Bob's Shop Notes: Hammering the Radio Shack 270-030 Filter into Submission . . .

Tools needed: (1) A soldering iron with a 1/16" or smaller tip . . . wattage not terribly critical but it needs to be hot enough to melt the tip of a strand of solder in one second or so. 40W is certainly enough, many 25W irons will do. We're looking for a 650+ degree iron. (2) Wire cutters and strippers. Materials needed: (1) 63/37 alloy (or 60/40 alloy) solder. I like Kester Resin 44 but there are several good ones. (2) Tube of ShooGoo athletic shoe repair cement. Also sold in many hardware, automotive and hardware stores as E6000 industrial adhesive. (3) Noise filter kit #270-030 from radio shack. The kit will contain an iron core filter choke and an electrolytic capacitor. (4) Lengths of 20AWG Tefzel wire. I used red, yellow and black wires but any other colors can be used as can ordinary white wire . . . the colors just make it a bit easier to avoid wiring errors later. Make your leadwires long enough to facilitate final installation in the airplane with no splices. Step 1 . . . Click here for larger image. Strip leads on choke to approx lengths show in this photo. Use adhesive to attach capacitor to choke frame as shown. Note that minus (-) lead of capacitor extends to upper right corner of image . . . toward choke's mounting base. Allow cement to dry an hour or two before proceeding.

Step 2 . . . Click here for larger image. Solder ends of two pieces of black wire to the capacitor's minus terminal. Solder red wire to junction of capacitor's (+) lead and one of the choke's lead wires as shown. Solder yellow wire to free choke lead. Note that all of the wires come from behind through the same gap between choke's windings and core frame.

Step 3 . . . Click here for larger image. Wrap ends of wires around back side of choke winding and feed through gap on other side. Here you can see a tye-wrap used to hold wires together in bundle on other side. Use layer of adhesive to bond wires down to the choke's winding as shown.

Step 4 . . . Click here for larger image. Form the wires down close to surface of the choke's windings. Put a thick layer of adhesive over all exposed components and solder joints on the front side. Allow cement to set up overnight. Next day, put another layer over the components and solder joints if there is less than about 1/16" coverage of any exposed joints. Let cement set up completely . . . another over-nighter wouldn't hurt. I have a small muffin fan salvaged from a computer power supply that I use to hasten the evaporation of solvents out of this adhesive.

Step 5 . . . Click here for larger image. When the adhesive is nice and hard, you can pull the free ends off the wires back through their temporary resting place in the core gap. The adhesive will provide solid strain relief and immobilization of the wires at the solder joints.

Step 6 . . . Click here for larger image. Note that you now have a compact assembly of components that can be mounted to the airframe using the choke's mounting tabs. This filter can be used to attenuate noise from the bus that is antagonizing a sensitive system -OR- it can be used to filter a noisy device. In each case, the filter's yellow (free end of choke) lead wire wants to face the noise source. Click here to view a wiring diagram showing these two variations on a theme. Use of the adhesive allows you to assemble these parts in a rugged, compact assembly with no additional connectors or metal work. Using the adhesive makes it a two day project but fortunately, total labor to assemble this filter is less than 30 minutes. To mount these components in any kind of enclosure adds bulk, weight, labor and possibly additional connectors. The adhesive is tough and stable . . . in this application, the filter may be mounted anywhere on the aircraft except under the cowl.

Questions or comments about this site? Click here to contact Bob at AeroElectric Connection