[TowerTalk] Feeding a quad

[Martin Sole]

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