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  What's Inside a
Motorola K1003A
Channel Element

By Robert W. Meister WA1MIK
With Additional Input from Glenn Little WB4UIV
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There is already a lot of channel element information on Repeater-Builder, but a little more never hurts.


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.

John W1GPO had a bunch of K1004A low-band transmit elements. He dissected several and supplied me with parts values for that element. The circuitry is identical. The low-band MICOR transmitter is phase-modulated and it doesn't modulate the actual crystal, which IS done on other MICOR frequency-modulated transmitters.


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):

The crystal frequency is 13280.00 kHz. The channel element frequency is 45.100 MHz. The formula for this radio/element combination is:

K1003A Crystal Frequency = (Operating Frequency - 5.26 MHz) / 3

The K1004A transmit channel element uses a simpler formula:

K1004A Crystal Frequency = Operating Frequency / 6

Parts List
NameK1003A DescriptionK1004A Description
C17.0 pF NP07.0 - 7.5 pF NP0
C27.5 pF NP09.0 - 13.0 pF NP0
C320 pF N470-N220018 - 20 pF N470-N2200
C4220 pF NP0220 pF NP0
C5190 pF NP0190 pF NP0
C60.01 uF0.01 uF
C73.5 - 14 pF NP0 trimmer3.5 - 14 pF NP0 trimmer
Q1M9571 transistorM9571 transistor
RT117-71k thermistor17-71k thermistor
RT2140-160 Ohm thermistor140-160 Ohm thermistor
X1~13 MHz crystal~7 MHz crystal

Glenn Little WB4UIV did additional analysis of the temperature-compensation components of the K1003A channel element. He supplied the data below.

Crystal FreqCrystal MarkingC1C2C3RT1
12406.666none7.5 pF 8 pF20 pF N1500Bead Green
12613.333377 pF 7.5 pF20 pF N1000Bead Red/Green
12613.333-37.5 pF 7 pF20 pF N150Bead Orange/Green
13986.666S84217.5 pF 8 pF20 pF N1500Bead Red
13986.666S83217.5 pF 8 pF20 pF N1500Bead Red
14006.666none7.5 pF 7.5 pF20 pF N1500Bead Red
14006.666S84207.5 pF 7.5 pF20 pF N1500Bead Green
14006.666S83217.5 pF 8 pF20 pF N1500Bar Green
14306.666107.5 pF 7.5 pF20 pF N750Bar Orange
14913.333S84527.5 pF 7 pF20 pF No TCBar Yellow
14913.333-197.5 pF 7 pF20 pF N470Bead Yellow
14920.000H097.5 pF 8 pF20 pF N1500Bead Green
14920.000AUL S84397.5 pF 8 pF20 pF N1000Bead Red
14920.000737.5 pF 8 pF20 pF N1500Bar Yellow
14920.000H037.5 pF 8 pF20 pF No TCBead Green
14920.000VND 7307.5 pF 7 pF20 pF N1500Bead Red
14933.333K-WJO7.5 pF 7 pF20 pF N1500Bead Red
14933.333S82467.5 pF 8 pF20 pF N2200Bead Red
14986.666527.5 pF 7.5 pF20 pF N1500Bead Red/Green
15010.150503855-1 EG&G7.5 pF 7 pF20 pF N1500Bead Red
15013.333S84267.5 pF 9 pF20 pF N3300Bead Green
15020.00031512 pF 7 pFnoneBar Black
15033.333ICM 160036 (34)7 pF 6.5 pF20 pF N750Bead Green


Contact Information:

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

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Article text, photos, schematic, and HTML conversion Copyright © 2008 by Robert W. Meister WA1MIK.
Article originally created 24-Oct-2008

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.