> BTW, precise phasing down to a few degrees is NOT
> necessary. Table 6-3 on page 6-14 of the W2PV Yagi
> Antenna Design book shows that with a 30 degree
> phase differential (and identical Yagi's), the maximum
> degradation in gain is 0.36 dB. Physically, 30 degrees
> represents 1/12 of a wavelength (WL) so you could
> have a 0.08 WL variation in coax lengths or a 0.08 WL
> physical displacement from the same axis and suffer
> no more than 1/3 of a dB performance degradation.
> (This amounts to about 4 ft of displacement on 15M
> therefore close works in horseshoes AND stacking.)
> de Tom N4KG
However, the effects are more pronounced on the stack's ability to deeply
cancel high angle reception. The effects can be easily modeled with EZNEC,
which allows the phase, and feed power levels to be individually varied in a
stack model. TA will allow easy modeling of horizontal displacement.
If one only considers forward gain, and a dB isn't all that much, is there
much reason to ever go past 3 elements? On the other hand, if you just want
to hear what you want to hear, these small gain changes can accompany much
larger changes in discrimination.
73, Guy,
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