Category Archives: Homebrew

CW Practice Oscillator

Mark I – Transistor Based Oscillator

Mark I protoboard and schematic
Mark I protoboard and schematic

(2015-04-03 This page has been copied to projects)

This was the first attempt at an oscillator for practicing CW. I don’t remember where I found this particular schematic but there are a ton of oscillator circuit designs available online.  Click here for a Google search that will result in a lot of options (over a half million hits!) The image results are a good place to start.

I committed to protoboarding this design because I wanted to play around with it some more. At the time I built it I was planning on getting an O-Scope but I didn’t have one yet.  Now that I have one I can revisit the circuit.

Mark I Oscillator - simple to build and only a few components. Not real stable though.
Mark I Oscillator – simple to build and only a few components. Not real stable though.

The AF (Audio Frequency) tone is unstable to say the least. It varies from 3kHz to about 200Hz . The wave form resembles a square wave, but only loosely.  It is very spiky and irregular.

While this is a simple circuit to build, uses only a few components, can be built very inexpensively, was a fun basic electronics project, and would be good as a beginners circuit / soldering project, I wouldn’t plan on using it for much more.

I would avoid it for a CW practice oscillator. If you are serious about learning CW, do it with a stable oscillator that will be pleasant to listen to. This thing can squeal at times.

Mark II – 555 IC Based Oscillator

The 555 IC oscillator is much more stable than the transistor based one
The 555 IC oscillator is much more stable than the transistor based one

As the section title above says, this oscillator is based on the 555 timer integrated circuit, a much more stable oscillator, also with few parts.

I documented the build on Flickr but the focus was more on the cabinet build and less on the electronics.

This circuit makes a good CW practice oscillator. Still a very easy build for beginners and fun. I was going for a steampunk look with the cabinet build. There are many things I think I would do differently in the cabinet build to make it easier, and smaller, but the oscillator works just fine as is.

The waveform is a pritty clean and produces a consistent 724.8 – 725.2 Hz tone. This circuit does consume more energy then the other. I put a fresh battery in the oscillator, had done a week of cw practice 20 minutes a day when life called and shelved it in May 2014. I just took it down and did some testing when the battery died.

Thing two I might change, a positive power cut off switch to completely lift the battery from the circuit. Just a thought.

Here is a short video of the cabinet and the oscillator in action with a CW key. There is no additional AF amplifier which brings up the one thing I might change. It my be a good idea to add a variable resistor on the output to adjust the volume.

BreadboardRadio Kits

Breadboard Radio KitsOn Wednesday I received some awesome mail, the kits I ordered from arrived! As I am inclined to do, I opened things up and began organizing and inventorying the contents there in. Counter to the habits of a younger Jon, I printed all of the distructions, what I tend call them, and read them all, cover-to-cover. Even before setting up the first project!

I completed the electronics of the Matchstick antenna tuner Wednesday evening. Without a receiver or transmitter I couldn’t do much with it. Yesterday I finished the electronics of the Sawdust regenerative receiver and proceeded to spend over four hours tuning up and down the 40 meter band.

There was some broadcast, not sure if it was AM bleed or SW though I am leaning towards SW, phone (voice), and some digital transmissions. I believe I heard both RTTY (Teletype) and PSK31 (ASCII keyboard-to-keyboard). No CW though. I was really hoping for some Morse Code. Lots of band noise. The solar storm this week is making for some interesting sounds.

Progress shots were taken and will be uploaded to the usual places, here, G+, and Flickr, but I wanted to get them all wrapped up nice and purdy first. Because they are kits and will be done over the weekend most likely, I figured it was worth the wait. I am going to post about each kit separately though.

When I said a kit was completed, I deviated from the distructions in one respect. They called for finishing the wood bases before the electronics so the mounting of said electronics goes directly onto a clean, freshly finished mounting. Well, I didn’t do that.

Matchstick antenna tuner kit from
Matchstick antenna tuner kit from

I wanted to finish all of the bases at the same time… and, okay, I wanted to get a radio on the air ASAP. So, yes I will finish the bases, but it will be all at once. I I am not sure with what finish I will be using so for now the kits get mounted on the raw base.

Before the kits arrived I built a simple ½  λ dipole to have something to test the radios with, and it does work, but I don’t like the feed point or the wire spools. I didn’t take any pictures because, well I’m not particularly proud of it. That may sound vane, and it is, but some hack jobs just shouldn’t have pictorial evidence.

To resolve the antenna issues and to address the bases for the the kits I think a little fabricating shop time is in order. This morning I am designing the feed point / spools and after day-job stuff I will look at finishing materials for the kits.



40 is dead, long live 40!

I had mentioned a little while ago that I was planning to work on a 40 meter receiver followed by a 40 meter transmitter. This is still the plan but there was a snag that I thought was worth mentioning, particularly for those new to Amateur Radio or to homebrew radios.

The 50 Ohm 5Watt dummy load I built last month, and most of the diagnostics tools I have been building recently for that mater, came from the book QRP Basics, second edition by Rev. George Dobbs G3RJV.  Another project in QRP Basics is the 40 meter (7-7.3 MHz) receiver I planned to build. The receiver in the book has some additional modifications to the RF (Radio Frequency) input section, an RF band filter and a modified tuner that replaces the VXO (Variable Crystal Oscillator) with a VFO (Variable Frequency Oscillator.) The VFO has a wider tuning capability, it can tune the entire band rather than 600-700kHz of the band centered on the crystal frequency in a VXO.

First go at the 40
First go at the 40

The diagram made sense, for the most part, and I could see and define the separate sections of the receiver. The challenge was my minimal knowledge of circuit diagnostics.

I got the AF (Audio Frequency) amplifier working fine. Likewise the AF input filter. It was the RF side of the equation that was giving me trouble.

It was clear that I needed to improve my skills in diagnostics so I picked up a copy of Experimental Methods in RF Design by Wes Hayward W7ZOI, Rick Campbell KK7B, and Bob Larkin W7PUA, here after referred to as EMRFD, with hopes that it would give me the information I need to better approach the radio build projects I have planned. Just 8 pages into the first chapter and it is making me think and work!

The receiver I originally planned on, and started, was from QRP Basics. A stripped down basic variation of this receiver is the first project in EMRFD starting on page 1.7. The nice thing is that this design has fewer parts, a VFO that uses a LC (an inductor capacitor network circuit) tuner that gives you the whole band, approximately 6.9MHz to 7.5MHz, best of all the complimentary transmitter is also in the first chapter.

EMRFD makes you think more about what you are doing and requires you to actually learn about each circuit segment. The first chapter outlines a very modular approach, the building blocks of the larger picture but in reverse. Start big with simple broad strokes, then narrow it to more manageable chunks, then further and further as you go. It encourages the start simple philosophy to get it working, then refine individual areas as you go.

The book goes on to give a more in-depth look at specific RF circuits, not a list of projects though, it gives you an idea as to how various RF circuits may be improved or incorporated into a design to improve the over all performance of a project. It seeks to instill an adventurous and experimental approach to RF design. Rather than a “you must” approach it is a “hay, what if” way of looking at overcoming the challenges in RF design work.

QRP Basics is a great book, and it covers homebrew radio, but more as a kit builder and operators guide rather than a circuit designers/builders guide which is what I am really looking for right now. I don’t see myself getting an electrical engineering degree, but I do need to up my game in RF circuits and basic electronics knowledge, big time.

Second go at the 40
Second go at the 40. Parts poked into an anti-stat mat grouped by receiver segment, RF to the left and AF to the right. Look at those sexy toroids!

About the title of this entry… Yesterday I completely disassembled the receiver I started two weeks ago and restocked all the parts.  The 40 is dead. Today I poured over the schematic of the EMRFD design and began picking the parts and planning the layout. Long live the 40!

While part of the goal of EMRFD is to use whatever parts you have lying around, I was going to have to make some weird choices in parallel and series multi-value/component clusters and I am not yet up to the challenge of re-designing things like LC tuning circuits so it was also shopping list time today as well. With a bit-O-luck HSC will have the variable capacitors, resistors, and jacks I need finish this project quickly.

My neatnic brain is not ready to go with “ugly” construction so my boards, at least for now, will be done on perf-board.  I know “ugly” is a perfectly acceptable prototype process, and has benefits in VHF/UHF/SHF frequency applications, but I am working in HF so a little attention to not building in inductive ground planes should be fine. My aversion to “ugly” includes using two 100 ohm resistors in series when I don’t have a 200 ohm resistor. I’m sure I will get over this affliction at some point, I’m just not there yet. In the mean time I will spend a little more time on the layout phase.

Until tomorrow the 40 is on hold. The plan is to have it up and running before April. I have a lot of projects to do this year. 😉


ETA: 2015-04-03 The new project page for the EMRFD 40 meter receiver is here.

Flickr photo set for the 40 meter receiver

My first homebrew toroid inductor. Aint she purdy?
My first homebrew toroid inductor. Aint she purdy?

Learning CW Online

Cheap USB mouse
Cheap USB mouse cost $7 new from Amazon or any spare junk drawer mouse will do.

There is a neat site Learning CW Online or I am just starting with.  Since I am just starting with them I don’t have a whole lot to say about the site, but, it did spark a short project idea.

LCWO has different sections for copying code and for transmitting code. The copy side is easy, just listen through the speakers on the computer or headphones. Transmit requires action, you need to key something, usually the left mouse button. I have a touch pad and not a mouse. Besides, a mouse doesn’t have the feel of a straight key (SK) and that’s what I will be using on the radio…

Enter the idea… a USB cw key! I’m cheap and more homebrew so I came up with an incredably simple USB mouse mod that allows me to use the key with any site or program that will allow you to key by clicking on a virtual key.

All I did was open up the mouse ans solder two wires to the left mouse switch and run those wires out the side of the mouse case and tie them down to the binding posts on the straight key. Now the key is parallel to the switch. You can still use the mouse, and you can use the key too.

I still need to do one thing before this project is done. I need to install a jack in mouse so I can easily unplug the key when I just need a mouse.

Helpful Hint: If the mouse keep sliding around while you are trying to use the key, just line it up with the on-screen button and slowly pick it up and turn it on its back. This will stop it from tracking.

Here is a link to my progress shots on Flickr.

ETA: The jack has been installed and it works great. USB mouse/cw key with jack

50 Ohm 5 Watt dummy load

I have been wanting to build a ham receiver and transmitter for some time but hadn’t found the right project, well now I have. A low power (2-5 watts) in the 40 meter band (7 – 7.3 MHz) for CW (Morse code.)

One of my reasons for this choice is its a good quality radio with tuning of the full 40 meter band and no crystals. I also need to get cracking on learning CW so this seemed to fit right in.

Anyway, I want to get started on the receiver next month so I am working on a few tools to work with and test the radio project as it moves forward.

I have five tools to build, all of them are relatively easy to build and don’t have many parts they are a Peak-peak RF probe, an RMS RF probe, an RF sniffer, a 50 Ohm 5 Watt dummy load, and an RF power meter. Today I built the 50 Ohm 5 Watt dummy load.

The dummy load is the black cylinder attached by a very short coaxial cable and connector. The guts of the load are twenty 1,000 ohm 1/4 watt resistors all connected together in parallel. One end of the resistor ribbon is connected to the shielding of the cable and the other end to the core wire. Then the whole thing is rolled up into a cylinder.

The roll of resistors is covered by a sleeve of heat shrink to insulate it from the copper casing made from two 1/2″ pipe caps and a short piece of pipe. With the resistor bundle insulated I put a small zip-tie as a strain relief on the cable. Then the copper tubing and caps are closed up and another piece of heat shrink is put over the whole thing holding it all together.

I futzed around for a while to make a cylindrical cage for the resistors and just wasn’t working out. The only reason I wanted to do it that way was to make in look a little classier… on the inside… anyway, now it is all done and works great. I can now test low power radios, up to 5 watts, without an antenna or transmitting spurious signals or doing damage to the radio. Yay!

50 ohm 5 watt dummy load