With my CW Messenger project complete, I can loop back to my S-Pixie project again and begin testing its transmitter. I’ll use the CW Messenger to help with testing until I become proficient in CW. I’ll start with some simple calling CQ tests of the PCB build, mostly because I’m curious to see what this …
S-Pixie: Audio Amplifier
The S-Pixie uses uses an LM386 as its audio amplifier (TI datasheet, note that I could not determine the manufacturer of the chip included in my kits). The design closely follows the design shown in Figure 12 of the datasheet. The 10 uF capacitor between pins 1 and 8 (shown as the two GAIN pins …
S-Pixie: Receiver Mixer Analysis and Testing
In the S-Pixie, the portion of the circuit including Q2 (8050 datasheet) serves dual purposes. It’s a mixer when receiving and a power amplifier when transmitting. Here is the relevant portion of the mixer circuit. When transmitting, the 10k resistor is shorted out by the CW key (not shown in the schematic above), biasing the …
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S-Pixie: Local Oscillator Redesign
Note that while this local oscillator redesign produces a better sinusoidal output it didn’t produce better audio output from the S-Pixie. This is because the mixer loads the local oscillator circuit, producing a signal very similar to the original design. I found that coupling the local oscillator and mixer with a 100 pF capacitor instead …
S-Pixie: Local Oscillator Analysis
If you’d like to join the discussion of the S-Pixie local oscillator check out Ham Radio Homebrew Projects on reddit. The S-Pixie uses a Colpitts crystal oscillator. I found a great video by Craig (devttys0 on YouTube) that explains how it works and discusses design considerations. Local Oscillator Analysis I’ve been having fun following along with Craig’s …
S-Pixie: Pi Filter Analysis
I bought a couple of Super Pixie Transceivers when I was studying for my Technician license but only got around to playing with them now. The S-Pixie is a low power, CW transceiver that operates in the 40 meter band at a fixed frequency of 7.023 MHz. The design for the radio has evolved over …