I always admire the versatility of digital chips and use them in many analog designs as well. My curiosity for their implementation in analog circuits threads back to mid nineties, following an article in QEX magazine. Later I used them in many designs and their inexpensiveness and outstanding performance impressed me to the added advantage of compact designs. this resulted in many successful designs including "DIGIRIG" and "NANO" transceivers. After publication of "DIGIRIG" (SPRAT 84 Page 10), late Bill Currie VK3AWC wrote me mentioning that he actually liked this kind of H.F. designs and he was doing similar sort of experiments.Later, between 1992 and 1999 we worked on many similar designs including receivers, multi-band mixer type VFOs and even weaver's exciter. This inexpensive diminutive multi-mode, dual band (80/40M) rig is designed on the similar lines, and is aimed for the novice amateurs. The schematic diagram shows the transmitter side of the transceiver.
As I already mentioned in one of my previous post that QRP is synonymous with simplicity and minimalism, the present design illustrates it very well. The audio from the electret mic is amplified by a simple single stage amplifier wired around BC548B. This is coupled to a differential AF amplifier wired around a pair of LM 386N, via an audio transformer having 1K:1K+1K impedance taps. This sort of coupling transformer isn't difficult to find and even digikey stocks it.
A 74HC4053 functions as a mixer. I used it as it is very cheap, easier to find and requires fewer peripheral components. S1, a double pole three way rotary switch acts as a mode switch that chooses the desired mode of operation. The output of the mixer is amplified by a single IRF530 and is fed to the antenna through an LPF. Too simple to say anything about. Do you still feel the need to burn your bucks to get yourself on the air! In my next post I will discuss the RX and VFO units of this ultra simple project.