ELECRAFT K2 SSB User manual

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DL-QRP-AG
© QRPproject Molchstr. 15 12524 Berlin http://www.QRPproject.de Telefon: [phone] e-mail: [email protected]e
Manual by: FIservice Peter Zenker DL2FI email:dl2fi@qrpproject.de
K2 SSB Modifikation
A compilation of the mods suggested by John, KI6WX, Karl-Heinz, DF7KHK and Frank, DJ3FR by DL2FI

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During the time there have been several suggestions do modify the SSB
Modul of the K2 do improve the the modulation which is named „a little
bit week and sometimes craspy by some users. Well known and often used
are the mods designed by John, KI6WX and Karl-Heinz, DF7KHK. The Mod
regarding the bandwith of the Xtal Filter suggested by John have been
overtaken for the series kits by elecraft some years ago.
The following description is a compilation of different mods. Frank, DJ3FR
had the chance to test all known SSB mods using a set of ten K2/100
which haven been built at the same time during a student course.
The described combination of mods if have been installed guarant a clean,
strong modulation on all bands. I have modified and tested a lot of K2
when servicing them as QRPproject supporter. The Berlin DXpedition Gang
is using now 3 modified K3/100 for DXPeditions e.g. to XV4D 5H1DF, A25/
DL7DF say they now get reported a „modulation like a man“ :-)
Improving the Quality of the modulation, Solving the
problem of less driver power on the upper bands
The following description belongs to:
1. Serialnumber K2 above > 3000
or if lower number installation of XFILMDKT 2nd Filter SSB Modification
Kit.
2. SSB PCB as describes in Manual Rev E July 20, 2004 or newer
(That means the new Xtals must be installed, caps CC and CM = 27pF, CG,
CH, CE, CK, CA, CP = 39pF)
If you modify an older K2, in any case check the Xtals on the RF board.
They must be signed with the same sign (4,915-S) as the Xtals on the SSB
board. If not, they must be replaced by the newer Xtals.
Elecraft number for replacement: K2KSB2XTLS 14 pieces paired Filter Xtals
coplete for main board and SSB board
Here we go, start with John´s Modifikation:
MOD 1: KSB2, More Gain for SSB
The original SSB board has a little bit low gain. If a mirophone with low
output is used, it cannot drive the K2 to full power at the high frequency
bands. Using microphones with higher levels it can happen, that the NE602
is over driven with causes AF clipping. This mod is a clean solution for both
problems.
John is using a PN2222 Emiter follower to cople the NE602 to the
low impedance side of transformer T2. This way he uses the Voltage
transformation of T2 and gives a much lower load to the NE602 output
stage. The 82 Ohm resistor together with the impedance of the Emitter
follower gives a good Imedance matching for the Xtal Filter. The resulting
gain of this mod in total gives a plus of about 10 dB..
The mor is easy to realize:
[ ] Remove D4
[ ] Desolder wire number 2 and wire number 4 of T2 ( you find them next
to the NE602).
[ ] Now solder former number 4 wire to solderlug number 2 and former

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number 2 wire to solderlug number 4. This will reverse T2 by 180 degrees.
[ ] Install a PN2222 (attention, 2N2222 has another pinning). Place it at
the right side of NE602 the flat side orientated towards NE602. The 3 Pins
look upwars.
[ ] Solder colector to PIN 8 of NE602
[ ] Solder Base to PIN 4 of NE602
[ ] Solder a 82 Ohm Resistor between Emitter and PIN 1 of T2. Use the
solderlug of C11.
[ ] Solder a 2,7kOhm Resistor between wire 4 of T2 and ground at the
solder side of the PCB. ( Use the junction between R6 and T2/4. This
resistor will hold the Base/Emiter junction of PN2222 at 3V to avoid Base/
Emitter breakthrough.
Alternativ you can do this mod complete at the solderside of the PCB as
shwn in the picture below.

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MOD 2: Decreasing distortions
If the Level for the NE602 Input gets to high, this will cause AF clipping
what means Intermodulations and Distortions of the AF signal.
To avoid this, we add a Resistor.
[ ] Check R2. If it is not 5k6 replace it with 5k6.
[ ] Solder 2k2 resistor between PIN 1 and PIN 2 of U5. This can easy be
done if you use the input / output pins of Trimpot R1 (do not use the slider
PIN)
MOD3: Increasing the level of cmpression (first decribed by DF7KHK
QRP-Report, Magazin of German QRP Club DL-QRP-AG)
The SSM2165 can be used up to a compression of 15:1. Expierence with the
German „Speaky“ transceiver say, that it makes sense to use compression up
to 1:10 for QRP-SSB Transceivers.
The following mod is simple and allows to stay with the standard menue
steps of K2 giving higher compression.
[ ] Remove RP5 on the SSB board.
[ ] Install 5 150 k Resistors
instead of the Resistor array. as
shown in th edrawing. Connect
PIN 2,3 and 4 on the solder side
of the PCB.
Upper drwaing: Original KSB2
Lower Drawing: Modified KSB2
1
150k 150k 150k 150k 150k

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Modifikation: Microphone Sensitivity (DF7KHK
The K2 feeds the the compressor chip
directly, not using any preamplifuer.
Regarding the KSB2 Manual the
microphone should give 100mVpp
(peak to peak) The Microphone signal
is attenuated by R14/R15 using R15 in
Menue settig SSBA=1 parallel to %14. If
you increase the value of R14, you can
use the microphon sensitivity. Using an
MH2 Mike, we found 3,3 kOhm instead of
the original 1k was the best value.
If you use other Microphones, you may
play around with the values of R14/R15
MOD: Optimizing (by DJ3FR)
This mods done now eventually generate so much power, that the ALC will
not work properly. You will see more than normal RF output in thi case. If
this happens with your 2, you must increase the values of R10 and R8 on
the KSB2 board.
This can be done experimental, but you can get the right values also by a
little measurement:
If you can measure the peak to peak Voltage at the Kathode of D14 during
transmitting, this voltage can tranferred directly into a resistor value: for
any 100mV you can substitute 100 Ohm. That means if you measure 300mV,
R8 and R10 should be replaced by 300R Resistors. If you measure 500mV,
you should replace them by 500R (use allways the nearest standard resistor
value). You should measure
The next table shows what we hae measured at a couple of different KSB2
boards:
Meßpunkt SSB unmodified SSB modified
U3.4 30 mVpp 60 mVpp
U3.7 1,5 Vpp 1,2 Vpp
U5.1 600 mVpp 300 mVpp
U5.4 800 mVpp 1 Vpp
D14.K 100 mVpp 500 mVpp
Alingnement:
After this mods have been done, you must do the CAL FIL procedure.
For all those of you who find the Noise Generator method to be good in CW
but uncomfortable for SSB, I will decribe a simple alternative methode.
Connect your K2 to a Dummy load
Tune a control receiver to the K2 frequency, Use Head Phones
Set control RX to LSB
Set K2- SSB A Menue to 1 and SSBC Menue to 1-1 setzen.
Set Cal Fil Menue to OP1 Filter and the value of BFO frequency to the value
recommended for OP1/LSB in KB2 manual page 10
Whistle into the microphone (PTT to send). Tune the frequency of the
control receiver until you hear as exact as possible the same tone (like you
do if you use the K2 SPOT function) If the RX signal is distorted, use RX
Attenuation until you hear your whistle undistorted.
If both tones are equal, you are transceive. Now speak into the Mike and
listen to the RX. If what you here is to low or to high in Frequency, go back
to CAL FIL and change the frequency by 100Hz up or down. Tap Menue to
leave CAL FIL and repeat. Repeat until you hear your voice „natural“ sound.
Repeate the complete procedure for USB (Don´t forget to switch the RX to
USB as well, use OP1 again)
K2 will use allways OP1 for transmit, so this procedure is not recommended

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for the other SSB Bandwith´s which will be adjusted to best sound in
receive mode only.
Addition:
We found at a very low number of K2
(mostly K2/100) a small anomaly in
the ALC funktion. Check the following
and modify if necessary
Switch Display to ALC
Push PTT and talk your normal way. Look at the Bargraph, it should light
the bars right to left. If MORE the 3-4 bars will flicker, you must do the
following modification:
[ ] Change R9 to 1.5K on the KSB2 board.
[ ] Cut the PCB trace to the base of Q1,
[ ] Solder a 1K resistor across the cut.