5w vs. 50w

[Josh380]

Is there really much of a difference in range on GMRS when we're talking about 45w?

I remember back in my CB days, they used to say that there really wasn't any difference in signal strength between say 100 and 400w (illegal, I know..just an example). Of course, that's Amplitude Modulation (the advantages here are obvious), not Frequency Modulation. I'm not too familiar with FM and the advantages of running more than 5w, and in an urban area.

 

[mmckenna]

You won't see much difference. It's not 10 times, like some might think.

It's inverse square of the distance, if I recall my math correctly.

UHF is more line of site, although you'll get some reflection off some buildings and some topographical features. If you are running a good external antenna in a mobile or base environment, you won't see a huge difference between 5 watts and 50 watts.

I used to be pretty active on GMRS, mobiles, bases, handhelds and even a repeater. I had a lot of opportunities to play around with different settings. In one instance I was in a truck with a 35 watt mobile with a 1/4 wave UHF antenna talking to another truck with the identical set up. We split off at an interchange, one of us heading south, the other north. Flat terrain, highway driving. We were able to talk simplex (radio to radio) over 19 miles before I went around a hill and lost contact. Up until that point we were able to switch between 35 watt high power and 4 watt low power with very little difference in signal quality. The additional power was a bit cleaner. The lower power had a bit of static, but entirely understandable.
Good antenna installs make so much more difference than power does.

 

[prcguy]

I use simplex several times a week between some guys in the neighborhood running handhelds with amplifiers and we ofter drive out of range running errands, etc. Going from 5w to 40 or 50w will usually take you from a very weak scratchy signal to full quieting and extend the range noticeably. A 10dB increase in power is a good thing if you have it and operate in fringe areas.

In free space and after you get out of the near field of an antenna, every time you double the distance the signal will drop 6dB or 75%. On the ground its much different with ground bounce and signals arriving in or out of phase causing signal addition or cancellation can add up to 6dB or fade 20dB, 30dB or more. Driving around even in the desert is a very dynamic environment and a busy city is much worse so free space calculations are usually out the window.
prcguy

 

[rapidcharger]

It depends on the circumstances. I use UHF a lot on the ham band. Going from 5 watts to 45 *usually* makes a very big difference for me in my area. VERY BIG.
Last week I was in a subterranian parking garage that also had an entire shopping mall in the way trying to get back into my system. It's digital. I was listening to the output. On 5 watts, couldn't get in. 25 watts, lots of garbles. 45 watts, perfectly clear. That's just once recent example of how you can go from nothing to a usable signal by increasing the power. Where you may not see anything is if you have substantial terrain obstacles or if the opposite is true and you have a perfectly clear path. In the case of the latter it's very likely you won't notice any difference between the power levels.

 

[mmckenna]

Interesting. I guess I never really tried it in those environments. Most of my GMRS use was open highway and we rarely saw much difference between 35 watts and 4 watts.

 

[hotdjdave]

When using my HT inside my home, switching from 1w to 5w makes the difference of hitting a repeater or not. I know it's not 5w to 50w, but just to show a little more power can make big a difference sometimes.

 

[Project25_MASTR]

Completely dependent on terrain.

The actual path loss, a radio that receives down to about -100 dBm and another transmitting 1W works out to be just over 100 miles.

Height is might when it comes to UHF communications.

 

[willgrah]

As a general rule, not completely 100% mathematical, is that when you double your power you increase your distance by around 20-25%. Simply put if you can talk clearly on 10 watts at 10 miles if you up it to 20 you will do 12.5 miles clearly. By far the best way to increase your distance is to increase your height. It's like climbing a tower, the higher you go, the more you see. Same goes for the radio.

 

[Jaxco]

Maximum - you will only get about 15% beyond the horizon on UHF with any amount of power. There are plenty of web pages that will help you calculate distances assuming no obstructions with varying antenna heights.

All of the power of any amplifier and gain through any antenna will still be limited by the physical and 15% more distant radio horizon. Antenna height is the only way to increase the distance to that horizon. The power and gain will only give you clarity within the confines of your radio horizon.

 

[mancow]

I use simplex several times a week between some guys in the neighborhood running handhelds with amplifiers and we ofter drive out of range running errands, etc. Going from 5w to 40 or 50w will usually take you from a very weak scratchy signal to full quieting and extend the range noticeably. A 10dB increase in power is a good thing if you have it and operate in fringe areas.

In free space and after you get out of the near field of an antenna, every time you double the distance the signal will drop 6dB or 75%. On the ground its much different with ground bounce and signals arriving in or out of phase causing signal addition or cancellation can add up to 6dB or fade 20dB, 30dB or more. Driving around even in the desert is a very dynamic environment and a busy city is much worse so free space calculations are usually out the window.
prcguy

Having used both HTs and 110 watt mobiles for vehicle surveillance in both urban and rural areas I agree completely with your description.

 

[zz0468]

Maximum - you will only get about 15% beyond the horizon on UHF with any amount of power. There are plenty of web pages that will help you calculate distances assuming no obstructions with varying antenna heights.

All of the power of any amplifier and gain through any antenna will still be limited by the physical and 15% more distant radio horizon. Antenna height is the only way to increase the distance to that horizon. The power and gain will only give you clarity within the confines of your radio horizon.

This is a gross oversimplification of how RF propagates, and fails to take into account any number of real-world factors that can either enhance or inhibit propagation.

A better way to approach the difference in power is simply in dB. 5 watts vs. 50 watts is 10 db. Put another way, it's the difference between 0.3 microvolts, or 0.1 microvolts... barely usable vs. unusable. This analogy simply doesn't square with the idea that 'it matters not what the power is, the horizon +15% is unchanging'.

RF bends, bounces, refracts, reflects, and scatters. Those web pages only know of a few ways to calculate what the RF is doing. Mother nature knows 'em all.

 

[Jaxco]

Hardly an oversimplification for UHF and above. UHF does not receive the benefits hidden in 1,000 other factors that VHF and below can benefit from. The 'line of sight' (antenna to antenna and their respective angles of radiation) is pretty much all you will get at uhf and above.

 

[zz0468]

Hardly an oversimplification for UHF and above. UHF does not receive the benefits hidden in 1,000 other factors that VHF and below can benefit from. The 'line of sight' (antenna to antenna and their respective angles of radiation) is pretty much all you will get at uhf and above.

How would you explain, then, amateur UHF and microwave contacts that extend to hundreds or thousands of miles? California to Hawaii has been spanned on every ham band up to and including 5.7 GHz. I have personally worked from Northern California to well into Mexico on 10 GHz, almost 1000 miles.

Your knowledge of propagation on UHF and above is lacking some real world experience. I expect that there are several other guys here that will attest to what can be done on non line of site paths.

 

[Jaxco]

Are you speaking of EME on UHF? I have 2 repeaters, one in the 70cm band and another on the 33cm band and have spent years tweaking and experimenting with nearly every type of communication on those bands including EME and satellite S&F contacts(70cm).

Microwave frequencies are one area I have never looked into to be perfectly honest, they provide little return on investment.

 

[zz0468]

Are you speaking of EME on UHF?

No. I'm talking about terrestrial non line of sight propagation.

...and have spent years tweaking and experimenting with nearly every type of communication on those bands including EME and satellite S&F contacts(70cm).

Then how is it that you're completely unaware of the propagation enhancements that take place!!???

Microwave frequencies are one area I have never looked into to be perfectly honest, they provide little return on investment.

The return on investment is fun, and knowledge gained. But yes, I guess I can see that you wouldn't get your money's worth.

 

[Jaxco]

So, you want to be a snarky kid and ignore someone's practical hands-on experience and observation. If you have the cash for high dollar parabolic antenna arrays, microwave transmission towers, etc, there are a number of things you can do theoretically but you ARE NOT going to do these things with a 5 to 50 watt 64cm (GMRS) radio with a maximum normal antenna height of 20ft.

So, in the context of GMRS, everything I said is absolutely spot on.

 

[zz0468]

So, in the context of GMRS, everything I said is absolutely spot on.

It was your erroneous assertion that transmitter power plays little to no role in range that made me comment in the first place.

You may have the closing comment. Its definitely not my intention to have a long protracted argument with you.

 

[prcguy]

There are all kinds of things that affect VHF/UHF propagation and your not limited to 15% beyond the horizon. If you have not experienced this then where is the experience? BTW, GMRS is not limited to 20ft antenna height, you can put an antenna on a 64 story building, etc.

On example of beyond line of site on UHF is a GMRS repeater that was used by a hospital on a channel I was licensed for many years ago, they were grandfathered in and would not move to a more appropriate commercial frequency.

I had several GMRS repeaters on mountain tops in So Cal ranging from 1,100ft to 5.700ft and got appropriate coverage from them. However, the hospital repeater in the middle of flat Los Angeles could be heard clearly 150mi away in the CA desert on a regular basis and much farther than my high performance mountain top repeaters.

Turns out So Cal is in a basin, surrounded by a range of tall mountains and signals from low lying areas will knife edge scatter off the sharp rocky mountains out of the basin into the outlying desert areas where the high mountain top sites do not scatter as well off the distant mountains. Otherwise how would you explain a 50w UHF repeater reliably talking through a 5,000ft mountain range to a distance of about 150mi?

To finish the story, not that its relevant to the thread. My repeater partner helped the hospital get licensed on another frequency but they kept lying to him on the radio shop coming by to re channel the repeater and this went on for months. My partner finally went into the hospital with a hand cart, found the repeater in a top story room, ripped it out and dumped in the the guys office he was working with. Problem solved, no more hospital on our GMRS channel.....
prcguy

So, you want to be a snarky kid and ignore someone's practical hands-on experience and observation. If you have the cash for high dollar parabolic antenna arrays, microwave transmission towers, etc, there are a number of things you can do theoretically but you ARE NOT going to do these things with a 5 to 50 watt 64cm (GMRS) radio with a maximum normal antenna height of 20ft.

So, in the context of GMRS, everything I said is absolutely spot on.

 

[rapidcharger]

When someone is wrong on the internet, even if it is the most minute detail, it is imperative to immediately get in there and let them and everyone else know they were wrong. Imagine what the world would be like if the Internet was full of minute details that were factually incorrect. Scary thought indeed!

 

[Jaxco]

At 1100 to 5700ft, the antenna was higher - increasing the radio horizon. The same applies to an antenna atop a 64 story building. knife edge diffraction can occur but just as some areas reflect reliably, you will have equally reliable dead zones.

I guarantee the radio horizon at 15% beyond the physical horizon between antennas will be correct far more often, in more circumstances for the run of the mill GMRS user who cannot access a 5700 foot hill or a 64 story building with roof privileges.