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  How I Made
an Antenna Nut
Spanner Wrench

By Robert W. Meister WA1MIK
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Several Motorola radios: Mitrek, Syntor, Syntor X, Syntor 9000, and MaraTrac, use a standard SO-239 UHF connector as an antenna jack, in a recessed well in the front of the radio's housing. Motorola calls this a spanner nut. It's completely round but has two wide slots across from each other and requires a special wrench to fit around the connector if you want to remove or install the nut. The photo below shows this jack and the locking key from the front of my MaraTrac low-band radio (click on any of the images for a larger view):

Motorola makes and sells an official tool, RSX4028A, for about $25US as of April 2009. I was not allowed to purchase it on Motorola On-Line, either because it was No Longer Available (NLA) or my account privileges aren't sufficient to let me buy a service-related part. Here's the description and a photo of this tool from the Motorola mobile catalog:

I built my wrench before I saw the official tool. Any resemblance, living or dead, is purely coincidental.

I looked into using copper pipe and iron pipe. The wrench needs to fit around the SO- 239 jack, which is 5/8 inch in diameter. The inside diameter of 5/8 copper pipe is exactly 5/8 inch, but pipe of this size is not carried by my local home improvement center. The inside diameter of 1/2 inch black iron or galvanized pipe is 0.622 inches, just under 5/8 inch, but it's close enough that it will fit. I purchased a 4 inch threaded piece of black iron pipe and a galvanized TEE connector to use as a handle.

The first problem I found was that while the inside diameter of the pipe WAS 5/8 inch, there was a ridge inside the pipe, probably as a result of the manufacturing process, that prevented the pipe from fitting over the SO-239. I used several reamers and rasps in my drill press to remove this ridge until everything was smooth. The pipe then fit over the SO-239 perfectly.

I used a grinding wheel to flatten the end of the pipe slightly, then made some marks completely by eye with a utility knife, to outline two tabs diametrically opposed on the end of the pipe. I used a hacksaw to make two cuts across the pipe, leaving the tabs about 0.070 inches across and about 0.90 inches deep. I guessed at the size because I had not removed the nut from my MaraTrac to try a test fit or to get actual measurements.

After cutting the outer edges, I used the grinding wheel to remove the majority of the iron pipe around the circumference, then used a hand file to finish the job, making the surface flat and clean. I had to use the rasps again to remove the burrs left from the grinding process.

After making sure the machined end of the pipe actually fit the antenna nut, I screwed it into the TEE connector to use as a handle. I made sure it was tight with a pipe wrench and a vise. This is a man's-size handle! Here's a photo of the finished tool and the business end:

The cost of materials was under $4US. The wrench took me about 1/2 hour to make. Even though I used a drill press to clean the inside of the pipe, a smaller electric drill or even a rotary tool (commonly called a Dremel tool) with a rasp would work just as good. A hand file, hacksaw, utility knife, pipe wrench, and a vise completed the list of tools I used. Most any homeowner or handyman would have these tools available.

If I manage to shear the tabs off this wrench, I can easily cut new ones into the end. This may not be as strong as the official Motorola tool, but it certainly cost a lot less, and for the convenience of having it, I'm glad I made one.

The author can be contacted at: his-callsign [ at ] comcast [ dot ] net

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This page originally posted on Thursday 02-Apr-2009



Article text, artistic layout, all photographs, and hand-coded HTML © Copyright 2009 by Robert W. Meister WA1MIK.

This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.