More Ham Radio Antenna Site Elevation Profiles and a Datasette Plugin

 As with most of my project, I'm probably having way too much fun with this elevation path thing! I got a new look at our usual Pantoll campground site this morning, and it's really, really cool! 

First though, let me point you towards the code that enables my recent fascination with our the layout of the terrain at our POTA activations. I've worked the datasette plugin that returns the coordinate's of a portion of the path between two points code through it's first very simple test case. I do not know if it will install correctly in any installation of Datasette yet, but it install's in mine, and it plays well with the instance in the test case, so here's the repository.

Note for new readers:

Datasette is a Python tool from Simon Willison, described as:

"Datasette is a tool for exploring and publishing data. It helps people take data of any shape, analyze and explore it, and publish it as an interactive website and accompanying API."

The gang and I have been slowly but surely working at applying Datasette to mapping our ham radio QSOs over the last several months, and in the process have been learning about ionosonde data sources, how to release Python packages, vector math, including cross products, (seriously, check that post out, it includes CoCalc plugins that let you see the cross product process we used to calculate the distance between a point and a path on the Earth. I think it's really cool), and GIS in the form of geocoding via Google Maps, We've use all that information to map the paths between QSOs along the ground as well as the paths of signals skipping between the ground and the F2 layer of the ionosphere. The maps have helped us better visualize high frequency radio propagation.

OK, so now onto more elevation paths! 

On our most recent trip to Mt. Tamalpais the gang and I, using TouCans on 20 meters, made POTA QSOs to both Alaska and New Hampshire among other places. I estimated—using a topo map—that the hill rolled down from our campsite at an 18 degree angle. Taking a look at the New Hampshire QSO with WK1V today, I was able to more accurately measure the elevation angle at 22 degrees. Here's the elevation profile of the starting from the campsite at the left hand edge, and extending down the mountain. My vague memories of RF engineering from grad school tell me that only the elevation over the first few wavelengths matter, but it's a lot of fun to look at the a longer path:

So, that's cool, but what about that Alaska, QSO? Does the elevation angle of our campsite point downwards towards Alaska as well? It's possible. Our campsite is at the top of a ridge. Let's look.

As it turns out, to get to Alaska from our campsite, you walk along the ridge and over Mt. Tamalpais!

What's that mean for my favorite radio journal assertion that the angle of the hill subtracts from the elevation angle? Well, for the first three wavelengths along the path, the ridge only rises 20 feet or so. Comparing that 20 foot rise over 60 meters to the 20 meter wavelength of the transmitted waves, that's basically flat, so while the upward slope may not have helped, it also just wasn't very noticeable to the signal at all. At least that's my contention at the moment.