[TowerTalk] Creating a Yagi Build Table with "Tape Measure" Dimensions

[Dan Maguire via TowerTalk]

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