Questions about these Antennas VHF/UHF only

Ok i been around radios for a long time but i just dont get it, an antenna is just an antenna, despite the style and all.

I just love the Skinny Whip Antennas for the UHF but i am more on my VHF then anything unless I have my UHF for FRS/GMRS stuff. I just dont get it, what makes these antennas so different between the UHF/VHF band splits for either High or Low Frequencies?

I know later on if i kept one on the other, one of the radios would be a RX only radio and I cant TX out at all.

I guess that answered my own question but does anyone else have an input that knows more then me for what i know?

Okay, dunno if you’re still around but in case you are here’s an answer…

For an antenna to radiate well, it has to be resonant on the frequency you’re transmitting on. To do that it has to be of the correct electrical length, which for a simple wire-whip antenna is mostly the same as its physical length. (adding things like load coils (those little bulges or coils in the middle of some car-mount antennas) changes its electrical length without changing its physical length).
If the antenna is non-resonant, RF waves pumped into it by the transmitter will bounce off the antenna and be reflected back into the transmitter. This can make the radio’s finals (the circuits which produce the final high RF power being sent to the antenna) overheat and in some cases can cause damage. That’s why you NEVER transmit on a radio that has no antenna hooked up.

To be resonant, the antenna must be the right electrical length. Since VHF has a larger wavelength than UHF, that means a larger antenna.

To make an analogy- take a crystal glass. When you tap it, it rings at a certain pitch (frequency). If you get an opera singer to sing at that exact pitch, the antenna will resonate (vibrate at that frequency with much greater energy because the vibrations from the singer perfectly match up with the vibrations of the glass). The result of that is that you get much more noise coming out of the glass than you do if the singer sings at the same volume, but a different pitch.

That glass is like your antenna- you want it to resonate and sing as loudly as it can. But if you transmit the wrong frequency into it (like the singer singing at a different pitch), sure some signal will get out but most of it will bounce off the surface of the glass (and be reflected back into the transmitter).

In contrast, the fat, flexible rubber antennas are usually ‘fully loaded’ coil antennas- it’s just a spring inside the rubber. This type of antenna is more flexible electrically (it won’t reflect nearly as much power back into the antenna) but also isn’t as efficient at radiating (more of the transmitter power is just wasted as heat).

That isn’t a great explanation, but hopefully it helps at least a bit…