This preserves the Reddit T41-EP community Wiki. It is mostly focused on the 4SQRP T41 kit and isn’t being updated. I doubt the Reddit page will disappear, but who knows how Reddit will treat low activity communities as they seek to increase profits. T41-EP Wiki My goal for this Wiki is to consolidate the available …
Back From Reddit
Since my last post, I’ve been writing about my ham radio related activities in two Reddit communities, r/HamRadioHomebrew and r/T41-EP. They have mostly served as my blog over the past several years. I like the less formal nature of the post/comment format compared to what I had been posting here. The ability for spam free …
S-Pixie: PCB Build Transmitter Testing
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 …
CW Messenger: Protoboard Build Start to Finish
This is a compilation of posts I made on the r/HamRadioHomebrew Reddit community documenting my build of the CW Messenger. I’ve expanded on those post where appropriate to provide more detail on the build. It’s Like a Puzzle I started the CW Messenger build by imagining the final protoboard with all of the components on …
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CW Messenger: Prototype Testing
I built part of the CW Messenger on breadboard to further test the CW Messenger software. Here is a video of it “sending” message #1 (note that I haven’t modified the author’s original stored messages yet). Notice anything in the video? The software is working as expected, but the buzzer is only clicking. That’s strange! …
CW Messenger: A New Project
I came across a book, Microcontroller Projects for Amateur Radio, that has a number of interesting projects that may interest some of you. Chapter 10 covers a CW memory keyer (one down from the top on the left). I decided to put testing of the S-Pixie transmitter on hold to start this project. It should help …
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 …