[Antennas] 7Mc vertical array

[dtx]

Short answer: get a book on low band verticals and build to spec.  Long 
answer: get a copy of EZNEC (or some other favorite modeling tool) and 
play for hours and hours.  I have no way near that much room here in 
Orange County where land is $900/sq ft or some ridiculous number, so I 
played in EZNEC 3.0 for an hr or so, just out of curiosity.  I think you 
will want them on a 33.x sided sq (1/4 wl) and that middle one is a 
waste of mast material.  I think.  You can get some very nice bi and 
cardioid patterns with 90 degree phase shifts on 1 or 2, +90 on 1 and 
-90 on another, etc.  But when all that is done, you now have to take 
the four sources and feed-line them together and get equal power 
splitting while somewhere winding up with close to a 50 ohm point to 
come back to your radio.

You may want to consider running feedlines to the shack and putting 
switching and phasing networks at arms length.  You may also think about 
using 2 rather than 4 masts.  I think you can get nearly the same 
patterns if you have a variable and not a fixed phased shift, i.e. 1/4 
wl lines switching in and out here and there.  And it will make 7070 and 
7500 easier to achieve as well<G>

Good luck, it is not a trivial journey you are starting on.

Gary WA6DTX



Bob Wilder wrote:

> Help:  I want to put up four 32ft masts in a square spaced 65 feet 
> apart with a fifth in the center to build a steerable vertical array. 
> All masts insulated from ground.
>
>                        O         65ft?        O
>
>
>
>
>                                   O          65Ft?
>
>
>
>                        O                      O
>
> Need info on how to make this work.  Will be designed for 7 to 7.5 MHz 
> operation. (Ham + MARS)
>
> Any suggestion would be appreciated.  TIA
>
>
> Bob  Wilder
> 6032 Idlemoore Court
> Theodore, AL 36582-4117
> 251-653-5274
> http://home.bellsouth.net/p/PWP-af2hd
> Asst USAF State MARS Director- Alabama
> AF2HD/AFA2HD
> {Ex W2ZRX, K4FEU, KG1BW, F7CP, W1HJL, W4NVH and W4RHW}