ELECRAFT KX3 User Manual download pdf

ELECRAFT KX3

EXTENDED VFO TEMPERATURE COMPENSATION

PROCEDURE

Rev. A9, November 14, 2012

Introduction

The KX3 standard VFO temperature compensation is entirely adequate for most operating modes. However,

narrowband data modes such as JT65 can benefit from the extended temperature compensation procedure

described here, especially on the higher bands. The procedure takes about 30 minutes to complete, not

counting possible warm-up time for the signal source.

Equipment Required

1. Stable signal source: During calibration, an RF carrier at about 50 MHz will be injected into the

transceiver’s antenna jack. The Elecraft XG50 is specifically designed for this purpose. If another

signal source is used it should be as temperature stable as possible. Note that the Elecraft XG3 lacks the

necessary stability and is not recommended. A high-quality signal generator with a stabilized oscillator

is preferred. Alternatively a ham-band transmitter covering 6 meters can also be used, if it can be

operated key-down in CW mode for up to 30 minutes at very low power. Another possibility is to use the

harmonic of a 10-MHz lab reference.

2. Heat gun (or hair dryer): The KX3 will first be cooled by placing it in a refrigerator, and then warmed

up gradually by about 30º C as VFO compensation data is collected. To speed up this process and attain

the desired maximum temperature, the transceiver must be heated with the heat gun or hair dryer. A

100W lamp may also be used.

Important Operating Note Regarding JT65 and Similar Modes

The KX3’s heat sink can handle maximum transmit power easily when used with modes such as

CW and SSB where transmit times are short or PA duty cycles are fairly low. In contrast, JT65 and

similar modes have very long transmitting times. If long transmissions are required, the KX3

should be operated at lower power and/or lower supply voltage, especially if the higher bands are

to be used. This will greatly extend the time you can transmit before the maximum heat sink

temperature is reached. For example, when using JT65 mode on 6 meters, we recommend using 1

to 2 watts and a max supply voltage of 13-14 V, or 3 watts and a supply voltage of 10-11 V. On 20

meters, power efficiency is higher; with a 13-14 V supply, you should be able to use 3 watts or

more depending on ambient temperature. Some experimentation may be required.

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2 Temperature Compensation Procedure Equipment Setup  If using the Elecraft XG50 for the first time, an 8 hour power-on aging cycle is recommen

3 Initial Reference Calibration In this procedure, the KX3’s synthesizer will be calibrated to the known frequency of the signal source, at room

4  If you can’t hear the signal, adjust the REF CAL frequency up and down using VFO A until you locate it. The signal should be quite strong (b

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5 Temperature Compensation Data Collection The KX3 will now be cooled down, then gradually heated up while VFO offset data is collected. At appro

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ELECRAFT KX3 User Manual