Category Archives: Amature Radio

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

Acceptable Tech Level

Today was a great day. I got up early to head out to the Saratoga Fire Station to take my Amateure radio Extra class exam. I am happy to report that I can now use the temporary callsign KK6GXG/AE, for those not in Ham radio, that means I passed. Needless to say I was stoked to reach this, the highest level of amateure radio licence. Lots of plans are piling up for radio projects on my desk/bench so there will be reports on those to come, this post however, is not about radio.

Water Grinder & MotorAfter the test the wife and I went to the De Anza College Flea Market. I found something I have been looking for for a long time, a sharpening stone (wet stone) grinding wheel. What I had been looking for was a manual, or hand-crank type that can be easily adapted to a foot-treadle or bow-spring drive. The one that I found was attached to a motor via a reduction pulley-and-belt system, though in honesty I didn’t realize how low the reduction was at first.

My initial reaction was to remove the motor and adapt the wet-grinder to a manual power source right off the bat. After looking up the patent info on the motor and seeing what it was originally intended for a story began to emerge on the origins of this particular assemblage.

The board everything is mounted on does not appear to be that old. The dimensions are modern, making the mounting 2 x 12, at oldest, from the 60s. The mounting hardware is a mix of 50s and contemporary. The casting and markings of the wet-grinder suggest that it was cast in the 1920s to 1930s. The patent date of the motor is from 1926. This particular 1/4 HP motor was designed for washing machines of the 20s and 30s. A newer motor was produced after the war and the model and frame numbers on the data plate suggest that this motor was produced in the 30s.

20140607_191708The story I have come up with is that these parts were cobbled together in their current configuration some time the 70s from parts and used regularly for a significant time as such and eventually shelved in a shed where they had been sitting for at least a decade.
I ended up doing a mechanical teardown tonight. I was planning on getting started with the electrical teardown and testing tomorrow. For the most part this was an inspection teardown. I didn’t do any “repair” although I did fill the water reservoir with a rust remover to begin prepping it, and to see if it still holds fluid. I didn’t detect any leaks and we will see if it develops any overnight.

20140607_191718The plan is to deal with the mechanical and electrical as completely separate restorations. The mechanical is the primary because I can still set it up as a manual wet-grinder and begin using it.
I have a number of sharpening projects that need to get done soon and this would be a big help in speeding things up. Once rust is abated I think a couple of coats of iron oxide primer followed up with a couple of coats of oil-based paint should provide a sufficient level of protection.

Once the mechanicals are all taken care of I will spend some time on the electrical motor. At this time I have no information on the motor other than what’s on the data plate.

20140607_114338So why the title “Acceptable Tech Level”? one of the reasons I wanted a manual grinder was to further the off-grid hand tool goals I have been trying to work with. With this particular configuration I can easily swing it over to manual and with the motor most likely being from the 20s-30s it falls into my era of interest in aircraft and is also from around the same time as several of my inherited and acquired hand tools meaning it fits right in with many of my vintage tools. The important part is that it CAN be used with manual power.

Until next time…

☮ ♥ ✈ & 73,
~FlyBoyJon / KK6GXG

Voice Communications

20140518_105456You may have noticed this placard over my shack bench desk. I didn’t have this made for me, I inherited it. It was my mom’s placard, traveling with her throughout her various offices at Amdahl/Fujitsu.

Mom had a long relationship with telecommunications throughout her life. My earliest memories of my mom working were of her plugging the switchboards at an answering service. She made a second career for herself as a bookkeeper for many years but returned to switchboard communications where she stayed the rest of her life. She was a very talented communications operator and supervisor.

I didn’t spend huge amounts of time at the answering service growing up, but I was there enough to learn about tip & ring, how switchboards worked, the old cord-boards, and what the miles of wire behind them were for. I was lucky I suppose, there was a phone company technician swinging lines fairly often while I was there. In some small way I think that experience influenced my desire to go work for the phone company, which I did for a short time.

20140512_170250Looking at mom’s placard this morning I got a little nostalgic and started thinking about how I have been involved in communications, at least peripherally, as long as I can remember. In some way it seems as though I inherited more than just the placard. Communications seems to run through our veins.

As it turns out mom wasn’t the only family member in communications. My grandfather Robert was in communications while in the Navy during WWII. My great-uncle Allan was a signalman in the Navy as well during the war (WWII.) Allan also worked for a military aviation contractor working with navigation and avionics equipment after his hitch ended. These two related fields seem to be hereditary in my family. Robert had some connection to aviation as well, but the details are sketchy.

I never met my grandfather or spent any time with my great-uncle when he was alive. I found out about their experiences with communications and aviation while doing genealogy work after my mom passed in 2006. Like so many other vets, they didn’t talk about these experiences with their families.

Radio and aviation have always been comfortable places for me. I feel good doing these things. Even when I am frustrated or stumped, I can always figure things out and learn new skills. There are vast communities to get involved with for both, but they also provide space for solitary practitioners looking for some alone time. Both fields also seem to interact easily and many skill sets translate from one to the other well. Both also are very broad in scope, they have many sub-sets of interest to keep an interested party busy with a seemingly infinite variety of new things to learn and do. I am very grateful to be a part of both fields and I look forward to years of continued participation and sharing in both of these communities.

☮ ♥ ✈ & 73,
~FlyBoyJon / KK6GXG

CW Oscillator

The shack/radio bench is rapidly evolving. I have been working on several radio projects, most of which have been relatively small. The most recent project is a CW (Morse Code) practice oscillator. It allows me to practice sending code while I learn.

I had built a transistor based oscillator which worked okay but the tone wasn’t that stable, or loud enough to be that useful. I had a drawn up a simple transistor amplifier that I planned on adding to the circuit board, but the design is still less that optimal from a stability standpoint
After building the transistor version I decided to try an IC (integrated circuit) based oscillator. The tone quality, stability, and volume are much better than the transistor type. I built the oscillator on a breadboard to test the circuit out and make sure everything was in working order.

After checking everything out I started laying it out on paper the way I would actually wire it all together on a proto-board.

Everything worked great so I was ready to get to the next phase of the project, building the housing for the whole thing
The plan for the case was to build a wooden box with as much of a vintage (read steampunkish) look to it so it was time to move operations from the shack/radio bench down to the workshop.

First up was to design a basic box. I chose Douglas fir for the frame pieces and mahogany plywood for the panels.

Since I was going for the steampunk look, brass, lots of brass. Everything was stuff I had around the shop so there was no waiting. More importantly, I have lots of the stuff so I can experiment a little.

 

The box was all hand cut and assembled. Everything is held together with glue though I did use brass pin nails for accent. The brass speaker grill doubles as a retainer for the analog acoustic speaker. I didn’t want to use the cheap plastic one in the project. The sound just isn’t the same as the paper speaker.

The other end panel was going to just be wood and nails, but I decided to go with an accent that would double as a way to open the panel. This panel needs to be removable because the battery is on this end. I went with a key hole on a whim, it just looked right. It was a bugger to hand file the whole plate but I think it’s worth it.
The box took two days to plan, cut out all of the materials and to assemble. The brass work was done the second day as well. It took a third day to apply the several coats of linseed oil that I used for the finish.

Once the box was all done and the finish was dried it was time, on the fourth day now, to plan out exactly how I was going to install the guts.

I know this was not a very thoroughly planned project. I planned out the electronics pretty well, but the case, well that was very much an on-the-fly thing.

Any way, back to the timeline, with all of the case work done it was time to relocate back to the shack.
Back in the shack I worked out the bugs in case design, well, I developed the work-arounds for the issues that arose from the case design. What can I say, one of the reasons I am doing this project is for a learning experience and I have learned a few things about project design, and project housing design in particular.

There are several things I would do differently if I were to do this project again. One would be to reconsider trying to stick mostly with hand tools. I could have saved myself a ton of time had I built the frame using my router.
I could have routed a single channel strip on the router and just cut the pieces and mitered it all together.

Another change would be to use tiny screws to hold the panels in. I would have had much better access while installing the guts.

As they say, hindsight is 20/20. Lessons well learned and worth learning.

Below is a short video of the oscillator in operation.

Until next time,
~FlyBoyJon

I’m a multi-bench kind of guy

20140317_142358While I was in A&P school almost everything I posted was, of course, aviation related. Since I graduated a lot of my time has been spent working with wood. One of the biggest projects, literally, was a new woodworking bench using traditional joinery and oak draw-bore pegs to tightly secure it all together. (later I added a crochet at the left front that was attached with 2 lag bolts which constitute all of the metal on the bench)

But wood isn’t everything. Back in October I took my first Amature Radio license test and earned my Technician class license, last month I took the General class exam and earned my General class license. I’m used to doing computer hardware work and in the past I did a little electronics work so I was familiar with some of the stuff involved in radio, but not a lot.

20140518_130113Back in the 80s I was into CB radio. Later in life when I was working in the towing industry I did a lot of electrical work on our tow trucks which included the radios, and of course, installing my own car stereos since I could drive. These other activities made me a little familiar with Ham radio, but only in a very cursory way. What pushed me to finally do what I had wanted to do for decades was learning more about aircraft radios in A&P school.

Now my “electronics bench” is shifting from computers to radio. I have some basic electrical diagnostic tools and a full compliment of basic hand tools, but I am lacking in some of the basic radio diagnostics and bench-tools. As with woodworking and other trades, what better place to cut your teeth than making some of your own tools.

Dummy Load
Dummy Load

This week on my radio projects list I had one bench tool, a dummy load. For those who may not know, a dummy load is what you would connect a radio transmitter to, instead of an antenna, to conduct a variety of bench tests, usually power output related. Not having a load while transmitting, an antenna or dummy attached, a radio can burn out; basically you are generating a lot of “power” but not giving it anywhere to go. While testing you don’t want to connect an antenna because you would be transmitting all of your tests on-air wasting air-time and occupying a frequency someone else could be using for communication.

So thats why a dummy load, now for the what. A dummy load is used to dissipate RF energy, that would otherwise be radiating from an antenna as radio waves. The load can be dissipated through a resistive material as heat instead of radio signals.

20140430_131228An easy way to accomplish this is to use a resistor with relatively low resistance and that can also handle high power loads. Another criteria is that it shouldn’t radiate, or leak, spurious signals.

That last part becomes tricky because you can’t use resistors that are made from coiled wire, normally the kind used in high power applications because the coils inside the resistors will generate inductive fields. Another more practical way is to use a bunch of lower wattage resistors in parallel so the wattage is accumulated and the resistance kept low.

A trick that can be used to help in the dissipation of heat from the resistors is to submerge the resistor package in a fluid medium that will help dissipate the heat generated by the resistors making them more efficient. The trick with this is to use a medium that has a high flash point so you don’t accidentally start a fire. This is called a “wet dummy load.” It is recommended that transformer oil is used; this is what utility companies use for the same purpose in their large power transformers. Unfortunately this stuff is very expensive. The last time I checked it was $2,300 for a 55 gal drum, about $42 a gallon if you could find it in anything less than 5 gallons. Fortunately there is an alternate, mineral oil, which is pretty close.

So what’s in store next you may ask… A field strength meter is on the list for next week. With any luck I will be able to get out and do some shopping for that project in the next day or two.

That’s all for now, and 73
~FlyBoyJon / KK6GXG