Trevor continued the KiCad layout, adding a simple power supply and RF bandpass filter.

The power supply uses two 9v batteries to generate about 15-18v input but another battery source (such as a rechargeable LiPo pack) could easily be substituted provided it supplies at least 12v. The K7805-500R3-LB is a high efficiency switching regulator that is a drop in replacement for the 7805 linear regulator. Since this is a battery operated device, conversion efficiency will prolong battery life and these regulators, although switching, are pretty clean and low noise and should not have a major effect on radio function. One of the transceiver parts most sensitive to power supply noise is the oscillator for traditional analog oscillators (Hartly, Colpitts, etc). The Si53451 is designed to be a digital clock synthesizer and uses a PLL so it is much more immune to supply noise. Amplifiers from transistors are also sensitive to noise but the MMIC amplifier used in this design is also quite resistant to noise. In addition to the 7805, there is an equivalent 12v converter, the K7812-500R3-LB used to generate a rail for the final power amplifier. When this is designed it may end up accepting a wide range of voltages and the second regulator might not be necessary but I've included it for now.

The band pass filter was designed with the help of Micro-Cap 12, a Windows circuit simulator that used to be a commercial product but was released as freeware some time ago. There are many filter design options including a number of websites, QUCS, and Lt-Spice. I'm familiar with Micro-Cap and it is a very powerful simulation tool with built-in filter generation. Selection Design->Passive Filter Design presents a dialog box with a number of options. I tried a number of these and settled on a Butterworth filter with the following properties.

• Center frequency: 14.25 MHz
• A 200 kHz bandwidth (3 dB)
• About 3 dB passband ripple
• A 1 MHz stopband (30 dB)

This was a fairly simple design only requiring a few components while still adequately attenuating out of band signals. A couple of standard, surface mount inductors provide two components but the higher inductance of the series inductor requires a hand wound inductor. A dual aperture ferrite core (BN-43-202) has good performance in the 20m band and only requires 6 turns of wire.