40m CW transceiver SST40

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Japanese : Jul. 13, 2009, English : Aug. 10, 2011
Last update : Sep. 10, 2016
Japanese page is here.

FlowerOverview of the SST

I built a 40m CW transceiver SST40 in June 2006.
I added a speaker to my SST40 in Jan. 2013.
I continuously modify it.

SST40

My SST40
( For modification, a push switch, a toggle switch, two LEDs are added on the front panel. )
( There are holes on the top plate for speaker addition. )

SST ( The Simple Superhet Transceiver ) is a QRP CW transceiver kit supplied by the Wilderness Radio.
SST is distributed by the Electro Design Co. for Japanese users.

SST40 PC board

SST40 PC board
( Because trimmers and jacks are installed on the PC board, there is not wiring and so it is easy to build. )

Rear panel of my SST

Rear panel of my SST
( 'FREQ-mite' is fixed by the screw on the upper-left. )
( From the left, key, power supply, power supply external / internal switch, antenna, RX RF gain. )
( There are holes on the top plate for speaker addition. )


FlowerMy SST40 overview (modification points)

Inside of SST40 before the 'FREQ-mite' is installed

Inside of my SST40 before 'FREQ-mite' is installed
( There are no wiring. )

Inside of SST40 after the 'FREQ-mite' is installed

Inside of my SST40 after 'FREQ-mite' is installed

Major modification points of my SST40 are as follows.


FlowerExpansion of the frequency range

Two kinds of variable capacitance diodes are included in the SST kit to select the frequency range when a user build.
In order to make the frequency range wide, I modified my SST to be able to change the two kinds of variable capacitance diodes with the toggle switch added on the front panel.

Two kinds of variable capacitance diodes with a toggle switch

Two kinds of variable capacitance diodes with a toggle switch

A ceramic capacitor from 2 to 4pF is added in parallel to the crystal in the VXO ( variable frequency crystal oscillator ).

Month, Year Capacitor added in parallel to the crystal in the VXO Frequency range
( Lower )
Frequency range
( Upper )
Remarks
June 2006 None 7.01017~7.01968MHz 7.01799~7.02544MHz
2.5 pF ( two 5pF capacitors in series ) 7.00128~7.01782MHz 7.01567~7.02520MHz Set value in 2006
3pF 6.99882~7.01762MHz 7.01529~7.02521MHz
Jan. 2013 2.72pF ( 5pF and 6pF capacitors in series ) 7.00671~7.01939MHz 7.01882~7.02607MHz
3pF 7.00548~7.01908MHz 7.01848~7.02594MHz
4pF 6.99932~7.01822MHz 7.01766~7.02592MHz Current set value

FlowerPitch frequency and BFO frequency adjustment

The pitch frequency (CW offset) can be adjusted by changing C24.
In order to make the pitch frequency close to 700Hz, C24 was changed from 56pF fixed capacitor to 50pF trimcap and fixed 33pF in parallel.

C24 changed to 50pF trimcap and 33pF C10 changed to 50pF trimcap

C24 changed to 50pF trimcap and fixed 33pF (Left photo)
C10 changed to 50pF trimcap (Right photo)

Month, Year C24 Pitch frequency Remarks
June 2006 33pF 590Hz
47pF 744Hz Set value in 2006
68pF 890Hz
Jan. 2013 43pF 720Hz Set value in 2013
Oct. 2015 50pF Trimcap
and fixed 33pF in parallel
570-870Hz
(Set to 700Hz)
Current
(BFO frequency changed too)

The BFO frequency can be adjusted by changing C10.
In order to set the center frequency of CW filter passband after product detector close to 700Hz, C10 was changed from 22pF fixed capacitor to 50pF trimcap.


FlowerFrequency indication

In order to indicate the frequency, Small Wonder Labs 'FREQ-mite' ( As of May 2015, we can get it from Four State QRP Group. ), a Morse-readout frequency-annunciating device, is installed, and a push switch is added on the front panel.

FREQ-mite

Small Wonder Labs 'FREQ-mite'

AF signal injection point

AF signal ( Morse code sound ) injection point is the additional 100k ohm resistor in the center.


花のアニメUpgrading of the filters

For spurious reduction, the band-pass filter after the transmit mixer was upgraded to two stages from one stage.

Circuit diagram of the upgraded band-pass filter

Circuit diagram of the upgraded band-pass filter
( The part surrounded in a dotted line is added. )

Side view of the upgraded band-pass filter Top view of the upgraded band-pass filter Bottom view of the upgraded band-pass filter

Upgraded band-pass filter
Side view ( Left photo : Right coil was added. )
Top view ( Center photo : Yellow trimming capacitor was added. )
Bottom view ( Right photo : Three capacitors were added. )

For harmonics reduction, the low-pass filter after the final transistor was upgraded to three stages from two stages.

Circuit diagram of the upgraded low-pass filter

Circuit diagram of the upgraded low-pass filter
( The part surrounded in a dotted line was added. )

Added part of the upgraded low-pass filter

Added part of the upgraded low-pass filter
( I cut the circuit pattern of the solder side, and installed a coil and two capacitors. )

The above-mentioned filters upgrading is very effective.


花のアニメSST Links

A picture of my SST was published in a great blog of Dave AA7EE in USA. His SST is a complete own work product based on the original N6KR SST.
Please visit his blog. In addition to circuital invention, his building technology is excellent and his SST is beautiful artistically.

  Arrow Dave Richards AA7EE' s blog -- A Scratch-Build of N6KR and Wilderness Radio’s SST for 20M


MePADs and MeSQUAREs of QRPme used in his SST are interesting.


Past images from June 2006 to Oct. 2015 are here(Japanese).


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