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What's Inside a Motorola K1003A Channel Element By Robert W. Meister WA1MIK

There is already a lot of channel element information on Repeater-Builder, but a little more never hurts.

Background:

I acquired a 72 MHz link receiver that contained one of these elements. I subsequently purchased an assortment of elements that had more than half a dozen K1003As in it, so taking one apart and possibly ruining it wouldn't cost me much. Eventually I planned on purchasing just a crystal for one without sending it out for compensation. This saves a lot of money, and for a low-band receiver that would operate inside my house I didn't care about temperature stability.

Construction:

The thin anodized aluminum can is held on with pressed-in tabs at the side that can be pried out with a thin pocketknife blade. The metal can be straightened out with a pair of needle-nose pliers afterwards. The plastic base and the circuit board slide out as an assembly. There is one thin layer of Mylar plastic wrapped around the entire assembly, and some insulating fish paper is glued to the back of the circuit board. A small piece of foam rubber inside the top of the can keeps the assembly from moving. The photo below shows the circuit board and base removed from the can:

A few parts are hidden under the crystal, so I removed it and took another photo:

After removing the sticky paper from the back, you get to the wiring side of the circuit board:

Here's a photo of the plastic base with its three socket contacts and the trimmer capacitor. As this element is only used for low and mid-band receive, there is no 4th contact that could be found in some other elements.

I spent some time drawing the schematic diagram. First I assigned designations to the various parts. This is the identification scheme I came up with:

After several hand revisions, I ended up with the following schematic (click on it to enlarge it):