Message-ID: <39230191.5B28@xtra.co.nz>
Date: Thu, 18 May 2000 08:31:13 +1200
From: "vernall" <vernall@xtra.co.nz>
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To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: Puckeridge Decca station - Big & small antennas
References: <28528.200005171129@gemini>
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James Moritz wrote:
snip
> The main motive for this expedition is to do some back-to-back
> comparisons between a big antenna (the 100m Decca mast) and a
> small, amateur-type antenna (an inverted L about 9m high and 50m
> long). The idea is to set the antenna currents so that the same
> effective radiated power should be obtained from both antennas,
> and then see how signal strengths compare.
> 
> There has been some vigorous debate lately about the advantages
> and disadvantages of big and small antennas, with some holding
> the view that big antennas have superior radiation patterns to small
> ones, and some holding the opposite is true. The aim of the
> experiment is to put this to a practical test. We did this before
> during the previous trip to Puckeridge, but due to time pressures
> and the dreadful weather, relatively little operating was done using
> the two antenna setup. The results then were that the two
> antennas gave roughly the same results, when transmitter power
> was set for same ERP from each antenna (this meant feeding
> about 500W into the small antenna, and less than 0.5W into the
> main mast!).

I think it was also raised before, but for doing such a test you should
have a convincing way of showing that mutual coupling to the big mast is
not swamping the result of transmitting from the small antenna.

A simple additional experiment could be to transmit on the small
antenna, with the big mast "floating", and then short the base of the
big mast to ground, and see what happens to far field readings.

73, Bob ZL2CA