Doug,
I'm pretty sure that won't work. The matching network can likely be
adjusted for a good SWR even if the element lengths are slightly off,
especially if its one of the directors.
IOW, there isn't necessarily a strong relationship between SWR and
radiation antenna pattern.
And the whole point of getting the element lengths correct is so the
radiation pattern is correct.
The EZ-NEC manual more or less says that one can ignore a conductive
boom at the center of connected yagi elements when the elements are near
1/2 lambda in length and the boom diameter is a small fraction of that.
I think that answers my question -- the measurement should be from the
center of the boom.
On 1/27/23 07:20, Doug Christensen wrote:
I would assemble it and check where the "dip" is in SWR. This is the only
real world measurement any antenna tech can make. Be sure to raise the
assembled array as high as you can and measure where the dip is. Ground
measurements should be made at least 2 wavelengths away from other
obstacles.
73
Doug
WB1E
On Fri, Jan 27, 2023 at 5:42 AM Art Greenberg <art@artg.tv> wrote:
The antenna is a 6 element 6m yagi, VB-66DX. The instructions are a
photocopy of a photocopy, I think. The drawing is too small to see
sufficient detail.
I have an earlier version of this antenna, the 6m "Long John", and for
that the elements were indeed pre-cut. There was only a little room for
adjustment, that being the depth into the element bracket that the
element was inserted.
This antenna has a short section of 7/16 dia. tubing at the boom end of
each element, and the 7/16 dia. tubing telescopes into that. That change
provides much more room for adjustment. I presume the change also
lengthens the life of the elements.
On 1/26/23 23:00, Jim W7RY wrote:
Most hygain antennas use a predetermined length of tubing at each
element. The measurements are usually just for the joints after the
first piece of aluminum that is hooked to the boom.
But, this TH-6 diagram shows the lengths of the pieces against the boom.
What do the instructions show?
73, Jim W7RY
On 1/26/2023 4:26 PM, Art Greenberg wrote:
I should proof read before posting. The DE is insulated from the boom.
Fed with a beta match. Its a Hy-Gain antenna.
On 1/26/23 17:24, Art Greenberg wrote:
I think I left out an important detail. Elements are all connected to
the boom. Even the DE, fed with a "beta" match.
On 1/26/23 17:22, Doug Christensen wrote:
From center of where the electrical connection starts near the
boom, to
where the element terminates at the outside of the array.
doug
wb1e
73
On Thu, Jan 26, 2023, 12:34 PM Art Greenberg <art@artg.tv> wrote:
The instructions for setting element length aren't clear. Do I
measure
from element tip to the side of the boom, or to the center of the
boom?
I think its the later ...
TNX
--
Art Greenberg
WA2LLN
art@artg.tv
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