The Dummyloads

Where ham brains come to fry

Where ham brains come to fry

kits

Building an FM Radio Kit w/Kid

As promised a video of Amelia and I building her FM receiver. Funny enough she doesn’t listen to it nearly as much as she listens to her AM radio. AM radio I suppose has lots of drama what with all the politics.

Building the 2P3 AM Radio

In an Episode of Ham Nation or Amateur Logic featuring Joe Eisenberg (K0NEB), I saw him recommend a few radios as good beginner projects. The 2P3 radio looked like an entertaining project and something I could probably tackle with one of the kids. Amelia had recently discovered an old “boombox” from my youth and was playing the radio a lot. We decided it might be fun to listen to a radio that she had built.

The 2P3 mid construction

I ordered the kit from Amazon. The instructions come on a beautiful HUGE poster. It has an enormous schematic of the radio. I had wanted to build the radio by stage and is recommended when home brewing a radio. We started from the power conditioning part of the circuit. Once we had all the parts of the power we went back and installed the audio amplifier and worked our way backward.

I had intended to test the build frequently as we went along. Initially I couldn’t get any of the measurements to come out according to the schematic. I would go back and study the schematic and I was absolutely certain we had put the parts in the right polarity, etc. and continued forward. On the final day of the build I finally figured out why. . .

The way the circuit is designed there are purposefully installed breaks in the circuit. There is an X to mark the spot in the 3 points. basically they don’t allow power from the power rail to the circuit block you just finished. Being confident I had quintuple checked everything I bridged the circuit breaks and turned on the power the tested all the levels on the schematic. It worked! first try!!

The completed 2P3 is a nice finished product

The 2P3 is definitely NOT a beginner kit. But it is a great kit to build with someone who knows just a little and the finished product is a really nice radio.

Tuna Tin 2 Finished

As you may remember I left you at a metal can with a hole cut out to an incorrect size and then mashed over.  You may also remember that there were a few components that I needed to acquire to complete the kit.  While I definitely had a stock of BNC panel mounts, I did not have a supply of SPDT switches.  This involved me scouring

the interwebs looking for inexpensive, panel mount, SPDT switches.  I ultimately chose to order from danssmallpartsandkits.net.  If you are thinking that this guy must be a real niche market seller and cater to his customers. . . You’d be 50% right. . . It’s definitely a niche market!  From what I can gather he is a nice guy, but he has rules that must be followed.  Read carefully and follow the instructions.  I’ve never had a problem.  I also always order a bunch of other random parts I don’t “need”, but hey. . . next time when I need an NPO bypass cap, I have a stock of them.  This is a practice that was recommended to me by an elmer some years ago.  It’s why I have parts on hand. . . not always enough, but sometimes enough and sometimes enough to make it inexpensive to order a couple other parts.  Get what you need plus 2-3 items you don’t need, but are generally speaking useful.

So a few weeks pass by and a boring, worn package shows up.  In it are my parts.  They smell as if they have been living in a smokers attic for at least a decade, but they seem to pass the test of working and that is all I need!  The next step is getting the case ready for the board.  I installed a coaxial power jack from my stash, 2 BNC panel mounts, and the SPDT switch.  I choose to wire up all of the internal components so that when I am ready to connect the board there is little work to be done.

This is where I made my second mistake of the build.  If you follow the manual, you will build the transmitter.  Then when you are done they will give you some options to improve the performance.  I read the manual in advance and had opted to install the circuit for preventing chirp ahead of time.  IF one were to build this radio and intend to build it with this mod installed from the beginning, one would not burn themselves with a soldering iron while trying to put an electrolytic capacitor between the coaxial power and a ground lug on a BNC ground lug because that capacitor is NOT necessary assuming the anti-chirp mod is installed. The joys of homebrew!

Anyway. . . I had the can wired up and it was time to start on the board.  The manual has great step by step instructions.  I won’t belabor them other than to say that in the last step, they have you run a capacitor between two terminals near an inductor on the bottom of the board.  If you read the manual in advance you would choose to put the capacitor in before the inductor.  I think it looks nicer and is less likely to short out any traces.  It also fits through the hole just fine if you put it in ahead of time and just bend it over out-of-the-way.

The last step was to build up the home-brew anti chirp mod.  It’s a simple circuit and I had all the parts on hand thanks to some prior orders from kitsandparts.com.  See how my advice from earlier has paid off in this build!  If I had it to do over again, I would use fewer of the manhattan pads.  I laid it out exactly as the schematic showed, but you really only need about 5 islands.

The rest of the build was uneventful.  I made a short video to show the first smoke test, but unfortunately I must have hit the slow motion button as the video is completely unwatchable and 20 minutes long for something that took about 2 minutes.  You’ll have to just enjoy the pictures.  It does work and I hope to make an actual contact at some point when the bands are cooperative!

More projects are in the works.  Stay Tuned!

KF5RY