uhf vs vhf

[kb1oar]

whitch will go farther outside on simplex vhf or uhf ? i thick that vhf does why is that ?

 

[Colin9690]

VHF since lower frequency waves tend to travel farther outdoors. However, inside buildings for example, UHF and 800 MHz will excel since they tend to bounce off the walls of the building, which will help reception inside the building.

 

[902]

whitch will go farther outside on simplex vhf or uhf ? i thick that vhf does why is that ?

Side by side, VHF does... all things being the same. HOWEVER, UHF can parallel distance or even exceed it because it is possible to obtain higher effective radiated power from UHF systems because of wavelength. UHF wavelength is shorter than VHF. A UHF quarter wave is ~ 6." A VHF quarter wave is ~18." A higher gain antenna (more collinear elements) can be had in the same physical space; i.e., a 20 ft. antenna in VHF is typically 5.25 dBd (a little less than 2x twice the power). The same 20 ft. antenna in UHF is typically 10 dBd (a 10x multiplier). Mobile antennas have similar characteristics. On portable radios, UHF goes further than VHF. Why? because of antenna efficiency. a UHF 6 inch "rat tail" is more efficient than a 6 inch VHF helical antenna. Both run circles around even a 12" lowband helical antenna. The antenna circuit is also less effected by the detuning from building construction, if inside.

 

[zz0468]

Free space path loss is a bit less on VHF, but antenna gain is easier to come by at UHF. Other than that, there are too many variables to say one is better or worse than the other. Believe it or not, 10 GHz ssb can out talk VHF ssb by a long way, much of the time. UHF can sometimes work on paths that VHF or low band can't because of the reduced Fresnel clearance requirements. It's really a matter of choosing the right piece of spectrum for the application.

 

[zz0468]

VHF since lower frequency waves tend to travel farther outdoors. However, inside buildings for example, UHF and 800 MHz will excel since they tend to bounce off the walls of the building, which will help reception inside the building.

In my experience, 800 MHz tends to be absorbed by the building materials much more than VHF, so that 800 coverage inside is considerably reduced when comparing VHF. Sure, it bounces off smaller objects better, but the absorbtion rate is higher.

 

[kb2vxa]

Hi all,

Just to clear up the confusion, watt for watt VHF travels farther than UHF, roughly one watt per mile so antenna gain and ERP has nothing to do with it. High gain base station antennas may make up the difference, however if you look in the FCC ULS database you'll notice that on average VHF systems are licensed for a much higher ERP than UHF systems. They don't need all that much power in their intended use usually in urban areas and industrial sites where a large geographical area need not be covered, penetration is more important.

The higher the frequency the more it behaves like light so UHF bounces around and therefore gives greater signal penetration in urban areas. There comes the point of diminishing returns such as ZZ mentioned, SHF tends to be absorbed by building materials, foliage and such. For that reason cell phone repeaters are often used inside buildings.

"Sure, it bounces off smaller objects better, but the absorption rate is higher."

That depends on the material in question, take radar and stealth technology for example. Early on radar engineers discovered the shorter the wavelength the greater the resolution, in other words smaller objects will give a return and the radar image will show more detail overall. Take it to the extreme and you have the electron microscope, electrons being smaller than light waves smaller objects such as large individual atoms may be observed. As for materials, stealth aircraft make use of radar absorptive materials as well as angling surfaces away from the radar thus reducing the return to the point of near invisibility.

When it comes to your 800MHz radio waves, the principles are the same. To cause a reflection (return) the object must not only be radio reflective but larger than the wavelength as well. Non reflective materials are absorptive to one degree or another and the higher the frequency the more absorptive they are. This just could be the reason why a ham or SWL's HF dipole will be OK in the attic while you guys with the scanners complain about indoor antennas particularly at 800MHz. Oh I'm expecting someone to say "mine works real good" because there's always a goat in the sheep's paddock, you can always tell by the distinctive "baa" in a chorus of "maa".

 

[N_Jay]

Hi all,

Just to clear up the confusion, . . . . . because there's always a goat in the sheep's paddock, you can always tell by the distinctive "baa" in a chorus of "maa".

Thanks, that clears up much!:roll:

watt for watt VHF travels farther than UHF, roughly one watt per mile so antenna gain and ERP has nothing to do with it.

Well, that is about the most confusing (and inaccurate) thing in the whole thread.:evil:

however if you look in the FCC ULS database you'll notice that on average VHF systems are licensed for a much higher ERP than UHF systems. They don't need all that much power in their intended use usually in urban areas and industrial sites where a large geographical area need not be covered, penetration is more important.

What a great generalization (that adds nothing to the topic, nor help anyone's understanding)

The higher the frequency the more it behaves like light so UHF bounces around and therefore gives greater signal penetration in urban areas. There comes the point of diminishing returns such as ZZ mentioned, SHF tends to be absorbed by building materials, foliage and such. For that reason cell phone repeaters are often used inside buildings.

When did cell phones come into the discussion?
When did cell phones start being used over 3 GHz?
:roll: :roll: :roll: (irrelevant and WRONG, glad you are "Clearing up confusion")
And this paragraph started off so well.

"Sure, it bounces off smaller objects better, but the absorption rate is higher."

Learn to use the quote feature! It makes reading so much easier (might even help you "clear up the confusion some day)

That depends on the material in question, take radar and stealth technology for example. Early on radar engineers discovered the shorter the wavelength the greater the resolution, in other words smaller objects will give a return and the radar image will show more detail overall. Take it to the extreme and you have the electron microscope, electrons being smaller than light waves smaller objects such as large individual atoms may be observed. As for materials, stealth aircraft make use of radar absorptive materials as well as angling surfaces away from the radar thus reducing the return to the point of near invisibility.

Thanks for the off topic history lesson. (with embedded errors)

When it comes to your 800MHz radio waves, the principles are the same. To cause a reflection (return) the object must not only be radio reflective but larger than the wavelength as well. Non reflective materials are absorptive to one degree or another and the higher the frequency the more absorptive they are.

You sure? You might want to double check your "Waves and Fields" textbook.

This just could be the reason why a ham or SWL's HF dipole will be OK in the attic while you guys with the scanners complain about indoor antennas particularly at 800MHz.

"Could be"? And you are always so confident in your knowledge. You disappoint me!:lol:

Oh I'm expecting someone to say "mine works real good" because there's always a goat in the sheep's paddock, you can always tell by the distinctive "baa" in a chorus of "maa".

Now we know what you do with your spare time!:twisted: :lol: :twisted:


And so I am not "off topic" some answers.

First lets stick to what is commonly called VHF and UHF in land mobile radio. 150-174MHz and 450-470(maybe 512)MHz.
Since he said simplex lets assume portable to portable (or Mobile to Mobile). (The OP can correct if this is a bad assumption.
TYPICALLY (since there are so many variables, that is about as accurate as you can get), a UHF portable will give you more range. When the UHF signal does not go as far, the additional antenna efficiency and lower typical background noise more then makes up for the difference.
In a mobile to mobile environment it is more equal since both antennas are usually equal, and the UHF may have additional cable loss.
VHF advantages will show in areas with terrain blockage, UHF will show an advantage in areas with building blockage.
In building portable use can show either depending on the building type, but usually UHF does better.

 

[Halfpint]

(Lotsa text bobbited for brevity)

Ding! Ding! Ding!

We have a winner!

Now *if* some certain people out this way were actually able to read and understand the last sentence systems like the CO DTRS would actually make sense and function like they keeping trying to claim.

VHF (Low and High), UHF (Low and High), and SHF propagation characteristics and equipment characteristics have many assorted niches and such where they shine above one another. One of the major problems these days is that so many people, especially those who actually should know better, try and make one or another range do work that it isn't suited for because it has been `sold' as being the `latest and greatest' thing to `come down the pike', that it works in certain circumstances for some other use, that it is `the only thing that will work this way, that it is `secure', that it will `cure all you ills' you `think!?' you have, ETC.. (I *will* admit that I *do* have a bit of a problem with certain frequency ranges that are being touted and used these days. But, having said that, I *will* also admit that I also realize that there *are* many quite legitimate areas of useage for said frequency ranges, too.) A really good example of trying to use a frequency range for something it isn't suited for would be the UHF-Hi freqs of 700 and 800 MHz over an extremely wide and varied terrain coverage area is the CO DTRS system. Even back when it was first conceived it was known that there were going to be coverage problems even in the small initial coverage area but they went ahead with it on mainly `political' reasons. When there came the siren call for `interoperability' the features that were supposed to provide that became the main `claim to fame' and the system was `pushed' / `pitched' as such a system capable of such whilst overlooking situations where it wasn't basically well suited. A perfect example of making `blanket' assumptions as to it being an all around `best' frequency useage. (One of the `assumptions' was in the propagation `department'. 800MHz is `supposed?' to be able to `bounce around' and `get into' all the `cracks and crannies' `better'.) We now have `real world' examples that show us quite graphically that it doesn't quite live up to that. (Another `assumption' was that both the modulation scheme, digital, and trunking was only really capable at those frequencies both `technically' and `financially'.) At that time about the only example of both were the ubiquitous cellphones and a few very limit test systems set up by certain manufacturers at certain `labs' and other sites / systems.

Even way back then it was well known that the above quoted sentence was an `operative' that had tremendous meaning. But, for various reasons that always seem to bring one all sorts of vituperation, screaming and shouting, and endless so-called debate, the installation of these `one size fits all' , or we *will* *make* it fit all, there are a lot of these `cookiecutter' type systems we now are seeing all over the place. However... There appears to be some hope on the horizon as some people, agencies, and even States are starting to realize that maybe there are places where they have to seriously consider, and use, other frequencies or even a `mix' of frequencies. This because each range has things it can `bring to the table' that another cannot. While this bring with it assorted other variables we now are finally capable of taking on the majority of them without tremendously making both the systems and the equipment horrendously complex, unwieldy, or co$tly. It also appears that the `old saw' about `vanishing RF "real estate"' is beginning to fall by the wayside as the `tech-no-golly' of trunking and the release of heretofor `congested' frequencies and ranges happen and those who can best use those released to use frequencies start picking them up and put them to use where they `fit'. (One of the things *I* am actually looking forward to are scanner radios that can follow a trunked system over not just 700 and 800 MHz but also over VHF (Lo & Hi) and good old UHF-Lo depending upon what was propagating the best at the time or in the particular situation with not any more hassles than current scanners. [Yeah, I know that sometimes the hassles can sometimes seem to be horrendous for some systems or situations. {WAN GRIN!}] I also expect that, taking into account the inflation effect, those scanners are not going to be really any more expensive than what we have had in the past and currently have. [For those who want to scream that the current radios are expensive I'll posit that a PRO-96, as an example, really isn't any more expensive now than a PRO-43 was back when it came out if one takes into account inflation and actually may be *less* expensive! Especially when one also takes into account what one actually gets for their money.])

Oh, well... Just an `Olde Fart's' 2¢ worth. {GRIN!}

 

[KC0CSE]

Vhf In Police Use

If you go to the country lets say the ozarks..you will not see local police use UHF...All freq's in the country are VHF only....look it up...most all of missouri is VHF OR 800 meg...except highway patrol...VHF goes further it the ozarks...or they would not use it....

 

[N_Jay]

If you go to the country lets say the ozarks..you will not see local police use UHF...All freq's in the country are VHF only....look it up...most all of missouri is VHF OR 800 meg...except highway patrol...VHF goes further it the ozarks...or they would not use it....

Well Well Well, another genius.

Maybe they are still VHF because when they got radios VHF channels were available and they have not made significant upgrades to the system.

Most agencies that are on UHF are there BECAUSE those were the channel that were available when they built the system.

Ain't it amazing when you know history instead of pulling (supposed) facts out of your arse!

 

[Thayne]

Arse? Are you from Canada?

 

[wlmr]

whitch will go farther outside on simplex vhf or uhf ? i thick that vhf does why is that ?

By simplex I understand you're not talking about repeated, just straight radio to radio.
Outside? The lower the frequency the less that things like folage absorb the signal.
Urban environments complicate the answer. In some instances 800MHz UHF frequencies MAY be able to pass through windows, etc. and make it into buildings better than 450 MHz UHF, 150 MHz VHF hi, or 30-50 MHz VHF lo . Note I said MAY.

In all situations, your milage may vary.

As far as what freq range gets used for a radio system? Sometimes they are dictated by what frequencies are available, sometimes they are what a vendor talks the user into buying.

In an ideal world, the frequency band that gets used would provide the best propogation (and isolation) available.

Sadly this is the real world.