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New Repeater Planned for Grand Junction, CO


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#21 Corey

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Posted 20 March 2016 - 08:48 AM

So the repeater was moved off the mountain? The antenna is at 100' AGL now? That will give about 15 miles LOS average.

 

My repeater is only a 150 AGL and I get a solid 45 miles in all directions, not sure why 100' would only give 15 miles LOS? I am getting almost 15 miles of HT coverage. From experience, if you have a decent repeater, good cable, quality antenna 100' of the ground and only see 15 miles something is wrong. I would have to estimate 25+ depending on terrain and type of equipment your using to work the repeater.

 

Just my $.02

 

Corey 


Just My $.02

 

Corey

 

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#22 WQWG565

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Posted 20 March 2016 - 11:11 AM

For this area the repeater serves the down town area great. The valley isn't too long, so even a 15 mile range would be just fine.

The feedback is greatly appreciated :)

#23 n4gix

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Posted 20 March 2016 - 11:16 AM

Corey, line of sight (LOS) calculation is nothing but the math of physics. It is a geometrical formula that determines the distance at which the tips of the antennas have a clear, unobstructed path between them, assuming no other man-made or natural obstructions.

 

The actual LOS could be much less, but never more! The earth is round after all. It would be so much simpler had the earth been flat... <snicker>

 

Rather than bore folks with the complex math, here is a screen clip of an LOS calculator. I was a bit low because I was relying on my faulty memory. The actual LOS is more like 17 miles. Note that this assumes that the receiving HT or mobile has an average height of 6'.

nNq9k.png

Screen clip courtesy of http://www.hamuniver...calculator.html

 

Now LOS is not an absolute predictor of actual propagation distance, as your observations illustrate. LOS assumes nothing is in the way of the radio signal between the antenna and the horizon at a chosen height above ground. It does not take into consideration any attenuation caused by weather, band conditions, antenna gain, path loss, or other factors such as dB loss in coaxial cable.

 

Likewise it doesn't consider any favorable circumstances such as signal refraction, reflection, or tropospheric scattering. Nonetheless, the physics and geometry do provide a solid basis for best case performance. :)

 

By the way, the actual LOS calculated for your 150' AGL is 20 miles. So your "guesstimate" of 25 miles is reasonable. Keep in mind that the higher the repeater's antenna, the more it is likely to "shoot over obstructions".

 

One neat site for generating a predictive propagation map is found here: http://www.ve2dbe.com/rmonline.html

As indicated on the Radio Mobile Online website, it uses digital terrain information and a mathematical model to simulate radio transmissions between two fixed sites or between a fixed site and a mobile. The digital terrain information comprises three databases: ground elevation, land cover, and population density, which combined total 200 GB of information.

 

Since the site is in French, a good English set of instructions may be found here: http://ham.stackexch...-for-a-repeater

 

Here is a screen clip from there for my repeater. I've been using this map as I drive around the area making tests. I've been very conservative in my estimates, figuring it's better to be surprised than disappointed... ;)

 

One thing is immediately clear from this. I really should have a more directional antenna with the azimuth aimed southwest. I'm "wasting" a lot of my system towards the northeast and the bloody lake!

nNs9N.jpg



#24 Corey

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Posted 20 March 2016 - 12:57 PM

Corey, line of sight (LOS) calculation is nothing but the math of physics. It is a geometrical formula that determines the distance at which the tips of the antennas have a clear, unobstructed path between them, assuming no other man-made or natural obstructions.

 

The actual LOS could be much less, but never more! The earth is round after all. It would be so much simpler had the earth been flat... <snicker>

 

Rather than bore folks with the complex math, here is a screen clip of an LOS calculator. I was a bit low because I was relying on my faulty memory. The actual LOS is more like 17 miles. Note that this assumes that the receiving HT or mobile has an average height of 6'.

nNq9k.png

Screen clip courtesy of http://www.hamuniver...calculator.html

 

Now LOS is not an absolute predictor of actual propagation distance, as your observations illustrate. LOS assumes nothing is in the way of the radio signal between the antenna and the horizon at a chosen height above ground. It does not take into consideration any attenuation caused by weather, band conditions, antenna gain, path loss, or other factors such as dB loss in coaxial cable.

 

Likewise it doesn't consider any favorable circumstances such as signal refraction, reflection, or tropospheric scattering. Nonetheless, the physics and geometry do provide a solid basis for best case performance. :)

 

By the way, the actual LOS calculated for your 150' AGL is 20 miles. So your "guesstimate" of 25 miles is reasonable. Keep in mind that the higher the repeater's antenna, the more it is likely to "shoot over obstructions".

 

One neat site for generating a predictive propagation map is found here: http://www.ve2dbe.com/rmonline.html

As indicated on the Radio Mobile Online website, it uses digital terrain information and a mathematical model to simulate radio transmissions between two fixed sites or between a fixed site and a mobile. The digital terrain information comprises three databases: ground elevation, land cover, and population density, which combined total 200 GB of information.

 

Since the site is in French, a good English set of instructions may be found here: http://ham.stackexch...-for-a-repeater

 

Here is a screen clip from there for my repeater. I've been using this map as I drive around the area making tests. I've been very conservative in my estimates, figuring it's better to be surprised than disappointed... ;)

 

One thing is immediately clear from this. I really should have a more directional antenna with the azimuth aimed southwest. I'm "wasting" a lot of my system towards the northeast and the bloody lake!

nNs9N.jpg

 

 

Here is a link to mine http://chainolakesgmrs.org/chain/ I have the interactive map hosted on the repeaters web site. I have found this to be vary close to real world experience as i have tested extensively. I totally understand how LOS works but it does not take into account HAAT this is why you will always see diffrent performance in the real world. Not only has this been true for my GMRS repeater but my multi site UHF business system as well. My 150' AGL tower has an HAAT 332', this is why i can work it just fine 40 plus miles away without any issues.


Just My $.02

 

Corey

 

Midwest GMRS

https://mwgmrs.com


#25 WQWG565

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Posted 20 March 2016 - 01:30 PM

I'm going to be using these links for sure! Thank you for all the valuable information!
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#26 zap

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Posted 20 March 2016 - 01:55 PM

Using those basic line of sight calculations is rather useless for coloroado as the terrain comes into play. I actually was looking at a site that though it was the highest spot for miles, it was in a valley an hour or so south of the OP and would cover the county entirely, but only 10 miles west, 10 miles east, and 15 north due to mountains and the gorge the Arkansas River cut its way through.

The basic calculations work well in this kind of terrain. 448d567f980191559ddc4e964f70b5ed.jpg
That grain elevator is 8 miles away and roughly 200 feet tall.


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#27 WQWG565

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Posted 20 March 2016 - 02:19 PM

Yeah, I get that the results may vairy when it comes to the mountain country big you look at I-70 MM 37 on the map, and MM46 on the map, there is a canyon between them. Even with this canyon, there is a clear transmission betwee the repeater and the 40watt radio in my truck. You can't see the repeater location at all, but at 50 watts of output, the repeater is perfect. The dips and hills in the area make it more difficult to properly calculate range.

Driving around and pinging the repeater works best in the mountains :)

#28 n4gix

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Posted 20 March 2016 - 02:34 PM

One would not use simple LOS alone, but when combined with the predictive model such as used by the Radio Mobile Online website, it is very useful. Note that RMO's calculations include topographical data, which is one reason why it might take up to two hours to plot a coverage map at the highest resolution! B)

 

Just for fun, I plotted a hypothetical system based in Asheville, NC where I used to live. The surrounding hills created a lot of "shadows" that mostly blocked coverage until the antenna height approached 500' AGL. Professionals use much more sophisticated software when doing site surveys of course, but for us relative "amateurs" sites such as Radio Mobile Online are about as good as we have available. ;)  



#29 zap

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Posted 20 March 2016 - 02:47 PM

One would not use simple LOS alone, but when combined with the predictive model such as used by the Radio Mobile Online website, it is very useful. Note that RMO's calculations include topographical data, which is one reason why it might take up to two hours to plot a coverage map at the highest resolution! B)

Just for fun, I plotted a hypothetical system based in Asheville, NC where I used to live. The surrounding hills created a lot of "shadows" that mostly blocked coverage until the antenna height approached 500' AGL. Professionals use much more sophisticated software when doing site surveys of course, but for us relative "amateurs" sites such as Radio Mobile Online are about as good as we have available. ;)

I used a command line based program called Splat!. I never was a fan of RMO. Now my favorite is SignalPro, which runs roughly $10,000 for the license unfkrtunately.

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