[TowerTalk] Triband Stacking Distance or antenna height?

[StellarCAT]

Hello Rich, I’m not sure if this will be inline with the thread you’ve 
created, a new thread or somewhere entirely separate... sorry if not inline 
where I intended it to be.

I've had what you're planning on doing - a 3 stack of C31's. See the picture 
on QRZ.com call sign search (K9RX). It was taken down in April of 2012 after 
having been up for 6 1/2 years (we moved).

I can tell you that first off there are few times that a separate antenna 
will be better than the stack. On 10 meters it would happen occasionally, 15 
less often and 20 probably less than a couple times all told! I had antennas 
at 41, 81, 121. I felt this was the best overall spacing. If I had it to do 
over again I'd probably reduce it to 37' or so as it really is too far apart 
on 10 and for a relatively short boom 20 if you model it you can find that 
37' is a slight increase in gain over 40' (with a slight reduction in FB). 
So using single or dual stacks just isn't something you'll end up doing much 
of. There's too much coupling into the non-connected antennas and thus 
little change in overall performance. Once - on 10 meters, the lowest 
antenna was 20 db stronger than the top ... but the stack was just a bit 
down from the stack.

And indeed - the overall heights matter just as much. My low antenna at 41' 
was really too low for 20 ... and it is beginning to be too high on 10... 
that stated I'd probably go with that one at 45' and then 37' spacing from 
there putting the top antenna at 119'. Note however - its really not that 
critical - just stack them 35' - 40' apart and around these heights...

I sold mine - I hope to be in South Carolina soon (this year - purchased 11 
acres in Piedmont - just have to move and build a house)... and this time 
I'm going with 2 stacks of 20m 5el and 15m 6 el on a rotating tower... the 
pattern and gain is better overall.

The C31 stack played quite nicely on 20... and on 15... but I never really 
felt it was doing what I'd expect on 10. I had it with a Force12 240N 2 el 
40 meter at 130' and their Magnum 80 meter rotary dipole at 136'. And the 
SWR on 15 was never great - I was one of those that had the 'notorious' 15 
SWR problems that I could never get quite right.

As an aside I'd often ask people to guess which of the antennas/systems 
worked best overall... most would say the 3 stack of C31's... but the best 
antenna on that tower was the dipole on 80 at 136'... it was awesome. Why? 
Because it was competing against mostly wire dipoles at 50' - 60'.

Gary, K9RX



I've been following the mail on this subject. I'm going to start my new 
tower this summer. The base and anchors are already in. It's going to be a 
137' rotating 55g tower with three F12 C31XR's stacked. I've been using HFTA 
to come up with the best compromise heights (compromise as I'm trying to get 
the best results on all 3 bands). Then it dawned on me. Should I be worried 
about stacking results or individual heights. Isn't the height of an antenna 
for a specific band at a certain time of day more of an advantage than the 
combined stacking?, and of course it's still a compromise since we're 
talking about tribanders. Don't get me wrong, I'm still going to try to come 
up with the best stacking distances for my location, but it seems to me that 
the most important feature of a stack is having 3 different heights to 
choose from, isn't it? I sure wish the project was finished, it would have 
come in handy this past weekend. Rich - N5ZC