VHF Site Clearance

One of the primary constraints on propagation from a site is the site clearance. Ideally, the ground should fall away rapidly giving full first Fresnel Zone clearance in the foreground of the site. If the Fresnel Zone is obstructed in the foreground, there will be high path loss.

My site in Kirkton is awful. Here’s the clearance for tropospheric propagation for 50% of the time for eight points of the compass. All clearance angles are negative! There’s high ground all around.

144MHz Clearance Angles

Simply, my site is heavily obstructed and no tropospheric VHF DX propagation will be possible.

However, the situation for sky-wave propagation (for auroral, sporadic E, and other ionospheric and scatter modes) is better – at least to the west (to the USA) and north-west (to northern Scotland, the Faroes and Iceland), and to a lesser extent due north and south. The high negative clearance angles will however constrain even sky-wave DX.

The clearance angles were assessed from profiles using the Radio Mobile application online from Roger Coudé VE2DBE.