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UHF Range Question
- Thread starter gman4661
- Start date
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SkipSanders
Silent Key
- Joined
- Dec 19, 2002
- Messages
- 1,059
Line of sight. Power has very little to do with range at UHF. It will help a bit getting through foliage, and that's about it.
The Motorola rule of thumb for reliable communications is (square root of antenna 1 in feet) + (square root of antenna 2 in feet) = range in miles
So two handhelds (antenna height about 5 feet) have a rough range of 2.23+2.23=4.46 (call it 4.5) miles.
In reality, in urban settings, it's gonna be more like anywhere from 1/2 to 2 miles, given buildings in the way.
Put an antenna on top of your house, at 20 feet, and it's more like 6-7 miles to an HT. Actual range can, in the best conditions, be up to double these ranges, but it's not the way to bet, unless you've got both ends on top of hills, with nothing else in between.
If you happen to have one end in space, a 5 watt HT can easily talk just fine 150 miles away... but that's sort of a special case.
The Motorola rule of thumb for reliable communications is (square root of antenna 1 in feet) + (square root of antenna 2 in feet) = range in miles
So two handhelds (antenna height about 5 feet) have a rough range of 2.23+2.23=4.46 (call it 4.5) miles.
In reality, in urban settings, it's gonna be more like anywhere from 1/2 to 2 miles, given buildings in the way.
Put an antenna on top of your house, at 20 feet, and it's more like 6-7 miles to an HT. Actual range can, in the best conditions, be up to double these ranges, but it's not the way to bet, unless you've got both ends on top of hills, with nothing else in between.
If you happen to have one end in space, a 5 watt HT can easily talk just fine 150 miles away... but that's sort of a special case.
stmills
Member
Is there a factor on the power of the radio to complete the line of site? I recall hearing somewhere that on hts factor of 1w per mile for ht to ht simplex.
Steve
Steve
N
N_Jay
Guest
The rules of thumb are worthless once you start hammering.
Loss comes from the path and what is in the way.
Gain comes from power out and sensitivity.
All the rest is math.
Loss comes from the path and what is in the way.
Gain comes from power out and sensitivity.
All the rest is math.
b7spectra
EMS Dispatcher
I've got a 40 watt Spectra in my truck and I'm using the Antennex Phantom (black can) for my antenna. In simplex mode, I'm lucky to be able to talk 3 1/2 - 4 miles in semi-rural areas. On my Saber portable, about 1 - 1 1/2 miles. Now, hitting the repeater that is 30 miles away is no problem due to the antenna is 245' above ground level!
SkipSanders
Silent Key
- Joined
- Dec 19, 2002
- Messages
- 1,059
When the planet is in the way, the difference between 45 watts and 4 watts is effectively zero. Maybe if you had a kilowatt, you'd get edge effects strong enough to help, but that's not gonna happen... and you'd fry your eyeballs if you used that kind of power, anyway.
I've gotten quite good signals to a repeater 20 miles away, with 100 milliwatts (on 2 meters). If you can see the other end, power is effectively meaningless once you're at 1-2 watts, at UHF.
I've gotten quite good signals to a repeater 20 miles away, with 100 milliwatts (on 2 meters). If you can see the other end, power is effectively meaningless once you're at 1-2 watts, at UHF.
prcguy
Member
In free space when you double the distance the signal drops by 6dB. Or in other words if you double the distance you need to increase power by 4 times to keep the same level at the other end.
In reality, terrestrial communications is hampered by ground bounce and cancellation due to signals arriving out of phase at the far end. Its very hard to predict so you can start with a free space loss calculator then add up to 6dB or take away 20dB or more due to signals combining in phase or canceling from ground bounce.
Then add attenuation from foliage and knife edging (Fresnel zone effects) over mountains and you have a real tough question to answer. Some of the real life examples given earlier are good starting points.
prcguy
In reality, terrestrial communications is hampered by ground bounce and cancellation due to signals arriving out of phase at the far end. Its very hard to predict so you can start with a free space loss calculator then add up to 6dB or take away 20dB or more due to signals combining in phase or canceling from ground bounce.
Then add attenuation from foliage and knife edging (Fresnel zone effects) over mountains and you have a real tough question to answer. Some of the real life examples given earlier are good starting points.
prcguy
Is the 3 1/2 - 4 miles mobile to mobile?
Is the 1 - 1 1/2 miles portabile to portable?
And much difference is there between a quarterwave and a high gain mobile antenna?
The higher the gain, the lower the angle of radiation and the sharper that profile gets. This means that with clear line of sight it focuses your power better but the terrain becomes even more of an issue as the radiation angle is so low.
I see this effect with my X510 roof antenna on UHF and also my Diamond 7900 in the mobile. Depending on terrain, you can be better off with a lower gain antenna at times because a slightly higher angle of radiation can get you 'over' some terrain where with a lower angle, you would just put all the energy into the side of the hill as it were. In hilly and urban environments, a simple 1/4 w mobile antenna can do better than the fancy high gain models.
The answer is still 'it depends' ;-).
I got a lot of experience with UHF and line of sight with a repeater my buddy and I bought and played with. We thought getting a 100' spot on a cell tower was awesome....until we realized it wouldn't even cover the entire township well...and this is relatively level coastal area with only moderate hills around. It wasn't until it was at 275' that it started working well. We're shooting for a 500' tower space now. It's all about the elevation over avg terrain.
I see this effect with my X510 roof antenna on UHF and also my Diamond 7900 in the mobile. Depending on terrain, you can be better off with a lower gain antenna at times because a slightly higher angle of radiation can get you 'over' some terrain where with a lower angle, you would just put all the energy into the side of the hill as it were. In hilly and urban environments, a simple 1/4 w mobile antenna can do better than the fancy high gain models.
The answer is still 'it depends' ;-).
I got a lot of experience with UHF and line of sight with a repeater my buddy and I bought and played with. We thought getting a 100' spot on a cell tower was awesome....until we realized it wouldn't even cover the entire township well...and this is relatively level coastal area with only moderate hills around. It wasn't until it was at 275' that it started working well. We're shooting for a 500' tower space now. It's all about the elevation over avg terrain.
N
N_Jay
Guest
The higher the gain the narrower the vertical beamwidth.
The angle of radiation is independent, but more noticeable with a narrower beamwidth
The angle of radiation is independent, but more noticeable with a narrower beamwidth
Although I've been using professional radios for 31 years, I'm not well versed in the technical aspects of antennas. I guess my question is that on average, and the average being somewhat hilly wooded suburban landscape, will a high gain antenna outperform a quarterwave on GMRS freqs?
N
N_Jay
Guest
Yes, but not in every case, and your case could easily be one where it is not an advantage.
OK, more specifically, I am thinking about using simplex GMRS for family activities, road trips and scout functions (which often take place in wooded areas). There are no known repeaters where I live. Does it sound as if I should be thinking quarterwave or higher gain?
Also, it seems that wattage is not normally a huge factor. Will additional wattage realistically help much in terms of penetrating wooded areas?
Also, it seems that wattage is not normally a huge factor. Will additional wattage realistically help much in terms of penetrating wooded areas?
N
N_Jay
Guest
You have to start understanding the variables to grasp why the answers you are getting are vague.
Let's convert a few rules of thumb into dB.
3dB is an almost unnoticeable difference (I little less or a little more static)
6dB is a noticeable difference. (A staticy but understandable signal becomes fairly clear signal) (A staticly and not understandable signal becomes a staticy but understandable signal)
10dB is a very noticable difference. (No signal may become a staticy but usable signal) (A staticy and hard to use signal becomes a fairly clear signal)
Assume a 1/4 wave is 0 dB gain, then a typical gain antenna is +3dB
Double the power is 3 dB
10 times the power is 10dB
Double the height is 6dB (In a cluttered environment)
Double the height is 3dB (in a clear environment)
Double or 1/2 the distance in a clear path is 6dB
Trees in the path are 6 to 30 dB
A hill blocking the view is 10 to 60 dB
So little things like clutter, trees and hills far outweigh the power and antenna.
(And all these figures are rough rules of thumb)
Let's convert a few rules of thumb into dB.
3dB is an almost unnoticeable difference (I little less or a little more static)
6dB is a noticeable difference. (A staticy but understandable signal becomes fairly clear signal) (A staticly and not understandable signal becomes a staticy but understandable signal)
10dB is a very noticable difference. (No signal may become a staticy but usable signal) (A staticy and hard to use signal becomes a fairly clear signal)
Assume a 1/4 wave is 0 dB gain, then a typical gain antenna is +3dB
Double the power is 3 dB
10 times the power is 10dB
Double the height is 6dB (In a cluttered environment)
Double the height is 3dB (in a clear environment)
Double or 1/2 the distance in a clear path is 6dB
Trees in the path are 6 to 30 dB
A hill blocking the view is 10 to 60 dB
So little things like clutter, trees and hills far outweigh the power and antenna.
(And all these figures are rough rules of thumb)
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A good "guess" would be between 1 - 5 miles, depending on an awful lot of unknown variables.
Are we talking portables or mobiles?
N
N_Jay
Guest
Real life answer will range from 100 miles at 1/2 watt with 0dB antennas to less than a mile with 20 watts and 3 to 5 dB antennas.
RADIOGUY2002
Member
From my experiences in using a simplex in semi wooded to heavy wooded areas is about 1-1 1/2 miles. Usually wooded areas having rolling grounds which brings an unwanted element into the scenario, these guys can not give you a straight forward answer as the variable changes for every environment or topography base area you enter into. My strong advice for you is that if it intend for field deploy ability simplex family communications take this route. Get either a tri-square radios for heavy commercialized areas or hot spot travel zones. If its wooded area, camping etc go with you maximum wattage achieved able on a radio (4 to 5 Watts) on GMRS. You can always introduce a repeater on gmrs later if you would like. Nowadays portable two way radios are fairly easy to obtain and program for GMRS repeater access. Plus, depending on what repeaters you purchase they can be relativity cheap for what you want to do and adequately small.
The most important rule, that I think was hit on here in a little bit is height. It's not so much the wattage or the gain as it is the height. The gain allows you less signal distortion and better penetration in and out of buildings. The other thing not mentioned is signal loss distortion which will effect your gain and your power out at the antenna. Not the power out at the box.
Simplex-
in picture format
Point A can hear and transmit to both Points. Point A acts as a repeater and transmits out as far as his/her radio allows for penetration from wattage out and proper gain at proper height. Point B and C get blocked from talking to one another by building, foliage-ie hills, trees, etc. No, structures or foliage blockage Point A transmits out farther, ie-tree stand would be a good example of this, however B and C can now talk to each other because nothing is blocking them, allowing for wider area of radio coverage by portable.
If the person is on the opposite side of the wall or sightly pasted the exterior wall they may be able to hear the traffic. Other rules of thumb, more wattage equals better punch through buildings-misleading. Localized areas the theory is correct, communications on the edge not so much.
This is the power theory, whats not taken into consideration here is height or gain. Another critical factor that is pasted on in small installs is proper grounding skills.
5 watts out 2-1/2 miles of coverage
4 watts out 2 miles of coverage
2 Watts out 1 mile of coverage
1 Watt out 1/2 mile of coverage
bubble packs .500 mill watts you figure out..... (not all bubble packs are created equal)
110 Watt mobile to mobile 55 miles of coverage
50 Watt mobile 25 miles of coverage
The most important rule, that I think was hit on here in a little bit is height. It's not so much the wattage or the gain as it is the height. The gain allows you less signal distortion and better penetration in and out of buildings. The other thing not mentioned is signal loss distortion which will effect your gain and your power out at the antenna. Not the power out at the box.
Simplex-
in picture format
Point A can hear and transmit to both Points. Point A acts as a repeater and transmits out as far as his/her radio allows for penetration from wattage out and proper gain at proper height. Point B and C get blocked from talking to one another by building, foliage-ie hills, trees, etc. No, structures or foliage blockage Point A transmits out farther, ie-tree stand would be a good example of this, however B and C can now talk to each other because nothing is blocking them, allowing for wider area of radio coverage by portable.
If the person is on the opposite side of the wall or sightly pasted the exterior wall they may be able to hear the traffic. Other rules of thumb, more wattage equals better punch through buildings-misleading. Localized areas the theory is correct, communications on the edge not so much.
This is the power theory, whats not taken into consideration here is height or gain. Another critical factor that is pasted on in small installs is proper grounding skills.
5 watts out 2-1/2 miles of coverage
4 watts out 2 miles of coverage
2 Watts out 1 mile of coverage
1 Watt out 1/2 mile of coverage
bubble packs .500 mill watts you figure out..... (not all bubble packs are created equal)
110 Watt mobile to mobile 55 miles of coverage
50 Watt mobile 25 miles of coverage
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