The AnyTone Tri-Band antennas are terrific for the 578 Tri-Band radio, but they are very heavy at length. Unfortunately, it is a very top-heavy antenna. Please note that although we sell this antenna, it does not come with a base. We offer a Trunk Lip Antenna Mount that we have found works well. The end of the antenna has a PL-259 connector and will require an SO-239 mount.
None of the magnet mounts we have tried it with are suitable. We do not recommend the use of this antenna with any magnet mount for any reason. We only recommend using bolted or screwed-on mounts such as bumper mounts, truck bed mounts, mirror mounts, etc. Use of a magnet mount with this antenna is an accident waiting to happen.
As of current, there is not a way of adjusting the spring tension on the bottom section. For certain vehicles, this causes the situation where the antenna hinges down while going down the road. We have experimented with many different solutions and the best/simplest is to cut a length of Grey 3/4" PVC plastic conduit about 6" long and slide it down over the center load to lock the base in place. This solves the issue for a couple bucks (2' length bought from Home Depot or Lowes) and the antenna can still be laid down when needed for overhead clearance.