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Estimating your GMRS Radio Coverage - Finally


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Posted

We have all asked or heard the questions before; “What kind of coverage can I expect” and “how far will those radios reach?” And we have all also heard the exact same text book answers; things like “It depends” and “that is not an easy question to answer.”

 

You’re asking valid questions, and you’re getting valid answers. The only absolute way to know what your coverage is going to be, and how far you can reach is to test it yourself using your actual equipment in the exact area you intend to use it in. That said, technology being what is, there is a better way to get a more realistic estimate.

 

Professionals RF engineers use software to assist them; software that will get them close.

 

An RF Engineer in Quebec (whom is also an amateur radio operator) has a website with a free online calculator that will help the knowledgeable radio user visualize an estimate of what there coverage would be based on many of the fundamental factors that affect radio coverage. Having now contrasted its calculated results with my personal radio experiments, I am gaining confidence in its ability to “get me close.” better than any other way.

 

For example, in some of my tests of base to HT and base to mobile coverage, the software predictions correlate with many of the spots, even along mostly level ground, where I experience complete radio dropouts, where I experience marginal reception, and where I experience highly reliable communications.

 

Here are some of the user supplied factors that go into estimating one’s coverage:

 

Location of Tx antenna.

Transmit Frequency.

Tx antenna height.

Tx antenna gain, tilt, azimuth.

Tx output power.

Signal loss in Tx cable

Rx antenna height.

Signal loss in Rx cable.

Real-world receiver sensitivity (which may or may not be published accurately).

 

The calculator can be found here: https://www.ve2dbe.com

 

The software takes into account the actual terrain around the antenna. It appears as though it may be adding factors related to ground coverage, which I assume is based on some statistical information. More detail about what goes into the calculations can be found here: https://www.ve2dbe.com/rmonlineinfoeng.html

 

I have been wresting with determining whether there would be real-world benefit to me adding another 20-40 feet of height to my proposed GMRS antenna mast/tower. What I really wanted to know is if I would experience tangible or zero benefit from increased height when it comes to simplex coverage around my property. I feel much better informed now.

 

I would be most curious to hear from those of you strong technical types regarding how predictions from the software align with your real-world conditions when it is configured accurately.

 

Here is an intro to the software from a user of it:

 

Moderators, I think this would be a useful sticky post.

 

Happy Calculating!

 

Michael

WRHS965

KE8PLM

 

 

Sent from my iPad using Tapatalk

18 answers to this question

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Posted

Radio Mobile is one of the best available online coverage calculators available - especially when you consider that it's Free to use (for amateurs).

 

My only comments would be that you need to bump up the "Required Reliability" % to something North of 95% to better reflect actual coverage. Also, realize that it's mapping Talk Out coverage for the most part - not taking into account the difference between a mobile mounted radio or a portable (other than antenna gain & height). I usually set antenna gain at Zero for a portable, with a 1 meter antenna height. I find that gives me a more accurate representation of Real World talk back conditions with a decent portable.

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Posted

I have been using this for yrs.

some things to keep in mind. gain is in dBi subtract 2.1 dB if antenna is rated in dBd.

line loss , don't forget the insertion loss of your duplexer typically .5dB-1.5 dB on average.

now the "required reliability" can change the map dramatically. I find that 85% works well in most applications.

JE

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Posted

Something not already mentioned is that if you want to plot GMRS coverage, you will not be able to enter 467.xxx since it is a ham oriented tool. 446.xxx is as close as you can get.

 

When I was trying to get a repeater up and running, after laying out well north of $2k I discovered much to my chagrin that I'l need to get my antenna up to at least 200' to get the minimum coverage that would be useful. I got very lucky and sold my three month old repeater for just a few hundred less than I paid for it.

 

Lesson learned: DO YOUR RESEARCH FIRST!!!   :wacko: 

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Posted

The frequency coverage for the tool is quite extensive in the online tool. Supported frequency ranges include the full range of frequencies in the GMRS 462 and 467 MHz spectrum.

 

There are currently 17 discrete frequency ranges supported by the tool that range from 10 MHz to 250 GHz. The complete list can be viewed here: https://www.ve2dbe.com/rmonlineinfoeng.html

 

Michael

WRHS965

KE8PLM

 

Something not already mentioned is that if you want to plot GMRS coverage, you will not be able to enter 467.xxx since it is a ham oriented tool. 446.xxx is as close as you can get...

[/b]

 

Sent from my iPad using Tapatalk

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Posted

The frequency coverage for the tool is quite extensive in the online tool. Supported frequency ranges include the full range of frequencies in the GMRS 462 and 467 MHz spectrum.

 

Thanks for the update. Apparently he expanded the allowed frequency ranges. It used to allow no higher than 450 MHz.

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Posted

So I've been playing with this for some time now and have difficulties in making it match real world conditions.  Using GMRS and my current setup I have some very specific spots that I know how they react reception-wise.  My house is a dead spot more or less.  I have a friends house that I get a good signal at and my Dads house that is extremely weak.  By the time I get my house to the weakness it is all the other spots drop off the map and turn white meaning zero reception which is far from reality.

Was wondering what parameters some of you are using to get your realistic power/reception levels.  It's probably the line of trees I have between my house and my repeater antenna, but I'm still curious as to your parameter setup.

Here's my inputs for me talking through the repeater with my truck mobile setup.

image.thumb.png.0f7bde4dbec1f56e3c0bad0ed8996c1f.png

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Posted

That app and no other app has any idea if there are trees or even buildings in the way. It can’t tell if an area has huge machines in an industrial park that are messing with signals.  It can’t tell if local homes have metal roofs or big metal shops/garages in back yards.  
 

some times it will show no service even when there is service in a particular spot and some times it shows great service when there is zero.  It’s just a basic estimate.  
 

the only way to know is to get out and try.   It may be so simple as moving 3 ft to the left or gaining 2 more feet in altitude. My wife and I were out yesterday riding our horse in the local mountains.  We went up hill and gained 750’ in elevation from the house and had a much better line of sight to the repeater 25miles away.  I had my ht mounted to my saddle with a corded mic. I had no rx or tx    When I lifted the radio 2ft up a had full quieting in to the repeater.   Just gotta put the apps down and get out in the field.  

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Posted

Of course I realize all of that.  Just trying to get a sense of what others using the app might be putting in there for the other numbers besides their own equipment.  Myself I'm surrounded by trees on 3 sides.  North of me is treeless in the immediate vicinity and it shows in my real world experience.  Now the leaves are falling and the signal is opening up.  So it's possible the app might register more accurately than it has been.  There is a check box on the app that says use land cover.  Checking this box decreases the signal quite a bit.  Also would like to know what the "Use 2 Rays" option is since it's checked by default.  Also the Strong signal Margin.  I've bounced between 14 and 20dB for the most part and the reliability seems to be more accurate the closer you get to 100%.  I tried 100% once and the program won't run.  So I keep things above 98% most of the time.


Just curious.  And there's pretty much no way an averaging program could get things spot on.  But getting it close would be nice.

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Posted
7 minutes ago, LeoG said:

Of course I realize all of that.  Just trying to get a sense of what others using the app might be putting in there for the other numbers besides their own equipment.  Myself I'm surrounded by trees on 3 sides.  North of me is treeless in the immediate vicinity and it shows in my real world experience.  Now the leaves are falling and the signal is opening up.  So it's possible the app might register more accurately than it has been.  There is a check box on the app that says use land cover.  Checking this box decreases the signal quite a bit.  Also would like to know what the "Use 2 Rays" option is since it's checked by default.  Also the Strong signal Margin.  I've bounced between 14 and 20dB for the most part and the reliability seems to be more accurate the closer you get to 100%.  I tried 100% once and the program won't run.  So I keep things above 98% most of the time.


Just curious.  And there's pretty much no way an averaging program could get things spot on.  But getting it close would be nice.

Have you downloaded the documents? https://www.ingenieros.cl/wp-content/uploads/2020/10/Radio-Mobile-related-documents-English.zip

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Posted

Those coverage maps are a good reference but not 100% accurate. We did a coverage map when we first installed our repeater. A few of us then drove around testing to see where we could and could not get into the repeater. We compared that to the coverage maps and it was close but not 100% accurate.

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Posted

OK, playing around with the links area of Radio Mobile Online Calculator.  Pretty cool the diagram and information it gives.  Like to know what the colored bars in the land picture are.  Is it just population density or manor of blockage of the signal?

image.thumb.png.f7ad8d2a8b1c8da6e437d44086ea6bde.png

  • 0
Posted
5 hours ago, LeoG said:

OK, playing around with the links area of Radio Mobile Online Calculator.  Pretty cool the diagram and information it gives.  Like to know what the colored bars in the land picture are.  Is it just population density or manor of blockage of the signal?

image.thumb.png.f7ad8d2a8b1c8da6e437d44086ea6bde.png

Have you looked through the tutorial or read the posts on the io group: https://groups.io/g/Radio-Mobile-Deluxe?

Tutorial: http://pizon.org/radio-mobile-tutorial/index.html

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