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Direct access: |
Basic K2: |
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Options: |
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Other: |
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Reference |
Description |
Comment |
Complexity |
K2 Status |
Source |
Basic K2: Improved Performance |
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Updated Apr 2004 |
4-5 components on control board plus an upgrade of firmware to ver 2.04. Upgrade kit available from Elecraft. Possible impact on very high speed CW (50+ wpm). |
Measurement of keying spectrum for original, pre-mod K2 and comparison with other rigs. |
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In all new K2s from serial # 4060 and up. |
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×Temperature compensation for PLL reference Updated Jan 2005 |
Uses a thermistor to temperature-compensate the varactor diodes in the PLL reference oscillator. Upgrade kit available from Elecraft. 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. |
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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) |
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Weird behavior around 7185 kHz. In addition to RFC and decoupling of serial 3000+ also add 68 pF between pins 12 and 13 |
Important and easy to do |
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In all new K2s from serial # 3xxx and up. |
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Magnetic shielding kit for VCO coil New Oct 2005 |
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 |
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May be purchased from Elecraft, but optional even for new K2s. |
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×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 |
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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 |
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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 |
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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 |
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| 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 | |||
Basic K2: Intermodulation, image rejection1 |
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Makes reception at frequency of strong tx close by possible |
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Two diodes as limiter in IF amp |
In all new K2s from serial # 3xxx and up. |
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alternative: Ceramic 7.02 MHz filterUpdated Oct 2006 |
Narrow 40m bandpass characteristics, especially for Region 1, 7.0-7.1 MHz band1 |
Important if you experience intermodulation from strong broadcast stations above 7.1 MHz.
Ceramic filter is Murata resonator SFE 7.02 |
Change 3 capacitors - or - |
DF7TH |
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×Wider 10 m 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. |
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Narrower bandpass filter, better stopband attenuation |
Reduces intermodulation from 13 MHz broadcast band, but loses sensitivity to 15 MHz WWV, RWM etc |
Change 3 capacitors |
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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 |
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Changes to all band pass filters Updated |
Bandpass filters
tuned
to band limits of amateur bands - only needed if there is an
intermodulation problem. 2006 update: wide/narrow 160 m & 40m (Region 1 40 m is about to become 7.0-7.2 MHz) |
New filters are: 10/12m, 20/30m, and 80/160m1. Harder to adjust as settings of combined filters interact. |
Change/add capacitors |
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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 |
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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). Some of the modifications above are specifically designed for Region 1. |
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Basic K2: Tweaking |
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Power control mod for more stable output level |
Increase R98 on RF board from 270 ... 1-5 k |
Due to finite bit-length in ALC voltage, and increased R98 reduces ALC gain. Mainly important for KPA100 |
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Application Note and in K2 manual, appendix E |
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More output on 10m: ×lift T2, new T2 core |
Lift T2 above PCB, space windings, wind with binocular core rather than toroid Updated Oct 2004 |
Better coupling to output stage at high frequencies |
AB7MY, W8IJN, |
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Replace one C with two Cs. |
Optional better temperature stability. |
GU3MBS: range reduced from 570 to 200 Hz |
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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. |
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WK6F |
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Updated
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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 |
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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. |
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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. |
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In K2 manual |
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×Faster QSK performance Updated |
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 |
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G4BJM |
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Increased headphone output |
Reduced series resistors (alternative: get more sensitive headphones!) |
Parallel R35 and R36 with e.g. 22 ohms |
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| 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 | ||
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×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. |
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Reduction of audio thump
when keying New
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Audio bandpass filtering in headphone output for reducing click (high frequencies) and thump (low frequencies). |
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A few capacitors |
WA8SRA |
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Only applicable to a small # of K2s |
Selec(fort a diode D1 on control board with higher Vf |
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Too little overall gain |
(Superseded by AGC mod in serial # 3000+?) |
Decrease emitter R from 10 to 3.3-5.6 ohms |
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Basic K2: Miscellaneous |
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Lightning
protection of antenna i/o |
~1 mH choke + neon light across antenna connector |
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2 K2s running
together Updated |
Audio switching and rx muting for SO2P (Single-op 2 radio) |
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ZL1AIH
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Digital controller for RS232 distribution and additional tx/rx switch |
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¤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 |
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×LEDs
in keycaps |
For CW zero-beat indicator, Split/Rit/Xit indicator, KAF2 and more |
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60m operation Updated |
Somewhat complex |
Replaced by K60XV |
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×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 diodes |
In K2 manual |
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| 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: 1, 2 | W3FPR | ||
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Add 0.1 mF between keyer inputs. Alternatively increase C1/C2 (0.001 mF) on RF board. |
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KG4ARN |
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Change range of power control for better QRP power control |
Nice to have if you are always running CW QRP |
Add a resistor |
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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 |
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WJ4P |
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K2 External Amplifier Keying Circuit Updated Nov 2006 |
For use with external power amplifier - only if you don't have the KPA100 or the K60XV |
Add 2 transistors and 2 resistors |
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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) |
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Memory doubling New March 2005 |
Two EEPROMS selectable by external switch for double CW memory keyer capacity |
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SSB Option KSB2 |
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| Recommended
modification of KSB2 (in German) New Nov 2005 |
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All of the KI6WX modifications + some more. Marked with * later in this table |
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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.
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Change Cs in x-tal ladder filter; requires a recent x-tal set. 2.5 kHz bw may require padding of BFO capacitors |
2.2 kHz filter is standard in KSB2 since summer 2004 and a mod kit is available New August 2004 |
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Handles low output microphones without audio clipping |
Preferable over AF gain increase mod since it gives less distortion |
More complex than increasing AF gain |
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×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 |
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W4WFB |
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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 |
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*×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 |
QRP-Report 3/2004 (DE) |
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×More roll-off of low-frequency response Updated March 2005 |
Better spectral balance and better equalization between USB and LSB, less change of overdriving the speech compressor and balanced modulator |
Decrease two coupling capacitors |
KD2BD
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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. |
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RF filter on input of compressor Updated Dec 2004 |
1 mH in series with input of U3, and 0.001 uF from pin 4 to ground prevents RF from reaching KSB2 input.
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1 coil and 1 cap |
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Anti-VOX New Sep. 2004 |
New PCB next to KSB2 |
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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. |
Of special interest if you use other than Elecraft microphones. |
Change R14 (and R2) or swap them. |
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Transistor gain stage |
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Increase R14 and use 1:10 transformer on input |
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Higher microphone sensitivity D New May 2004 |
External transistor stage |
N0MF |
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New Dec 2004 |
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G3RXQ/W8UR
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Separation of PTT and CW dot line Updated May 2006 |
Uses a logic circuit to separate PTT and dot key line
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PTT LED indicator on front panel New March 2005 |
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×Grounding crystals near
bottom |
Less filter blow-by |
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Filter AGC IF signal with 153 kHz bandpass filter |
Add 1R, 2Cs, 1 L |
TF3MA
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Updated
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Protection against stray RF and static electricity. More considerations on grounding ("pin 1 problem" - K9YC) |
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Simple |
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Makes it easy to switch between differently wired microphones without soldering |
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W1EUY |
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Audio Filter/Real-time Clock KAF2 |
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Change L1,L2 from 82 mH to 56 mH |
In KAF2 manual |
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Increase R9 from 10 K to 12-15 K or more |
In KAF2 manual |
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4 alternative responses for second stage, AF2 |
Nice to have if you do not like the ringing characteristics of the supplied filter. |
Change 3 resistors and a capacitor |
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Real-time clock runs a little fast (>+/-1.7 sec/day) |
Add 10-50 pF in parallel with C19 (33 pF) |
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Noise Blanker KNB2 |
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Add 33 pF between pins 7 and 8 of MC1350 |
In KNB2 manual |
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NB1: 10us ->70us NB2: 70us->500us or 1ms |
If your QTH is affected by electrical noise from motors, electrical fence etc |
Increase C11 & C12 |
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Internal Battery KBT2 |
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Direct charging of internal battery without series diode or extra connector Updated |
Gives direct access to battery from power connector. See also this comment by PA3GYU.
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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+) |
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WA6EGJ |
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Lithium batteries New May 2004 |
Replace sealed lead acid batteries with lithium polymer batteries, saving 0.77 kg - 1.7 pounds, and gaining in capacity. |
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100 W Power Option KPA100 and antenna tuner KAT100 |
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Updated Nov 2006 |
The T/R switch may resonate in the low 80m band and creates buzz/rough AM, see also here. |
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K7FJ/N6CM/ |
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Low power on 20, 17 m (sometimes 30 m) Updated Nov 2006 |
First attempt at a fix was to increase C80/81 from 4700 pF to 5600 pF. However this only moves the resonance, the real cure is to remove the resonance by making sure R19/20 are of the noninductive kind |
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In Elecraft KPA100 Upgrade kit |
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 | |||
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Handles higher SWR before power roll-back Updated |
In all KPA100s from early/mid March 2004. |
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Instability Updated Dec 2004 |
Grounding strap or parallel 270 ohms resistor (not required for upgraded KPA100) |
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×KPA100 and KAT100 installation in separate enclosure
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In EC2 enclosure instead of in cover of K2 and integrated with KAT100 |
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Some cabling |
Not FCC approved if sold as a stand-alone kit |
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Updated Dec 2004 |
Add one 270 ohm resistor (not required for upgraded KPA100) |
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¤ Remoting the KPA100 without a KIO2 Updated March 2005 |
Will not get RS232 interface in the KPA100 |
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Running the KAT100 without the KIO2 Updated Oct 2006 |
If you want to run the KAT100 in anticipation of the KPA100 |
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KK7P/ KD5NDB |
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See also power control mod |
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Computer polling noise elimination New March 2005 |
Tuck the ribbon cable up as high as possible - away from the main board. |
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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. |
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×Using the KPA100 loudspeaker when the KPA100 is remoted New March 2006 |
Makes the loudspeaker accessible from the outside through the loudspeaker plug. |
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160 m and 2. RX Port K160RX |
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Adjustment of VCO lock range |
VCO control voltage outside of recommended range. |
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Internal Digital Signal Processing Filter KDSP2 |
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Elimination of pop when changing from rx to tx Updated |
Add delay to audio mute |
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EI6IZ and KK7P |
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Negative impact on mute off-time: Here is an alternative and here |
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For details on this mod, see list of upgrades for pre-# 3000 K2’s |
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DL2WRJ |
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WA8SRA |
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Installation of KDSP2 affects other options, e.g. KNB2 |
Aux bus timing problem which will be resolved by doing the #3000+ aux bus mod |
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RS232 Interface KIO2 |
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Reduction of spurious noise |
The 16.289 MHz crystal oscillator which gives internal -12 V for RS232 i/f may be disabled and RXD signal is used for negative power instead. Lift R2 on KIO2 board. |
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×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. |
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Cut PCB traces for all but pins 2,3,5 |
Only applicable if KIO2 is used for computer control without KPA100/KAT100 |
AG5Q |
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Use
15 pin connector instead of 9 pin New |
Extra 6 pins may be used for internal PSK interface (audio i/o), etc |
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WD8QW |
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×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. |
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60m and transverter interface K60XV |
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VCO adjustment for 60m New |
Increase C70 |
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Tune mode issue with
KAT2/KAT100 New |
Change R6 on the KAT2 from 47 ohms to 470 ohms, otherwise the KAT is loaded too much. |
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KD5NDB |
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Header
on board to allow the old BNC connectors
New |
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. |
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PSK31 |
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Audio in/out and PTT |
Minimum setup for PSK31 |
Everything is external to K2 |
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WA7SPY |
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Audio in/out and PTT |
Almost minimum setup |
Audio out -> mic. connector |
WG4S |
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I/O via mic connector |
SSB compression is automatically disabled in PSK31 |
Simple mod to K2, external switchbox |
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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 |
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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. |
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Input/Output |
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input for internal frequency counter New Oct 2005 |
Connector in the back of the K2 |
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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 |
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For spectral display |
Output right after mixer |
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For demodulation in second receiver |
Output after x-tal filter |
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W5YR |
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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 |
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× 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 |
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Install J5 (Aux. AF) connector and use a buffer amplifier |
Output is independent of KAF2 or KDSP2 filtering |
Best with AF pot mod for pre serial # <3000, else |
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WK6F |
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4. Amplified fixed level AF output using commercial kit New July 2004 |
Output is filtered by KAF2 or KDSP2 |
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5. Kit for amplified fixed level AF output New July 2004 |
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Output is filtered by KAF2 or KDSP2 |
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0 dBm input that bypasses mic connector, and compressor |
For use with external speech processor (filter/compressor) |
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2 m <-> 10 m 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 |
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Updated |
I/O from J13 to combined IF input/output at 28 MHz. Better alternative is Elecraft’s K60XV |
Small board w/relay that fits on top of J13 |
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Universal Transverter Interface Updated Apr 2004 |
I/O from J13 to separate XVTR input output connectors.
Better alternative is Elecraft’s K60XV |
Board w/relay that fits on top of J13 |
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| 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 | |||
Accessories |
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×Un-modules Updated March 2006 |
Replacement connectors with a few components for the KSB2, KNB2, K160RX. Corrected KNB2 un-module. Here is one for the KDSP2/KAF2 also |
Nice to have if you want to remove/insert option boards without soldering. |
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Add-on frequency detector. LED in key cap of Rate/Lock switch or OR’ed into right-most segment of LED bargraph (W7DZN) |
Nice for the tone deaf (‘tonally challenged’) |
Add-on board |
Kit from N0SS |
KR5L |
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New Dec 04 |
Kit from N0SS |
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Add-on audio filter |
Bandpass filter is now in KAF2 or KDSP2, auto-notch is in KDSP2. |
Complex |
WJ4P |
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Mounted on rear of K2 (externally) |
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Superseded by KDSP2 |
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Test Equipment |
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Generator for setting up the IF filters and BFO frequencies with spectrum analyzer program. |
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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. The authors of these modifications or the author of this web-page will 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 28 November 2006.
