stock -106 duck and RS 800 MHz, but IMHO it seems to hear more signals when I swap antennas around. It is sturdier by a long shot. The W-801 claims coverage of 25-1900 MHz, just 2 inches longer than the -106 duck.
Thanks trsundstrom - I'll look into the Watson antenna. I'm basically trying to get a little better reception on the P25 700/800MHz systems (so a tri band seemed the obvious solution). I have the GRE 800MHz antenna, and while it does an adequate job there’s still some room for improvement.
One of these days I've got to get an outdoor antenna for the Pro-197 too - the fun just never ends.