LF: Re: Receiving antennas at LF
Mon, 01 Feb 1999 22:36:29 -0500
Peter Dodd wrote:
> I would like to add some comments to what John, G4GVC has to say on
> LF receiving antennas. This may be of interest to the USA group if
> they plan any further listening tests.
Dear peter,see my separate msg announcing that we will have access to 1,200 feet
tall antenna located at the US Navy station at Annapolis
> I think that you have to consider Capture area or Aperture, which is
> the effective area over which an antenna extracts power from an
> incident plane wave.
> The ratio of power at the receiver antenna connection to the power
> density of the incidental wave is an area is P = S*A (ignoring
> transmission line losses)
> Where P is the power at the antenna termination or receiver, W
> S is the power density of the incident wave, W m^2
> A is the area in square wavelengths (Lambda ^2)
> In other words the bigger the better. But there is more.
> For a given size a sharply tuned wire antenna has is a greater
> capture area than broad band antenna. For LF it does not seem to
> matter that the antenna is very high, it just needs to be long,
> resonated and matched to the receiver antenna input. In practice any
> long RESONATED wire seems to outperform anything else at LF. Even the
> massive OH1TN antenna is less than a quarter wavelength long so there
> is no danger of overdoing the length thing.
> I am suprised that the American team did not complain much about
> Loran QRM.
it was not too bad
> with electrically short antennas the polar diagram is
> omni-directional with an null at high angles. Another good reason for
> using a very long wire antenna is that this null is filled in so that
> it is more sensitive to any sky-wave propagation that might be around.
We will let you know in advance when we plan to connect the 1,200 ft antenna to
our receivers (and we will be watching for serious corona effects on tall