KG4GPJ/R: Coverage Map vs. Real World

I’m always skeptical when it comes to simulations. Earlier this week I posted coverage maps of our repeaters to get an idea of where exactly one can be and be able to reach the repeater. However, what good is a coverage map if it isn’t accurate?

Today I had to make a run up to Robbinsville. On the way over I decided to ping the repeater going through Andrews, NC. My mobile rig consists of a Yeasu FT-2900D, 75-watt 2 meter radio and a 5/8 wave antenna, with some terrible coax that I need to replace. So I’m positive my setup is less than optimal.

Likewise very good coverage between my QTH and Murphy along the main highways of US 64 and US74. However, I was curious of the results once I reached Andrews. I was lucky that Charlie, KK4JTF was on the air and was able to hang out and have a QSO while I was driving down the road. Signal reports were pretty much on par with what I was expecting, scratchy but full copy. This was the case until I got past Andrews, about a couple miles past Hardee’s going along 74. My destination was just a few miles outside of the city limits of Robbinsville right off US 129 and gave one last call on the repeater. I was able to open the squelch but was not readable and vice versa. I heard only a portion of Charlie’s transmission and was below the squelch threshold.

So looking at the coverage map and my route, I think we can agree that the coverage map is remarkably accurate. Each pixel on the map is equal to 100 meters x 100 meters, so this doesn’t take into account of mobile flutter. At the VHF frequencies, moving a few feet in any direction can make the difference between an S5 signal to nothing given the terrain and distance. Folks up in Andrews may or may not get into the repeater down here, propagation favors those on the northern parts of Andrews and at the peaks of the mountains. Realistically however, once you get past Andrews it’s time to switch to the KI4AIH repeater.

Overall the coverage map is a reliable way of determining where you can reach the repeater with a decent mobile setup. I will also be looking into producing coverage maps and site to site maps that would determine coverage from handheld and low powered stations from strategic locations. It’s a good thing to know as hand held radios often have a -5 db gain on the “rubber duck” antennas and have a reduced range and yet are very important part of a ham’s arsenal. More on that coming soon.

 

KG4GPJ/R Repeater Coverage

One of the biggest problems here in the mountains is VHF coverage. In some places 100 watts can’t get you anywhere. Radio Mobile online provides online tools to estimate and produce coverage maps, and from my experience are surprisingly accurate when used appropriately.

The maps below indicate the estimated coverage area. Yellow is a weaker signal, where you can typically expect noise and trouble establishing two way communication, specifically 1 µV (-107 dBm). Green are stronger signals are are areas where you should easily be able to talk on the repeater as well as access it via a handheld, specifically 71 µV (-70 dBm). The reason why there is such a gap between weak and strong is due to the vast differences in receiver sensitivity, noise, antenna setups. So if you are “in the green,” and have trouble getting into the repeater, it may not be because the map isn’t entirely accurate; the purpose isn’t to pinpoint mobile fluttering, but to be as a guide to where you should be able to establish communications.

Regional Coverage

KG4GPJ-R_Regional

 

Clay County

KG4GPJ-R_Clay

 

Cherokee County

KG4GPJ-R_Cherokee