German VHF E Boat Emissions

[Steve Crandell]

Isn't VHF subject to atmospheric skip? I seem to recall communicating with someone half way around the world with a ham radio vhf set. Maybe my memory is faulty.

[A Raven]

Two reasons for anomalous propagation.

(1) A rapid increase of moisture with height.

(11) A rapid increase of temperature with height. (ie a temperature inversion).

One operational example of many:
"August 1944. An MTB using an American SO radar in the Gulf of Genoa, detected two German Destroyers leaving Genoa 39 miles distant. They were plotted to close range and a torpedo attack carried out on them, one being sunk. The other was then plotted out to a range of 45 miles." Normal range of type SO is about 8 miles.

[Dave Saxton]

Isn't VHF subject to atmospheric skip? I seem to recall communicating with someone half way around the world with a ham radio vhf set. Maybe my memory is faulty.

This type of thing is much more likely to occur with very long wave lengths with a strong vertical lobes structure. For example, Over the Horizon Radar systems usually use the HF band which is of several meters wave length such as used by Type 79 or Chain Home. At these wavelengths it can be used fairly reliably and consistently. VHF is a higher frequency compared to HF, of a few meters wave length, such as Type 281 or Freya, and so VHF is not used for Over the Horizon radar because such a thing could not be relied upon. In most cases it would not propagate far beyond the horizon.

Anomalous propagation can occur, however, to any wave band. As Tommy pointed out earlier, a distant radio station might be picked up very far away in certain conditions. This happened once when I was riding in a car pool. We picked up an FM (borderline VHF) radio station from about 1,000 miles away for several minutes. I still recall another guy in the car exclaiming: "But this is impossible for FM!" As Mr Raven has alluded to, it happened in the case of SO radar. SO was centimetric, so it can even happen in the case of centimetric systems. Another example of an S band radar encountering anomalous propagation was Prince of Wales's early model 273 tracking a light cruiser to something like 56,000 yards once. Anomalous propagation may or may not be caused by skipping.

Mr Raven's explanation about humidity and temperature is interesting in light of the centimetric bands' known high probability of reflecting off of weather and humidity.

[A Raven]

From an official RN wartime RCM history.

" On VHF and UHF it has been found that, if we take the range under the usual unsettled weather conditions in England as normal:-

(1) Range is increased when weather conditions are settled, with a high steady barometer, and may rise as high as five times the optical distance.

(11) Range may be reduced to as little as a quarter of the optical distance when the air is much colder than the sea, as for instance in the Artic."