31 December 2020

20m magloop update

Considering the success with a magnetic loop for 20 metres, now I wanted to be able to use a bit more power than 2.5W (at 5W it heated the RG-58 coaxial capacitor, at 10W the tip produced sparks).

I got a thicker coaxial cable that serves both as main loop and coaxial capacitor stub. That's about RG-213 size, with 3 mm solid copper inner conductor: the main loop is stronger, but the stub gets more on the way. Also soldering the whole thing together was not easy, let alone cutting the capacitor to the right length!

The current upgrade is shown in the picture at the right. The loop is slightly longer than Spring 2020 edition, while I have not modified the small coupling loop: this results in SWR of 3:1 at resonance point. Still, reports on the reversebeacon.net are a bit better than with the previous version.

First task for 2021 will be to fix the coupling loop to get a match as close a possible to 1:1. And do have some CQ QSOs!

29 December 2020

FNIRSI DC-6006L Power Supply and a bug

During "Black Friday|Week" 2020 I bought the DC power adapter FNIRSI DC-6006L. I would not call it a "power supply" since it requires an AC-DC adapter (like an old laptop PSU). Provided there is enough "juice" provided by the external PSU, the DC-6006L is capable of 0.1-60V output up to 6A: that's 360W in a aluminum case lighter than a smartphone and smaller than a sandwich! You can find a good description of the product (in decent English language) on their website or on the usual Far East sources that sell it.

Check out the size comparison with the Nissei SPS-250A:

FNIRSI DC-6006L vs Nissei SPS-250A.

First things first. The Fnirsi unit is not very RF silent, so it will increase the background noise if used to power an HF receiver. But it works OK as a lab power adapter.

I have found one dangerous bug. When DC is applied to the input of the DC-6006L, there appears voltage on the output even though it is configured to start in OFF position at "cold boot". It might last 100-200 milliseconds, enough to burn whatever is connected on the output! Looking at the output on the oscilloscope, the voltage reaches 6-7V regardless of the output voltage set. I did this test both with 19Vdc input on the barrel jack and with 14Vdc input on banana sockets. I have an analogue oscilloscope so I cannot do proper measurement of amplitude and duration. Just consider that an Arduino based circuit springs to life. This happens before the boot screen appears on the DC-6006L display.

On annoying thing is that the beep cannot be disabled via software. While it is useful when over-voltage/current protection triggers, you might not want to hear it for each key press or knob rotation. And it is quite loud too.

I tried serial communication without the FNIRSI software, but all I get is a string that changes in sync with operator's actions through the front panel controls.

I have drawn 45W on a resistive load without ill effects.

I paid about 30€ and it is worth it, especially if you already have a fixed DC source.

27 December 2020

Eight TIL308 displays in a clock

I would not say that the long lockdown and alike has allowed me to reach the bottom of the to-do bucket, but it slowed down the consumption of projects in the waiting list.

When I spend the whole work-day at the computer, writing firmware in the remaining hours is not so pleasant. In the Xmas break I finished the code for the clock that uses eight Texas Instruments TIL308 vintage LED+logic displays.

Final firmware onboard! I can solder the remaining capacitors to complete symmetry.

Hardware design files and software source code have released to github.

This clock is self-standing if the RTC module is inserted perpendicular to the display board. Adjustments are accomplished through a linear potentiometer and a push-button. With a software trick ;) the same analog input is used both for reading the light-dependent resistor to adjust display luminosity and the push-button. I had to adjust resistor values and add a couple of them outboard.

I like these clocks to do something unexpected, so every 60" it might display a word built using available letters (or lookalike) and numbers:

// Available letters are:   ABCEFIOSG-
// Mapped to these symbols: A8CEF1059B  (mind the mix of letters and numbers!)
// Plus space ("D") and all the numbers are at your disposal!

TIL308 is not a full hexadecimal display because it maps "B" to "dash" and "D" to whitespace. This reduces the possibilities of long words and exercises your fantasy a bit further to find meaningful text to display randomly. Don't forget you can use multiple languages for your words!

A nice addition would be to be able to add words at runtime (and store them in EEPROM), rather than at compile time. That means more firmware to write ...