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My QRP Rigs --
Low-power CW operation
 

One of the enjoyable aspects of the amateur radio hobby is that, with an amateur radio operator's license, you can build your own equipment from scratch.  In fact, back in simpler times most equipment was either homemade or was modified from old commercial or military equipment.  Now that 99.9 percent of electronic devices use integrated circuits, micro-computers, transistors, and tiny parts, and because it's often difficult to find suppliers who sell small quantities -- as in one or two of an item -- most amateur radio equipment is commercially made.  However, there are several individuals and companies that still produce kits and sell individual parts for the experimenter.

Another fun aspect of amateur radio is that not a lot of power is required to communicate with other stations.  While most amateur radio equipment operates at around the 100-watt level -- and amateur radio operators can run as much as 1,000 watts -- a lot of amateur radio operators enjoy using low and very-low power equipment. 

This is a long story -- I'll keep it short.  Originally all amateur radio operation used Morse code and, because Morse requires that every word be spelled out, a system of abbreviations was developed.  Some of these abbreviations are the "Q" signals -- for example -- QTH means "location."  If you send QTH?, that's the same as aksing "What is your location."  If you send QTH New York, that means "My location is New York."  The Q signal QRP means "reduce power" -- and over the years the term QRP has come to mean low power operation.  Generally, if a piece of equipment is described as a QRP rig, that means it runs 5 watts of power or less.

Currently I have six small QRP transceivers that operate on CW -- Morse code; I built each of these from kits that I purchased from the folks who designed them.  My current QRP rigs are:

•  SW-40, -20, -80 : 40-meter, 20-meter, or 80-meter band; 1.5 watt CW transceiver; superhet receiver.
• S&S Engineering ARK-4:  40-meter band; 5-watt CW transceiver with built-in keyer.  (An EXCELLENT rig, no longer available as of December 2008.)
•  RockMite 40 and RockMite 20:  40-meters, or, 20-meters; CW; 400 milliwatts -- less than1/2 watt; fits into an Altoids box.
•  The FreqMite, a PIC-based frequency counter and readout from Small Wonder Labs.

  ---

UPDATE: 

As of early 2014, I use two rigs interchangeably:  an Elecraft K1  and a Yaesu FT-817 .  The rigs described below are either rigs I have owned and no longer own, or, rigs that I have built, no longer use regularly, but pull out from time to time and put on the air.

Over the years, I have had a number of QRP rigs, most of which I built from kits, some of which I bought on eBay or eham.net classifieds.  The following is a list of the QRP rigs I now own or have owned.

SW-80, SW-20 and SW-40 from Small Wonder Labs

Dave Benson — an amateur radio operator and radio engineer — for several years operated a home-based business, Small Wonder Labs.  He designed, tested, and sold a number of kits for low-power operation.  I purchased and built several of his SW-series rigs -- SW-80, -40, and -20 for the 80, 40 and 20-meter amateur bands respectively.  Here is a link to my page describing my experience with these very good little rigs.      

My Experience with the SW-40 for 40 Meters

I built Small Wonder rigs for 80, 40, and 20 meters.  Here I will describe only the SW-40 as the rigs are quite similar.

I ordered my SW+40 on 19 January 2010 and received it two weeks later, on 30 January.  The kit arrived in the mail at the beginning of a HUGE snowstorm.  When I went to the mailbox, the wind was blowing from the north — across the Potomac River — at 20 MPH with gusts to 30 MPH and snow was falling at the rate of an inch an hour.  I brought the kit into the house, ate lunch, then started assembling the rig.

Assembly was straightforward.  Dave includes with the kit a CD that has the latest version of the assembly instructions.  Also, you can print the instructions from his website.  I printed extra copies of the parts list and the parts placement diagram to use while building the rig.  As I placed parts on the PC board, I checked them off on the parts list and the parts placement diagram.

Total construction tie from opening the box and dumping out the parts to putting the rig on the air was six hours, including an occasional break.

I had no problems in building or tuning the rig — it worked perfectly the instant power was applied.

Here are some photos

First is a picture that I copied  from the Small Wonder Labs website showing a close-up view of the PC board.

Note the four crystals lined up from right to left down the center of the board.  Three of these form a crystal filter for the receiver that makes it quite sharp and knocks out most interference when the band is crowded.

After building, tuning, and inserting the pc board in the case, I made two contacts with the rig, one in central Tennessee and one in New Hampshire.

Here are photos of the finished SW-40 in a case provided by Small Wonder Labs.

Specs for my SW+40

Frequency coverage:  7026 – 7068 KHz.

Power output:  1.25 watts.  The rig is capable of putting out 2.5 watts and output power is adjustable from under 1 watt to 2.5 watts.  I set mine at 1.25 watts.

Tuning:  Tuning is accomplished by varying the voltage across a varactor diode.  The big knob in the photo above is attached to a 100K ohm potentiometer, which is the tuning control.

Here are more details from the SWL website:

•  Single-board transceiver, 2.8 x 4.0″ (7 x 10.1 cm)
•  Commercial-quality board, masked and silkscreened
•  True VFO: 35-40 kHz coverage
•  Superheterodyne design, with crystal filtering
•  Quiet solid-state T-R switching (QSK)
•  Output Power Adjustable- 2.5W max.

Conclusions

Although I have had the rig on the air for only a few minutes before preparing this article, I can tell that I will enjoy this rig and it likely will be my main QRP rig.  The receiver is very sharp and sensitive; the rig is small and has low power requirement; and, all-in-all it’s an excellent piece of equipment.

Important:  Frequency readout for the Small Wonder rigs

Small Wonder Labs produced a kit, the FreqMite.  This kit consists of a programmable frequency counter and an audio output that sent Morse code numbers corresponding to the frequency on which the radio was operating.  I installed the FreqMite into my Small Wonder Labs rigs and found it to be a very useful addition.  This link takes you to the bottom of this page where you will find instructions for adding the FreqMite to the SW-series QRP rigs.

Small Wonder Labs Update

In November 2013, Dave Benson shut down Small Wonder Labs.  As he explained so well on his website (which is no longer active -- Jan 2020), Dave had been designing and selling QRP rigs since 1996, then, in 2013, he decided there was more to life than putting parts in little plastic bags.  Dave's website was shut down in November 2014.

Rex Harper, W1REX, has taken over producing and selling a version of the Small Wonder Labs Rockmite, which Rex calls the Rockmite ][ -- it's on his website at QPRme.com.  Here is a link to his Rockmite][  page.  Rex has a lot of other QRP rigs, accessories, and parts available on QRPme.com.  Rex is NOT producing the SW-80, -40, -30, -20 rigs -- only the Rockmite ][.

S&S Engineering QRP Rigs

Previously, I owned three QRP rigs that I built from kits manufactured by S&S Engineering.  I don't know the history or current situation of S&S; I encountered them at a hamfest in the Washington, DC, area in the mid-1990's and, over the course of a year, I bought and built two of their rigs:  ARK-4 40-meter CW tranceiver (5-watts), and, TAC-1 80-meter CW transceiver (4-watts).  In May 2010 I purchased an S&S Engineering TAC-1 for 40-meters on eBay.

After a few months I realized I was not using these rigs, so, I sold two of them on eBay and kept the ARK-4 that I purchased and built back in the 1980's.  I use it very rarely.

The company still has a website but their products are no longer available.  The kits produced by S&S Engineering are EXCELLENT pieces of equipment.  The guy who designed these rigs is an engineer who designed military and commercial communications equipment and his kits are made to the same quality as military and commercial equipment -- solid, top-quality components, very stable and reliable designs.  It's a real shame that these kits are no longer available.

S&S Engineering TAC-1

I had two of these, one for 80-meters, one for 40 meters -- sold them on eBay.  I built the 80-meter rig from a kit in 1994 and purchased the 40-meter rig on eBay in May 2010.

•  40-meters, synthesized; tuned by the TUNE knob in the top right corner.  Turn the knob to tune up/down in 1 KHz steps -- push the knob in and the tuning switches to 100 Hz steps -- push again to return to 1 KHz steps.
•  7.000 - 7.199 MHz
•  4 watts output
•  Built-in keyer with adjustable speed and weight.  The keyer defaults to 12 WPM.  When the rig is turned on, the LCD display shows the keyer speed -- 12 WPM -- then shows the frequency.  On the rear of the rig is a small push button -- push the button and the LCD display shows keyer speed -- turn the TUNE knob to increase/decrease keying speed -- push the button again to adjust keyer weight -- push again to return to frequency display.
•  Very sensitive and selective receiver
•  Very good keying characteristics.
•  The 80-meter TAC-1 is identical to the 40-meter version except for frequency coverage;  3500 - 3750 KHz.

S&S Engineering ARK-4

Here's a picture of the rig.  I still have this rig and put it on the air from time to time.

 

•  40-meters, synthesized; tuned by the push-buttons on the left.
•  7.000 - 7.199 MHz
•  5 watts output
•  Built-in keyer
•  Very sensitive and selective receiver
•  Very good keying characteristics.
•  The pushbutton tuning is a bit cumbersome -- notice the frequency indicator, it's now reading 7.041 -- reading left to right:
  •   The 7 MHz is fixed.
  •   Next is a slide switch that selects one of two 100 KHz band segments -- 7.000 to 7.099 or 7.100 to 7.199.
  •   Next are two pushbutton switches -- pushbuttons are located above and below the numbers.  These select the 10 KHz and 1 KHz -- pushing the button above the number decreases the frequency, the bottom button increases the frequency.
  •   The knob to the right of the pushbuttons is fine tuning and tunes between the 1 KHz points.

I purchased this kit from S&S Engineering in 1994 or '95. 

S&S Engineering ARK-20

I no longer have this rig -- sold it on eBay

• 20-meters, synthesized; tuned by the push-buttons on the upper right.
•  14.000 - 14.500 MHz
•  3-4 watts output
•  The kit had a built-in keyer option but this rig does not have the keyer
•  Very sensitive and selective receiver
•  Very good keying characteristics.
•  The pushbutton tuning is a bit cumbersome.  There are four pushbutton BCD switches.
  •   The 14 MHz is fixed.
  •   There are four digits, each with one button above and one button below the digit.  Pushing the button above the digit increases the frequency, the lower button decreases the frequency.
  •   Tuning step is 100 Hz.
  •   For example, if the digits read 1251, the, the frequency is 14.1251 MHz
  •     The RIT knob in the bottom right corner tunes the receiver between the 100 Hz points.

From time to time S&S Engineering rigs show up for sale on eBay or in the eHam.net website classified ads.  The ARK-4 and ARK-20 sell for $150 - $200 and the TAC-40 and TAC-80 sell for $175 and up, usually around $225.

The Rock-Mite 40 and 20

This rig is produced by Small Wonder Labs located in New Hampshire.  Dave Benson, K1SWL, operates SWL where he produces kits for various pieces of equipment.  Dave's equipment is miniature, high-quality, and well-designed.  One of his most popular items is the Rock-Mite Transceiver -- a tiny transmitter and receiver (transceiver).  The Rock-Mite puts out less than 1/2 of a watt -- about the power to light a flashlight bulb.  The RM operates on only two frequencies but comes in different models for different amateur bands; it transmits CW (Morse code) only.  The RM includes an electronic keyer.

I have built three Rock-Mite rigs; from time to time I use one of them on the air.. 

• Two are for the 40-meter amateur band (7.000 - 7.300 MHz).  One operates on 7030 KHz and the other is on 7040, plus or minus a bit. 
•  The third RockMite is for 20 meters (14.000 - 14.350 MHz); this one is on 14.030 MHz.

These rigs are VERY small -- in fact, the rig was designed to fit in an Altoids box -- here are some photos of my Rock-Mite in an Altoids box.

On the left end of the box are, top to bottom:  Power input (requires 9-12 volts, DC); jack for the paddle that operates the keyer; and, jack for headphones.  On the right end of the box, top to bottom:  antenna connector; button switch that when pressed does several things -- changes frequency, switches between paddle or straight key, or, changes speed of the internal keyer.  The RockMite keyer chip does not have memory -- that is, you cannot load CW messages into the keyer as is common with electronic keyers.  There are a couple of places who sell replacements for the keyer chip that have message memories.

(Left) Rock-Mite with the lid not quite closed                          (Right) End view of the Rock-Mite

Because the Rock-Mite runs such a tiny amount of power, making contacts with it is a challenge because it's signal is usually so weak that it is swamped by higher-powered stations.  My experience varies -- sometimes I call and call and never get an answer and there have been times when I have called and was answered right away.  Still, operation with this low power takes a lot of patience.

Here are some Rock-Mite resources I have found helpful:

•  The Rock-Mite Files -- somewhat dated but lots of good info.

• Building the RockMite.

• Here's another Rock-Mite.

• And another RockMite.

•  A very nice box in which to mount the Rock-Mite if you don't want to use an Altoids tin.

•  And here's a keyer paddle just the right size for the Rock-Mite -- built like a tank.  if you get this paddle, you should look at the base -- the paddle is fine without the base but the base makes it really stable.  Here's a photo of the miniature paddle mounted on the accessory weighted base:

Small Wonder Labs and Rockmite Update

In November 2013, Dave Benson shut down Small Wonder Labs.  As he explained so well on his website, Dave had been designing and selling QRP rigs since 1996, then, in 2013, he decided there was more to life than putting parts in little plastic bags.  Dave's website was shut down in November 2014.

Rex Harper, W1REX, has taken over producing and selling a version of the Small Wonder Labs Rockmite, which Rex calls the Rockmite ][ -- it's on his website at QPRme.com.  Here is a link to his Rockmite][  page.  Rex has a lot of other QRP rigs, accessories, and parts available on QRPme.com.  Rex is NOT producing the SW-80, -40, -30, -20 rigs -- only the Rockmite ][.

FreqMite by Small Wonder Labs

One of the problems with very small radios is the frequency readout.  It's important to know what frequency you are operating on.  However, a dial mechanism that is big enough to display the operating frequency adds a lot of size to a rig and, if your goal is to make the rig as small as possible, a frequency display can be a problem.  Also, if you try to use a frequency display with LED or liquid crystals for a digital display, these types of displays consume a LOT of power, defeating the goal of keeping the rig small so it can operate on battery power.

PIC-based Frequency Counter

Enter the PIC-based frequency counter with Morse code readout. A PIC is a "Programmable Interface Controller."  Basically, a PIC is a tiny computer on an integrated circuit.  Here's a photo of a PIC that I snipped from somewhere on the Internet.

The programming instruction set for PIC's is limited but powerful.  These devices are in everything -- bread machines, microwave oven, vehicles, TV sets, DVD players -- you name it.

A PIC-based frequency counter is used in a circuit that takes a small bit of signal from the rig to which it is attached.  The signal is, or is converted to, digital data equal to the frequency to which the rig is tuned. The PIC is programmed to read that digital data then convert it to Morse code and send the Morse code to an attached speaker or headphone, or to inject the Morse code into the audio circuit of the rig to which is is attached.

The FreqMite -- A PIC-based Frequency Counter

The answer is simple.  Dave Benson of Small Wonder Labs -- who makes the RockMite and the SW+ CW transceivers -- makes a PIC-based frequency counter that he calls the FreqMite.  Here's a description from Dave's website:

QUOTE

The 'FREQ-Mite' is a PIC-based Morse frequency counter measuring only 1.25" x 1.75" x 0.45" (H) and is capable of operation to more than 30 Mhz. To get this compact size, frequency readout is in audio (Morse code) form .

When used in 'transceiver' mode, it outputs three Morse digits corresponding to frequency (hundreds/ tens/ units Khz). The FREQ-Mite is shorting-jumper programmable to any offset (0-999) and may be run in either normal or inverted (high IF) readout. It can also be configured as a general-purpose counter, and in this mode outputs 4 or 5 digits up to a maximum of 32.767 Mhz. The RF input is high-impedance and requires a minimum of less than 200 mV p-p up to 10 Mhz and under 600 mV p-p at 30+ Mhz. Accuracy is +/- 1.5 Khz to 25 Mhz and +/- 2 Khz at the high end. It's activated by pressing a pushbutton switch, and enters 'SLEEP' mode when not in use to preclude receiver interference.

The default speed readout on the FREQ-Mite is 13 WPM, but a fast (26 WPM) mode may be selected upon power-up. The output is an 800 Hz tone; this signal is tri-stated off when not in use to minimize 'thump'. The output is capable of driving an "external-drive" type Piezo annunciator or speaker/headphones directly at modest audio levels. It really shines, though,when installed into a QRP transceiver to augment whatever dial-marking scheme you've been living with until now.

The FREQ-Mite uses a high-quality double-sided PC board, which is solder-masked on both sides and silkscreened. The kit provides all on-board parts, interconnect wire, mounting hardware and a comprehensive 6-page set of instructions.
 

END QUOTE

So -- the FreqMite is a tiny PC board frequency counter that attaches to any rig.  The FreqMite (FM) taps a small RF signal from the rig's VFO, reads the frequency, applies an offset equal to the IF frequency ( if needed ), and sends the frequency in a three-digit Morse code signal that can be attached to the rig's audio line so you hear the operating frequency sent in Morse.

For example, if I am on 7.039, when I press the button that activates the FreqMite , I hear in the headphones Morse code "0 3 9."

I built a FreqMite and installed in into my second Rockless QRP rig.  Here is a photo.

This FreqMite is completed.  The wires hanging off the PC board are the interconnections to the rig -- power, ground, RF input to the FreqMite, audio output to the rig, switch to activate the FreqMite.  About the switch -- it is a momentary contact, normally open pushbutton switch.  Push the switch momentarily and it causes the FM to read the rig's frequency and send the frequency in Morse.

Here's a picture that is more in focus -- I stole this photo from the SWL website.

Configuring the FreqMite to work with the Small Wonder Labs SW-series transceivers

 Here is a hook-up diagram photograph.  Look at the bottom right of the photo, between ACTIVATION SWITCH and GND -- the double row of pins sticking up is J1 -- these are the jumpers that are used to configure the FreqMite to read the frequency of your rig.  The kit comes with ten jumpers that are inserted over sets of these pins as described in the setup instructions that come with the FreqMite.  Read further to see how to configure the jumpers for the SW-40 and SW-80.

I have installed a FreqMite in my SW-40 and SW-80 QRP CW transceivers.  Here is how I did it.

Setting the jumpers:  The FreqMite J1 has ten sets of jumpers used to configure the FreqMite to measure the rig's operating frequency.  I have installed a FreqMite in only the SW-40 (40 meters) and the SW-80 (80 meters)

SW-40:  DO NOT INSTALL ANY JUMPERS ON J1.

SW-80:

Number	Jumper - ?
1	Yes
2	Yes
3	Yes
4	Yes
5	Yes
6	No
7	No
8	Yes
9	No
10	No

When you power up the SW rig with the FreqMite installed, the FreqMite sends three CW messages -- this is how to respond to those messages.

Where can you buy the FreqMite kit?

For several years, the FreqMite was produced by Small Wonder Labs, owned and operated by Dave Benson,

In November 2013, Dave Benson shut down Small Wonder Labs. 

Four States QRP Group has picked up production of the FreqMite.  Their website has ordering information as well as links to photos, construction and operating manual, and the like.