Homebrew SGC SG-237 Control Box

Steve Yates - AA5TB

SGC SG-237 Control Box

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Last Update: November 04, 2009

In about 2000 I purchased a SGC Smartuner, model SG-237. The SG-237 is an automatic antenna coupler that can be remote mounted and is microprocessor controlled. I presently use it with a 65 foot long inverted-L antenna and I can operate all bands from 160m to 6m with it. My rigs operate from QRP to the 100 W power levels and this coupler has no problem sensing this power level and finding a match properly.

Photo of SG-237 at Base of Tower (at old QTH) Under a Rubbermaid container to prevent Hail Damage

As it comes from the factory the SG-237 only really needs 12 VDC and RF input to automatically tune the antenna system. Although if you want the added flexibility of turning the unit on and off, viewing tune status, or placing the present tune position on hold a simple control box needs to be constructed. SGC includes a schematic diagram of an appropriate circuit on page 26 of their SG-237 manual.

Inside View 1 Inside View 2

I decided to build a nice box to put in my ham shack. I chose to build the simple circuit in a Hammond die cast enclosure. All of the parts are pretty generic and can be obtained from places like Radio Shack. I used a 2-conductor "Molex" style connector for the DC power since I have standardized all of my 12V gear to use this type of connector. The connector for the autotuner cable is a 4-pin microphone style connector.

Control Box In Use Rear View

The paint finish is just some metallic green Krylon that I had laying around. The labels may be a bit unique. I drew up the labels in yellow and green using Microsoft Power Point and printed a reverse image of them onto InkJet ready transparencies. I then sprayed adhesive onto the print side of the transparency and applied the whole thing to a sheet of white paper. After the adhesive was dry I cut out the labels to the desired size. I then sprayed adhesive to the paper side of each label one at a time and attached them to the enclosure. When that adhesive was dry I applied several coats of clear Krylon paint leaving the recommended curing time between each coat.

The overall effect was to my liking and makes a pleasant addition to my shack.