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When I get asked why I only use VHF/UHF frequencies for my Summits On The Air (SOTA) activations, I usually reply with:

Height Above Average Terrain

More specifically, I mean that using VHF for SOTA is fun because Height Above Average Terrain (HAAT) has a dramatic effect on the propagation of my radio signal.

HAAT has a specific definition, found in the FCC regulations. HAAT basically describes the height of a transmitter relative to the surrounding terrain in all directions at distances of 3 to 16 km. This HAAT calculator tool provides the HAAT of a site based on its latitude and longitude. Note that the FCC definition of HAAT compares against the terrain relatively close to the transmitter, 16 km (10 miles). For SOTA purposes, we are more concerned with distances further away.

In a recent presentation on mountaintop VHF operating (Hamcon Colorado), I provided these two contrasting examples to drive home the importance of HAAT.

Punkin Center

Punkin Center is a small town located on the eastern plains of Colorado. The elevation is 5364 feet, and its HAAT is roughly zero feet. That is, the terrain is flat. Punkin Center is a fine place to be, but it is not a very good VHF location. The radio range using a 5-watt VHF handheld radio is about 4 miles.

Pikes Peak

Compare this to America’s Mountain, Pikes Peak, which has an elevation of 14,115 feet and a HAAT of 4,445 feet. That is, it rises more than 4,000 feet above the surrounding terrain. (The height advantage is even more pronounced when looking further east towards Kansas, where the highest elevation is ~4,000 feet.) Based on my experience operating from there, the VHF handheld range is over 100 miles.

The improved HAAT of Pikes Peak provides a VHF radio range that is 25 times better than Punkin Center. Again, nothing wrong with Punkin Center, but if I want to make VHF contacts, I’ll choose Pikes Peak.

Let’s compare this to using the High Frequency (HF) bands. The normal propagation mode on HF is skywave propagation via the F layer, which supports radio propagation across North America and around the world (depending on frequency, time of day, solar conditions, blah blah blah). The radio signal refracts off the ionosphere and can go very long distances. From Pikes Peak, I can work the world. From Punkin Center, I can work the world. Not much difference, except the views from Pikes are generally better, and the oxygen is less plentiful.

So when I hike up a mountain, I am excited to get out the VHF gear and see what contacts I can make due to the improved HAAT. I don’t get as excited about working HF, because I can do that from home…or Punkin Center, or other places, with similar results.

Other SOTA activators see it differently, and that is just fine. (VHF contacts represent only ~20% of all SOTA contacts.) There are many ways to enjoy SOTA and ham radio. Just make sure you have fun messing around with radios.

73 Bob K0NR

The post Height Above Average Terrain appeared first on The KØNR Radio Site.

One Response to “Height Above Average Terrain”

When I get asked why I only use VHF/UHF frequencies for my Summits On The Air (SOTA) activations, I usually reply with:

Height Above Average Terrain

More specifically, I mean that using VHF for SOTA is fun because Height Above Average Terrain (HAAT) has a dramatic effect on the propagation of my radio signal.

HAAT has a specific definition, found in the FCC regulations. HAAT basically describes the height of a transmitter relative to the surrounding terrain in all directions at distances of 3 to 16 km. This HAAT calculator tool provides the HAAT of a site based on its latitude and longitude. Note that the FCC definition of HAAT compares against the terrain relatively close to the transmitter, 16 km (10 miles). For SOTA purposes, we are more concerned with distances further away.

In a recent presentation on mountaintop VHF operating (Hamcon Colorado), I provided these two contrasting examples to drive home the importance of HAAT.

Punkin Center

Punkin Center is a small town located on the eastern plains of Colorado. The elevation is 5364 feet, and its HAAT is roughly zero feet. That is, the terrain is flat. Punkin Center is a fine place to be, but it is not a very good VHF location. The radio range using a 5-watt VHF handheld radio is about 4 miles.

Pikes Peak

Compare this to America’s Mountain, Pikes Peak, which has an elevation of 14,115 feet and a HAAT of 4,445 feet. That is, it rises more than 4,000 feet above the surrounding terrain. (The height advantage is even more pronounced when looking further east towards Kansas, where the highest elevation is ~4,000 feet.) Based on my experience operating from there, the VHF handheld range is over 100 miles.

The improved HAAT of Pikes Peak provides a VHF radio range that is 25 times better than Punkin Center. Again, nothing wrong with Punkin Center, but if I want to make VHF contacts, I’ll choose Pikes Peak.

Let’s compare this to using the High Frequency (HF) bands. The normal propagation mode on HF is skywave propagation via the F layer, which supports radio propagation across North America and around the world (depending on frequency, time of day, solar conditions, blah blah blah). The radio signal refracts off the ionosphere and can go very long distances. From Pikes Peak, I can work the world. From Punkin Center, I can work the world. Not much difference, except the views from Pikes are generally better, and the oxygen is less plentiful.

So when I hike up a mountain, I am excited to get out the VHF gear and see what contacts I can make due to the improved HAAT. I don’t get as excited about working HF, because I can do that from home…or Punkin Center, or other places, with similar results.

Other SOTA activators see it differently, and that is just fine. (VHF contacts represent only ~20% of all SOTA contacts.) There are many ways to enjoy SOTA and ham radio. Just make sure you have fun messing around with radios.

73 Bob K0NR

The post Height Above Average Terrain appeared first on The KØNR Radio Site.