[450] Fwd: [VHF] Close Vertical stacking distances [was: Horizontal stacking distance question]

[djmay at comcast.net]

Test. 




----- Original Message ----- 
From: "David McKenzie" <k1fsy at vhfwiki.com> 
To: "144.450 Mailing List" <450 at lists.vhfwiki.com> 
Sent: Monday, December 20, 2010 4:52:27 PM 
Subject: [450] Fwd: [VHF] Close Vertical stacking distances [was: Horizontal stacking distance question] 

Interesting reading re: stacking for those of you not on the VHF list 


---------- Forwarded message ---------- 
From: Ev Tupis < w2ev at yahoo.com > 
Date: Sun, Dec 19, 2010 at 7:02 AM 
Subject: [VHF] Close Vertical stacking distances [was: Horizontal stacking distance question] 
To: Stanford VHF email Remailer < VHF at w6yx.stanford.edu > 


I've taken the liberty of re-presenting Jay's informative plots.  Thanks to Jay, 
we can study data rather than shooting from the hip. 

I can clearly see that the text attributed to Kent's observation held true: 

------ Original Message ---- 

> > Kent WA5VJB did some experiments that were presented at Central States  this 
> > year. He found that when single Yagis for different bands were  stacked on 
> > one mast, they could be practically on top of one another (as  little as 5 
> > inches apart, I think) and had virtually no effect on one  another. When two 
> > Yagis for one band were used on the same mast, this  did not hold true. 
---------------------------- 

The "purist" will say "I told you that there would be interaction!"  And, of 
course there is.  The "practicalist" will say, "so what? it is so insignificant 
I don't care." 

See what I mean, below... 

I've restated Jay's post a little differently below... 

Note: "ascii figures" are NOT to scale and are left-justified. The assumption is 
that all antennas are centered on the mast instead.  I'm including this as a 
visual aid only. 

Antenna Scenario #1 

http://s509.photobucket.com/albums/s339/K0GU/K0GU%20MISC/?action=view&current=222-5wl.jpg 


The stack lays out like this: 

-----------------------  (222-5wl w/23' boom) 
 two feet 
 spacing 
------------------------------- (17b2 w/31' boom) 
 two feet 
 spacing 
------------------------------- (6m7jhv w/31' boom) 

Jay's modeling shows a slight "upward" skew to the 222 beam's main elevation 
pattern.  However this is only when compared to the same pattern in "free space" 
w/o any ground interaction at all.  Even so, the difference is only fractions of 
a dB between the 222 antenna in free space vs within 24" of a 17b2 "ground". 

Overall 222 MHz gain in elevation is -0.18 dB vs. free space 
Overall 222 MHz gain in azimuth is   +0.04 dB vs. free space 

Mast needed above the tower: 4' 

Of significant note:  The wind survivability of a 4' mast is greater than that 
of a mast that is long enough to conform to "perfect" stacking distances for 
these antennas. 

Cheers, 
Ev, W2EV 
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