MURs vs GMRS -- All things equal...

[HarrisRF]

as a general rule, all things being equal... the lower the frequency the farther it travels. Think about the thug driving his car down the street. you hear his low frequency bass because it carrys farther. The physics do not change due to much higher frequencies than the audible sound.

 

[nd5y]

I haven't messed with it much, but does Radiomobile allow you to somehow simulate the range you could expect handheld to mobile, or mobile to mobile?

That's what I did was attempt to simulate the range of two hand helds. The pictures I posted are from polar coverage mode. In this mode it calculates the received signal strength out to a certain maximum radius through 360 degrees. It can also do it only between two fixed points or several other ways.

The program doesn't know or care what type of radios they are or if they are moving.
It only knows what power output, antenna gain, hieght and radiation pattern, feedline loss, receiver threshold, etc. that you enter, and general paramaters for all stations like the frequency, terrain data, land cover data, soil conductivity, climate type, and several other things.

It downloads the terrain data and land cover data and various types of street maps from the internet and calculates received signal strength based on the parameters particular to each station or all stations in a network and displays the results in several ways.

 

[jassing]

It would b interesting to see a comparison of say murs @ 2 watts with a 6db gain antenna and gmrs @ 40 watts with 3db I have a quick try with the app but didn't have much success.

This definitely has me re-thinking gmrs for family radios...

 

[brndnstffrd]

For those of you that may be interested that have tablets/ android cell phones, there is and android app called RF signal for making those coverage maps. I have found it very useful for determining the wattage to use on the mobile repeater or where to park to get the best coverage.

 

[UPMan]

The reason the range difference is insignificant is that VHF and UHF are line-of-sight services. Yes, there are some propogation through foliage and reflected signal efficiency differences for different signal wavelengths, but once the receiver goes over the horizon (or behind a hill), it is going to lose reception. The exceptions are when there is a significant structure or land mass that allows for some signal reflection back into the "shadowed" area. Filling in these shadow regions is really all you get with more power.

To improve range, then, what you need to do is increase antenna height (i.e. make the horizon be further away). Try running the coverage plots with two antennas at 3 feet each (i.e. users are sitting down) vs. two antennas at 10 feet each (i.e. users are standing on top of their cars). vs. two antennas at 30 feet (each of you are "hilltopping"). In open, flat terrain, you'd see a huge difference in range. In mixed topology, it will still depend on the height of the surrounding terrain, but you should still see a noticeable difference.

 

[UPMan]

Ok, I actually ran the plots. First is at 1-meter antenna heights for both ends. 2nd is for 10-meter antenna heights at both ends. Both cases are 146 MHz at .5 Watts.

10-Meter:

 

[ramal121]

Boy, this begs the question "how far will this thing talk" and nobody can answer that with any real number.

To get to basics you have to look at free space propagation (loss from transmitter to receiver). I penciled some numbers out, but be aware this is for a theoretical isotropic antenna on both ends. For the frequency listed there are two numbers, one for a distance of 1000 meters and the second of 100,000 meters. The loss is in dB.

154.600 MHz -76.2dB, and -116.2dB
462.600 MHz -85.7dB, and -125.7dB

You will see right off the bat, the lower frequency will "punch" through better than the high frequency.
If you check the difference between the two frequencies at both distances you will find 9.5dB and 9.5dB respectively. This means the higher frequency will always be at a constant lower level than the lower frequency as it moves farther out.

The propagation maps based on the Longley-Rice equation account for major topographic obstructions and frequency angles beyond line of site, but what if you are down at the bottom of a steep canyon trying to call to your buddy that your quad has broken down and you can't get out?
In the pacific northwest where the trees and ferns and moss will more or less suck up a higher frequency, I'd rely on VHF MURS to get out. If, however, this was a rocky canyon in the southwest, UHF GMRS may be a better bet to bounce your way out.

You can play with antenna gains and transmit power, but the deciding factor on communication distance is your frequency and environment.

 

[UPMan]

what if you are down at the bottom of a steep canyon trying to call to your buddy that your quad has broken down and you can't get out?

If your buddy is not at the top of the canyon you are in, then you are going to have to do some walking.

We achieve 50+ miles (actually physically measured, not some lab estimation) with 1.75 Watts on GMRS in testing. Over 30 miles with just under 1 Watt. But these tests are performed between a unit at the top of a tall land formation across an unobstructed vista. Coverage maps notwithstanding, actual reliable communication range for VHF/UHF is only a couple of miles under most circumstances, and this will also depend heavily on the receive sensitivity of the radio when the signal is taking some indirect path.

Another factor the Longley-Rice method fails to consider is RF noise floor...you will get better range in the middle of New Mexico (no RF sources) than in Denver, even though you might be able to get close approximations to similar topographic conditions.

 

[nanZor]

One factor I encounted often was when users would not hold their radios upright, but hold them like a cellphone nearly horizontal to the sides of their head, or horizontally like they were looking into a compass. Bad cross/random polarization. Making sure everyone in the group actually held the radio vertically helped a lot.

 

[nonperson]

You may be interested in this. A part of it covers this topic. Introduction to Communications Systems - YouTube

 

[jassing]

Some of that video droned on and on... but -- what I came away with is: Why isn't CB more popular?

 

[nonperson]

Some of that video droned on and on... but -- what I came away with is: Why isn't CB more popular?

Depending on the area and terrain it is a viable option but being AM it is more susceptible to interference. I've heard some folks make comments about the length and looks of the CB antenna on vehicles. With that comes a compromise of style, design and performance. Then there are some annoying people on there but I still use it.

 

[jassing]

I recently pulled my radio and gear out of boxes and put it back in my truck -- other than the "out checkin da mail talking to to ... " crap; it's pretty quiet here; occasional drunks ranting -- (Why can't they get busted from DUI's when they're clearly driving?) gets louder during dusk...

but in rural areas, it seems the better choice -- sort of going on the "lower frequency does punch better" theory -- it almost seems a 2 watt small handheld with a big ulgly antenna would be better still than murs for punching thru the trees and such.

I cannot find some compact cd radios (compact enough to consider carrying around) Maybe a modified 10 meter handheld? but then we get into fcc rules for type acceptance...
gmrs works fine for us normally; but at the cabin; it's range is really horrible; we'll try murs... lesson I learned recently is there's no "the one" radio out there for mobile or handheld use for all situations...

 

[nonperson]

I recently pulled my radio and gear out of boxes and put it back in my truck -- other than the "out checkin da mail talking to to ... " crap; it's pretty quiet here; occasional drunks ranting -- (Why can't they get busted from DUI's when they're clearly driving?) gets louder during dusk...

but in rural areas, it seems the better choice -- sort of going on the "lower frequency does punch better" theory -- it almost seems a 2 watt small handheld with a big ulgly antenna would be better still than murs for punching thru the trees and such.

I cannot find some compact cd radios (compact enough to consider carrying around) Maybe a modified 10 meter handheld? but then we get into fcc rules for type acceptance...
gmrs works fine for us normally; but at the cabin; it's range is really horrible; we'll try murs... lesson I learned recently is there's no "the one" radio out there for mobile or handheld use for all situations...

If you want my opinion on CB HTs they're not the best as far as range is concerned but they do have there uses. On the other hand a mobile unit with a 1/4 wave length antenna etc would work excellently in the woods.
If you want a HT radio, maybe a MURS radio would be a little more practical as far as license free radio services go.

As for 10 meter HTs ..... Magnum 1012 HT AM/SSB I don't think they are FCC approved but they look neat as far as capabilities go... I never ordered anything from that web page. It was just the first one that popped up with a picture and description.

 

[treborx]

I know someone who tested HTs with stock antennas on MURS and GMRS in a rural area with woods and at about 1/4 mile, the MURS did not work but the GMRS did. I thought about this, and the explanation is that the stock antennas are just not as good at 150 Mhz as at 146.

If you ordered custom-tuned antennas from someone like Smiley - one set for MURS and one for GMRS - that is the only way to really do a comparison.

These are very wide-band radios and there is no single antenna that can cover all of the bands. This also explains why some people give a certain model of antenna a 5-star review, and other people give it a 1-star review. Different bands.

I even saw a guy give an antenna a 1-star review because of his comparison with the stock antenna for FM radio!

 

[KD8DVR]

Some of that video droned on and on... but -- what I came away with is: Why isn't CB more popular?

Illegal operators running illegal power to talk long distances Will wipe out local communications. Also AM is a poor choice for communications. Also people are rude and interfere with or try to include themselves in your private communications.

 

[K5MPH]

For all the years of going hunting,fishing,and outdoor stuff and playing around with radios I have found that murs has done a lot better than frs and gmrs I would use murs any time over uhf.........

 

[KD8DVR]

I've achieved better indoor coverage with GMRS.

 

[Project25_MASTR]

I think it truly depends on terrain. Remember, NASA sent video over 1/4 million miles from the moon using less than 6W on a UHF signal.

Ever wonder why microwave ovens have those little holes in the viewing port? The theory is if you make holes smaller than a wave at a given frequency, the signal is effectively blocked. The viewing ports allow light waves to pass while block microwaves and keep them from boiling our eyeballs because we are sitting there watching our food cook even though we've always been told not to watch.

The theory could be applied to the great outdoors as well. Depending on how thick the scrub brush/foliage may be, UHF may be significantly more effective at punching through the foliage.

 

[KB7MIB]

I once read that pine needles are typically a quarter wavelength long at UHF frequencies. So, if you live in an area where the majority of trees are of the coniferous type, this may be an issue.

John
WPXJ-598
Peoria, AZ