Topband: Fresnel Zone

[shristov]

> donovanf at starpower.net wrote:

> The classic source for Fresnel zones as they apply to HF site
> selection is NBS Technical Note 139:
> https://nvlpubs.nist.gov/nistpubs/Legacy/TN/nbstechnicalnote139.pdf


This indeed is a classical source, but it should be noted that the derivation
assumes that the elevation angle actually used for communication
is equal to the elevation angle of the peak of lowest ground reflection lobe.

This may or may not be the case.

In amateur operation, communication is often done using elevation angles
well below the peak of the lowest lobe, because of inability to erect very high antennas.
In such cases, the first Fresnel zones extends much further than the
equation 3.4-4 predicts. Correct formulas may be derived using the same
procedure, while separating communication angle from lobe peak angle.

Using vertical antennas additionally complicates matters.
I am not aware of any work on this topic.


73,

Sinisa  YT1NT, VE3EA