[Towertalk] ping-pong stacks

[Bill Tippett]

N2EA wrote:
>Anybody experimented or modelled with less than 180 degree 
phase reversals?  i.e. 90, 60, 30...and what happens with
vertical angle lobe steering?  

        Here are two KLM 610's at 1 and 2 wavelengths.  These are
are old EZNEC models which are not as accurate as what I have now but
the relative change should be a reasonable indication of what happens 
as phase changes on the higher antenna relative to the lower one:

Phase   Gain    @TOA`   -3 dB at
0       16.85    8      4.0,  12.9
30      16.57    8      4.0,  12.7
60      15.72    8      3.9,  12.5 
90      14.13    8      3.8,  12.6
120     14.25    20     15.3, 24.7 
150     15.42    20     15.3, 24.6
180     15.84    20     15.1, 24.5
210     15.55    20     14.5, 24.5
240     14.55    19     7.2,  24.5
270     14.38     9     4.1,  23.0
300     15.86     8     4.1,  14.0
330     16.63     8     4.1,  13.2
360     16.85     8     4.0,  12.9

Maximum gain occurs at 0 and 180 degrees when the power is
concentrated into lobes at 8 and 20 degree TOA's.  The other
patterns are smearing these two patterns together as phase
is rotated.  Phase of 0 and 180 only leaves the hole between 
12.9 and 15.1 degrees, but that could be filled by using the 
lower antenna alone:

0       14.58    13     6.6, 20.8

                                          73,  Bill  W4ZV