I’ve got some UHF radios (Motorola GP340) and they current have 3.5? VHF antennas attached for some unknown reason. They seem to transmit and receive ok so just wondering if there is any difference in the UHF and VHF antennas, or if the performance of the radios is going to be degraded and just hasn?t been noticed as we?ve only used the radios over shorter distances.
Along with reduced performance, you risk blowing the output transistor of the radio, thus rendering it useless. Get the proper antennas.
Handheld radio antennas are not expensive, but the radios can be pricey, so simply replacing the mismatched antennas makes a lot of sense.
A quarter wave for some VHF frequencies IS a 3/4 wave at UHF. I have a VHF antenna on my van that matches quite well at UHF as a 3/4.
Jwilkers - remember that practically no hand-held antennas remotely match to 50Ohms. In over 40 years I have never found a handheld designed badly enough to be damaged by bad VSWR - in fact, most of them function quite happily when users forget the antenna fell off! I’ve had them back for repair, and the complaint is it doesn’t have the range anymore - where’s the antenna? Oh - is that bit important? I took it off because it fitted my pocket better without it!
The difference between VHF and UHF antennas is the length. UHF antennas of the same type/style are shorter than VHF antennas.
Some VHF antennas can be used on UHF, but there are very specific ‘catches’ about doing so. If that UHF frequency is a harmonic of the frequency that VHF antenna is tuned for, then you -may- be able to use it on UHF. And then there are some antennas specifically designed to work on both VHF and UHF.
This whole post amounts to a big “maybe”. Not very satisfying, huh?