Mobile antenna with Handheld radio

We are in a fairly rural area and am on the volunteer fire department. I am using a Motorola XTS 1500 with a Lapel Microphone in my pickup. I have the radio hooked to a external mobile antenna NMO mount. I am wondering if these radios are meant to be used with an external antenna? Used it the other day and dispatch told me I was really scratchy. Just don’t know if a handheld radio has as much power as a mobile for a antenna other than the rubber duckie antenna. Thanks for any info!!

Some radios have proper antenna connectors - constant impedance coaxial connectors - SMA, BNC or TNC ones being very common. These are 50 Ohm impedance and you can connect properly to vehicle or base station antennas and benefit from the extra performance. The snag with the 1500 is it uses a stud connection, not a coaxial one - so there is no connection to the chassis of the radio so if you buy a stud to BNC connector adaptor - the shield of the cable isn’t connected to anything on the radio. It makes it unbalanced and the coax is a poor match. electrically. It will work, but performance is impacted to a degree on receive and transmit. With a portable already having lower power than a mobile, you lose the balance between receive and transmit. A good test is to stand outside the vehicle and get a radio check on the rubber antenna, then swap to the vehicle antenna and get another check and see which is better. Without the screen being connected, things like power meters don’t work properly or VSWR meters. The positive side says that the rubber duck inside will still be poorer than the external antenna connected to the radio with a bit of a mismatch.