The MT Blog

In The Zone

08 July 2017
Simon, G4TJC

All you need to know about the Activation Zone

So, you're about to activate a summit. You hiked to the top and now you're setting up. But where do you have to be for the activation to be valid?

Well, the programme is called Summits on the Air, so obviously your target is the summit. But just what does that mean? For programmes based on man-made features (e.g. trig points) it's pretty obvious, and they can specify a really easy rule such as "within 25 metres". But on a lot of SOTA summits it would be very hard to locate the actual summit anything like accurately enough.

Summit of Fumat

Fumat - A pretty obvious summit

Also we need to consider other people on the summit who might not share our passion for radio!  Sometimes it's more diplomatic to move away from the true summit to allow room for others to enjoy the hill.

So, we have a rule which allows a bit more flexibility and lets you operate even on a flat-topped hill without having to worry excessively about finding that last little 6-inch rise! It will help when you want to squeeze in a top-band monster dipole too!

Introducing General Rule 3.7.1 paragraph 4:

The Operating Position must be within the Activation Zone. The operating position must lie within a closed contour line at the permitted maximum Vertical Distance below the summit. (Typically the contour line is 25 metres below peak height of the summit). The Operating Position is taken to be the position of the operator.

So, this is our definition of the Activation Zone (AZ). Is there a contour all the way around the summit, no more than 25 m down the hill, that encloses your operating position? There's another way you could put it...

From where I'm standing is there a path to the summit that would take me no more than 25 m below the summit?

Note that I mean path in a mathematical sense, so there doesn't have to be an actual track! It just means there has to be some route across the ground surface from the summit to the activating position, not necessarily in a straight line, which dips no lower than 25 m down the hill.

So, you're on your hill, and the actual summit doesn't look too good for operating (covered in people, next to a windy cliff, whatever). You've seen a nice looking spot some distance away, but is it in the AZ? If you've got a map with a sufficiently fine contour step you can probably point to an area that's sure to be good. Let's turn to Fumat, as in the picture above, with an excerpt from the Spanish mapping.

Map of Fumat

Map of Fumat - The base layer used for this map is © National Geographic Institute (Spain) © Instituto Geográfico Nacional. Used in accordance with Order FOM / 280/2015 licensing.

This is quite a lucky case. The summit is at 335 m so the edge of the AZ comes at the 310-m contour line. Often you'll just have to do your best to interpolate, or better just play it safe and stay inside the lowest contour that is definitely Ok for the AZ.

Now for a more difficult example - Kinder Scout. Below is a map of the hill, from OSM Thunderforest (base data for these maps © Thunderforest, Data © OpenStreetMap contributors).

The (large) summit area of Kinder Scout G/SP-001

It's very hard to pick out the contours across the very broad summit. Actually it's better on the British Ordnance Survey map, but still not easy.

Now I'm going to pull in a digital elevation model that's been made from an aerial LIDAR survey. In the map below I have shaded all the land from the summit (blue) down to the level 25 m lower (red).

This shows just how far the AZ extends - over 4.9 km2 in fact. Why did I go to such trouble? Towards the north-west of the AZ is a second trig point (The Edge,  TP6378) and I wanted to be sure that this one is Ok for the SOTA summit. I found the dip between there and the summit, which must not go over 25.0 m, leaves a good 1.5 m in hand.

Another important feature of the AZ is that it can determine when we allocate a new SOTA reference code. From time-to-time we become aware of mistakes, even in the well-surveyed UK associations. If when we find we misidentified the highest summit we were simply to relocate the coordinates of an existing reference that might mean we were moving it to a clearly separate hill. If it's a very small shift that is Ok, but we need a criterion for deciding what makes a new position distinct from the old one. So we look at the AZs. The new position (which will be higher) determines a new AZ. If the old, lower, position is within this AZ (in which case it follows that the new position must also be within the old AZ) we keep the old reference and just change the data. If the old position is outside of the new AZ the two hills are considered distinct and a brand new reference is issued. Below is an example.

Horse Head Moor map

Horse Head Moor, G/NP-021, and Birks Fell, G/NP-031

This is another case of rather flat moorland. The original summit (G/NP-021) was found to be about 1 m lower than a higher point on Birks Fell. I've shaded the old AZ around G/NP-021 green-to-purple and the new AZ around G/NP-031 blue-to-red. Clearly the ground dips enough (not a lot, but enough) in between to make for distinct areas. So Birks Fell was given a new reference and G/NP-021 was retired. Note that old summits are not deleted (you can find their database pages if you run a summit search), so activations made whilst they were valid remain on the system and still count for points.

Of course most associations don't have freely-available LIDAR data (actually coverage is quite patchy in G), but this is a good way to illustrate the principle. In most cases you're just going to have to find the best available map and go, conservatively, by the contours.

One final point to make about the Activation Zone is that it can also affect which stations you can log. If the other station is within your AZ you can't log it. I put my determination of Kinder's AZ into practice the other day, working from The Edge, only find somebody else activating from Kinder Low! Of course we enjoyed a chat over the radio but it didn't count for SOTA.