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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