any outside antenna beats the inside antenna. The Workman brand, they are sort of a diamond clone, far cheaper but it us, they have held up fine for me. I use a uvs300, costs about $70.00. 8.3 gain on vhf and 11.4 on uhf. These are isotropic but still good figurers. It is tuneable. I use it for monitoring and transmitting. I use a good quality switch box to isolate the scanner from the transamitter. I take it you will not be transmitting on 300 mhz sop it will listen fine. It is 18ft tall with radials that are 18". Takes the wind and ice good. I did have one at 190 feet on a water tower. The wind tore it up in 1 year. The mast clamps were not strong enough.