Hi,
Looking forward to a good few weeks of free time in the near future and
one of the things I want to try and achieve now the better weather is
coming is to finish the rework of my 5 band quad. Actually I plan to
make it 7 band ala EI7BA ( http://www.qsl.net/ei7ba/Cubical%20Quad.htm
). Whilst understanding the compromises and pitfalls I am very
comfortable with what I expect will be as good a performance as I had
when this same quad ( in 3 band common feed ) was last in service.
The pentaband quad in the ARRL antenna book has had a couple of
recommendations as a good design based on my web reading and it makes an
interesting point with regard to the feeding method. As has been stated
by numerous sources a common feed is not a good idea and this time round
I plan to use a relay switch box. The article points out that it is
preferable to use individual band feed lines to all loops that are an
odd number of quarter waves long on 28MHz if to an ungrounded relay
switch box, or a number of half wave length lines at 28MHz if to a
grounded switch box. This to ensure that the unused loops all appear to
be a short at their feed point in the presence of 28MHz energy since
this is the band most likely to suffer ill effects of adjacent open loops.
This is the first time I've seen this mentioned in this way and is of
great interest since I cannot see any way to guarantee a closed loop
based on transmission line where the frequency of excitation from an
adjacent loop can be anyone of 4 or 5 different bands.
Is this a safe bet? Would there be some worthwhile benefit exploring
other lengths to ensure minimal interaction between different bands? If
so, which are the bands on a 5 band quad likely to need the most
attention (if not 10m)?
Thanks
Martin, HS0ZED
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