[TowerTalk] TH-11DX and 40/30m dipole

[StellarCAT]

I’ve done quite a bit of modeling on 40’s and their interaction to 15 (and other bands)... I’m installing a 40M4LLDD 30’ above the top of a 12 element (6/6) 15 stack. Others have measured this antennas (40) SWR on 15 and found it to be very low – so it will couple in energy and thus will re-radiate screwing with the pattern and potentially the SWR. In all the modeling I’ve done I’ve found that the FB is first hit – then gain/SWR. If the SWR is changed (on the 15) then you’ve more than likely significantly impacted the FB. 

So I’ve designed a stub to be placed on the 40 and am now testing said stub. Depending on its length and placement I can find a place where it completely cancels any 15 issues – but in the process introduces 17 issues. Its really difficult to find a stub that won’t impact any ham band although I’m still early in to the process. I’ve got a 36’ tower with a Razor on it so its relatively easy for me to raise and lower it. I’m currently only testing one element of the 40 which is all that is needed. 

In general if you do nothing you will be best served by rotating the antenna 90 degrees. ESPECIALLY if you’re less than 10’ spaced... there will be serious impact otherwise. Whether or not the boom of the TH11 now impacts the dipole is an unknown – it could be modeled somewhat easily ... but if you’re going to do it anyway I’d just do it and see what is what. Note any impact of it on the 40/30 I believe will be slight and won’t effect the pattern – SWR would be the only potential issue and I’d be surprised if it did much to it. 

Gary
K9RX


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Based on several responses thus far it would seem I asked a stupid question or at least one which is not possible to answer. The reason I am not finding articles with general advice on stacking 40 and/or 30 meter dipoles on the same mast with a TH-11 or other complex multiband antenna is most likely because each case is different and there are no applicable rules of thumb. Modelling the whole thing would be great but by the time I came up with a workable and reliable model for the TH-11 I probably won't be needing antennas for DXing. :) 
I will proceed with the understanding that this entire venture is an experiment and may or may not work. Nothing ventured, nothing gained. Given that this is the only solution which *might* substantially improve my situation on 40/30 I deem it an acceptable risk. At the very least I will have gotten some exercise and will end up with a pile of aluminum which might be put to another use at a later time. Of course I'm hoping for a somewhat better result. 
Although budget is always a prime concern, I am no stranger to uncharted waters. All of my former EME arrays were far enough off the beaten path to be considered risky experiments. 
I will report back with my results later. I do not have a precise time table for this project other than to have it done no later than the end of September. 
73,
Paul N1BUG