UHF or VHF?

[N7IFU]

Being a ham, I feel like an idiot for not knowing this, but which frequency range has a longer range?

I'd assume UHF has longer range because it requires less power, for instance, my FT857 has a max on UHF of 20 watts, whereas the max is 50 on VHF.

Which one has longer range, and what are they most suitable for?

 

[kb5udf]

Lower=longer

The general thing to remember is lower=longer (range), within reasonable bounds of course.
Thus your 2m HT SIMPLEX range will be significantly greater than that of 70cm. Same thing for mobiles and bases. The most common (and about only one I can think of) where 70cm would have better range is in certain buildings (and some automobiles). Two reasons for this that spring to mind: 1. the 70cm signals are more reflective 2. the shorter wavelength makes many buildings less like a Faraday cage at 70cm than 2m.


So basically, aside from being in a building with an HT (or a base with ant inside building), you'll go further
with VHF.

JB

 

[N7IFU]

Okay I understand. But what I don't understand is why some radios such as mine have a higher max output on a frequency range that has a longer range. Is it because some manufacturers believe that everybody maxes out every possible inch they can get?

 

[kb5udf]

RF issues

As I understand it, there are a few factors that come into play here. It's generally harder, from what I here
to get transistors to output the same amount of power at higher/uhf frequencies. There are also issues, I believe, with the fact that at a higher frequency, it tends to take more power to produce the same watt output, because the frequency "repeats" so many more times per second.

At uhf, many PA transistors are simply less efficient. I'll leave it to the more technically adept to comment
as to why.

JB

 

[N7IFU]

Okay thanks.

 

[N4DES]

Okay I understand. But what I don't understand is why some radios such as mine have a higher max output on a frequency range that has a longer range. Is it because some manufacturers believe that everybody maxes out every possible inch they can get?

UHF have exposure limitations and have to operate at a lower power than VHF as mandated by the FCC OET -- Bulletins On-line

Current draw and efficiency plays a role in it as well, but the FCC rules when it comes to maximum power output.

 

[N7IFU]

Oh okay. So there are FCC limits on power in UHF that are much lower than other bands. I understand. Thank you!

 

[WA1ATA]

This is an interesting question.

Here's my understanding of the VHF vs UHF. Corrections and comments welcome!

The path loss for a dipole to dipole link is higher for UHF than VHF, because the capture area of a 1/2 wavelength dipole is smaller at UHF.

When size is the limiting factor (as it is on handheld radios), the antenna performance at UHF will be better. So for HT to HT communication, UHF would seem to have an advantage.

The effect of terrain and buildings is different for VHF vs. UHF. VHF seems to work better in hilly terrain than does UHF. Anecdotal reports are that VHF is more likely to be diffracted by hilltops and be able to be heard in valleys.

UHF seems to work better in urban areas. Perhaps because it is more prone to bounce off of buildings to fill in what would otherwise be a dead zone caused by a building blocking the signal path.

I bet there are forum members out there with a lot of experience in commercial or public safety systems, both VHF and UHF. What are your observations ?

 

[N4DES]

When size is the limiting factor (as it is on handheld radios), the antenna performance at UHF will be better. So for HT to HT communication, UHF would seem to have an advantage.

I bet there are forum members out there with a lot of experience in commercial or public safety systems, both VHF and UHF. What are your observations ?

I was going to bring up the same a few days ago as the experiments that I have done, essentially 2 Quantar repeaters at the same tower site with almost the same receiver sensitivity out of each duplexer and almost identical antenna heights (within 50' of each other). What I found is that the UHF beats the VHF in overall usability by a few miles on the outlying areas even though the VHF is higher on the tower. What I also found, locally in my situation and probably the same in many areas, is that the overall noise floor is 3 to 4db lower on UHF than VHF also increasing usable real world sensitivity.

As to portable to portable performance, I will agree on the efficiency of the UHF antenna having "real gain" vs the made up gain that the manufacuters claim on these pocket sized VHF antennas that are on the market.

Mark

 

[N7IFU]

Thanks for the replies guys! I get it!