Lowfer JH on 181.818khz Part 15 Station
I stumbled across LWCA.org one day while researching radio transmitters. I often thought about building a transmitter. After looking though the site, I knew this would be the place to start.
I used the same class B style transmitter that many people use for this type of project. I decided it would be easiest for me to use a microcontroller to supply the pwm signal, because that is what I have experience with. All I had as far as crystals went were 2, 4, and 8 mhz. I found that I could use the pwm hardware to get 181.818khz with the 8mhz crystal. Here is the schematic I came up with.
The next step was to build a pcboard. I decided to make the board myself using the toner transfer method. This is what the layout looks like.
As you can see, I decided to put everything on one board. This is something I would do differently next time. I think it would be better to have a pwm/keyer board, an amplifier, and a filter board. This way, I could experiment with frequency shifting, or different filters, without having to layout the entire board. Here are some pictures of the board after etching and silkscreen.
Here is a picture of the final board. The external pot controls the variable voltage regulator on the pcb, which allows me to control the output power.
This is a video of me testing the transmitter through a dummy 50 ohm load.
My next task was to build an antenna. My initial goal was to make it 40 feet tall with a 10 foot radius top hat. After I started welding some sections together, I quickly realized that 40 feet was much bigger then I felt comfortable setting up next to my house. I ended up with a 30 foot antenna and a 5 foot radius top hat. I plan on extending this to my original plans one day. Here are a few pictures of the antenna.
The last major building step was the loading coil. I used a cardboard cement cylinder mold from lowes. I used a piece of PVC to make a tuning coil. Here are a few pictures.
The microcontroller allows me to transmit morse code. I usually run QRSS30. The main problem I have with this setup is tuning. I do not have a way to match the impedance with this setup. The next problem I have is contact resistance. I will solder and braze all of the cctions next time. Even with these problems, Dexter McIntyre managed to get a pretty clean copy of my signal from Stanfield, North Carolina. This is about 80 miles from my house. Here is a picture of one of the better argo captures from October 2012.
UPDATES!
February 16, 2015:
I made a loading coil for a long wire receive antenna and figured I would use it to experiment with inpedance matching. The loading coil is basically the same as the one for the transmitter antenna with the addition of a tap on the each of the first 8 turns. I made it out of parts I had around the house, so there are different gauge wires.
I tested the antenna/loading coil with my Rig Expert AA-30. I could get the impedance to 43 ohms at resonance. At this point I decided to connect my transmitter to it and see how it preforms. Dexter McIntyre (W4DEX) in Stanfield, NC and Ben Hall (KD5BYB) in AL setup grabbers for the day. The signal came in strong on Dexter's grabber, but never showed up on Ben's. I was hoping the results would be better.
The next step is to finish the modifications to my antenna and build a copy of this loading coil out of lower gauge wire. Here is an image from Dexter's grabber.
Here are a few sites that helped me design my station.
KØLR's Project Page. (Great antenna information!)
BUILDING A MANHATTAN STYLE LOWFER BEACON