LA3ZA Radio & Electronics: General modifications applicable to any Elecraft K2

General modifications applicable to any Elecraft K2

Part 1 of LA3ZA Unofficial Guide to Elecraft K2 Modifications

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Basic K2:	Performance	Intermodulation	Tweaking	Miscellaneous
Options:	KSB2	KAF2	KNB2	KBT2	KPA100/KAT100
	K160RX	KDSP2	KIO2	K60XV
Other:	PSK31	Input/output	Accessories

Basic K2: Improved Performance

Reference

Description

Comment

Complexity

K2 Status

Source

Setting range of AGC level adjustment
New Oct 2009

Normal variations in the 8-volt voltage regulator may make it impossible to adjust the AGC threshold voltage to 3.80 volts.

Consists of adding one 15K-ohm 1/4 watt resistor to the K2 control board. Easy to do if needed.

Elecraft

×Reduced
CW keying bandwidth
Updated Apr 2004

4-5 components on control board plus an upgrade of firmware to ver 2.04.
Possible impact on very high speed CW (50+ wpm).

Measurement of keying spectrum for original, pre-mod K2 and comparison with other rigs.

In all new K2s from serial # 4060 and up.

Upgrade kit K2KEYMDKT
Updated Apr 2013

Elecraft

Faster risetime mod

KI6WX

×Temperature
compensation for PLL reference

Uses a thermistor to temperature-compensate the varactor diodes in the PLL reference oscillator.
Compensation adjustment (see manual):
May be fine tuned by adjusting RA 33k resistor in range 15-56k, ZL1TW experience.

Here is an explanation of the circuit.

Reduces oscillator's temperature coefficient by as much as a factor of 10. Of particular
interest to K2/100, or mobile/outdoors K2 operation.

Replace RP3 on RF board with a small PCB

Is included with all K2s with serial #3446 and up. Upgrade kit E850138
Updated April 2014

KI6WX & Elecraft

From Elecraft manual

Guideline for PLL series inductor value
Updated May 2006

Must have 9.8 kHz pulling range, If not large enough use 12 uH inductor, otherwise 10 uH (depends among others on particular x-tal batch)

KI6WX

×Interaction between VFO and PLL reference oscillator (Note, no C70 in post 3000 K2's)
Updated April 2014

"Weird at one frequency" (WAOF) behavior around 7185 kHz. Pre-3000 K2's need C91 and RFC15. May also add 68 pF between pins 12 and 13 of U4.

Important and easy to do, but in general fixed in K2 A to B upgrade (3000+ K2's). May still appear if some of the components around U4 have too long leads.

Fixed in all new K2s from serial # 3xxx and up.

Elecraft

VCO magnetic field shield

The K2’s VCO (voltage-controlled oscillator) may be susceptible to low-frequency modulation by very large power transformers, such as those in linear amp power supplies and antenna rotator controllers.

Only for K2s with a significant modulation problem which cannot be solved by moving things around.

Image from AD5HD

Adds a ferrite sleeve on top of a smaller version of toroid T5.

May be purchased from Elecraft - Upgrade kit
K2VCOSHLDKT
- but optional even for new K2s.
Updated April 2014

Elecraft

×Eliminate possibility
for chirpy CW on 40 meters
Updated Apr 2004

Steps to test to get VCO voltage within range:

Remove RF board C70 (4.7pF) (40m), add 10 pF to C72 (80m), or add 10 pF to C73 (40m, 30m, 15m).

Decrease max VCO control voltage to 5-6 Volts instead of 7.5 Volts.
Especially important with new CW click mod

Elecraft

×Improved low frequency from K2's audio
New April 2008

Two capacitors changed from 0.1 µF to 0.22 or 0.33 µF

Report of improved audio

TF3MA

Extra IF prefilter Updated March 2005

Additional KSB2 7 X-tal filter in KNB2 socket

A need for an attenuation pad for better termination of post-mixer amplifier

Kit with PCB/parts available from Elecraft, K2PREFILTER
Updated April 2014

G3RXQ

Removal of RF board C180

CW part of 2^nd stage crystal filter mod for KSB2

Only applicable to CW-only K2s.

Extremely simple: break off or desolder C180

Is in all K2s from serial #3000, see KSB2

Elecraft

Not enough pulling range of BFO crystals

Updated Sep 2005

Add to capacitances in BFO oscillator.
Here's a newer and simpler way
with only a single capacitor.

Applicable if BFO Test in "Alignment and Test, Part II" fails.
May also be required for 2.5 kHz KSB2 filter mod

Elecraft

Hard to start AGC crystal oscillator
New May 2006

AGC does not turn on after it has been turned off. Add to capacitance of C8 or C7 in 5.068 MHz crystal oscillator

Elecraft

Input bandpass filters (Elecraft)

Basic K2: Intermodulation, image rejection¹

Reference

Description

Comment

Complexity

K2 Status

Source

×Handling of extremely strong on-frequency signals

Makes reception at frequency of strong tx close by possible

Two diodes as limiter in IF amp

In all new K2s from serial # 3xxx and up.

Elecraft

¤Change 40m band filter

Narrow 40m bandpass characteristics, especially for old Region 1, 7.0-7.1 MHz band¹

Important if you experience intermodulation from strong broadcast stations above 7.1 MHz.

Change 3 capacitors

Elecraft

Alternative:

Ceramic 7.02 MHz filter

Updated Oct 2006

Ceramic filter is Murata resonator SFE 7.02

Ceramic filter can be mounted on UN-K60XV (rev G) from unpcbs.com

DL2FI/
DF7TH

Change 20/30m band filter

Narrower bandpass filter, better stopband attenuation

Reduces intermodulation from 13 MHz broadcast band, but loses sensitivity to 15 MHz WWV, RW M etc

Change 3 capacitors

Elecraft

×Wider
10m bandpass filter New Apr 2004

The 10 m filter of #3000+ K2s is too narrow for satellite operation

Harder to adjust as settings of 10m and 12 m filters interact.

Add a single 1.8pF (1.5-2.2pF) cap.

LA3ZA

Changes to 10/12m band filter

Narrower bandpass filter, better stopband attenuation

2 options for broader pass band response - intermediate values between original
filter and that of #3000+

Change 2 or 3 capacitors.

DL1IAQ

Changes to all band pass filters
Updated
Oct 2006

Bandpass filters tuned to band limits of amateur bands - only needed if there is an intermodulation problem.

Clever way of getting wide and narrow band-widths in combined BPFs

New filters are: 10/12m, 20/30m, and 80/160m¹. 2006 update: also wide/narrow 160 m & 40m¹.

Change/add capacitors.
Note that filters are harder to adjust as settings of combined filters interact.

DL7MAJ

×Add series resonance circuit to bandpass filter

Trap for attenuating 19m broadcast image in 12m band

Increases image rejection in 12m band.
(New tighter 10/12 m filter of # 3000+ also improves image rejection)

Add a toroid and two capacitors.

LA3ZA

¹Note that primary allocations in 160, 80, and 40 meter bands in IARU Region 1 (Africa, Europe, former USSR countries, Middle East) are narrower than in Regions 2 (Americas) and 3 (rest of Asia and Oceania), especially before 2009. Some of the modifications above were specifically designed for this.

Basic K2: Tweaking

Reference

Description

Comment

Complexity

K2 Status

Source

×Power control mod
for more stable output level

Increase R98 on RF board from 270 to 1-2 k.

Due to finite bit-length in ALC voltage, an increased R98 reduces ALC gain. Mainly important for KPA100.

Application Note and in K2 manual,
appendix E.

Elecraft

More output on 10m:
×1: lift T2,
2: new T2 core,
3: lift T1 also and add gain to predriver/ driver
Updated Aug 2013

Lift T2 above PCB,
space windings, wind with binocular core rather than toroid.

Experiments with other cores:
#1, #2

Better coupling to output stage at high frequencies

Lifted T1 and T2, DL7MAJ

AB7MY
W8IJN
KI6WX
DL7MAJ

× Easier adjustment of 4 MHz reference

Replace one C with two Cs.

Optional better temperature stability.
N6KR 4 MHz oscillator calibration method.

GU3MBS: range reduced from 570 to 200 Hz.

KI6WX

More accurate voltmeter

Replace control board R9 (806k) with 1M 10-turn pot

Adjust to same reading as an accurate voltmeter, while measuring after D10.

Compensates
for tolerance in voltage of 5V regulator.

WK6F

×Sidetone
mod
Updated Nov 2006

Even more sinusoidal tone than the mod in serial #3000+ gives

Important to have an inductor with correct series resistance (KT5X)

Simple, one more capacitor

TF3MA

Less loss in CW filter at low bandwidths
Updated Oct 2006

Filters with old crystals may have large losses at low bandwidths. This mod changes the filter termination from 150 to 38 ohms. An undesirable effect is that it also changes termination of KSB2 filter.

Limits
usefulness of
CW filter to about max 1000 Hz.

Add
one toroid,
rewind toroid T7.

Better alternative is to get a new set of crystals from Elecraft, either kit E850006 (7 Xtals) or K2KDSB2XTLS (14 Xtals) Updated April 2014

Elecraft

¤Improved
Tx efficiency
at low power levels

Remove one turn from PA transformer

Saves 25-30%
battery at 5 W power output, but this mod is only applicable if you operate
exclusively at 5W PEP/CW or less.

In K2 manual

Elecraft

×Faster
QSK performance Updated
March 2005

1. Decrease R17 on control board (~1M in parallel)

2. 220k in series with mute line

Makes it possible to hear between dots at 20wpm and between characters at 40wpm

Basic K2: Miscellaneous

Reference

Description

Comment

Complexity

K2 Status

Source

K2 Miscellaneous Accessory Board Project
New Mar 2014

Fixed-level audio output (W3FPR)
CW tuning indicator (K6XX)
Circuit that enables a computer to key the K2
Can be used with or without the Internal Mic Adapter (unpcbs.com)

Limited production run

Image KW4M

KW4M

Separated front-panel
New Mar 2014

K2 Bicycle Mobile Project

N8MX

Output to drive an analog S-meter
New Feb 2014

Voltage taken from Control board U2 pin 1 through a buffer amplifier

W3FPR

×Blackened edge of the display bezel
New Aug 2013

Take a magic marker and carefully run it along the edge of the bezel (after removing it from the radio).

5 minute job

KS1U

Lightning protection of antenna input/ output
New March 2005

~1 mH choke + neon light across antenna connector

F5UL

SO2R - 2 K2s running together
Updated
Dec 2006

Audio switching and rx muting

KT5X's SO2R controller in EC2 chassis:

SSB Option KSB2

The SSM2165 chip (Microphone preamplifier with variable compression and noise gating) is obsolete and was replaced by the SSM2166 in rev Rev G (July 2, 2011) of the KSB2. This shouldn't affect any of the modifications listed here. New Aug 2013

Reference

Description

Comment

Complexity

K2 Status

Source

Recommended modification of KSB2

(German original)

Updated Aug 2013

New crystals, if old KSB2 (~March 2002). Upgrade kit K2KSB2XTLS Updated April 2014
Increased ALC delay, if old KSB2 (~Sept 2001). Upgrade kit KSB2MDKT (KI6WX) Updated April 2014
2.2 kHz bandwidth (KI6WX)
Increased RF gain (KI6WX)
Reduced Intermodulation Distortion (KI6WX)
Increased compression ratios (DF7KHK)
Increased microphone gain (DF7KHK): R14 from 1k to 3.3 k
Adjustment of ALC (increase R10 & R8) (DJ3FR)

All of the KI6WX modifications + some more.
Marked with * later in this table

QRP- project (DE)

*×Crystal filter bandwidth modification

2.1, 2.4, or 2.6(×) kHz bandwidth and flatter response than original 2.0 kHz bandwidth

Highest bandwidth seems to be the favored one.

Change Cs in x-tal ladder filter; requires a recent x-tal set.
2.6kHz bw may require padding of BFO capacitors

2.4 kHz filter is standard in KSB2 since summer 2004.
Mod kit is SSBCAPKT
Updated April 2014

KI6WX

*×Increased RF gain and optional reduced intermodulation

Handles low output microphones without audio clipping

Preferable over AF gain increase mod since it gives less distortion.

More complex than increasing AF gain

KI6WX

×Increased RF gain mod will upset ALC loop gain with KPA100 unless 2 resistors are changed.
Alternative don't do this mod with the KPA100
Updated June 2006

Elecraft/

W4WFB

Increased compression ratios

Compression ratios 1:1, 1:5, 1:8, 1:10 instead of 1:1, 1:2, 1:3, 1:4

Higher compression is consistent with AD5X
(1:12) and Funkamateur (1:4...9,
nominally 1:6) compressors.

Replace RP5 with a 6 pin connector with resistors.

G3RXQ

*×Increased compression ratios
New Dec 2004

Compression ratios 1:1, 1:3, 1.6, 1:9 instead of 1:1, 1:2, 1:3, 1:4.

Replace RP5 with 5x150k, connect pins 2, 3 and 4, or
use 2x 150k + 47k as in image:

DF7KHK, QRP-Report 3/2004 (DE)

×More roll-off of low-frequency response
Updated March 2005

Better spectral balance and better equalization between USB and LSB, less chance of overdriving the speech compressor and balanced modulator

Decrease two coupling capacitors: C31, C32

KD2BD

Improved roll-off of low-frequency response
New Dec 2014

Decrease three coupling capacitors C20, C31, C34

G3RXQ

× Increased VOX sensitivity (item c)

Small compression for VOX to increase sensitivity (Note: this adds a small compression to the 1:1 setting, - probably too small to bother digital modes)

G3RXQ recommends a 5k pot instead of the 4.7k resistor to set the VOX threshold.

Break a PCB trace and add a pot.

G3RXQ

× RF filter on input of compressor

Updated Dec 2004
1-3 mH in series with input of U3, and 0.001 µF from pin 4 to ground prevents RF from reaching KSB2 input.

1 coil and 1 cap

G3RXQ

Anti-VOX New Sep. 2004

New PCB next to KSB2

G3RXQ

×*Higher microphone sensitivity A

Several simple ways to increase AF gain. KI6WX gain mod above has better balance between AF and RF gain and therefore less chance of overdriving the NE612. Be aware especially that if R2 is decreased the NE612 may be overdriven.

Of special interest if you use other than Elecraft microphones.

Change R14 (and R2) or swap them.

Higher microphone sensitivity B

Transistor gain stage

G3RXQ

Higher microphone sensitivity C

Increase R14 and use 1:10 transformer on input

K9YC

Higher microphone sensitivity D New May 2004

External transistor stage

N0MF

Clean 5V for external preamp
New Dec 2004

Use unused pin on front panel board

G3RXQ/ W8UR

Separation of PTT and CW dot line
Updated May 2006

Uses a logic circuit to separate PTT and dot key line

No QSK in CW mode when enabled

W3FPR

×Grounding crystals near bottom
New May 2004

Less filter blow-by

W3FPR

×Decreased S-meter/AGC activation by out-of-band signals

Filter AGC IF signal with 153 kHz bandpass filter

Readjust AGC threshold

Add 1R, 2Cs, 1 L

TF3MA

×Grounding of mic jack
Updated June 2005

Protection against stray RF and static electricity.

More considerations on grounding ("pin 1 problem" -K9YC)

Simple

Elecraft

Reconfigurable microphone header
Updated Aug 2013

× Microphone configuration header block plug which makes it easy to switch between differently wired microphones without soldering

W1EUY /N0SS

Kit from unpcbs.com which is much more versatile and reconfigurable and accessible by just removing a side panel

Image from unpcbs.com

Very favorable eham.net review

KI4GGX/ WB2ART

Image from Elecraft

Audio Filter/Real-time Clock KAF2

Reference

Description

Comment

Complexity

K2 Status

Source

Higher bandwidth in permanent LP filter

Change L1,L2 from 82 mH to 56 mH

In KAF2 manual

Elecraft

¤Higher audio gain

Increase R9 from 10K to 12-15K or more

In KAF2 manual

Elecraft

×Modifications to filter response

4 alternative responses for AF2 bandwidths 79, 136, 162, 189 Hz (Standard AF2 is 99 Hz, AF1 is 258 Hz)

Nice to have if you do not like the ringing characteristics of the supplied filter.

Change 3 resistors and a capacitor.

KI6WX

More accurate clock

Real-time clock runs a little fast (>+/-1.7 sec/day)

This adjustment may only be valid at room temperature

Add 10-50 pF in parallel with C19 (33 pF)

Elecraft

Image from Elecraft

Noise Blanker KNB2

Reference

Description

Comment

Complexity

K2 Status

Source

If the LO THR setting causes intermodulation

Add 33 pF between pins 7 and 8 of MC1350

In KNB2 manual

Elecraft

Gain reduction or threshold increase
New Jan 2007

Reduce coupling or gain in MC1350 amplifier. Replace D2 and D3 with Si diodes for higher threshold.

Elecraft

¤ Increase time constants
Updated Oct 2013

NB1: 10µs → 20 or 70µs

NB2: 70µs → 0.6 or 2.2 ms

For electrical noise from motors, electrical fence etc

NB1: Increase C11 (0.001 µF) by paralleling it with 0.001 or 0.0068 µF.
NB2: Increase C12 (0.0068) by paralleling it with 0.068 µF or 0.22 µF

G3LUB

× Increase low threshold sensitivity
New Aug 2008

Add 0.1 µF capacitor to emitter of Q2 and make low threshold more stable

Makes the noise blanker more sensitive

DL7MAJ

Image from Elecraft

Internal Battery KBT2

Reference

Description

Comment

Complexity

K2 Status

Source

Direct charging of internal battery without series diode or extra connector
Updated
March 2005

Gives direct access to battery from power connector.
See also this comment by PA3GYU.

Charger controller gets direct access to battery, without series diode.
BUT: Short-circuit and reverse polarity protection is bypassed!

Utilizes unused part of power switch
(Less need for this mod if D10 is re-placed as in serial #3000+)

DK3RED

External charger for internal battery
New Aug 2013

Charges through power-connector J3 and thus includes protective Shottky diode in circuitry

DL7MAJ

External smartcharger for internal battery
New Aug 2013

A fused direct connection to the battery with a connector on the rear panel.

W3FPR

Integration of Sunlogic Micro M+ charge controller

WA6EGJ

LiPo batteries
New May 2004

Replace sealed lead-acid batteries with lithium polymer batteries, save 0.8 kg/ 1.7 pounds, and gain capacity: 11.1v at 3.2 Ah rel to 2.9 Ah

No balancing circuitry that monitors individual cells

WB6ZQZ

LiPo batteries
Updated July 2014

12V 9.8 Ah, compared to 2.9 Ah of standard battery.
Although it fits physically, it is probably not a good idea to put it inside the K2 due to the power switch and indicator LED

Has protective circuitry that accesses and monitors all battery cells.

Some of the cheapest batteries on Ebay are not up to spec, perhaps because they have been fitted with worn-out laptop cells.

F5VJC

LiFePO4 battery pack
New Aug 2013

12.8V 3300 mAh inside K2, smartcharger

Heavier than Li-ion, but safer

N9LVG

LiFePO4 battery pack
New Feb 2017

12.8V 4500 mAh inside K2

Custom-built for the K2 by Batteryspace,
Smartcharger

KZ1X

100 W Power Option KPA100 and antenna tuner KAT100


Image from G3VGR	Image from Elecraft

The KPA100 was upgraded in October 2006 (Upgrade kit KPA100UPKT) and those modifications are essential. Most of them are the same as those discussed below.

Reference

Description

Comment

Complexity

K2 Status

Source

×KPA100 Shield Upgrade
Updated April 2014

Improves grounding of the KPA100 shield, reducing RF coupling between the KPA100 and the K2 RF board. Especially
important when load SWR is high.

Modification kit KPA100SHLDKT

Elecraft

×T/R switch resonance
Updated Nov 2006

The T/R switch may resonate in the low 80m band and creates buzz/rough AM, see also here.

Parallel RFC3 with 1K resistor, change R4 to 39k

In Elecraft KPA100 Upgrade kit, KPA100UPKT
Updated April 2014

K7FJ/N6CM/
Elecraft

Low power on 20, 17 m (sometimes 30 m) Updated Nov 2006

First attempt at a fix was to increase C80/81. However this only moves the resonance, the real cure is to remove the resonance by making sure R19/20 are noninductive (Upgrade kit KPA100RESKT) Updated April 2014

In Elecraft KPA100 Upgrade kit, KPA100UPKT
Updated April 2014

G7BQM

40 m parasitic oscillation

New May 2006

Move RFC10 (the RFC back at the SO-239 in the KPA100) further inward.

Dealt with in Elecraft KPA100 Upgrade kit (RFC10 removed)

Handles higher SWR before power roll-back
Updated Apr 2004

Modification kit from Elecraft, KPA100MODKT
Updated April 2014

In all KPA100s from early/mid March 2004.

Elecraft

Instability Updated Dec 2004

Grounding strap or
parallel 270 ohms resistor
(not required for upgraded KPA100)

×KPA100 and KAT100 installation in separate enclosure

In EC2 enclosure, instead of in cover of K2, and integrated with KAT100

Some cabling

Not FCC approved if sold as a stand-alone kit

KK7P

Alternative 2
Updated Dec 2004

Add one 270 ohm resistor (not required for upgraded KPA100)

KI6WX

¤Remoting
the KPA100 without a KIO2
Updated March 2005

Will not get RS232 interface in the KPA100

LA3ZA

Elecraft on KAT100 w/o a KIO2 - KK7P on running the KAT100 w/o the KIO2

Updated Oct 2006

If you want to run the KAT100 in anticipation of the KPA100

KK7P/KD5NDB

160 m and 2. RX Port K160RX

Reference

Description

Comment

Complexity

K2 Status

Source

Adjustment of VCO lock range

VCO control voltage outside of recommended range.

Too low VCO voltages, or too high

Image from Elecraft

Internal Digital Signal Processing Filter KDSP2

Reference

Description

Comment

Complexity

K2 Status

Source

Elimination of pop when changing from rx to tx
Updated March 2005

Add delay to audio mute

Experience from AC5LA

See also QSK time-constant and KPA100 clicks

EI6IZ and KK7P

Negative impact on mute off-time.
Here is an alternative and
here

Elecraft

AF gain control mod reduces KDSP2 hiss and artifacts

For details on this mod, see list of upgrades for pre-# 3000 K2’s

DL2WRJ

Hiss reduction by adding the KAF2 LC-filter

WA8SRA

Installation of KDSP2 affects other options, e.g. KNB2

Aux bus timing problem which will be resolved by doing the
#3000+ aux bus mod

Elecraft

Image from Elecraft

RS232 Interface KIO2

Reference

Description

Comment

Complexity

K2 Status

Source

Reduction of spurious noise

The 16.289 MHz crystal oscillator which gives internal -12V for RS232 i/f may be disabled
and RXD signal is used for negative power instead. Lift R2 on KIO2 board.

In KIO2 manual

Elecraft

×Connector modification to prevent insertion of other cables.

Use of regular computer serial cables may damage the K2 MCU, KIO2, KPA100/ KAT100, and KSB2 since pins 4, 7, 8, 9 carry the K2 specific ALC, RF Detect, 12 V, and 8R lines.

KH6NO/W7 connector modification

KH6NO/W7

Cut PCB traces
for all but pins 2, 3, 5

Only applicable if KIO2 is used for computer control without KPA100/ KAT100

AG5Q

Use 15 pin connector instead of 9 pin New March 2005

Extra 6 pins may be used for internal PSK interface (audio i/o), etc

WD8QW

×L1 on AUX2 board has too small current capacity
Updated Nov 2005

L1 is in 12V line for remote devices and may fail when used with the remote KPA100.
See also KK7P's description.

KK7P

Image from LA8OKA

60m and transverter interface K60XV

Reference

Description

Comment

Complexity

K2 Status

Source

VCO adjustment for 60m
New May 2004

Increase C70

G4DMP

× Tune mode issue with KAT2/KAT100 New July 2004

Change R6 on the KAT2 from 47 ohms to 470 ohms, otherwise the KAT is loaded too much.

Elecraft/
KD5NDB

× Header on board to allow the old BNC connectors
New Jan 2005

A 4-way header on the top of the board which allows one to use the BNC connectors on the top cover and remove the cover without soldering.

G4DMP

Reference	Description	Comment	Complexity	K2 Status	Source
PSK31
The basic set up for PSK31	Audio in/out and PTT	Minimum setup for PSK31	Everything is external to K2		WA7SPY
"Fat wire" digital interface	Audio in/out and PTT	Almost minimum setup	Audio out -> mic. connector		WG4S
A Switchbox for Soundcard Digital Modes	I/O via mic connector	SSB compression is automatically disabled in PSK31	Simple mod to K2, external switchbox		W3FPR
K2 digital interface II.2 K2 digital interface III	Data plug in the rear of K2, audio driver	AF output is independent of AF level control; disables mic and PTT during digital transmit. Brings out mic configuration header for easy reconfiguration	PCB inside K2, data connector	Ver II PCB interferes with KAF2 or KBT2 (user's choice), fixed for ver. III	EA3BLQ (SK)
K2DI-PCI - K2 computer interface New July 2004	In combination with K2 dig I/O ver III, it makes up a complete PSK31 setup inside the K2, ready to connect to a computer.				EA3BLQ (SK)

Input/Output

Reference

Description

Comment

Complexity

K2 Status

Source

External input for internal frequency counter
New Oct 2005

Connector in the back of the K2

VA2VYZ

Balun inside K2

Balun connected to Ant 1 or 2 of KAT2. May use transverter holes for binding posts

There is room for a NJQRP W1CG balun,
but it is not recommended by W1CG

DK3RED

IF output, kit
New Feb 2017

Signal from noise blanker connector, i.e. post mixer

"K2 ZF adapter" discontinued end 2022. Here is a redesign inspired by it (by PH2LB) March 2023

QRP Project, Germany

IF output
Updated May 2021

For spectral display. Z10000 Board.
Use of Z10000 with a panadapter (W8FGU)

These have their output right after the mixer.

K8ZOA board

K8ZOA & DX Engineering

IF output for Softrock: Original in German

Shorter version in English New May 2007

DJ9CS

For demodulation in second receiver

Output after x-tal filter

Elecraft

Output from AGC mixer

W5YR

¤1. AF output, independent of AF pot setting

Output from top of AF pot directly to mic connector.

Output is filtered by KAF2 or KDSP2

Requires AF pot mod for pre serial # <3000

LA3ZA

×2. Amplified fixed level audio output combined with zero-beat indicator
New July 2004

Output from top of AF pot amplified and optionally mixed with sidetone.
Output goes to mic connector and to zero-beat indicator

Output is filtered by KAF2 or KDSP2

Requires AF pot mod for pre serial # <3000

LA3ZA

3. Amplified AF output independent of AF pot setting

Install J5 (Aux. AF) connector and use a buffer amplifier

The only one where the output is independent of KAF2 or KDSP2 filtering

Best with early AF pot version as in pre serial #3000, else

WK6F

4. Amplified fixed level AF output using commercial kit
New July 2004

Based on Velleman kit 1803 (mono preamplifier).

Output is filtered by KAF2 or KDSP2

Velleman 1803

PC2A

5. Amplified fixed level AF output
Updated Dec 2019

Output is filtered by KAF2 or KDSP2

Kitted version by W8FGU, 2019. Manual

W3FPR, N0SS

High level audio input for KSB2

0 dBm input that bypasses mic connector, and compressor

For use with external speech processor (filter/compressor)

NP2B

2m transverter inside K2

2m <-> 10m transverter with 100 mW output

Claim that this is the best performing 144 MHz receiver on the market. Intended as an IF for microwave applications

Uses space for KBT2 and KAT2 options

Down East Microwave

Transverter Interface
Updated Apr 2004

I/O from J13 to combined IF input/output at 28 MHz.

Small board w/relay that fits on top of J13

Better alternative is
Elecraft’s K60XV

Down East Microwave

Universal Transverter Interface
Updated Apr 2004

I/O from J13 to separate XVTR input output connectors.

Board w/relay that fits on top of J13

Requires some adaptations to the K2.
Better alternative is
Elecraft’s K60XV

Down East Microwave

Wireless computer interface (Bluetooth)
New Jan 2007

Custom-designed for the K2 and draws power from the K2's serial port.

Lynovation (KU7Q)

Internal Bluetooth interface
New October 2009

Internal Bluetooth module which can be used instead of wired RS-232 connector.
Can be turned off for normal RS-232 connection.

VA2SS

External control knobs (Using the RS232 I/O)
New Oct 2006

External control of BAND selection, MODE, PASSBAND (FL filter settings),
Front-end gain, AGC, and SQUELCH.

WA1SEO

External keypad allows control of up to 8 front panel buttons
New Aug 2013

G3PJT

External automatic antenna switch
New Aug 2013

Decodes KIO2 data with a PIC processor

G3PJT

Accessories

Reference

Description

Comment

Complexity

K2 Status

Source

Un-modules
Updated Aug 2013

× Un-modules: Replacement connectors with a few components for the KSB2, KNB2, K160RX.

Corrected KNB2 un-module. Here is one for the KDSP2/KAF2 also

KE1L

× Kit from unpcbs.com - even for the K60XV. Boards w/ connectors if you want to remove/ insert option boards without soldering.

Image from unpcbs.com

Highly recommended! Very favorable eham.net review

KI4GGX/ WB2ART

Audio Notch and Band-Pass Filter

Add-on audio filter

Bandpass filter is now in KAF2 or KDSP2, auto-notch is in KDSP2.

Complex

This mod is not recommended, use instead KDSP2 or KAF2

WJ4P

Audio DSP interfaced to K2

ADSP² – filtering, noise reduction, and auto-notch

Mounted on rear of K2 (externally)

Competes with KDSP2 which is much better integrated with the K2

SGC Inc

Items marked with × are implemented in my K2, while ¤ denotes modifications that I have tried, and then removed.

Disclaimer: The modifications presented here have not all been officially endorsed by Elecraft. They should not be implemented before the K2 works and is tuned properly. Even though we try very hard, we cannot guarantee them to be correct. The authors of these modifications or the author of this web-page will therefore not be liable for any damage that they may cause to the K2. However, these modifications have all been implemented by home-brewers and we have no reason to believe that they will not give the desired effect on other K2s.

First version 22 Nov 2001, last update 1 april 2023.

73, Sverre Holm, LA3ZA

Reformatted for blogger and moved here 30. July 2013 (47373).

LA3ZA Radio & Electronics

Pages

Labels

General modifications applicable to any Elecraft K2

Part 1 of LA3ZA Unofficial Guide to Elecraft K2 Modifications

Basic K2: Improved Performance

Basic K2: Intermodulation, image rejection¹

Basic K2: Tweaking

Basic K2: Miscellaneous

SSB Option KSB2

Audio Filter/Real-time Clock KAF2

Noise Blanker KNB2

Internal Battery KBT2

100 W Power Option KPA100 and antenna tuner KAT100

160 m and 2. RX Port K160RX

Internal Digital Signal Processing Filter KDSP2

RS232 Interface KIO2

60m and transverter interface K60XV

PSK31

Input/Output

Accessories

Pages

Labels

General modifications applicable to any Elecraft K2

Part 1 of LA3ZA Unofficial Guide to Elecraft K2 Modifications

Basic K2: Improved Performance

Basic K2: Intermodulation, image rejection1

Basic K2: Tweaking

Basic K2: Miscellaneous

SSB Option KSB2

Audio Filter/Real-time Clock KAF2

Noise Blanker KNB2

Internal Battery KBT2

100 W Power Option KPA100 and antenna tuner KAT100

160 m and 2. RX Port K160RX

Internal Digital Signal Processing Filter KDSP2

RS232 Interface KIO2

60m and transverter interface K60XV

PSK31

Input/Output

Accessories

Basic K2: Intermodulation, image rejection¹