# UHF simplex distance

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#### vs1988

##### Member
I noticed some PDs have a car-to-car channel that's in simplex. How far can UHF (453.xxx) usually travel? I know factors like topography, weather, buildings etc. can shorten the distance. What does an average mobile radio put out in terms of watts? Is there a formula to calculate the distance the signal can travel based on watts?

Thanks

Vince

#### aaronp

##### Member
It's all about line of site.
I once contacted the MIR space station with a 5 watt handheld.

#### KC8JPZ

##### Member
It would be really hard to put a formula on simplex distance for UHF. Like Aaronp has stated it is all about line of site. Most likely the car to car thing is going to be used within a few miles up to 10 max in ideal situations. The antennas being so low to the ground make it very difficult to get over the terrain and obstructions. I would guess that a commercial radio that a PD may use would be in the range of 50-75 watts possibly more. Most amatuer rigs are good for the about 35-50 watts mobile.

#### kb5udf

##### Member
1-5 Plus or minus 3

In practice two cars will talk on UHF frequencies, reliably, about 1-5 miles, give or take
3-4 miles, depending on terrain, folliage, and buildings.

#### ke5lvt

##### Member
some police radios are 40-45 watts but i have seen some at 110 watts. also what antenna are they using, 5, 3db or unity 0 db. that can make a difference. a 110 watt radio with a 5db antenna can talk pretty far.

#### KC8JPZ

##### Member
If there is anyone in the Columbus Ohio area that would like to try this out, I would be glad to give it a shot. I have a 35 watt UHF mobile and a 5db gain antenna. I'm currently working on a 21 db UHF antenna but that is not very mobile.

#### K6PCW

##### Member
100 miles, believe it or not!

Using Motorola MX series handhelds, 6" rubber duck antenna, at 2 watts transmit power, 506.xxxx MHz, we tested loud and clear (handheld transmitting) from the summit of Soledad Mountain in La Jolla (San Diego), California with our base system in Los Angeles, which was utilizing a RX/TX site on San Pedro Hill.
(Yes, the base was using StationMasters on a tower with plenty of gain, but heh...)

The signal had a clean, unobstructed line-of-sight channel path over water (namely the Pacific Ocean, for those of you unfamiliar with these locales).

Now, to be fair and realistic, the same radio, operating in the same frequency range, using the same transmit power, might encounter difficultly transmitting to another radio, even a few city blocks away, if the environment presented certain challenges (buildings in the way, excessive RF energy in the area, adverse signal reflection, etc.).

So, simply put, channel path (or whatever you want to call it) is a signficant issue. Are you working inside buildings or other structures? In a vehicle? In a basement? In an urban area? Hills and valleys? Expect varying results.

Out in the desert? Over water? Airborne? Good line-of-sight? (i.e. top of mountain to bottom of valley) Expect signicantly better (or fantastic) results!

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#### hotdjdave

##### K9DJW - Senior Member
How Far?

The formula for calculating the horizon is 1.17 times the square root of your height of eye = distance to the horizon in nautical miles. This would make it about 25 miles at the beach looking at the ocean, based on the average height male adult. It varies with terrain by a few miles, and would be increased if one point was on a mountain top (which, for example, would be about 70 miles on a 3,330 foot (from its base) mountain top to a visible point below). Line of site is only to the horizon of ones view, unless the object on the other side of the horizon is very tall and can be seen. See my signature below.

Line of site is a general rule. In an urban setting with trees and tall buildings, line of site radio transmission may only be a few miles or less (even a few hundred feet). Inside a building is even worse (less). In a rural setting, the distance may approach the horizon and even surpass it. This is why agencies (public and private) put the radio transmissions sites as high as they can get them (tall buildings, hill tops, mountain tops, towers, etc.).

However, propagation of RF signal doesn't work exactly like that - line of site. First, standard radio communications RF propagation is not normally a flat line or a beam, but rather an omni-directional wave (from a standard antenna). The wave goes out in all directions (left, right, forward, backward, up, down, etc.). Of course, there are RF transmissions that are directed in a beam or flat line, such as microwave and unidirectional propagation. Second, frequencies penetrate, bounce, and refract off of or through objects (structures,
leaves on trees, moving vehicles, hills, mountains, etc.), bodies of water, atmosphere, and other elements, causing either a reduction in distance or an increase in distance. In fact, a RF signal can be bounced off the moon and received half way across the Earth.

The power of the transmission has much to do with how far the signal will travel. For example, my kids little toy 49 MHz walkie talkies would not propagate much further than about 1/16 of a mile. However, I have picked up transmissions from FRS radios of hikers in the hills below Muholland Drive in Encino, about three miles from my home. FRS radios aren&#8217;t very high powered either. My 5.8 GHz phones work about 1/4 of a mile from my home.

I have tested a 5-watt Motorola MTS2000 900 MHz trunked radio in simplex mode, and was able to transmit and receive more than three miles away in Downtown Los Angeles (plenty of tall buildings and other obstacles). The same day and the same location, we tested a 2-watt Motorola HT1000 on VHF-hi and it only got about 1.5 miles and an older Motorola (can&#8217;t remember the model) 5-watt HT in the 42 MHz band (around there) and got less than a mile. The 42 MHz HT did much better when we took it to a wider open area &#8211; I think we got about 5 miles. The other radios did the about the same in the wide open area as they did Downtown (the VHF-hi did slightly better).

Note: the higher the frequency, the better it penetrates objects; the lower the frequency, the better it travels far distances. This is why public safety uses VHF-hi, and in more recent times, UHF in urban settings and why many public safety agencies like highway patrol uses VHF-low for the state-wide or rural settings (apart from statewide linked systems, both TRSs and conventional RSs).

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#### kb2vxa

##### Completely Banned for the Greater Good
Banned
Hi again,

WOAH HOSSIE! You guys sure know how to muddy the water! The question was UHF car to car simplex and you gave soup to nuts answers, totally confusing and off topic.

In a nut shell, UHF is used in an urban to suburban environment usually and for reasons of penetration. In such environments a power of 2.5W for hand helds and mobile converters gives a few blocks for the hand held and in the car into the usual 3dB gain antenna generally half a mile to a mile is normal. Most mobile units put out 40W into the same antenna for an effective radiated power of 80W which generally covers about 5-8 miles in a suburban environment, considerably less in center city.

Remember we're talking environment, a portable may not get out of a tunnell without a slotted coax antenna and a repeater, then those familiar with "mountain topping" know how height is might.

No arguements please, my Amateur Radio experience overrules your guesses. If you want to argue transmitter power and ERP please reference the FCC license database. I will however accept that your mileage may vary but usually not by much. Am I arrogant? Not by intention but I AM a straight shooter.

#### hotdjdave

##### K9DJW - Senior Member
Who's Arguing?

kb2vxa said:
Who said I was guessing and my Professional experience should count for something. Anyways, you basically said the same thing I did, just with less words and less technical information. Of course a 40 watt mobile unit attached with an antenna attached on the roof of a car is going to transmit much further than a 2.5-watt or 5-watt hand held walkie talkie.

By the way, I am not arguing, just responding.

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#### OpSec

##### All your WACN are belong to us
Wow. I guess the rest of us that deal with RF have no clue what we are talking about, because your ham experience trumps us all. I'm not looking to pick a fight, but it appears you fail to realize that this site has members that are not just scanner listeners.

#### KC8JPZ

##### Member
I appologize and withdraw all my statements in this thread. My amatuer radio expeirience must be in the null of the real amatuers. When I heard car to car I was assuming that he was reffering to mobile. How silly of me. Today, UHF simplex activity is high due to the amatuers traveling through Columbus on their way to Dayton. I lost contact with another mobile at about 9 miles.( sub urban )

#### kb2vxa

##### Completely Banned for the Greater Good
Banned

At least you understand where I'm coming from, tired of pointless arguments from know-it-alls. I guess a couple of fellow hams found themselves embarrassed for those remarks like QSOing with MIR which never used UHF and those 100W police radios also not on UHF and ham rigs that transmit more than 20W on 70cM. Try that on QRZ and my remark sounds like a firecracker amid a full scale atomic war. (;->)

Then too they don't recognize the target, they thought it was themselves. Wazzup guys, got issues? Get with the program, show your expertise. If you're a step above the plug n' play 2M CBers and have gotten out there and put some of those theories to the test you're operating in accordance with the Intent and Purpose of our very existance.

Subpart A--General Provisions

Sec. 97.1 Basis and purpose.

The rules and regulations in this part are designed to provide an
amateur radio service having a fundamental purpose as expressed in the
following principles:
(a) Recognition and enhancement of the value of the amateur service
to the public as a voluntary noncommercial communication service,
particularly with respect to providing emergency communications.
(b) Continuation and extension of the amateur's proven ability to
(c) Encouragement and improvement of the amateur service through
rules which provide for advancing skills in both the communication and
technical phases of the art.
(d) Expansion of the existing reservoir within the amateur radio
service of trained operators, technicians, and electronics experts.
(e) Continuation and extension of the amateur's unique ability to
enhance international goodwill.

#### OpSec

##### All your WACN are belong to us
In your last post, I don't know if you are trying to say there are not 100w public safety radios on UHF or not...but there are, right along side of their 100w VHF twins.

Also, you are correct that the ham rigs are more than 20 watts, but having a 35 or 40 watt transmitter on UHF won't get you much more than 20 watts as it relates to real-world signal strength...which is contrary to many hams' belief that it makes a huge difference.

#### Al42

##### Member
hotdjdave said:
The formula for calculating the horizon is 1.17 times the square root of your height of eye = distance to the horizon in nautical miles. This would make it about 25 miles at the beach looking at the ocean, based on the average height male adult.
Check my numbers but if "the average height male adult" has his eye even 6 feet from the sand, sqr(6) = ~2.45 and 1.17 times that = ~2.87 miles, or a range of ~5.75 miles between them, which sounds just a bit much from my experience. 25 miles sounds like way too much.

#### hotdjdave

##### K9DJW - Senior Member
Al42 said:
Check my numbers but if "the average height male adult" has his eye even 6 feet from the sand, sqr(6) = ~2.45 and 1.17 times that = ~2.87 miles, or a range of ~5.75 miles between them, which sounds just a bit much from my experience. 25 miles sounds like way too much.
You are correct. I forgot to put the point (.) between the 2 and the 5 - should have been 2.5 nautical miles (or 2 1/2 nautical miles), which is about 3 statute miles. I used 5.5 feet (5' 6") of the average height of a man's eyes.

However, you can see objects beyond the horizon. Use the same formula of the height of the other object and add it to the formula of your height and that is how far beyond the horizon you can see the other object.

Ex. You are 9 feet high (above the ground). Your view to the horizon is 3 miles. The object is also 9 feet high. You could see this object 6 miles from you over the horizon. This is assuming you are looking out at the ocean where the curvature of the earth is at its most natural curve, not altering the calculations by hills, valleys, etc.

Note: the atmosphere can bend the visible light and alter the calculations. There are other calculations using trigonometry to calculate the distance to the horizon, such as: distance = sqrt((1.8+R)^2-R^2), R being the the Earth's radius (R=6,378,100 meters).

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#### kb2vxa

##### Completely Banned for the Greater Good
Banned
Hi Stateboy and all,

"In your last post, I don't know if you are trying to say there are not 100w public safety radios on UHF or not...but there are, right along side of their 100w VHF twins."

No, while there may be UHF transmitters that put out 100W they're not all that common. I mentioned the FCC database which gives both the transmitter power and ERP of the radios in a given system, they must comply with the construction permit (CP). You'll notice that some base stations have an ERP of several hundred watts considering transmitter power, antenna gain and HAAT or AMSL all listed. You may have to look at the CP for more site specific information.

Edit;
I just realized I may have confused you a bit. Most ham UHF rigs put out 20W with a few exceptions. Right, a power gain of 3dB which gives 40W will give a quarter of an S unit increase, nothing to write home about. That's why the only REAL advantage is going all the way to a "full gallon" meaning a kilowatt. Then on UHF or VHF you can still do better than a KW with a BMF beam and it works like a receiver preamp too (;->) so you won't be an alligator, all mouth and no ears.

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