When doing VHF activations for Summits On The Air (SOTA), the radio range is dependent on the height of the summit and the surrounding terrain. The Radio Mobile website from Roger/VE2DBE is a great tool that can be used to estimate the radio range from a particular site. Repeater system owners often use tools like this to predict the coverage of their repeaters. I don’t normally do this type of analysis for SOTA…I just look at a topo map and get a rough idea of how far my signal will go. Then, I decided to spend a little time analyzing a few summits in Colorado to see what I could learn.
Pikes Peak (W0C/FR-004)
Pikes is a 14,115-foot summit that towers over the eastern plains of Colorado, making it an ideal radio site. The Radio Mobile plot shown below shows the solid radio coverage in blue and the fringe area in yellow. I won’t go into how to use Radio Mobile on this post. As you’d expect, you enter the location of the radio site (summit) along with various parameters such as frequency, minimum detectable signal level, transmit power, and antenna gain. I entered some nominal parameters consistent with typical SOTA stations on 146 MHz (2 meters).
Pikes covers about half of the state of Colorado, reaching out to the Kansas state line. To the west, the coverage does not go as far because the radio signals are blocked by other mountain ranges. In particular, the signal tends to drop off at the Sawatch Range, west of Buena Vista. I’ve activated Pikes many times and this plot lines up well with my general experience. The blue area can be worked quite reliably with a decent station on both ends. By “decent” I mean a 20-watt transmitter on the summit with a small Yagi antenna and a 40-watt radio with an omnidirectional antenna at the chaser station. Working stations near the Kansas state line is usually easy on 2m FM. The highest spot in Kansas (Mount Sunflower, not a SOTA summit) can usually be worked without much trouble. However, longer distance contacts are possible, especially using SSB or CW. I’ve written before about the Myth of VHF Line-Of-Sight.
When using VHF for SOTA activations, It is important to consider the potential stations that will be within range and on the air for you to work. Besides being a high summit, Pikes overlooks the major cities in Colorado, from Fort Collins to Pueblo, so finding someone to work on 146.52 MHz is usually easy. It is common to have a pile up of stations calling you.
Colorado has over fifty 14,000-foot mountains and all those are workable from Pikes Peak on 2m FM.
Mt Herman (W0C/FR-063)
Mt Herman is another popular SOTA summit, with an elevation of 9063 feet, not nearly as high as Pikes Peak. This summit also looks out over the eastern plains of Colorado, as shown in the coverage plot below. Although the range is not as good as Pikes, it still covers the major cities, so again it is easy to do a 2m FM activation from Mt Herman. It is more difficult to work stations to the west. I can usually work stations in Woodland Park and Divide from Mt Herman, but reaching Buena Vista is a challenge.
Threemile Mountain (W0C/SP-107)
VHF activations can be much more challenging when the summit is further away from populated areas. Let’s consider Threemile Mountain, which is 10,020 feet in elevation, located about 20 miles south of Hartsel, CO. This summit tends to get blocked to the east by the Front Range and to the west by the Sawatch Range. Even though the summit is higher than Mt Herman, its radio range is not as good.
In particular, it does not cover Denver, Colorado Springs, and Pueblo very well, so the number of available stations to work drops dramatically. There are a number of stations that monitor 146.52 MHz up in the mountains, so if you are patient you can usually make some VHF contacts. This can be a source of frustration for VHF activators, or you can take it on as a challenge. I have activated Threemile five times and I don’t think I’ve ever worked a Denver station on 2m FM. I have worked some Denver stations from there using 2m SSB, during a VHF contest. Oh, I did manage to work Larry/N0LL in Smith Center, KS on 2m SSB for a distance of 372 miles. See Radio Fun on Threemile Mountain (W0C/SP-107). So you never know what you’re going to get on VHF/UHF.
So what conclusions can we draw from this analysis?
- Radio Mobile does a good job of predicting typical 2m FM coverage. My experience on these summits aligns well with the Radio Mobile predictions.
- But much longer distance contacts are still possible. VHF is not limited to line of sight. Radio Mobile is intended to predict reliable radio coverage, not the exceptional radio contact.
- Be aware of the population density of the coverage area because that is a huge factor for making radio contacts. New VHF activators should start on summits that overlook the major Colorado cities.
- Improve your VHF activator station. Every additional dB of signal improves your ability to make those weak-signal contacts on the edge of the coverage area.
As always, get off the couch, gather your radio gear, and head for a summit.
73 Bob K0NR