Tag Archives: homebrew

All Aboard the Project Train

April 15, 2015 KK6GXG

Sometimes it is indeed a project train, not just a project; occasionally a train wreck, but it’s early so we’ll hope for the best.

Now that I have built several receivers and a transmitter for 40 meters, I probably should have an antenna that does more than pick up all the RF noise around the shack. The antenna, and I use the word loosely, is nothing more than a dipole of 26 AWG insulated wire strung around the house. While it might work well if the wire was straightened out on a hill top, or even in a backyard, elevated 15 feet or more above ground, in its current incarnation, in a word, it sucks.

Next up on the project block, an antenna, sort of…

I have been looking at several small footprint antenna options like spiral coils that look like those God’s Eye yarn and popsicle stick things you may have made as a kid, the one in the movies from the 40s when the resistance spy transmitting Nazi secrets and the SS storms in. It looks like a X and has thin wire wound around it.
And Small Loop antennas that look more like old direction finding antennas on aircraft. And by the way, according to the formulas and general information, for 40 meters, not so small, 10′ diameter.

Now there are lots of variations and tons of experimental configurations to run with, and I do want to play with many of the possible configurations, but I need a stable, small, portable option for the immediate future. Something I could mount on the car, throw up on a pole, or stand up on the back porch, all without much effort. I also need to keep the cost down.

Scan from the 1975 ARRL Handbook, page 606.

Enter the Helically-Wound Short Vertical. I ordered some 14 AWG lacquered copper magnet wire and a 72″ long 5/8″ diameter fiberglass rod, I need to learn to make these so I also ordered a How-To book on making composite fishing rods, and I’m in $20 so far. I have all of the hardware items including the 12″ spike for the top. What I don’t have is the variable inductor, or a tuner.

Whooooo Whooooo! Here comes the train.

Lets start with the one I haven’t done any research on yet, the variable inductor. The mechanics are fairly simple, rotate the coil and the follower moves up and down the coil creating a tap point. As long as the coil is perfectly cylindrical, the follower makes good contact, and smoothly moves down its axis rod, no sweat. ~~he he he, no sweat~~ I only need the one variable inductor according to the diagram so I really need to find out what value I need. I already have several small value iron-core variable inductors so I may not need to make this one, but if I do, it will be a homebrew. These things are a high-dollar item otherwise.

Moving on to the antenna matching unit. I have plans for one that is fairly simple and straightforward, I even have most of the parts on hand. What I don’t have is the variable capacitors. Sensing a theme here? Variable…

A funny coinky-dink on capacitors; while I was doing research on the Small Loop antennas I came across several websites that went into some lengthy discussions on making variable caps. Turns out, they aren’t that hard to make, I even have nearly all of the materials to make several. Not only are they fairly easy to make, but the formulas for calculating the capacitance based on the area of the plates, number of plates, and the distance between the plates is also fairly straight forward.

So lets see where we are now…
I have three receiver and one transmitter for 40 meters. There is an antenna for them, but it sucks particularly in this location. My next project is to build another transmitter, But I will need a better antenna first…

Antenna
Resonator for antenna (variable inductor)
Antenna tuner
Variable capacitors for the tuner

Now, after these are done I can move on to the new transmitter. As a side note, with the next transmitter project I wanted to pump up the power all the way to a couple of watts, not just miliwatting it. I also want to include SSB (Single SideBand, voice) as well as CW so I can incorporate digital modes into the shack. For all of this the antenna really needs to be better than what I am using.

That’s all for now, 73,
~Jon KK6GXG

Amature Radio

40 Meter Loose End

April 10, 2015 KK6GXG

Today just started off good. The post came early and an expected package came a few days early, my QSL card order from Vistprint.

I’m not quite sure when I will need to send any out, but now I have them and I am very happy with how they came out. I’m also very proud of them, I spent the better part of a day working on the layout and confirming the text-safe areas around the card. The finish product is just what I was hoping for.

A couple of days ago I got a package in the post from another ham, Brad (AA1IP) and oh my, what a box it was. A medium sized USPS Priority Mail box filled to the top with stuff.

I started sorting it out that evening and last night and again this morning. Its all sorted into like or similar components. There is still a lot of sorting to do, particularly with resistors and capacitors. Among the jumble there were a few packets of resistors already sorted by value and those are my project for tonight. Get them all stowed away.

The sorting process will take a while and I’m in no rush, so bag by bag over time it will all find homes. Once I get everything stowed I may ask for another. Mmmm, a masochist, I am *in my best Yoda voice*.

A small follow up project got completed over lunch today. I finally finished the power cable for the 40 meter receiver I built. The original plan was to build the receiver and a follow up transmitter, package them together, and power them both with a solar charger / battery pack. Also in the original plan was to build out the cable from scratch.

Funny thing about plans… I dont have any good multi-conductor cable anymore. The closest I have is some cat 5 and some twisted-pair for telco work. Nether is appropriate for this project. I was waiting to go to the Electronics Flea Market @ DeAnza this weekend but I also have plans to go to a radio builders club meeting on Sunday and check things out there. I was encouraged to bring my project along, and since the build was complete I thought I should power it as planned.

Long story short, I know, too late, I decided to pull an extra USB printer cable out of my computer junk box and use an existing cable, clip an end, and install the power plug. Easy peasy. The plug isn’t quite big enough for the cable but I adapted it and heat shrunk that end for some extra stability. Thoroughly checked it for shorts and opens twisting it about and we are good to go.

The radio can now be powered by a computer, USB car adapter, or the solar power supply I had originally intended to use. Any standard USB source with the appropriate 5 volts will do.

I’m sure I’ll have more to post about after the Flea and the club meeting.

Until then, 73,
~Jon KK6GXG

Amature Radio

Fresh Prespective

April 2, 2015 KK6GXG

Over the last few days I have been working on a direct conversion receiver project I found in the book Experimental Methods of RF Design last month. I had been planning and even started a very similar design back in February. I was having problems with that project so I picked up the EMRFD book to help figure out what the issue was.

There in the first chapter was this design and I decided to scrap the other project and started working on this one. It wasn’t like “oooo, a new shiney…” because they are very similar designs and the goal was to build a direct conversion receiver for 40 meters, not specifically that receiver.

Now that I have finished unnecessarily defending my position on hitting the reset button on the project, we can continue.

This time I decided to go with the “ugly” method of prototyping. I was not aware of the induction issues with the plastic pinboards or the other problems that can arise with high-speed or precision circuits. I had seen a few things on ugly construction and comments on its superiority over the plastic breadboards, along with other similar prototyping methods like “Manhattan.”

Since I had never done ugly before I was a bit nervous about it. I have used perfboard successfully on other projects and while perfboard does not have the same negatives as pinboards, it doesn’t have a ground plane ether. This can be problematic in RF circuits.

Any hoo. Yesterday I finished soldering the board and started mounting stuff. The project is screaming along and I have been pulling back regularly to make sure I don’t rush to finish. I have been going back an checking the new additions for physical problems, shorts, cold soldering, and the like. So far things have gone nicely.

This morning I sat down and looked at the partially mounted project box and some things crossed my mind. If I only put an antenna port on the back, instead of including a power port, I could actually have an internal battery pack. I could even add the power port and include a charging circuit for the internal battery…

I nixed this idea on this build because I intended to use a battery pack / solar charger that I already have so the power possibilities will be saved for later.

I do plan on adding a transmitter to this case. This brought my attention to the front panel. I am installing a power switch and headphone jack for the receiver, but I would need a jack for the cw key and a TX/RX switch. I could fit both of these components in the front panel integrated with the receiver parts without a problem. I could even install them now to prepare for the inevitable. I even have the parts in stock.

What I didn’t think about last night was the tuning of the transmitter. I don’t have the room for the tuning components on the front panel. I don’t know if I could modify this oscillator/mixer to work in conjunction with a transmitter thus converting the whole thing into a transceiver. I will have to get back to the book and read on.

In all honesty there are a couple of other things too. I would want a beat oscillator which would need a momentary switch and some other logistical elements to think about as well.

I spent a lot of thought on keeping this board small. I didn’t want to crowd things too much, but I wanted a small planform. I got what I wanted and I learned a few things about experimental design.

Planning ahead is not just about where the rest of this circuit is going. It includes thinking about the likely evolution of the project. Would I convert this project to a transceiver? Probably not. I would more likely build a new project ether from a different design already established, or take a lot of time and build modular circuit clusters testing them as individual units and working out the logistics of placement, interfaces, and housing configurations as the project developed.

I am actually surprised at how much I have learned from building this little DC RX, and I’m not even finished with it yet!

73,
~Jon KK6GXG

Amature Radio

Lab Book Conundrum

March 28, 2015 KK6GXG

I have been doing a fair amount of homebrew electronics projects as of late and I am coming to a point where I need to address documentation. With my woodworking projects I really don’t worry too much about documentation. Some projects don’t even have plans beyond a couple of dimensions on a post-it note. Electronics projects are a bit different.

So far my projects have been taken from articles online, from magazines, and from books. I have kept hard copy of the designs for the most part, and any changes or additions I may have made have been noted on the hard-copy or attached as separate sheets.

Now that I am delving into the world of bigger projects and doing tests of the circuits beyond continuity at various stages in the build I should be keeping more in depth notes with test results and the like. The question is in what form should these note be. There are so many options that I’m just not sure which route to go.

The obvious choice is an electronic notebook. I use OneNote currently and have used Evernote in the past. A part of me is a bit paranoid about data loss, so exclusively electronic notes make me uncomfortable.

I do regular backups and I keep redundant sets of data, but there is always the contingency you didn’t or couldn’t prepare for. There is also something to be said for Long Now thinking when it comes to data storage. I have come across a lot of stored data in formats and on hardware that are now very difficult to retrieve and if you manage to get the data out, the big question is will it be complete.

Any body remember 5¼” floppy discs? How about 10″ floppies and 8-track tapes?

This of course leads me to a hybrid solution. Digital notes occasionally printed out to hard copy and kept in binders. It’s not like I’m doing any cutting edge work or something involving national security, but if I have learned nothing else in life, I have learned this, you never know where things will lead or when you will need information you have gathered. Data hoarder, maybe.

How long is long? This book is over 100 years old.

One definite advantage to digital notes is the ease in which that data may be shared. Another is the ease in searching through pages upon pages of notes for a specific piece of information. How about the ease in linking to other resources rather than copying that data, though this is a double edged sword. If data is not long-tail, it may not remain at its current location for very long. How long is long anyway? There is also the typographical concideration; typed notes are much more legible, by my hand anyway, than handwriting or printing.

Time for a little more research and thinking, the clock is ticking …

73,
~Jon KK6GXG

Amature Radio

CW Practice Oscillator

March 23, 2015 KK6GXG

Mark I – Transistor Based Oscillator

(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

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.

https://www.youtube.com/watch?v=3yoo2oZG714

Amature Radio

BreadboardRadio Kits

March 20, 2015 KK6GXG

On Wednesday I received some awesome mail, the kits I ordered from BreadboardRadio.com 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 BreadboardRadio.com

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.

73,

~Jon KK6GXG

Amature Radio

40 is dead, long live 40!

March 15, 2015 KK6GXG

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.

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. 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. 😉

73,
~KK6GXG

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

Flickr photo set for the 40 meter receiver

Mark I – Transistor Based Oscillator

Mark II – 555 IC Based Oscillator

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