Ridge Crossing Technique

The ridge is the universal radio obstacle, and the fix is embarrassingly simple: get to the crest. This page is the technique, with the physics that explains why it works.

The crest rule

A signal does not need to see over a ridge; it needs to diffract over the edge. The diffraction point is the crest, and its effectiveness depends on the clearance of the Fresnel Zone. The practical version:

• On the ridge: full signal.
• 20 m below the crest: often nothing.
• On the crest line, 100 m along it: full signal again.

The difference between dead and alive is measured in meters of height and meters of lateral position.

The technique

1. Reach the ridge crest before attempting the transmission.
2. Walk along the crest until the beacon’s bearing is roughly perpendicular to the ridge: that is the diffraction sweet spot.
3. Hold the receiver high (see Antenna Height Matters).
4. Test, and if the signal is marginal, walk 10 - 20 m further along the crest and retest.

The search application

For a searcher with a receiver, the ridge is not the end of the search: it is the observation post. Check the crest before descending into the next valley, and use the Homing Technique from the crest to refine the bearing.

The antenna polarization note

At the crest, the diffracted signal can be depolarized. Tilting the receiver antenna 45 degrees sometimes finds 5 - 10 dB the vertical position missed.

Related pages

• Mountain Effects on Radio for the physics
• Antenna Height Matters for the height lever
• Search Patterns and Procedure for the search