[TowerTalk] Christman Phasing help!

[Richard (Rick) Karlquist]

Great article Gary.  It wasn't clear whether the purpose of this was 
just a receive antenna or if it was also used for transmit.  In any 
event, my SOP when I do want a transmit array, is to first build a 
receive array in order to make it easy to tune up using small receive 
type components.  Then the receive components can replaced by QRO 
components of the same value.

Figure 7 tells the essential story.  This is exactly what I do.  Quarter 
electrical wave drive lines.  I see that the bury flex lines appear to 
be based on a velocity factor of 82%.  I know that is what the vendor 
claims, but I bought a batch of bury flex and it had a VF in the low 
70's.  I don't know if you measured it or just assumed 82%.  If it 
measured 82% then ... you got lucky.  There is an LC delay network 
inserted in front of just one of the verticals.  The beauty of this 
paradigm is that you can dispense with EZNEC, and DG8SAQ, etc. and 
simply experimentally adjust L and C until the VOLTAGES at the drive 
ends of the coax are 90 deg out of phase and of the same magnitude. 
Then the CURRENTS at the antennas will be likewise.  The phase and 
magnitude can be determined by the "3 voltmeter" method described in the 
article I previously cited in this thread.  Then there is an L C 
MATCHING network to transform whatever the drive impedance is to 50 
ohms.  Again, this can be tuned up experimentally with just an SWR 
meter.  The impedance matching adjustment doesn't affect the 
phasing/pattern.

A couple of additional comments.  You say that is it OK to use N1500 
capacitors because the tempco doesn't matter.  True, but what does 
matter is the dissipation factor for the high drift dielectric, which is 
something like 2%.  Better to use NP0/C0G ceramics or else mica.

You also say that the verticals have "plenty" of high angle radiation to 
work close in stations.  Every vertical I have built was completely deaf 
to stations within a few hundred miles.  If yours are not as such, then 
I would check for feedline radiation, etc to explain what you are seeing.

BTW, I normally use 1/8 wave spacing between a pair of verticals.  You 
pick up a dB or so additional gain that way.  It is easy to retune the 
LC phasing network to work with the reduced spacing.

Keep up the great work at N6RO.

73
Rick N6RK

On 9/7/2025 9:17 AM, Gary Johnson via TowerTalk wrote:
> Getting any phased array properly aligned and optimized is never a case of throwing it together with fingers crossed. Sure, it may radiate, but which way and how well? Adjustable LC networks make it possible to compensate for the actual feedpoint impedances. But it is a process. I learned how to do it by studying ON4UN's Low-Band DXing. Here is a link to my report on a 2-element phased array that used those techniques:  https://na6o.com/amateur_radio/ewExternalFiles/40m_Phased_Verticals_at_N6RO.pdf
> 
> 73,
> Gary NA6O
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