ELECRAFT KXPA100 User manual

Elecraft • www.elecraft.com • 831-763-4211
Elecraft KXPA100
Serial Data Noise Suppression
Revision A, February 4, 2014
Copyright © 2014, Elecraft, Inc. All Rights Reserved
Introduction
Under certain conditions when the KX3 and the KXPA100 are connected to a personal computer via the RS232
port, noise from serial data may be audible in the receiver. Adding a bypass capacitor eliminates this noise.
Parts and Tools Required
You will need a temperature-controlled ESD-Safe soldering station, fine solder, and your normal hand tools such
as needle nose pliers and diagonal cutters.
A kit containing the required parts is available from Elecraft. Order KXPAMDKT1.
QUANTITY DESCRIPTION ELECRAFT PART
NUMBER
1 Capacitor, 0.01 µF, 50V, 0.1”LS E530019
1 Capacitor, 0.01 µF, 0805 SMD E530305
Procedure
A grounded wrist strap and ESD dissipating mat are recommended whenever you work inside your
KXPA100. Optionally, touch a bare metal ground frequently while working.
1. Remove the KXPA100’s bottom cover.
2. Remove the front and rear panel. Unplug the TMP jacks from the SO-239 Antenna connections to the
boards.
3.Remove the KXAT100 antenna tuner board, if installed.
4. With the LED bar graph at the front of the amplifier turned to your left, locate the square microprocessor,
U1 near the upper left corner of the LPF board. Locate the capacitor position C211 above the microprocessor.
You do not need to remove the LPF board from the PA board.

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5. Install ONE of the supplied capacitors in location C211 as shown below. Either the surface mount or the
leaded capacitor may be used. Only one is necessary.
Installing a 0.01 µF surface mount capacitor at C211
Installing a 0.01 µF leaded capacitor at C211.
6. If you do not have the KXAT100, skip to step 10.
7. Reinstall the KXAT100 Antenna Tuner board using the four 4-40 machine screws and four split
lockwashers that you removed earlier.
8. Connect the TMP plug from the rear panel ANT 2 to the ANT 2 TMP jack on the rear of the KXAT100
board.
9. Connect the TMP plug from the rear panel ANT 1 to the ANT 1 TMP jack on the rear of the KXAT100
board.
10. Connect the TMP plug from the rear panel RF IN to the RF IN TMP jack on the rear of the LPF board.

KXPA100 Serial Noise Reduction Page 3 of 3
11. If you do NOT have the KXAT100, connect the TMP plug from the rear panel ANT 1 to the ANT OUT
TMP jack on the rear of the LPF board. Note that ANT OUT is not used when the KXAT100 is installed.
12. Replace the bottom cover, taking care to replace all of the screws into the heat sink.
13. Replace the front panel, taking care to align the LED bar graph(s). replace all of the screws.
14. Replace the front panel. Replace the feet and all hardware. This completes the modification.