A suggestion or two for when you've resolved your signal issue.
1) Replace the UHF connector by the scanner with a BNC. Not only will you reduce loss (not enough to matter, but still) but you'll reduce the strain on the scanner's antenna connection. They're somewhat fragile and repairs aren't that easy for the typical user to repair. If you use the antenna for more than just scanning and need to keep the UHF connector on that end of the cable OK, but if not you'll save yourself grief by using the correct connector.
2) On a somewhat related note, get yourself one or two BNC Right Angle (or elbow) adapters (like this for example
BNC Right Angle Adapter | BNC Male to BNC | Female Elbow). With one, you'll reduce the strain by a great deal while with two (forming a "U") you'll nearly eliminate it (unless your coax is very tight). Without them you will put lots of stress on the connection (especially with additional adapters like your existing UHF to BNC) since the pull from the coax is amplified by that long stretch of unbending metal. With one 90 degree adapter, the top of the scanner will help to reduce it by a large amount. With two in a "U" configuration, the strain is downward and helps the coax remain stationary behind the scanner so strain is nearly eliminated. As a side benefit, the elbows provide a swivel effect to further reduce strain when the coax or scanner moves around a bit while driving.
