Analog UHF Antenna vs. P25 700 MHz Antenna?

[JethrowJohnson]

Hi everybody, I was wondering if there's a specific visual difference between an antenna for a mobile analog conventional UHF radio and one for a mobile P25 trunking 700 MHz radio? I had thought that the longer thinner ones were for UHF and the tiny ones that look like oversized pencil erasers were for P25. My police department uses UHF, (although that's expected to change sometime soon) and their cars have the longer antennas, and so does the FD, but at least 2 out of the 4 Medic units they have, have MARCS radios used for patient transports to MMH or Selby. But I've noticed that these Medic units have three long antennas, which I figure one is for their own UHF channels, another for the hospitals' VHF channels, and another for the hospitals' MARCS channels. They don't have any short antennas. My sheriff's office is on MARCS and I noticed that their 2015 and newer units have short antennas, but that there older ones have long antennas. So does it matter which antenna is used for a particular band or are they different for other reasons? And when my PD starts to switch to MARCS soon, will a short antenna on their cars mean that that one has a MARCS radio, or isn't that a way to be able to tell if it is or not?

 

[Whiskey3JMC]

The antenna doesn't care about voice mode used (analog vs P25). Generally the shorter the whip the higher the resonant band. Certain exceptions exist

 

[JethrowJohnson]

You mean the shorter antennas are for higher frequencies?

 

[Whiskey3JMC]

You mean the shorter antennas are for higher frequencies?

Exactly what I said., though reworded slightly

Generally the shorter the whip the higher the resonant band

 

[JethrowJohnson]

Okay. Thank you! 🙂👍

 

[AM909]

It really depends on the type of antenna. About the only type you can be reasonably accurate spotting at a distance is if it's a single stainless-steel rod like this, it's likely a "quarter-wave" and has a length in inches of about 2805/f, where f is the frequency in MHz. So, VHF Low midpoint 40 MHz is 70", VHF High 150 MHz is 18". UHF 460 MHz is 6", 7/800 MHz is 3.5".

You can also have longer or shorter versions of such antennas, providing gain or loss in exchange for size, with a typically black plastic cylinder at the bottom and/or up the rod a ways.

Then there are plastic/fiberglass things of various shapes, like a "puck" or "shark fin" with no exposed antenna rod, and which may contain multiple antennas (I did one with 5 cables hanging out of it the other day that looked like a Portuguese Man of War. )

 

[JethrowJohnson]

Thanks. The longer ones aren't very long but they're black and at about a 45° slant, and I'd say they're probably about 5 inches or so. The tiny ones I was talking about look something like this: Robot or human?
I don't think it's the same kind since this says it's VHF/UHF and my SO uses them on MARCS, but they look similar.

 

[speedway_navigator]

Back when I was installing VHF gain antennas someone told me the San Diego PD moved from those to the 18" unity gain antennas because an officer slammed the trunk and the tip of the whip hit his glasses and broke the lens. That became a safety hazard.

 

[mmckenna]

because an officer slammed the trunk and the tip of the whip hit his glasses and broke the lens. That became a safety hazard.

I guess justice is only half blind?

I remember doing that once, and only once. Fortunately it didn't hit me in the eye.

 

[kb4mdz]

Back when I was installing VHF gain antennas someone told me the San Diego PD moved from those to the 18" unity gain antennas because an officer slammed the trunk and the tip of the whip hit his glasses and broke the lens. That became a safety hazard.

Over application of force, by one (dumb) officer, so the solution is to change something in the whollllllle rest of the system. Yup, that's manglement there.