Here's a little Excel trick that will convert a decimal inches numeric value to
the "closest eighth" or "closest sixteenth" as would be found on a typical tape
measure. For example, a value of "26.683" would be converted to "26 5/8".
If the decimal inches value to be converted is in cell A1, entering this
formula in another cell would show the closest eighth:
=TEXT(A1, " 0" & IF(ABS(A1 - ROUND(A1,0)) > 1/16, " 0/" &
CHOOSE(ROUND(MOD(A1,1) * 8, 0), 8,4,8,2,8,4,8), ""))
This formula would show the closest sixteenth, such as "26 11/16":
=TEXT(A1, " 0" & IF(ABS(A1 - ROUND(A1,0)) > 1/32, " 0/" &
CHOOSE(ROUND(MOD(A1,1) * 16, 0), 16,8,16,4,16,8,16,2,16,8,16,4,16,8,16), ""))
Note that each formula contains four references to cell A1. If the numeric
value is in a different cell you'll have to change all four "A1" addresses as
appropriate. These formulas should work just fine in Excel clones such as
OpenOffice or LibreOffice.
Putting this idea into practice, here's a build table for a 20m 4-element OWA
direct 50-ohm feed Yagi. The "ctr to tip" is the distance from the boom center
line to the element tip; "outer sec" is the length of the outer (smallest
diameter) section of the element.
http://ac6la.com/adhoc/BuildTable.png
In this case the build table was created directly on the Variables sheet of the
AutoEZ workbook (http://ac6la.com/autoez.html). That way when the AutoEZ
optimizer finished finding the best set of dimensions given the user's
optimization criteria it was only necessary to print out this portion of the
sheet and take it to the assembly location. No need for any manual data
entries or multiple copy/paste steps into another workbook.
If you're curious as to the values shown, the project was to convert an old
Hy-Gain 204BA from beta match to 50-ohm direct feed, with a Reflector to D2
restriction of 280 inches. The antenna will be mounted at 30 ft as the lower
Yagi of a 2x vertical stack. The optimizer computed the "Model" dimensions to
a ridiculously precise 3 decimal places. The build table shows more reasonable
"Tape" closest eighths.
The "Boom Correction Factor" is based on modeled results compared with
measurements taken via a DG8SAQ VNWA. The VNWA calibration plane was set to
the antenna feedpoint. The antenna was temporarily raised using a
trailer-mounted telescoping tower. The correction factor shown gave the best
fit between model and measurements. The antenna will be lowered, the element
tips tweaked, then installed on its permanent tower.
Note that the boom correction factor is not the same as the compensation for
the element-to-boom clamps. That was already included in the model using the
AutoEZ "Clamps" dialog.
http://ac6la.com/adhoc/ClampsDialog.png
This dialog calculates the Leeson "equivalent diameter" of the clamp which is
then used as a "short and fat" center section for each element.
Dan, AC6LA
http://ac6la.com
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