Business radio power output question

[Pr999]

I don't know if this question has already been asked or not but please notify me if it has and link me to the original.

To simplify: Why does VHF use 5 watts while UHF uses 4?

Full Explanation:
I want to know; why are VHF radios set at 5 watts while UHF is set at 4? Since UHF has a shorter wavelength, shouldn't it have a harder time with reach, unlike VHF? So why does VHF get a +3 watt boost but UHF only gets +2? (Differentiating from the standard 2 watts every VHF/UHF/800? handheld has.)

It just doesn't really make much sense to me other than UHF is more standard in denser populated areas, whereas VHF is more standard in open terrain. But one thing that catches me is, why VHF needs a full 5 watts even though it doesn't struggle much in those wider areas but UHF which is also sometimes used in those same areas only gets a -1 watt difference?

Maybe I'm getting a bit too over my head about this, I'm surely not mad or frustrated about it either, it just makes me kind of curious as to why. Also, I get there's not much of a difference in wattage.

 

[alcahuete]

UHF Portables: Why Only 4 Watts Instead Of 5?

How come some UHF portables only give you 4 watts of transmit power instead of the full 5 watts? Sometimes you'll have a radio model that comes in VHF and UHF versions. The VHF version will do 5 watts, but then they'll often make the UHF one only 4 watts. Why?

forums.radioreference.com

There's a good start.

 

[Pr999]

Thank you!

 

[mmckenna]

I don't know if this question has already been asked or not but please notify me if it has and link me to the original.

To simplify: Why does VHF use 5 watts while UHF uses 4?

Full Explanation:
I want to know; why are VHF radios set at 5 watts while UHF is set at 4? Since UHF has a shorter wavelength, shouldn't it have a harder time with reach, unlike VHF? So why does VHF get a +3 watt boost but UHF only gets +2? (Differentiating from the standard 2 watts every VHF/UHF/800? handheld has.)

Not sure where you are getting the 2 watts thing from.

It depends on the radio. I have Harris hand held's that do 6 watts on VHF, 5 on UHF and 3 on 700/800MHz.
I have Kenwood's that do 5 on VHF
I have other Kenwood's that do 3 on 7/800MHz.

Part of it has to do with the design of the radio and the capability of the RF amplifiers used.

In reality, that little bit of power doesn't make that much difference. People, especially hobbyists, get really hung up on the power output of their radios.

It just doesn't really make much sense to me other than UHF is more standard in denser populated areas, whereas VHF is more standard in open terrain. But one thing that catches me is, why VHF needs a full 5 watts even though it doesn't struggle much in those wider areas but UHF which is also sometimes used in those same areas only gets a -1 watt difference?

It's not the power, it's the wavelength. Longer wavelengths tend to do better outdoors in more rugged terrain. That's why it is very often used for wildland fire fighting.

UHF, 700 and 800MHz work better for penetrating buildings, so it's common to use those in urban areas where getting through reinforced concrete is a challenge.

The power output of the radio doesn't play into this very much, especially 1 watt difference.
The efficiency of the antenna system, does. It's much easier to make an efficient antenna on higher frequencies.

 

[RFI-EMI-GUY]

Motorola Systems Saber: VHF 6 Watts, UHF 5 Watts.

Two things affect the power level:

1) Battery life, If two radios of same model series share battery design, the UHF may have lower power as a result of the design requiring more current drain per watt of RF power. Public Safety users are concerned with battery life and duty cycle, so the numbers tend to be published in response to bid specs.

2) FCC limits on MPE/SAR RF Safety limits. 47 CFR § 1.1310 - Radiofrequency radiation exposure limits. Usually not the ultimate limiting factor but must be tested and reported for radio certification. You wont see 10 or 20 watt handheld radios being certified.

One of the reasons FRS radios are limited in power and fixed antenna being required is that FRS radios are used by children and ignorant adults that may stick the antenna in their eyes while transmitting. This was discussed in 2017 when FCC was debating making GMRS license by rule, 50 watt moble radios would be banned, power of mobiles and portables strictly limited and non removable antennas mandated.

The GMRS license gives freedom to be a dumbass and suck on the 50 watt mobile antenna.

Going back to VHF vs UHF. UHF has an advantage in that the UHF noise floor is lower than VHF and that UHF antennas are more efficient than VHF antennas. UHF really doesn't "struggle", VHF has a bigger battle. An extra watt at VHF does not make much difference.

 

[jeepsandradios]

You wont see 10 or 20 watt handheld radios being certified.

Geeze dont say that around the ham crowd....they all have a CCR doing 10 watts

 

[RFI-EMI-GUY]

Geeze dont say that around the ham crowd....they all have a CCR doing 10 watts

Yeah but they are just special!

 

[speedway_navigator]

I found this while updating my GCT-1 class notes, MPE is being phased out in favor of exposure reference level from my research.

The standard uses the term exposure reference level (ERL) to refer to exposure levels generally and safety program initiation level to refer to the upper limit of the lower tier. These terms replace the deprecated terms maximum permissible exposure (MPE) and action level, respectively.

IEEE Standards Association

.Safety limits for the protection of persons against the established adverse health effects of exposures to electric, magnetic, and electromagnetic fields in the frequency range 0 Hz to 300 GHz are presented in this standard. These exposure limits are intended to apply generally to persons...

standards.ieee.org