[Lf] - Big & small antennas

[Andre' Kesteloot]

James Moritz wrote:

> Dear LF Group,
>
> This weekend, I am hoping to make another expedition to the
> Puckeridge Decca station, which has been made available again
> through the good offices of G3JKV and the Crawley club.
>
> 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!).
>
> For this weekend, I have put together a tuner/attenuator circuit that
> will hopefully allow changing between the antennas with a single
> switch, making the comparison much quicker and more direct. I am
> hoping this will enable lots more people to take part. The level of
> ERP will be very roughly 100mW for both antennas.
>
> The plan for the weekend is roughly this:
> Friday evening - Install gear
> Saturday morning - get working, and obtain comparative reports.
> Later on Saturday - run station at 1W ERP from main antenna
> Sunday - open to suggestions; I have notified RA in case anyone
> would like to try 73kHz QSO's.
> Sunday afternoon - pack up and go home.
>
> Due to this being a small-scale expedition, I will probably stick to
> normal CW, but might be prevailed upon to drag my PC across a
> field if people are really keen to hear some QRSS.......
>
> Of course, nothing ever goes entirely according to plan, but it
> should be fun. Any QSO's, listener reports or measurements would
> be welcome. If you have any suggestions, please let me know.
>
> Cheers, Jim Moritz
> 73 de M0BMU