{"id":1075,"date":"2016-06-06T06:10:17","date_gmt":"2016-06-06T12:10:17","guid":{"rendered":"http:\/\/play.fallows.ca\/wp\/?p=1075"},"modified":"2016-12-12T18:55:22","modified_gmt":"2016-12-13T01:55:22","slug":"high-frequency-communication-terrain","status":"publish","type":"post","link":"https:\/\/play.fallows.ca\/wp\/radio\/ham-radio\/high-frequency-communication-terrain\/","title":{"rendered":"High Frequency Communication and Terrain"},"content":{"rendered":"

\"high<\/a><\/p>\n

High frequency communication between my location and Europe is great.<\/p>\n

<\/p>\n

Recently, I have been exploring the performance of my antenna using High Frequency Terrain Assessment<\/a> software. This article describes the details. High frequency communication involves bouncing radio signals off the ionosphere, a patch of our atmosphere about 50 to 600 miles above the earth. These radio signals are a combination of direct and reflected (and diffused) rays from your antenna. The slope of the terrain near your antenna can influence how these rays reinforce each other over great distances.<\/p>\n

The diagram at the top right shows my terrain towards Europe over three directions: 10 degrees from north (blue), 25 degrees (red) and 40 degrees (green). For comparison, the aqua line shows what things would look like \u201cif\u201d the terrain was flat at my location. In reality, though, you can see that towards Europe I am on a local hill that slopes down about 100\u2019 for the first quarter to half mile.<\/p>\n

When a radio signal reflects off a downward sloping terrain, the reflection tends to be at a lower angle of incidence to the earth. In effect, this moves the stronger parts of my radio signal downwards towards the horizon. Why does this matter for high frequency communication?<\/p>\n

High Frequency Communication \u2013 All About Angles<\/h2>\n

In the lower left of the above picture, the purple bars show the most frequent angles of incidence experienced for radio signals between Calgary and Europe. This is called the takeoff or signal angle. Most of the high frequency communication signals between Calgary and Europe arrive\u00a0at less than 10 degrees from the horizon, and virtually all of them at less than 20 degrees. These angles and their probabilities have been determined by both experience and analysis.<\/p>\n

The performance of my antenna over a hypothetical flat terrain is shown by the aqua curve above on the left. The performance of my antenna over actual terrain at the three directions towards Europe is shown by the blue, red and green lines.<\/p>\n

Basically, the higher the lines are in the graph, the more signal gain and better performance. This is especially important for the most common takeoff angles experienced between Calgary and Europe.<\/p>\n

As you can see, my terrain provides a big performance boost for signals arriving at the lowest angles, below 12 degrees elevation, when compared to flat earth. In some cases, my terrain provides a boost of more than 10 dB gain, which is quite a lot. It turns my small antenna into a great performer for free!<\/p>\n

You can obtain a copy of HFTA<\/a> with the ARRL Antenna Book<\/a>, and get your terrain data from the K6TU<\/a> web site after your register. Have fun.<\/p>\n","protected":false},"excerpt":{"rendered":"

High frequency communication between my location and Europe is great.<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":true,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","_share_on_mastodon":"0"},"categories":[5],"tags":[67,193],"series":[],"class_list":["post-1075","post","type-post","status-publish","format-standard","hentry","category-ham-radio","tag-antennas","tag-hfta"],"yoast_head":"\nHigh Frequency Communication and Terrain - Making It Up<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/play.fallows.ca\/wp\/radio\/ham-radio\/high-frequency-communication-terrain\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"High Frequency Communication and Terrain - 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