How to check your horizon for HF & VHF propagation

If you're interested in the upper HF bands or any of the VHF and UHF bands then your horizon is all important. On bands like 144 MHz and above, the vast majority of signals are coming in from the horizon and just above it.

On bands like 28 MHz, 50 MHz & 70 MHz, the signals may be coming in at a slightly higher angle with Sporadic-E but they are still very close to the horizon. Whether you're operating from home or thinking or going portable then knowing your horizon can help explain what's going on.

First off, the website for checking your horizon is https://www.heywhatsthat.com/

In this post, we'll look at how to use it and some tips on getting them most out of it. To help explain it, I am going to do a profile of Paul Logan's location in Lisnaskea in Co.Fermanagh, Ireland. Paul is an avid listener to the Band 2 FM band from 88 to 108 MHz and logs hundreds of radio stations from all over Europe every year.

Getting started...

After going to the HeyWhatsThat site, click on the 'New panorama', zoom in to find your own location on the map and then click on it. 

I have done this in the example above for Paul's location and them zoomed back out. On the left side of the screen, your latitude and longitude will be automatically filled in after you click on the map. You can also select the height above ground so I selected 8-metres which is the height of Paul's antenna.

Note that the site uses the general topography to calculate your horizon, it doesn't take buildings or trees into account.

Also make sure to select 'Metric' at the bottom of the screen to use proper measurements.

Then click 'Submit request'.

Using the results...

After a short while, a map is generated. I clicked on the 'Visibility cloak' to show the areas that are visible from Paul's location. The Red triangles are distant peaks and I clicked on 'Contours' to highlight the topography.

This is that the horizon looks like for Paul...

I have exaggerated the vertical scale and added some numbers to make it clearer.

There is a large hill with an elevation of about 5 degrees to the north-east of Paul's location (45 deg bearing) and this is clearly shown on the image above. This would have a major impact on all signals at 144 MHz and above. As Paul notes himself, he finds it very difficult to get distant stations on Band 2 in that direction. 

That hill would also impact on all long distance single hop Sporadic-E coming from that direction on all bands from 28 MHz to 144 MHz. Short skip arriving at a higher angles on say 28 MHz or 50 MHz would probably clear the hill.

Due east at 90 degrees, there is an interesting gap which might might allow some distant Band 2 tropo or Sporadic-E through.

From 100 to 140 is another impediment to low angle signals but it gets much better after 150 degrees or so. Paul has a very good take off at about 190 degrees towards the Canary Islands and even those distant line of sight peaks around 270 degrees are so low that there are unlikely to be much of a problem. As a result, his location will be wide open to say the USA on 28 MHz once the sunspot numbers increase.

Example 1: Poor tropo path to Scotland.

In this example, I have shown what the path is like to Scotland and how the hill is in the way. If you are trying this from your location, then just click on any location of interest and the site will show you the path and where it is on your horizon.

Example 2: Good tropo  path to Spain

As can be seen from the horizon profile, Paul has a good path to the south and this can allow him to gain access to the marine duct that sometimes occurs between Ireland and Spain. The distance shown is about 1200kms which is really good for Band 2 tropo.

Example 3: Sporadic-E footprints...

Using the 'Up in the air' button, I was able to simulate what the limit for one hop Sporadic-E from Paul's location might be. One the left above is the approximate range if Paul had a completely flat horizon. The one on the right is the reality.

For Italy, the local hill restricts signals further south than Rome.

For Poland, signals from the east of the country should be easy to hear except the local hill makes things more difficult. Belarus and the west of Ukraine are also more difficult. Notice that that little gap at 90 degrees is reflected in the Sporadic-E footprint.

For the Baltic states and Finland, they should be well within Sporadic-E range but again, the local hill makes things difficult.

It's possible in many cases that some local tropo conditions will extend the footprint further east but overall, the local hills make hearing these areas more challenging.

Example 4: F2 propagation...

As the sunspots increase, there will be weak F2 openings on 28 MHz. Towards the west, Paul should have no problems reaching Newfoundland and Nova Scotia in Canada. With the help of a more southerly second hop, he is well placed to hear signals from well into the USA.

Towards the eastern Mediterranean, the local hill will block some of those signals when the band is just open. Ironically, it may actually be easier to hear signals further away in places like the Arabian peninsula once there is a second hop.

'Up in the air' Values... 

For your own propagation footprint maps, try 360000 for Sporadic-E and 1300000 for F2.

Example 5: Line of sight paths...

The HeyWhatsThat site can also be used to examine line of site paths. The map above shows the path from Paul's location to Clermont Carn in Co.Louth, about 75kms away. This is a major transmitter site for Irish radio stations.

Let's say for example, Paul wanted to get a line of sight path for a contact on the microwave bands. The profile below shows the local hill in the way but there is a location 7kms away that is line of sight to Clermont Carn.

It's not hard to imagine how it might be used for finding suitable paths on the microwave bands or even if someone was just curious if a distant mountain was visible or not.

Other uses... Here's a few...

Portable operation, DX-peditions, Summits on the Air (SOTA) activations, contesting ... are there obstructions in the way? Is your 'perfect' contest location blocked at a low angle on the upper HF bands say to the USA?

In summary... This is a very useful utility to have and the more you use it, you tend to think of other uses.

For the bands like 28 MHz and 50 MHz, short skip can hide the shortcomings you may have in a certain directions. Your horizon profile should make you aware of these and you're looking for no more than 2 degrees.

For the higher bands like 70 MHz, 88 to 108 MHz, 144 MHz and above, tropo becomes a more important propagation mode. This time, you're looking for a very low horizon and the lower the better.

There's a very good reason why people put antennas up as high as possible on the VHF and UHF bands.

Link...
1) HeyWhatsThat website