Elecraft KXFL3 User Manual
Elecraft® KX3
KXFL3 Roofing Dual-Bandwidth Filter
Installation and Calibration Instructions
Revision A2, June 14, 2012
Copyright © 2012, Elecraft, Inc., All Rights Reserved
Introduction
The KXFL3 is a high-performance, narrow-band analog filter module that helps reject strong signals that could
cause receiver blocking (desense) or intermodulation distortion. It adds two additional bandwidths to the KX3
that are automatically selected as the receive bandwidth is adjusted.
Installation involves installing the KXFL3 plug-in module in your KX3 and then calibrating the filter for proper
operation. No test equipment is required to calibrate the filter although a signal generator may be used, if
available.
CAUTION
The KXFL3 module and many components inside your KX3 may be damaged by
Electrostatic Discharge (ESD) simply by touching them or a circuit board containing
them unless you take specific steps to prevent such damage. See Preventing
Electrostatic Discharge Damage on page 2 before opening the package containing the
KXFL3 module or working inside your KX3.
Specifications
Filter type: Two filters, each having dual balanced Butterworth sections
Gain/phase match: Typ. 0.1%. Additional matching accuracy provided by DSP
techniques.
FL2: 1500 or 3000 Hz low-pass, depending on demodulation method in use.*
FL1: 500 or 1000 Hz low-pass, depending on demodulation method in use.*
* The narrower bandwidths apply in all modes except when Weaver-mode SSB demodulation is
being used. Filters switch in at predetermined points in each mode, varying with passband center
pitch, width, and shift amount.
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Setup and Operation
If you haven’t already done so:
Follow the instructions below to install your KXFL3 module.
Turn to page 4 to calibrate the KXFL3.
With the KXFL3 installed and enabled, the KX3 will automatically use its narrow filters, FL2 and FL3,
whenever possible. Some receive settings require the roofing filters to be bypassed, which automatically selects
FL1. These include: AM and FM modes, dual watch (DUAL RX menu entry), RX I.F. shift (RX SHFT menu
entry), and some noise blanker settings. Refer to the KX3 owner’s manual for details.
Installing the KXFL3 Module
Preparing for Installation
Preventing Electrostatic Discharge Damage
ESD damage may occur with static discharges far too little for you to notice. A damaged component may not
fail completely at first. Instead, the damage may result in below-normal performance for an extended period of
time before you experience a total failure.
We strongly recommend you take the following anti-static precautions (listed in order of importance) to ensure
there is no voltage difference between the components and any object that touches them:
Leave the KXFL3 module in its anti-static packaging until you install it.
Wear a conductive wrist strap with a series 1-megohm resistor that will constantly drain off any static
charge that accumulates on your body. If you do not have a wrist strap, touch a ground briefly before
touching any sensitive parts to discharge your body. Do this frequently while you are working. You can
collect a destructive static charge on your body just sitting at the work bench.
WARNING
DO NOT attach a ground directly to yourself without a current-limiting resistor as this poses a
serious shock hazard. A wrist strap must include a 1-megohm resistor to limit the current flow. If
you choose to touch an unpainted, metal ground to discharge yourself, do it only when you are
not touching live circuits with any part of your body.
Use a grounded anti-static mat on your work bench (see below).
If you pick up a pc board that was not placed on an anti-static mat or in an anti-static package, touch
first a ground plane connection on the board such as a connector shell or mounting point.
If you use a soldering iron to work on a circuit board, be sure your iron has an ESD-safe grounded tip
tied to the same common ground used by your mat and wrist strap.
Choosing an Anti-Static Mat
An anti-static mat must bleed off any charge that comes in contact with it at a rate slow enough to avoid a shock
or short circuit hazard but fast enough to ensure dangerous charges cannot accumulate. Typically, a mat will
have a resistance of up to 1 Gigaohm (10
recommend that you choose an anti-static mat that comes with published resistance specifications and clean it as
recommended by the manufacturer. Testing has shown that many inexpensive mats that do not specify their
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ohms). Testing a mat requires specialized equipment, so we
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resistance have resistance values much too high to provide adequate protection, even after they were cleaned
and treated with special anti-static mat solutions.
Suitable anti-static table mats are available from many sources including:
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U-line (Model 12743 specified at 10
Desco (Model 66164, specified at 10
TM
3M
Portable Service Kit (Model 8505 or 8507, specified at 106 to 109 ohms)
ohms)
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to 108 ohms)
Tools Required
1. ESD Protection (see Preventing Electrostatic Discharge Damage, pg 2).
2. #1 size Phillips screwdrivers. To avoid damaging screws and nuts, a power screwdriver is not
recommended.
3. Soft cloth or clean, soft static dissipating pad to lay cabinet panels on to avoid scratching.
Parts Supplied
Be sure you have the following components in your kit. If anything is missing, contact Elecraft customer
support (pg 12).
ILLUSTRATION DESCRIPTION QTY.
KXFL3 Module
1 E850492
ESD SENSITIVE!
Test Antenna 1 E850543
Screw, 1/2" (13mm), Flat Head, Black 1 E700178
ELECRAFT
PART NO.
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Installation Procedure
Disconnect all cables attached to the KX3 and remove the KXPD3 paddles if installed.
Open the KX3 just as you would to install or remove batteries (see Internal Batteries in your
Owner’s Manual for details about how to do this).
Remove the internal batteries (if present).
Taking ESD precautions, remove the KXFL3 and plug it into J3 on the KX3 RF board as shown in
Figure 1. The screw is there only to ensure the KXFL3 module cannot be knocked out of its socket by
rough handling of the KX3. It does not provide a ground return or other function.
Figure 1. Installing the KXFL3 Module.
You must run the calibration procedure below for proper filter operation. You can use an external
signal generator to pick up a calibration signal internally. If you do not have an external signal
generator, leave your KX3 open until you have installed the test antenna.
Calibration
Calibration adjusts the gain and phase of each filter to provide optimum rejection of the opposite-sideband
image.
The procedure requires a signal source in the 14-MHz range that can provide a signal level of between
approximately -73 and -33 dBm. This can be provided by an external signal generator such as an Elecraft XG1,
XG2 or XG3. If you do not have a signal generator you can use an internal signal picked up by the antenna
assembly provided with your KXFL3 that will “sniff” adequate signal from a 16 MHz oscillator inside the KX3.
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