Henry,
There is no need for guess-work or asking others for their comments. Just
model the situation(s) you want to investigate. For example, 4 ele 20 @ 90 ft
and another 4 ele at various heights that you have available (missing guy
wires, etc.). I'd start with 90/45 ft. The stack genarally likes the bottom
antenna at h/2 (where h = height of top antenna). But, the model will tell you
if it's "worth it" at whatever height you want to check out in the model.
Computer models are so sophisticated today that they will tell you nearly
exactly what you will expect in final operation.
I use EZNEC from W7EL.
Also, you should read W2PV's book (Yagi Antenna Design, by Dr James L. Lawson,
published by ARRL). That'll give you a feel for how the stack works and some
stacking combinations to consider which were developed on a computer, but
pre-PC.
The TH7 on another tower will not even come close to the performance of a
well-designed stack, and it will certainly not "fill in holes".
The gain improvement from the stack is dependent on the
heights/size/characteristics of the antennas. The model will tell you all you
need to know. BTW, much of the gain of a stack appears in the combining of the
radiated energy in the direction you wish to radiate it (forward, low angle)
and reducing radiation in the direction you don't (straight up, high angles,
backward). The model will show you graphically and numerically what will
happen in the stack.
Ask some more questions after you have done some research. Only you will be
able to design around the conditions at your location.
Bill, N3RR
http://www.erols.com/n3rr
henry gillow-wiles wrote:
> I have a 4ele 20m monobander at 90ft. I have another 17m 4 ele monobander
> that I can make into a 20m and mount on the tower somewhere below the first
> beam. Can I get enough seperation to make it worth stacking?
>
> Or would it be better to leave the 17m a 17m?
>
> Another piece of the puzzle is that I have a TH7 DXX at 33 feet on another
> tower. Is this antenna (the TH7) going to fill in the same incoming signal
> holes that the lower monobander would?
>
> What kind of gain improvement might I be looking at if I stack the
> monobanders?
>
> I went from the TH& and a 402-CD on one tower to monobanders on 10-40 and
> 3 towers.
>
> Too many choices.........
>
> Thank you .....
>
> end
>
> Henry
>
> KB7RTA
> henry@pacinfo.com
>
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