General modifications applicable to any Elecraft K2

Part 1 of LA3ZA Unofficial Guide to Elecraft K2 Modifications


Tips for use:
  • Use your browser's search function to find all new or recently modified items, e.g. "2014".
  • Search directly for a keyword, e.g. "QSK" or "click".
  • Search for source of modification, e.g. W3FPR, KI6WX, G3RXQ, LA3ZA, unpcbs etc
  • Access the mobile version for a wider view.
  • Go directly to option or category by clicking in the table below.

Basic K2: Performance  Intermodulation  Tweaking Miscellaneous  
Options:KSB2KAF2 KNB2 KBT2KPA100/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. 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 2nd 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 WWVRW 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
See also KPA100 clicks and
KDSP2 pop





Elecraft

G4BJM

¤Headphone
modification

Increased
headphone output

Reduced series resistors (alternative:
get more sensitive headphones!)
Parallel R35 and R36 with e.g. 22 ohms
LA3ZA

Reduction of speaker buzz

New May 2006
Sticky fibrous pads on inside of top cover It helps if the battery is fitted in the top cover N4YM
×Remapping of Keyer Speed Pot Range New March 2006 Larger part of pot's range is used for low and medium speed CW as 22 WPM is now in the mid-position rather than 30 WPM.


LA3ZA
Reduction of audio thump when keying New
July 2004
Audio bandpass filtering
in headphone output for reducing click (high frequencies) and thump
(low frequencies).

A few capacitors
WA8SRA
×Poor S-meter action Only applicable to a small # of K2s Select a diode D1 on control board with higher Vf

Elecraft
More RF preamp gain Too little overall gain Has been superseded by AGC mod in serial # 3000+ Decrease emitter R from 10 to 3.3-5.6 ohms

Elecraft


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:


See also KRC2 Band decoder ZL1AIH
Digital controller for RS232 distribution, audio switching, frequency/ mode swapping G3PJT
SO2R with N1MM logger and Winkey, dims inactive K2's display backlight K6MR
SO2R with TRlog using SWAPRADIOS and EXCHANGERADIOS commands K5WA
¤Split/ Rit/ Xit LED indicator (N0SS)

Front panel LED.

Here is an alternative
smaller LED and step by step photographs (KH6NO/W7)


Uses SRDOUT
output from MPU, requires rev 2.03 firmware

Drill hole in front panel, above Rate button
KH6NO/W7

Elecraft

PTT LED indicator on front panel
New March 2005
More details of implementation
Hole in front panel above Rate button


4Z4TL
CW zero beat detector Add-on frequency detector.

LED in key cap of Rate/Lock switch (W3FPR) or OR’ed into right-most segment of LED bargraph (W7DZN)
Nice for the tone deaf (‘tonally challenged’)
Add-on board
Kit from N0SS (SK)
KR5L
×Low-power, QRP, version

LA3ZA


SMD zero beat detector
Updated Oct 2013
Kit for N0SS SMD add-on board, and for button LED kit (from WB3AAL)
Kit review by KH6NO/W7 (image)

K6XX
×5 LEDs in keycaps

New
June 2005
For CW zero-beat indicator, Split/Rit/Xit indicator, KAF2, Tx on, and Ext Rx ant

LA3ZA
60m operation
Updated Aug 2013
Modify 40 m BP, modify VFO/PLL, external switch

Experience from G4DMP Somewhat
complex

Don't do this mod as it has been
replaced
by K60XV

Elecraft

×Auto-detect
diodes for keyer Updated June 2005
Internal in K2 using a
second jack or external to K2. Useful if you frequently connect both a keyer paddle and a keyer or computer.

More reliable triggering with Shottky diodes instead of Si diodes because of PIC's input threshold

Two Shottky diodes

In K2 manual


Elecraft/
LA3ZA
Bug mode
New May 2006
One diode between the dah side and the dit side of the paddle Works in principle, but not well in practice. Experience here:  #1, #2
The problem is that the firmware isn't fast enough in switching between manual to iambic modes, not as fast as needed from a dah to a dit.
W3FPR
Better debouncing of straight key input Add 0.1µF between straight keyer terminals. Alternatively increase C1/C2 (0.001 µF) on RF board.



KG4ARN

QRP output power control Change range of
power control for better QRP power control


Nice to have if you are
always running CW QRP


Add
a resistor


DK3RED

QRPp
output power control

Switch between two
ranges: standard and <1 W


Nice to have if you like QRPp operation

Add switch (hole in bottom panel) and a few resistors and a C



WJ4P

K2 External Amplifier Keying Circuit
Updated Nov 2006
This is the improved version by WA5PB/N0SS For use with external power amplifier - only if you don't have the KPA100 or the K60XV Add 2 transistors and 2 resistors
Kit was available from N0SS (SK)

Elecraft

More steps/rev for tuning control Changes main tuning knob from 1 kHz/rev at 10 Hz step size to 4 or 8 kHz/rev. See also experience of W5MR.

Only works with
firmware 1.xx and 2.02 and later, firmware may not able to keep up with fast spinning of dial.


Replace
optical encoder (expensive)




N6TR

Memory doubling
New
March 2005
Two EEPROMS
selectable by external switch for double CW memory keyer capacity










WB9KZY


Image from Elecraft

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
  1. New crystals, if old KSB2 (~March 2002). Upgrade kit K2KSB2XTLS Updated April 2014
  2. Increased ALC delay, if old KSB2 (~Sept 2001). Upgrade kit KSB2MDKT (KI6WX) Updated April 2014
  3. 2.2 kHz bandwidth (KI6WX)
  4. Increased RF gain (KI6WX)
  5. Reduced Intermodulation Distortion (KI6WX)
  6. Increased compression ratios (DF7KHK)
  7. Increased microphone gain (DF7KHK): R14 from 1k to 3.3 k
  8. 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


1.9, 2.2(×), or 2.5 kHz bandwidth and flatter response than original 2.0 kHz bandwidth

2.5 kHz seems to be the favored bandwidth.
Change Cs in x-tal ladder filter; requires a recent x-tal set.
2.5kHz bw may require padding of BFO capacitors

2.2 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
Alternative by G3RXQ

Decrease two coupling capacitors

KD2BD

Increased VOX sensitivity
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 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 considerationson 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



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
See also power control mod




Computer polling noise elimination
New March 2005
Tuck the ribbon cable up as high as possible - away from the main board.



K8DD
Clicks on rx unmute 
New Jan 2005
Increased C72 which increases time-constant for unmuting + increased C71.
Removes clicks when the KPA100 and the DSP are both active.


See also QSK time-constant and KDSP2 pop


K2VCO/
Elecraft
×Using
the KPA100 loudspeaker when the KPA100 is remoted
New March 2006
Makes the loudspeaker accessible from the outside through the loudspeaker plug.



LA3ZA

Image from Elecraft

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


PSK31


Reference

Description

Comment

Complexity

K2 Status

Source
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
Updated Jan 2007
For spectral display. Board for purchase + measurements These have their output right after the mixer

K8ZOA board


K8ZOA
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. Kit for amplified fixed level AF output
New July 2004

Output is filtered by KAF2 or KDSP2


W3FPR
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 3 July 2014.

 73, Sverre Holm, LA3ZA
Hit Counter by Digits Counter-logo

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