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My Small Wonder + 40
QRP Transceiver
-- Modifications --

After operating my SW+40 for a few days, I decided to make a few modifications to the rig.  As of 10 February 2010, this is a list of the mods and a couple of photos.

Modifications

Replaced the 1-turn tuning potentiometer with a 10-turn pot.

The SW rigs use a varactor to tune the rig.  Voltage to the varactor is controlled using a 1-turn potentiometer; in the case of the SW+40, the tuning pot is a 100 Kohms linear potentiometer.  The rig covers slightly over 40 KHz, making tuning with the single-turn pot a little fast.  I replaced the single-turn pot with a 10-turn unit from Mouser Electronics, part number 652-3590S-1-104L, Bourns Precision Potentiometer.

The 10-turn pot spreads out the tuning considerably.  Now, it is a chore to tune from the low end of the range to the high end -- or vice-versa.  However, I rarely make such big shifts in frequency. Instead, most of my tuning is incremental steps, tuning back and forth over a weak signal to try to dig him out of the noise.  I am pleased with this mod.

Replaced the stock volume control with a volume control that has an on-off switch.

As originally configured, the SW rigs do not have a power on-off switch.  To turn the rig on or off, you plug in or unplug the power connector.  The volume control (audio gain) is a 5 KOhm potentiometer.  I replaced the stock unit with one of the same size and value that has an on-off switch.  I then ran the power lead from the power connector to one terminal of the switch and connected the power leads to the rig to the other switch terminal.

The unit with the switch is from Mouser Electronics, part number 313-1100F-5K, Taiwan Alpha Panel Mount Potentiometer, Linear w/switch 5K.

Added a FreqMite frequency counter that reports the frequency via Morse code through the SW+40 audio circuit

This modification is described on the previous page.

Added an electronic keyer

The SW rigs use a straight key -- the rig does not include a keyer.  I added a tiny, PIC-based keyer from Jackson Harbor Press. 

This keyer requires a paddle.  I wired the keyer as follows:

•  Keyer output:  Wired directly to the SW+40 key jack.
•  Power:  The keyer requires 5 volts.  I installed a three-terminal 5-volt regulator on the keyer PC board and tied the input of the regulator to the SW+40 on-off switch.
•  Ground:  Grounded to a convenient spot on the main PC board.
•  Audio output:  I made a small RC circuit to connect the keyer audio to the SW+40 audio circuit.  The 470 K ohm resistor controls the level of the audio output.  Originally I had a 100 K resistor in this location but the keyer audio was much too loud.  The 470 K does not give enough audio -- I have to strain to hear the keyer output.  I plan to replace the 470 K with a 330 K or 270 K to give a little more audio volume from the keyer.

•  Paddle jack:  I will add a paddle jack to the rear panel of the SW+40.  This will result in two key jacks on the rear panel -- one for the keyer paddle and one for the straight key.

Photos of the SW+40 with mods in place

Here's the SW+40 as it is now configured -- the enclosure (small metal box) is on backorder from Small Wonder Labs.  Here's a description of what's in this photo:

Lower left corner:  Black pushbutton switch controls the keyer.  Power cord and power connector.  To the right of these two parts is the audio gain (volume control) with on-off switch -- black knob installed.  Notice the red wires going to this part -- those are the power leads coming from the power connector, running through the switch, then going to the rig, freq counter, and keyer.
Top left - center - right:  The large black knob above the main PC board is the tuning control.  The 10-turn pot is standing vertically and is hidden beneath the knob.  To the lower left of the tuning control is a tiny PC board -- this is the keyer.  Above the tuning control to the right is the stereo jack for the paddle.  Below the paddle jack is the BNC antenna connector and below it are the jack for the straight key and jack for the headphones.  In the far right upper corner is my American Morse Equipment KK-1 straight key.  The red pushbutton switch below the straight key is the switch for the FreqMite frequency counter.
Center of photo:  The SW+40 main PC board is in the center of the photo.  The small PC board to the right of the main board is the FreqMite frequency counter.

And here's another view of the same thing:

	Tuning control         Paddle jack             Straight key                                                    |                       |                                   |
Power connector Keyer pushbutton switch		<- BNC connector for antenna <- Straight key jack <- Headphone jack <- FreqMite pushbutton (red)
	Volume control/on-off switch     Main PC board     FreqMite PC board

Back to SW+40 first page