[TowerTalk] Christman Phasing help!

[David Gilbert]

And in turn, there is a lot of great information and advice your post, 
Rick.  I'm archiving it.

Take care,
Dave   AB7E


On 9/7/2025 12:55 PM, Richard (Rick) Karlquist wrote:
> 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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