How much does wattage factor into uhf range ?

[DRoberts]

Hi everyone , I am a newbie so don’t beat me up to bad. I have looked all around in the forms hear and elsewhere for this topic but have not found any straight answers . 
 

We use an MXT400 with 6db antenna, MXT115 with 3db antenna and 805g ht (with Nagoya NA771g antenna) to communicate in our heavily wooded flat area. The MXT115 and 805G seem to “reach out” just as well as the MXT400 and I was wondering why the MXT400 doesn’t perform a little better then the smaller radios . I know uhf is line of sight and in our wooded area that’s not far but I would have thought the bigger radio would “burn” through the woods a little better. 
Any advise is much appreciated 

thank you 

WRKL657

[kidphc]

No direct range calculation for wattage.

It is just more umph to get through the noise floor. So it will get you some more distance, in perception.

If you took all three in an airplane and cranked then at max wattage. All three would get the same distance. But the highest powered one would come in stronger and louder at the edges due to the umph making you heard over the noise floor (if you use squelch, it would open the squelch depending on the setting). Hence, the monitor button on most radios.

When search for weak signals you turn off the squelch. Most of the time you can barely get any copy but sometimes, sometimes.

Through trees and such yes a little power can help. But trees do a great job of attenuationing vhf/uhf signals. They do an even better job of blocking signals when wet.

Also when you double the power you only net 3db worth of signal strength. In theory.

The gain of the antenna also will affect what you perceive. The 3db antenna is probably better in hilly terrain. The 3db antenna is more like a sphere in radiation pattern. Where the 6db it is more akin to a platter. That is why you have higher gain. You don't get something for nothing. With a yagi yet get 10-12 db in gain but it is highly direction like a pie wedge.

Hope that helps a little. Antenna and radio theory are fun aren't they. That is why you need to experiment.

All this is why in Lone Survivor Murph gave his life to try and get as high and as clear as he could. He probably knew he was going to silhouette his entire body to every living thing for miles. In an attempt to get help.



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[mbrun]

Hi everyone , I am a newbie so don’t beat me up to bad. I have looked all around in the forms hear and elsewhere for this topic but have not found any straight answers . 
 
We use an MXT400 with 6db antenna, MXT115 with 3db antenna and 805g ht (with Nagoya NA771g antenna) to communicate in our heavily wooded flat area. The MXT115 and 805G seem to “reach out” just as well as the MXT400 and I was wondering why the MXT400 doesn’t perform a little better then the smaller radios . I know uhf is line of sight and in our wooded area that’s not far but I would have thought the bigger radio would “burn” through the woods a little better. 
Any advise is much appreciated 
thank you 
WRKL657

Good day DR.

Power does play a factor, but it plays a minor factor in practice. Higher power can “burn” through the woods, but only if you put out enough power to “burn” through them. An increase from 5-50 watts is no where near enough to do that. While in outer space you could measure the increase in distance this extra 10dB would get you, on earth you have variable obstacles, terrain, curvature of the earth and variable RF noise conditions to contend with. All of these obstacles quickly chip away at what little power you have to give.

This phenomena is truly why want you antenna a high as practically possible when long-range local communications is desired. The higher it is, the less obstacles the signal has to go through or around, thus the stronger the resulting signal will be at a given distance.

Case in point. I can achieve achieve .6 miles reliable communication HT to HT in my heavily wooded area (level terrain) and unreliable communication out to 1.4 miles. Yet, using the same HT with same power I can open repeater 50 miles away when I stand in my front yard. What’s the difference? 1) The repeater antenna is perhaps 500-1000 foot higher in elevation than me. 2) There are no hills between me and the repeater to block my signal from reaching it. 3) There are no trees of consequence for the first 1-1/2 miles from my house in the exact direction of the repeater and 4) The performance of the repeater receiver is first rate.

Hope this helps answer your question a bit.


Michael
WRHS965
KE8PLM

[OldRadioGuy]

Your own test seems to answer the question pretty well.

Trees don't absorb 450MHz that badly unless they are just loaded with snow or something.   Maybe not even then.

Terrain is the dominant factor and higher power will just extend the fringe a small amount.

 

Of course there are different factors in different situations - like cars or houses blocking your signal.  You could also have beneficial reflections of your signal that help you reach over the horizon.  In these cases the high power could make a bigger difference.  I suspect in the city the higher power may be a bigger factor.  But it's very tricky to put a number on. 

Vince

[DRoberts]

Thank you everyone for helping educate me on this.
Would it be safe to say that open level terrain and/or elevated antennas such as base stations and repeaters  is where higher wattage comes into play as an asset? 

[kidphc]

It can. I know terrible answer. But no definitives.

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[SkylinesSuck]

I had a handheld 8w CCR hooked up to a Jpole 0dbi gain antenna on my kid's treehouse.  I upgraded all the cables to lmr400 and put a 50w radio in.  I could still only open up the same repeaters.  I just installed a 9dbi gain antenna with the same setup and can hit 3-4 new repeaters.  I am anxious to test out how my simplex range has changed with a specific other base station I couldn't reach before, but it appears the antenna did a lot more so far than the extra watts ever did.  

[mbrun]

Thank you everyone for helping educate me on this.
Would it be safe to say that open level terrain and/or elevated antennas such as base stations and repeaters  is where higher wattage comes into play as an asset? 

Every bit helps, but not significantly. Let me help by giving you a very, very crude illustration.

A 5 watt radio provides 37dBm output. A typically radio has a receive sensitivity of -120dBm (the lowest level the radio needs to produce usable audio). That is 157dBm of difference. Now, imagine all 157dBm is lost in only 1 mile due to all the obstructions in the path, for an average of 1 dB loss per 33 ft. So now lets say you increase your radio power from 5 to 50 watts. That is an increase of 10dBm (37 to 47dBm). Ok, so now that you have increased your power 10 fold. How much further will you get if you assume the same linear average path poss of 1 dBm per 33 ft. You got it, 330’. So in this example, you increased your power by 10 fold yet your effective distance increased only from 5280 to 5610’.

Now, if you were not battling the losses from all the obstructions in the path and went into outer space that same 5 watts would get you 225 miles, and 50 watts would get you 700 miles. There, signal level will drop based purely on inverse square law.

The point I am trying to illustrate here is that presence of attenuation of signal caused by obstacles in the signal path plays a significant role in how far your signal will and will not travel. It takes a lot of extra power to “burn” through the obstacles. Much better to raise the antenna to remove the obstacles from the path in the first place.

I hope this helps a bit.


Michael
WRHS965
KE8PLM

[DRoberts]

Thank you everyone for helping me understand a little better. 
 

C. David Roberts 

WRKL657 

[tweiss3]

Quick example of line of site/elevation is king:

I've been working a local contest that is metroparks on the air. Saturday I was at one parking lot that I thought was pretty high, elevation 971. I got one contact, report was that I was extremely scratchy at 50W, so I went to another parking lot, elevation 990, and picked up 4 contacts immediately. Inversely, I went to the next park, which happened to be in the valley right next to the Cuyahoga River, and managed a single contact that I know lives in the valley 5 miles away, but couldn't get a friend only 3 miles away at the top of the hill.