1N34A diodes

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One of the projects I've been considering for a while is trying my hand at building some crystal radio receiver. Crystal radios are pretty simple and traditionally use a germanium diode as the detector element because of its low forward voltage drop.

Found several people selling 1N34A germanium diodes on eBay and ordered a batch of 100 a couple of weeks ago. They arrived in the mail yesterday, and today I got around to checking them out. The diodes themselves are unlabeled so there's really no way to tell what they are by looking at them.

1N34A.jpg

The forward voltage (Vf) drop of 1N34A diodes is supposed to be around 0.25V. According to my DMM, a random sampling of the ones I got showed a Vf of 0.29-0.30V. I figure that's pretty close.

1N34A_Vf.jpg

For comparison, the Vf of some random 1N4148 silicon diodes was around 0.6V.

1N4148_Vf.jpg

Now to do some homework and see how to go about building a crystal radio receiver.

Shack relocation

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We're getting ready to move the shack out of the office/shack into what used to be the guest bedroom. It will still be the guest bedroom for the rare occasion we actually have people stay over, but it will become mostly the shack.

It should be a much better room for playing radio, especially from a temperature standpoint. The office tends to get pretty warm in the summer and especially so when the computer/heater is running as well.

The room is also a lot closer to the antenna and I'll be able to have a much shorter coax run out to the antenna than I do now. The room is all prepped for painting, and we've selected what we think is a nice shade of blue for the room. A day to paint with primer and let it dry, another day for the paint and we should be ready to move the shack into the room.

Right now the plan is to have a long table with the radios against the inside wall.

DSC01802.JPG

The antenna feed point is just outside the windows, so I'll bring the coax through one of these windows and run it along the walls to the radio.

DSC01803.JPG

This should also make it easier to use the back yard for antenna projects since it will make the feed line runs shorter and easier.

Morse code at 25 wpm

For a while now, I've been listening to Chuck Adam's (K7QO) code course. It's a good, methodical course that first takes you through each letter, with a cumulative test after every second letter. You get lots of practice hearing each letter by the time you get to Z. I'm starting to recognize most of the letters up to K now.

The course sounds like it's recorded at somewhere between 15-20 wpm. For most people that's probably plenty fast enough but it's just slow enough that my brain still wants to count the dits and dahs and then convert to the corresponding letter rather than just listen to the rhythm of the sound.

What I needed to do is convert or generate a new set of files that plays the code faster. With a bit of experimenting at lcwo.net, I found that 25wpm was where my brain stopped trying to count dits and dahs, letting me focus more on the sound of each letter.

A little bit of searching brought me to a program called ebook2cw by Fabian Kurz/DJ1YFK, who also happens to be one of the people behind lcwo.net. From there, it was a trivial exercise to feed the answer files from Chuck's code course into ebook2cw to generate a new set of audio files (OGG turned out to be about half the size of MP3) at a character speed of 25wpm and effective speed of 15wpm.

Here's the shell script I used to generate the OGG files

#!/bin/sh
for file in *.txt
  do /opt/bin/ebook2cw -O -p -o `basename -s .txt $file` $file;
done

Do this in the directory where you've extracted the text files from K7QO's answers file and you'll end up with a bunch of .ogg files. Then copy them to the media player of your choice (if it can't handle OGG files, it's time for a new player). If you insist on MP3 files, just drop the -O parameter. The file names will have some trailing 0's tacked on before the extension (chapter numbers automatically added in by ebook2cw) but it doesn't affect anything.

Radio updates

What have I been doing in the amateur radio world lately?

Well, not a heck of a lot actually. I've even skipped a few of the big contests happening this fall.

Lately most of my spare time has been spent reading up on and learning about electronics and Arduino related things. I've spent a little bit of time playing at the workbench. Nothing terribly complex. Just soldering together simple circuits and practicing ugly construction techniques.

My reading list for the past few months:

I'm no expert yet, but I think I know a little more than I did a while ago.

In the next couple of weeks, the plan is to turn the guest bedroom into a ham shack/guest bedroom. First we'll empty out the room, paint the walls and then move everything back in. I'll have to get back into the crawl space to pull the coax out, but the antenna feed point will be closer to the radio which means a shorter coax run that won't have to go under the house.

The guest room also stays a lot cooler than the office so playing radio during the summer will be a lot more comfortable.

VA6BUG wallpaper

My dad forwarded my Canadian amateur radio certificate to me, and it arrived in the mail today. Looks pretty spiffy. Now I need to get a frame for it.

VA6BUG certificate

I'm quite pleased and proud of this accomplishment.

Canadian Ham

I was able to take both the Canadian Amateur Radio Basic and Advanced certification tests this morning, and much to my surprise, managed to pass both of them.

I was pretty sure I'd pass the Basic test with at least Honours (80%+). The Advanced test I was a little less optimistic about since I didn't have as much time to prepare for it as I had wanted. Fortunately I managed to score high enough to pass both tests, so now I have my Basic with Honours and Advanced qualifications!

Less than 30 minutes after the examiner left, I was already able to apply for my call sign through the Industry Canada website (wasn't expecting to be able to do that for another day or two based on what the examiner told me). Hopefully that will go through by the weekend and then I'll be official!

Update: My new Canadian call sign is active! VA6BUG

Charleston Hamfest preparations

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Preparations are under way for the 2015 Charleston Hamfest. As usual, it's scheduled for the first Saturday in February and will be at the same location as last year in North Charleston. Door prizes, forums, VE exams, and all the normal fun things you expect at a hamfest. It's not a large hamfest, but I've enjoyed going to the last few and being able to meet other hams. I've also managed to score a few decent deals too. Looking forward to this next one.

CHSHamfest2015.jpg

Ugly construction attempt

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My first attempt at building a circuit using the ugly construction technique. It's supposed to be a simple oscillator circuit using a J310 transistor.

Ugly construction oscillator circuit

One of the advantages of ugly construction is that if you're working from a schematic or circuit drawing, building is pretty easy. I found that soldering components to the copper clad required a bit of patience, because it's essentially a very large heat sink. Put the soldering iron on the copper clad, add solder until you get a good sized pool, leave the soldering iron in place and place the component.

For this particular circuit, Vcc is applied to the big resistor with the free lead and output is off the capacitor with the free lead. I soldered on a piece of wire to make the ground connection easier. Haven't applied power to test it out yet. Will see if it works later on.

SA602/SA604 soldering practice

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After getting a bit of advice from some locals about soldering, I thought I'd get in a little more practice with the SA602s and the breakout boards. It was also a good excuse to see how my new glasses are for working at the bench.

To get a little more room to work, I switched to a conical tip on the soldering iron and soldered the board onto the header pins first. This makes for a pretty stable platform to work on.

SOIC-8 breakout board on header pins

SOIC-8 breakout board soldered to header pins

Add a little bit of flux paste, tin one of the pads and then tack on the SA602 to the tinned pad.

SA602 tacked onto breakout board

Then flip it around and solder a pin on the other side.

SA602 soldered onto breakout board

Then solder the rest of the pins, making sure not to leave the soldering iron on the board too long, and waiting a few seconds between soldering each leg to let things cool down a bit. A method that I found worked pretty well was to place the soldering iron tip on the pad, apply a touch of solder to the tip, push it towards the pin, and then draw the tip back along the pad.

SA602 soldered on

I soldered a total of 4 SA602s onto the breakout boards. Here's the result of about an hour's worth of practicing.

SA602s soldered onto breakout boards

Using the same method, I soldered one of the SA604 chips onto the SOIC-16 breakout board. Although the SA604 is about the same width as the SA602, just longer, the SOIC-16 board is quite a bit larger than the SOIC-8 board. Having the header pins on the same side as the pads gives you a little less room to work with as well. Still, soldering the SA604 was pretty easy.

SA604 soldered onto a breakout board

My attempts at cleaning off some of the residual flux left some cotton fibers behind from the swab I was using. I don't think it will affect how these work, but I'll spend some time trying to clean them off.

I think I'm getting the hang of this now. Next, learn how to use these.

SA602 and SA604 to play with

Last week, Dave/AA7EE announced that he had a bunch of SA602s and SA604s to give away. I emailed Dave to ask for some, and he sent me 18 602s and 6 604s. Thanks Dave!

These are surface mount ICs, so I ordered up some SOIC-8 and SOIC-16 breakout boards from Adafruit.

The package from Dave arrived earlier this week, and the breakout boards arrived in the mail today.

SA602

SA604

The breakout boards came bubble-shrink wrapped which was a little unexpected. I thought they'd just come loose in a ziplock bag or something.

DSC01742.JPG

The boards are double sided, with SOIC-8/16 spacing on one side and TSSOP-8/16 spacing on the other side.

Adafruit SOIC-8/TSSOP-8 breakout board

Adafruit SOIC-16/TSSOP-16 breakout board

Interestingly enough, the SOIC-8 boards are half the thickness of the SOIC-16 boards, which are a regular thickness circuit board. Both have sets of holes (standard 0.1" spacing) to solder header pins to, making them convenient to use in breadboard projects. Or you could just solder wires to them if that's what the project calls for.

Off to the workbench to do some soldering. For SMD parts, these are actually pretty large, and soldering is relatively easy. First, tin one of the pads and then with tweezers, line up the IC and then heat up the tinned pad. Use the soldering iron to push the solder towards the IC pin and you're done.

SA602 first pin soldered

I used a toothpick to apply a little bit of flux paste to the rest of the pads, and then soldered the rest of the pins. That part goes pretty easily with flux.

Pro tip #1: Don't do this with the board clamped in a vise, or if you do, don't leave the soldering iron on the board for too long. These SOIC-8 breakout boards are pretty thin and too much heat will make them melty. Oops.

Adafruit SOIC-8 breakout board - too much heat

Once you're done, it's time to add some header pins. This part is easy. Stick the header pins into a breadboard, put the breakout board on the header pins and solder.

SA602 soldered onto an Adafruit SOIC-8 breakout board

Pro tip #2: In your enthusiasm to solder, don't forget to pay attention to where Pin 1 of the IC is supposed to go (ignore that bad solder job on Pin 2...easy to fix). That stripe on the SA602 should be where the 1 is printed on the board. Oops.

Oops, upside down SA602