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RE: Reflow Micro Table: Compact USB PD Reflow Table with Browser Control

DAB — Sat, 11 Apr 2026 19:35:45 GMT

Great project.

RE: Simple DCR (Direct Conversion Receiver) – Part 2: Common Emitter Amplifier

michaelkellett — Fri, 27 Mar 2026 16:13:31 GMT

That's a really weird pre-amp.

R16 - R19 set up the DC biasing of Q5 with 3.3 mA of collector current.

The AC impedance at the emitter is the impedance of C13//R19, the LF breakpoint is at 0.72Hz - why !!!!!!

At higher frequencies the emitter load impedance tends to zero.

The AC impedance at the collector is more complex at low frequencies 1k//(180R + ZC12).

The LF breakpoint is 19Hz.

The input impedance will be very low (because Q5 emitter is effectively grounded for AC).

The actual gain will depend on the emitter resistance of Q5 .

Since the intention is to drive about 100mV into a 1k load a lower Q5 collector current would be fine.

I tried this (in simulation)

It has good PSU rejection (18dB worst case at 30 Hz and 90dB at 100kHz.

About 2mA current drain.

Much smaller capacitors.

It's not the best way to use two transistors but not bad. It still uses the first transistor open loop so the gain at 1kHz is lower that you would expect from the ratio of R3 to R4 because of emitter resistance.

It manages 28.7 dB of gain (you would expect 33.4) and can drive 1V pk-pk into the 1K load.

RE: Simple DCR (Direct Conversion Receiver) – Part 2: Common Emitter Amplifier

DAB — Tue, 24 Mar 2026 19:40:26 GMT

Very good post.

Excellent walk through the circuit and the changes you made.

Well done.

RE: Simple DCR (Direct Conversion Receiver) – Part 2: Common Emitter Amplifier

jc2048 — Tue, 24 Mar 2026 13:11:03 GMT

Good fun.

This is for SSB and morse?

I'm not much of a transistor circuit designer, but I've noticed that one thing they sometimes used to do in the old days was to flip the polarity of stages. As you've got it, the transistor Q3 develops its output through R10 (ie relative to the rail), but the input to Q4 is relative to GND (the BE junction). If you flip the entire 2nd stage, so that Q3 becomes PNP, then the output will be relative to GND and that then isolates somewhat from the supply noise. The input to that flipped second stage is then relative to the power rail and can come from the pot going to the rail rather than ground, which matches what the output of the first stage is doing anyway. The input of the first stage remains relative to ground, which suits the mixer output. The only potentially poor PSRR is then the output stage, but I think that one works ok because of the transformer coupling to the loudspeaker. You'd have to be careful around the pot, but you need to take care there anyway with so much gain following it and a middling impedance.

Whilst it might improve the situation, you'd probably still need to work on the power side of things.

Another approach is to transformer-couple between all the stages (which is essentially how it works going through an IF strip).

RE: A 4-zone universal transmitter node for open-drain sensors (Proof of Concept)

DAB — Sat, 21 Mar 2026 20:42:19 GMT

Interesting post.

Most of the questions you pose do not have simple answers.

In circuit design, decisions are usually based on the needs of the end product requirements.

RE: Simple DCR: Assembling a 7 MHz (40m) Direct Conversion Radio Receiver – Part 1

shabaz — Fri, 13 Mar 2026 02:49:39 GMT

I took another look at the construction, and realized that for the transistor biasing, I had set R12 to 56k, and R13 to 10k (I don’t know why; I have forgotten, since I soldered those resistors almost a year ago!). This resulted in very little current through the transistor, just a few milliamps, which is great for battery life, but not so great for generating more output.

I’ve experimented a bit, and now replaced with R12 = 18k, and R13 = 8.2k, and that results in a value closer to about 15 mA. Now with a 64 ohm load, I can drive the input to about 40 mV p-p, and see 1.35 V p-p output.
However, with an 8 ohm load, I can drive the input higher, to about 80 mV p-p, and see about 830 mV p-p output (these values are with a 1 kHz signal). Even at 100 mV p-p input, the distortion would be tolerable.

So, the conclusion now is, that the 8 ohm speaker would be better – the amplifier stage can be driven with more input, and the power output should be higher. I didn’t have an 8-ohm speaker to listen to it, but I’m going to go with those resistor values, and use an 8-ohm speaker speaker.

For anyone curious about the transformer, it has about 89 ohm DC resistance at the primary, and 3.3 ohm on the secondary. I put some impedance measurements in the table below, but I’m not sure how useful they are, I don’t think there’s much value trying to improve this circuit much further, since it is based on an AliExpress transformer which could be very different when ordered a year later that the one I measured.

RE: Simple DCR: Assembling a 7 MHz (40m) Direct Conversion Radio Receiver – Part 1

DAB — Thu, 12 Mar 2026 19:15:52 GMT

Nice post.

I never got into the amateur radio hobby, but I did have a 2nd Class FCC license that would allow me to work with commercial grade devices.

I never used it, but it did get me an A for my radio communications course.

RE: Simple DCR: Assembling a 7 MHz (40m) Direct Conversion Radio Receiver – Part 1

michaelkellett — Thu, 12 Mar 2026 11:06:04 GMT

This article:

https://www.vintage-radio.com/repair-restore-information/transistor_output-stages1.html

suggests that you are getting about what you might expect from a low bias current single transformer power amplifier.

Time to go fully complementary capacitor coupled I think !

RE: Simple DCR: Assembling a 7 MHz (40m) Direct Conversion Radio Receiver – Part 1

BigG — Thu, 12 Mar 2026 10:46:48 GMT

Wow, yet another excellent post. Not to nit pick, but it should really be saying "this is a popular licensed band for amateur radio enthusiasts."

RE: EoRa-S3-900TB with FreeRTOS — LoRa Camera Control System --Avg 174 µA

AB9NQ-William — Tue, 03 Mar 2026 10:39:23 GMT

Before moving to the apartment; there was a wetland pond behind our backyard; we had a Wyse Cam 3 mounted above our shed. Camera had to be powered by a 10,000 mAH power bank; barely would get ~24 hours of continuous use before swapping out the power bank. What I needed was a way to only power the camera only when there is a web request from my domain hosted, web site videofeed link. Clicking Observations II link brings the viewer back to the main menu.

Project uses a LoRa transmitter on mains power and a battery, powered LoRa receiver. Lora transmitter receives web request. sends Lora preamble and payload. Wake on radio, preamble wakes deep sleeping Ebyte, EoRa-S3-900TB (ESP32S3 with LoRa SX1262 on dev board), turns on power bank, sets EXT0 wakeup by timer for viewing live Wyse Cam 3 viewing “videofeed”, calls radio.sleep() to power down LoRa radio, receiver goes to sleep until wake up timer expires. Receiver wakes, inits the LoRa radio bringing LoRa radio out of radio.sleep(); which has no transmit and no listening, LoRa radio is put back into autoDutyCycle (no parameters) to listen for the next web request.

AutoDutyCycle is responsible for the ~174 µA resulting average current reading. When listening for 9 ms, it consumes 11 mA. Current consumed between the “spikes” is ~17 to ~18 µA during radio.sleep()!

Nordic Power Profiler Kit II Observations

NPPK II_Battery Life Analysis

I did this project for the open-source community; in five days on Github; has already been cloned 376 times!

William,

RE: Easy Xmas Gift: Simple LED Name Signs or Night-Lights

DAB — Tue, 09 Dec 2025 20:13:26 GMT

Neat project.

RE: Easy Xmas Gift: Simple LED Name Signs or Night-Lights

genebren — Tue, 09 Dec 2025 14:53:39 GMT

Very nice! My granddaughter has asked for some LED lighting creation for her room. We are going to do some planning over the weekend. I will have to share this as a possible part of her design. Well done!

RE: Easy Xmas Gift: Simple LED Name Signs or Night-Lights

robogary — Tue, 09 Dec 2025 14:26:10 GMT

Amazing how some simple designs can be ingenious.

RE: Easy Xmas Gift: Simple LED Name Signs or Night-Lights

colporteur — Tue, 09 Dec 2025 13:41:31 GMT

What did it take you for time?

RE: Easy Xmas Gift: Simple LED Name Signs or Night-Lights

e14phil — Mon, 08 Dec 2025 14:50:59 GMT

Thats cool. I love those noodles