
			   Hairpin Match Calculator

Hairpin.exe calculates rod length and antenna reactance for unity SWR given the
other dimensions of a hairpin match.

Program Installation

Double-click on Hairpin.exe, click on the title bar icon, and select Properties.
Under Font, select a font and size.

When it quits, Hairpin saves the design in Last Design.hp. Rename this file to
preserve it. Set Hairpin.exe as the default app for .hp. (Right-click on an .hp
file. Under "Open with" navigate to Hairpin.exe, select it, and check "Always
use this app to open .hp files.") Double-click on an .hp file to load it.

Hairpin Model

The hairpin uses parallel rods with a shorting strap at the far ends. The near
ends connect to each side of a split driven element. The feedpoint is at the
near ends.

Using the Program

Dimensions are between conductor centerlines. Enter everything but rod length
and Zi. These values are yellow to indicate that Hairpin has calculated them for
unity SWR. To experiment, you can override the calculated values and enter your
own. To recalculate rod length and Zi after experimenting, press R or reenter
any other dimension.

Obtain Zr from an antenna model or by antenna measurement. Adjust driven element
length until it yields the required Zi. If Zr changes, update the Hairpin value.

Feedpoint capacitance accounts for dielectric in element mounts or for conductor
proximity. Examples: 26.5 pF for Hy-Gain 20-meter Yagis, 9.5 pF for 15- and
10-meter Yagis. A pF or two can make a difference at VHF.

Enter the length of one feedline lead. Lead length is the distance to where the
leads join, either at a balun winding or as coax. Hairpin models straight leads
that converge to a point. Click on Lead to model them as parallel transmission
line. This is useful when they connect to a half-wave coaxial balun.

At VHF it may be convenient to make the hairpin from a continuous length of stiff
wire. Click on Strap for Wire Gauge and enter it. Click on Rod Diam for Rod Gauge
and enter the same value.

Click on Aluminum to select the hairpin metal/alloy.

Click on Inductance to ignore mutual inductance between leads and hairpin. You
can connect a coil with the green inductance value in place of the hairpin. Note
any Zi change. Use this program to design a high-Q coil:

http://ham-radio.com/k6sti/coil.htm

Hidden Functions

Click on "	Millimeters
Click on Induc  Ignore leads/hairpin mutual inductance
Click on Strap  Round wire
Click on Diam   Gauge
Click on Lead   Leads as transmission line
Click on metal  Hairpin metal/alloy
R		Recalculate rod length and Zi
Esc		Exit

Methods

Hairpin uses the telegrapher's equations to model the rods and parallel leads
as lossy transmission lines. It corrects for end effects with the Getsinger
equations. It accounts for radiation loss from the hairpin and leads. The
shorting strap inductance calculation cancels internal inductance for HF while
the resistance calculation uses Payne's method. The program calculates mutual
inductances between all conductors. It uses the Nelder-Mead downhill simplex
method to solve the model for rod length and Zi.

Limitations

Any metal in contact with the shorting strap, such as the boom or a mounting
bracket, can reduce its inductance. Hairpin does not model this effect. For a
strap that passes through the boom in the style of Hy-Gain HF Yagis, a reasonable
correction is to add 25% of the boom diameter to calculated rod length.

Hairpin models the leads in the rod plane and on the opposite side of the driven
element from the hairpin.

Hairpin assumes uniform rod spacing, but some designs bend the rods near the
driven element. Enter the parallel spacing. Then measure calculated rod length
along the rods, not in a straight line from shorting strap to driven element.

Recommendations

Use short leads in the rod plane. Insulate the shorting strap to prevent
unmodeled inductance reduction and to inhibit current flow onto the boom.

Tips

Enter Zi without the minus sign.
Incorrect Lead/Line is easy to overlook.
Average inner conductor and shield diameters for split-coax leads.
Lead length turns red when less than half of rod spacing.
Altering driven element length may degrade an optimized pattern.
Hairpin requires a Pentium Pro and Windows XP, or later.
Latest program version: http://ham-radio.com/k6sti/hairpin.htm

References

https://ehpes.com/n6mw/HairpinArticleFix.pdf
https://ieeexplore.ieee.org/document/231662
https://ieeexplore.ieee.org/document/4810162
https://aemjournal.org/index.php/AEM/article/view/254
https://en.wikipedia.org/wiki/Telegrapher's_equations
https://en.wikipedia.org/wiki/Nelder-Mead_method
https://www.researchgate.net/publication/351307928_THE_AC_RESISTANCE_OF_RECTANGULAR_CONDUCTORS
