GMRS vs MURS at 5 Watts.

[WSAA635]

Hypothetical question. If you TX a MURS channel at the same 5 Watts you use for a GMRS channel would MURS give you a bit more range since it in the lower VHF range as opposed to the higher UHF range of the GMRS frequency? 

[Ian]

Let's make this question legal.  You have access to a MURS base station and a GMRS base station.  The GMRS unit is turned to low power, 2W.  Both radios feed identical coax lines, leading to a tower extending 20' above your chimney (close to the limit for a MURS base station).  Each is connected to a similar, functionally equivalent antenna of 3-5 dB gain.  

I still can't tell you without more specifics!  In terms of range, Height Is Might.  Now you have the same line-of-sight for both radios, and because of that, they'll both go approximately just as far.  Depending on your local foliage, the VHF might have an advantage -- pine needles really interfere with UHF frequencies, so if you have to punch through a stand of pine trees, the MURS will likely have the advantage, for now.  The other place it counterintuitively wins is with its poor building penetration.  If you're trying to communicate with someone outside the building, you're swimming upstream… but that means all that RF energy bounces around INSIDE the building, leading to crystal clear radio calls between two people inside of the same stainless steel BigBoxMart building.  

Ultimately, I'm giving the win to the GMRS unit, since you can flip the power from "low" at two watts to "high" at fifty, and suddenly you're loud and clear waaay out at the distances where MURS is noisy and scratchy and you're mostly hearing the local Wal-Mart and not the person you're trying to communicate with.  

If we're going to play the two-watt game, the real winner might be the new FM CB radios; it's not unheard of (but not legal for) people to communicate across the Atlantic on four watts, if they have a good antenna and good conditions.  150 MHz and 465 MHz are both line-of-sight bands, whereas down in HF around 25 MHz you can start to get some ground-wave effects as well as being able to bounce off the ionosphere.  Depending on sunspot conditions, this can increase your range __wildly.__  CB is in the region where it's also vaguely feasible to attempt near-vertical-incidence-skywave propagation, which again depends on near-perfect conditions, but covers the donut between simplex communication and sky-bounce propagation; this range donut is actually significantly important for deployed military forces.  America's current method is to use a repeater in the sky, be it drone, AWACS or satellite, but historically jeeps with skywave antennas were used in this role.  

A surprising contender might be 900 MHz ISM radios; they're limited to just one watt, but if you struggle with intelligibility more than signal strength due to your local terrain and foliage, they will remain perfectly legible right up until the moment you go below a critical signal-to-noise ratio and fall off the "digital cliff".  However, these radios can ping each other, so you can push a button and KNOW if you're in range, or not, with zero ambiguity.  900 MHz also has excellent building penetration, rather the opposite of VHF's problem.  Sometimes, multipath "interference" is your friend!

[fremont]

Purely anecdotal, but I and a friend have tried MURS vs GMRS in high desert country (no buildings or big mountains, etc), and MURS wins at 2w vs GMRS at 5w.  He lives there year-around and had no idea what MURS was until I loaned him my Wouxun KG-805M (and a Smiley OEM antenna).  He said "Thanks, I'm buying two of them."

[Lscott]

40 minutes ago, fremont said:

Purely anecdotal, but I and a friend have tried MURS vs GMRS in high desert country (no buildings or big mountains, etc), and MURS wins at 2w vs GMRS at 5w.  He lives there year-around and had no idea what MURS was until I loaned him my Wouxun KG-805M (and a Smiley OEM antenna).  He said "Thanks, I'm buying two of them."

You buy what works for you. GMRS isn't the solution in all cases.

[Sshannon]

4 hours ago, WSAA635 said:

Hypothetical question. If you TX a MURS channel at the same 5 Watts you use for a GMRS channel would MURS give you a bit more range since it in the lower VHF range as opposed to the higher UHF range of the GMRS frequency? 

MURS is limited by regulation to 2 watts.

The answer to your hypothetical question is “it depends.”  There’s not a simple yes/no answer. It depends on what’s limiting your range.  Terrain can limit both.  Both are line of sight, but UHF is slightly more so.  UHF is also less capable of passing through moisture.

[WSAA635]

Let me also add that I'm coming from a musician's point of view with this question. I know that when I use to play electric guitar it could sound loud in the room but the high frequency didn't penetrate walls that well. When I switched to bass it might not sound as loud but the lower frequency could be felt through the entire house.

Thanks for the great answers. 

[WRYZ926]

What @Sshannon and @Ian said is correct. VHF will have an advantage over UHF when all things are equal. The same goes when comparing 2m and 70cm bands. 2m being VHF will have better range than 70cm UHF from the same radio with the same antenna and coax when transmitting at the same exact power level on each band.

And HF frequencies will do better than both VHF and UHF. The longer the frequency wavelength, the farther you can communicate.

[WRWE456]

10 minutes ago, WRYZ926 said:

The longer the frequency wavelength, the farther you can communicate

It's the same with sound. High frequencies fall off quickly (a few feet) while bass (low frequencies) can travel over very long distances (miles) as well as pass through most barriers.

[WRYZ926]

3 minutes ago, WRWE456 said:

It's the same with sound. High frequencies fall off quickly (a few feet) while bass (low frequencies) can travel over very long distances (miles) as well as pass through most barriers.

This is very true.

[SvenMarbles]

The simple answer is yes, but with all use cases in radio YMMV. Depending on your unique terrain and challenges.

In a sterile "laboratory sandbox environment" where you're in open space, there actually is no difference. Unless you want to get into lightyear distances with redshifting because of the radiation spectrum difference and blah blah.

VHF has properties that can more "contour" to terrain rather than just beaming into a hillside and getting absorbed like UHF tends to. But at a general rule they're both line-of-sight. But a slight nod to VHF (murs) if you had equal wattage for it's terrain managing characteristics.

Conversely, it's also said that UHF has an advantage of being able to more robustly punch through obstacles. Not elevations in terrain itself, but mad made structures, trees, and such. So there's something to be said for both bands, and depending on your environment, you might make an educated preference for one versus the other.

 

[gortex2]

As said the rules limit MURS to 2 watts. For SAR use we run VHF and UHF stuff. VHF is better in the woods and same power level on commercial LMR radios will work better on VHF vs UHF. 

[Sshannon]

2 hours ago, WRWE456 said:

It's the same with sound. High frequencies fall off quickly (a few feet) while bass (low frequencies) can travel over very long distances (miles) as well as pass through most barriers.

That’s a very good observation.  Lightning has a crack, sizzle, and boom, but we’re usually too far away to hear the sizzle.  Frequently we can still hear the crack, but we can almost always hear the boom, reverberating as a rumble.

Radio is quite like that.  For space and space communications, where distance is usually the only thing limiting range, VHF and UHF are both used.  People literally talk to people on the ISS using handheld 5 watt ham radios often.

Communicating from one place on earth to another is all about atmospherics, terrain, vegetation, even humidity.  Since I became a ham i just learn more each day about how little I truly understand it all.  I recently spoke to several people who were hundreds of miles away in all different directions, but I accidentally had my power set to 10 watts instead of 100. They could still make me out, albeit weakly.  But there are other days when one of them tries to transmit with 600 watts and I have to really listen to hear them. So don’t expect consistency.

So, in general:

Mountain top to mountain top, either will work just fine and you probably won’t notice a difference.

Within a densely vegetative forest, VHF will usually get through the leaves better.  UHF can choke on a heavy rain.

In an urban environment, tall buildings, lots of metal, UHF usually does a little better.

As an example, aircraft and marine communications, which have a real necessity for reliability, usually use VHF.  Ocean going vehicles use HF.  Submarines used ELF because it worked better under water, or they surface and raise an antenna and use whatever they want.

[intermod]

IEEE TECH TALK: IS VHF DEAD?

Date: 13 Feb 2024
Time: 05:30 PM to 06:50 PM

Online Join link

• Join Zoom Meeting
  https://us06web.zoom.us/j/87613850683?pwd=VGhYQmxsU0dlbE5qRnMyS3o2Vmxqdz09
  
  Meeting ID: 876 1385 0683
  Passcode: IEEESEA

https://events.vtools.ieee.org/m/401815

 

[SvenMarbles]

11 minutes ago, intermod said:

IEEE TECH TALK: IS VHF DEAD?

Date: 13 Feb 2024
Time: 05:30 PM to 06:50 PM

Online Join link

• Join Zoom Meeting
  https://us06web.zoom.us/j/87613850683?pwd=VGhYQmxsU0dlbE5qRnMyS3o2Vmxqdz09
  
  Meeting ID: 876 1385 0683
  Passcode: IEEESEA

https://events.vtools.ieee.org/m/401815

 

VHF is such a great slice of spectrum. I can’t understand why it wouldn’t be used more fervently. 

[intermod]

55 minutes ago, WSAK691 said:

VHF is such a great slice of spectrum. I can’t understand why it wouldn’t be used more fervently. 

High noise floor, particularly in the metro and suburban areas, can be the controlling factor.  This is primarily caused by microprocessors, associated clocks and switching power supplies in electronic products (including many LED light sources).  This effectively deafens VHF receivers so that they are no longer as sensitive as they used to be.   If you ever get a chance to use 700, 800 or 900 MHz, or even 1200 MHz, it will become immediately obvious.  As was said above, while VHF propagates really well outdoors, in some cases the 700-1200 MHz bands can actually do better, except when the signal hits dirt (hill or mountain) or a dense foliage.

Another factor to consider in VHF is portable antenna efficiency.    Most portable radios are equipped with the 10" flexible helical antenna, versus something that more approximates a 1/4 wave length (18").    The 10" has an effective gain of -11 dBd.  That takes a 2-watt MURS radio and degrades it to less than 0.2 watts.  And it does the same to reception of signals......so VHF is really being hammered. 

UHF has become degraded but not as bad.  But the antennas (for a given length) are more efficient. 

[WRYZ926]

5 hours ago, Sshannon said:

Communicating from one place on earth to another is all about atmospherics, terrain, vegetation, even humidity.  Since I became a ham i just learn more each day about how little I truly understand it all.  I recently spoke to several people who were hundreds of miles away in all different directions, but I accidentally had my power set to 10 watts instead of 100. They could still make me out, albeit weakly.  But there are other days when one of them tries to transmit with 600 watts and I have to really listen to hear them. So don’t expect consistency.

Last Friday was a perfect example of that. It was very foggy early in the morning here in mid Missouri. After the fog lifted, the sky was really hazy for the rest of the day. It had an effect on HF, VHF, and UHF. UHF was effected the worst that day.

[SvenMarbles]

2 hours ago, intermod said:

High noise floor, particularly in the metro and suburban areas, can be the controlling factor.  This is primarily caused by microprocessors, associated clocks and switching power supplies in electronic products (including many LED light sources).  This effectively deafens VHF receivers so that they are no longer as sensitive as they used to be.   If you ever get a chance to use 700, 800 or 900 MHz, or even 1200 MHz, it will become immediately obvious.  As was said above, while VHF propagates really well outdoors, in some cases the 700-1200 MHz bands can actually do better, except when the signal hits dirt (hill or mountain) or a dense foliage.

Another factor to consider in VHF is portable antenna efficiency.    Most portable radios are equipped with the 10" flexible helical antenna, versus something that more approximates a 1/4 wave length (18").    The 10" has an effective gain of -11 dBd.  That takes a 2-watt MURS radio and degrades it to less than 0.2 watts.  And it does the same to reception of signals......so VHF is really being hammered. 

UHF has become degraded but not as bad.  But the antennas (for a given length) are more efficient. 

Noise floor? not on my SDR. The biggest curse are the pagers. I get a low ambient noise floor here in a major city. 2 watt murs here gets out.

[intermod]

1 hour ago, WSAK691 said:

Noise floor? not on my SDR. The biggest curse are the pagers. I get a low ambient noise floor here in a major city. 2 watt murs here gets out.

You may be one of the few.  What does your SDR show for noise floor at 16 kHz bandwidth?

[SvenMarbles]

52 minutes ago, intermod said:

You may be one of the few.  What does your SDR show for noise floor at 16 kHz bandwidth?

How about 10Mhz wide? SNR is outstanding.

I’m properly antenna’d outdoors . Not listening to my refrigerator indoors with a ducky…

 

 

 

[intermod]

15 hours ago, WSAK691 said:

How about 10Mhz wide? SNR is outstanding.

I’m properly antenna’d outdoors . Not listening to my refrigerator indoors with a ducky…

 

 

 

Looks like about -119, which is low for VHF.   If you have good coax then you are doing better than my area.... 

[GreggInFL]

This conversation reminds me of the decades spent on Marine VHF.  25W with a large antenna will reach a loooooong way.