This article is broken into two parts. First comes the “Oscar” preselector/preamplifier. As I said, I intended it to be either part of the overall receiver or used as a standalone where desired. The second part deals with the WBR upgrades. Both designs were built using the same techniques and I’ve tested both and found that—especially in concert—they do about as well as some of my boat anchors! So if your soldering iron is ready, I’ll start by describing “Oscar.”
However, what you might notice is the presence of image products in the waterfall. The processing of the signal suppresses all but the very strongest of these so they don’t appear as audio but it is mighty confusing when they are on the waterfall but actually not there (if you see what I mean)!
I am in the process of building a QSD or Tayloe Detector, which should provide better rejection of images. I have breadboarded one of these, it works but not very well. I think that this might be due to the length of leads I have on the breadboard so I am trying to use Eagle CAD to design a circuit board to overcome these problems.
Vasily Ivanenko has written an article detailing his AF dummy load project:
I’ll describe a simple 8, or 4 Ω dummy load to test your home brew guitar power amplifiers.
Low cost 16 Ω / 25W wire wound, aluminum shell, chassis mount resistors seem abundant. I got mine on eBay. Wire wound resistors vary in quality, design and tolerance. Some even exhibit low inductance by winding with an Ayrton-Perry bifilar technique. Resistor tolerances range from 10% down to ± 0.5 % + 0.05 Ω. Typical manufacturer power ratings are done at 25C, however, these devices are meant to sit on a heat sink when used and that’s why the aluminum housing contains 2 relatively large mounting holes.
In the first installment of this series, we discussed why we’re building a Direct Conversion receiver and talked about some basic ideas. In this installment, we explore what it takes to make the leap from a printed schematic to something physical that works. Follow along!
The implementation is simple genius. It’s a browser that starts up full screen (kiosk mode) and just sits there and updates occasionally. DakBoard provides the private webpage and tools to make that happen. You can certainly build this yourself with any number of open source tools. I chose DakBoard because it was simple, beautiful, and I was able to get the whole thing done in less than an hour. I’m sure I’ll spend many hours tweaking it through. There’s also the very popular MagicMIrror platform, so lots of choice and power in this space!
The main impetus for this was to have a homebrew controller that actually featured an analog joystick, since there were few if any guides elaborating how to fashion one from an existing controller. I acquired a couple Parallax 2-axis joysticks with breadboard mounting capability to do the trick.
The Vectrex comes with a game in its ROM — Asteroids — thus you can play without needing a cartridge. However, with the traditional controller, this requires lots of button-mashing since it has no auto-fire feature. Using a 555 timer, potentiometer, and clever values within an RC circuit, I have given it the ability to auto-fire.
Several years ago, National Semiconductor came out with some very high performance, easy to use audio power amplifier ICs. I was in need of an extra amplifier so I could biamp some of my home-built electrostatic loudspeakers so I tried the LM3886 chip.
This part was chosen because of the ease of use, power output, turn-on and off thump suppression, low distortion, and built-in protection against shorts and thermal runaway. There isn’t much more to ask of a power amp than that. When driving electrostatic speakers, you can’t have too much protection!
The Pocket High Voltage Generator that I made a few weeks ago proved to be a very handy tool. I have been testing Zener diodes very often since I use many Zeners in 12V to 91V range.
However I wanted to give it a bit more power so that I can test Nixie tubes clearly – the previous design can only give less than 0.5 mA through most Nixie tubes, some digits don’t lit up completely.
I made some upgrades to the components to give it a modest 2 – 5 mA (depending on the voltage) output. While still keeping the same form factor.
After completing my VGA Generator project a while back, I’ve embarked on a new electronics project: building a simple 6502-based homebrew 8-bit computer on a breadboard. There are a bunch of similar projects online from which to draw ideas. Some projects set constraints such as only using contemporary parts of the 8-bit era, no FPGAs, no microcontrollers etc. In my case, I opted instead to keep the constraints minimal and the project simple.
What are you thinking — I am not trying to break any world record? My XYL asked me that question today — why are you building another rig? Followed up by a snide comment that I had so many rigs now why do I need another one. Well the answer plain and simple because I can!
For the longest time in the late 60’s early 70’s my success rate with homebrew SSB transceivers was miserable. At that time I lacked the more sophisticated test gear and let’s face it some of the technology wasn’t that great. Crappy Analog VFO’s were high on the list of impediments! I also had to work and to give a fair share of my time to the family — it is that balance thing.
But today that is all changed –better test gear, better technology like Digital VFO’s and a bit more time. The latest project is to demonstrate that some of the components out of boat anchors can indeed be reworked to provide a very modern, very capable rig.