The Two-fer, with an output filter upgrade

Improved output filtering in the classic Two-fer QRP transmitter, designed by a QRP Amateur Radio Club International team led by John Collins, KN1H, in 1986, can be achieved through the use of a Cauer / elliptical stage in the Chebyshev output filter. Chuck Carpenter, W5USJ, of Point, TX, who conducted the harmonic attenuation studies, recommends adding a 118pF capacitor across L5, greatly improving harmonic attenuation and bringing the rig into new FCC specification guidelines. (A 120pF silver mica capactior is acceptable.) Full details appear in the QRP column in the September 2006 edition of WorldRadio magazine.

To create an enlarged image of this graphic:
+ RIGHT CLICK on the image
+ Select SAVE TARGET AS. . .
+ Save the file to your desktop
+ Open the JPEG file from your desktop for a larger version of the graphic

If you are building the Two-fer using Manhattan-style construction, be sure to add 118pF or 120pF capacitance across the pads where L5 is mounted in the color template featured below.