Message-ID: <17200.200003291443@gemini>
From: "James Moritz" <j.r.moritz@herts.ac.uk>
Organization: University of Hertfordshire
To: rsgb_lf_group@blacksheep.org
Date: Wed, 29 Mar 2000 14:51:02 +0000
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Subject: LF: Decca antenna tests
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Reply-To: rsgb_lf_group@blacksheep.org
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<?color><?param 0100,0100,0100>Dear LF Group,<br><br>G3KEV wrote:<br>&gt;<?/color>At this frequency with both antennas resonant on 136 khz on the  &gt;same site, the induced rf from the small vertical into the larger  &gt;one would distort any meaningful tests.<br><br>It certainly would, which is why I wrote that the Decca antenna  would have to be grounded or otherwise made non-resonant at  136kHz. If both antennas were resonant, the un-driven one would  act as a parasitic element, as in a yagi array. Under these  conditions, the small antenna might be viewed as a rather  inefficient antenna feed for the nearby big antenna. This would still  happen if the parasitic antenna was non-resonant, but the induced  currents in it would be greatly reduced, and the effect on radiation  pattern reduced greatly also.<br><br>&gt;The antennas would need to be sited several kilometres apart...<br> <br><br>The professional antenna people seem to have no great problem  with co-sited 'antenna
 farms', although they have to take care to  avoid inadvertant resonances in guy wires, etc. There are at least  4 MF verticals in use across the road from me, a few hundred  meters apart; the BBC seems to be quite happy with them like that!<br><br>Cheers, Jim Moritz<br>73 de M0BMU<?color><?param 0100,0100,0100><br><br>