Towertalk
[Top] [All Lists]

[TowerTalk] Hairpin Match Calculator

To: towertalk@contesting.com
Subject: [TowerTalk] Hairpin Match Calculator
From: Brian Beezley <k6sti@att.net>
Date: Sat, 16 Dec 2023 16:01:21 -0800
List-post: <mailto:towertalk@contesting.com>
I've applied the Getsinger corrections for transmission line end effects to leads in my coil calculator (http://ham-radio.com/k6sti/coil.htm) and rods in my ground probe calculator (http://ham-radio.com/k6sti/gnd.htm). These nifty corrections seem unknown to hams, perhaps because they've spent the last 30 years behind an IEEE paywall. I thought it might be fun to apply them to the transmission line in a hairpin match.

Optimized Yagi designs have a naturally low impedance. When forced to exhibit 50 ohms with no matching network, forward gain can drop 0.5 to 1 dB. A hairpin match avoids this loss by efficiently transforming a low impedance to 50 ohms.

I wrote a Windows program that calculates hairpin rod length and antenna reactance for unity SWR given the other dimensions. In addition to end corrections, it uses an HF expression for shorting strap inductance, also paywalled. It accounts for the boom, which I always thought had no effect. The program models feedline leads as orthogonal wires with no mutual inductance or as a transmission line.

I have no data available to verify program results at the intended level of accuracy. Perhaps hairpin match builders, armed with a NanoVNA, will try it and provide feedback. You can find the program here:

http://ham-radio.com/k6sti/hairpin.zip

Your antivirus software may inhibit downloading the file. First pass the URL to VirusTotal (https://www.virustotal.com). It will check the file with dozens of antivirus programs and report the results. Once you're satisfied the file is safe, temporarily disable your antivirus software, download the file, and then reenable it.

Brian

_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk

<Prev in Thread] Current Thread [Next in Thread>