The W7JI QRP-40
5 Watt Crystal Controlled QRP Transmitter
What's new and improved about this little QRP transmitter.......absolutely nothing!. If you haven't yet explored the world of QRP then you're missing one of the last challenges left in ham radio. Not only the challenge of operating at the QRP power level but also building your own equipment. In case you haven't noticed, there's not many hams buying soldering irons these days . I have always been a builder and enjoy that aspect of ham radio more than operating. The gratification of building your own equipment and using it on the air to contact others is something that must be experienced to be fully appreciated. In my opinion, QRP offers a rather broad spectrum of opportunities to someone who is ready to take on a new challenge and enjoy the numerous benefits.
If you've seen any of my recent projects you will notice that they are all housed in the same enclosure. I designed a circuit board that fit's into a PAC-TEC LH43-100 plastic box with removable front and rear panels. This enclosure is very small, measuring 3.1"x4.5"x1.2" but large enough to house many accessory type projects. It would be possible to replace the plastic panels with sheet metal panels if desired. The ease of removing the panels in order to drill them to fit the project is a major factor for consideration when planning the project. Using these boxes provides my projects with a consistent look and due to their physical size they are easily packed for traveling.
When I decided to build a QRP transmitter, my first design decision was to use through-hole technology and not SMD. I felt this would greatly improve the number of people who might actually build the transmitter. It soon became apparent that everything I wanted to incorporate into the design simply would not fit into the space available. I didn't want to increase the physical size of the transmitter so I had to choose between crystal control and VFO, automatic antenna switching, and various other features My final design is a very basic circuit consisting of a colpitts crystal oscillator using two crystals which are switch selectable, a broadband amplifier/driver and a class C Mosfet final. The output network is a standard 50 ohm low pass filter. The antenna port is switch selectable and is manually switched between transmit and receive. Yes, it is a throw back to operating in the 50's. If you forget to throw the switch when transmitting there is no danger to your receiver because the transmitter output simply operates into an open circuit and is not routed to the receiver input. Operating the transmitter into an open circuit does not damage the Mosfet final but I wouldn't hold the key down for extended periods of time. Transmitter output is very clean. Since the oscillator and driver are both keyed the keying is crisp and chirp free. I have received several compliments on the keying characteristics and overall great sound of the rig on the air. Below is the schematic of the transmitter.
From my QTH in Southeastern Kansas I have made contacts in FL, AZ, WA, TN, IL, MN, NE, IA, CA, OR & UT all with signal reports varying from 449 to 599. Most people are very surprised when they discover that I am operating QRP. I have really enjoyed building and operating this little transmitter and am very pleased with the operation of the transmitter. Below is the complete Parts List available from Mouser Electronics.
This is a photo of the completed transmitter mounted in the enclosure. Please notice that only one adjust is necessary and requires nothing more than a simple volt meter. The trim pot must be adjusted to produce 3.0 VDC on the gate of the final transistor. I recommend doing this adjust prior to installing the final transistor. I always leave the final transistor to be the last component to be installed in order to adjust the bias prior to installing the IRF510. I have built three of these transmitter and each one fired up and worked perfectly upon completion.
You will notice that the PC Board does not contain a silk screen of the component parts on the top of the board, nor does it have a solder mask on the bottom of the board since this board was to be a test board to make sure that everything worked and that no mistakes were built-into the board. If there is sufficient interest in readers wishing to build this transmitter I will take orders and produce professionally manufactured boards with silk-screen parts overlays and solder mask. I have also thought that I might produce a kit with all necessary parts to build the transmitter as shown. This would be quite an undertaking for me so it really depends on the level of interest from readers.
