AB4UG Radioblog

Spent the afternoon yesterday playing in the North Carolina QSO Party and finished up with 49 contacts (including 2 bonus stations and 1 bonus county) and 40 multipliers. Like last year, it was all on 40m. There were a few very faint stations that I could hear on 20m, but none clear enough to work.

Haven't worked out my final score yet (over 4000 according to N1MM+), but it easily topped last year's total. Had a lot of fun playing in the contest and it was nice getting back to the radio.

The Amateur radio presentation I gave at the Charleston Library's DIY Festival on Saturday went pretty well. Had about 10 people sit in on the presentation where I talked a little bit about what amateur radio is, what can be done with it, the licensing tests and then some construction techniques. To augment my presentation and emphasize the DIY aspect of ham radio, I brought in some of the projects I worked on including some of the Etherkit radios, my Arduino work station and some of the other circuits I soldered up.

There were a couple of people who were very interested, and asked a lot of questions, which was good. Hopefully they continue on to get licensed.

The DIY Festival itself was a pretty neat event. Lots of crafty-type things for the kids and lots of tables with people showing off their craft. Nice to see the Makelab Charleston guys there showing off a few things. One table had a Makey-Makey set up with bananas and carrots, which I saw a lot of kids having fun playing with. Looked like there was a great turnout of people for the DIY Festival.

Had another good time at the Charleston Hamfest today. There were a lot more vendors (including in the tailgate area) this year than last year. The day got off to a bit of a cool and frosty start, but warmed up nicely. Good sized crowd of people attending the hamfest. Here are the early birds. Even shortly after 8 there were a fair number of people browsing around the tables.

Started off the day picking up a couple of items off the Free Stuff table: a 1971 edition of the Radio Amateur's Handbook, and a CueCat.

I'm looking forward to going through the 1971 handbook. I think it will be cool to see what amateur radio was like when I was 1 year old.

I remember CueCats from my Apple //e days and always thought it would be cool to have one. Should be fun to play with this.

Browsing around the hamfest, I picked up an Ethernet shield, a big bag of resistors and some perfboard to mess around with.

The Ethernet shield will fit in nicely with the growing collection.

5200 1/4 watt 1% tolerance resistors (100 each of 52 values). I should be set for resistors for a good long time.

2 large plain perfboards, and 8 prototyping boards with solder pads. I like using the perfboard for quick prototyping and experimenting with circuits.

I was also able to find most of the things I'll need to build a window pass-thru block for the antenna.

Two 3 inch SO-239 bulkhead connectors and some screw-on caps for the cable ends.

There were a lot of other things I wish I could have picked up too (isn't that always the case?), but I'm pretty pleased with what I got today.

To top things off, I won one of the door prizes being given out too, a $50 ARRL gift certificate. Not sure what I'll get with it, but it will be something good.

The VE testing session at the hamfest went very well. There were 16 people taking tests today, 9 of whom were taking the Tech (Element 2) test. Everybody left with either a new license or an upgrade, so very successful on all accounts.

Time to see if I can build myself a crystal radio set. Or two. Or three.

I decided rather than demonstrate building a radio at the Charleston Library's DIYFest, it would be easier to bring in some examples of some simple crystal radios that could be built using stuff easily obtained around the house. Found three nice cylindrical objects and started winding magnet wire.

The inductance of an air wound coil, according to Section 2.12.1 of the 2014 ARRL Handbook, is approximately

L (μH) = d²n²/(18d + 40l)

where d is the coil diameter in inches, l is the coil length in inches and n is the number of turns. Converting it to use more sensible metric units, it becomes

L (μH) = d²n²/(45.72d + 101.6l)

where d and l are in centimeters.

The first coil is 182 turns around a toilet paper tube. d = 4.5 cm, l = 6.7 cm, n = 182, and L = 757 μH.

Coil #2 is 110 turns around the cardboard core of a packing tape roll. d = 8 cm, l = 4 cm, n = 110, and L = 1003 μH.

Coil #3 is 118 turns around an empty plastic pill bottle. d = 4.8 cm, l = 4.1 cm, n = 118, and L = 504 μH.

This is the basic schematic I'm planning on using.

I want the radios to be able to tune in the AM broadcast band (540-1710 kHz) so the capacitance I'll need for coils #1 and #2 is around 10 pF and around 17 pF for coil #3.

Since I have three coils, I think I'll make one with a variable inductor, one with a variable capacitor, and one with a variable inductor and capacitor.

I don't have any high impedance earpieces (I've seen some builds say you can use a telephone handset though), so I might add an amplifier or impedance matching transformer and see if I can get regular headphones to work.

Got my first QSL cards from the incoming QSL card bureau! 

I had received an email from the SPARC QSL Bureau a few months ago saying I had a bunch of cards waiting for me, and to send a SASE if I wanted to receive them. Sent off an envelope with postage attached, and today they arrived in the mail! So cool!

Now I have 17 cards to respond to. I'll have to figure out how to use the QSL bureaus first.

The Charleston Hamfest is coming up in a few more weeks! Looking forward to seeing what kinds of things interesting things I'll want to pick up. There are a few specific things I'll be looking for to build some projects.

Helped out yesterday with comm support for the Charleston Marathon again with my fellow amateur radio ops. Like last year, it was a pretty cool start to the event, but the weather warmed up nicely by the end of the race. This year I was assigned to two positions on the marathon course at Mile 2 and Mile 18.

Had a good time helping out with comm support, and fortunately there were no incidents along the course. Had a good time and I'm glad I was able to help out with the event.

I've been asked to give a presentation at the Charleston Library's DIY Festival that's happening on Feb 28.

Sounds like it's going to be a neat thing. My plan is to give a modified version of the amateur radio talk I've given at the last few BarcampCHS, and augment with a demonstration build of a crystal radio using some magnet wire and the 1N34A diodes I acquired recently.

Time to start messing around with building...

Jason/NT7S launched the crowdfunding campaign for his version of an Si5351 breakout board last night, and already this morning it's at over 150%. The stretch goal at $1 500 involves spending some more time on the software library to make the board easier to use.

It's a neat little oscillator chip that seems to provide a lot of capabilities for not a lot of money. He's been documenting his investigations on the chip at his blog for the past year now, including building a couple of receivers and transceivers around the Si5351.

The Si5351A is quite a capable IC at a very modest price. It is a PLL clock generator with three independent outputs which can each generate a separate signal from 8 kHz to 160 MHz. A 25 or 27 MHz reference oscillator is used for the two internal PLLs (the Etherkit breakout board uses a 25 MHz reference oscillator), which allows the user to choose the amount of frequency stability and accuracy required. 

Go check out the Si5351 breakout board campaign on Indiegogo, and pick one up if it's something you'll find useful in an upcoming project.

With the radio all set up now in the new shack and connected to the antenna with a slightly shorter length of coax than before, and after being up in the air for two years now, I figured it was a good time to check the SWR performance across the bands to see how/if it changed.

Compared with two years ago, there haven't been too many changes. SWR has gone up a little bit in general for all the bands, but not a whole lot. The biggest change seems to have happened on 80m, with the SWR around 3.8 MHz dipping down to a range that I think the radio's tuner might be able to handle. The SWR on 15m has also gone above the range the radio's tuner will handle, so that's one band I seem to have lost.

Things still seem to be looking pretty good for the antenna so far. Hopefully I'll be able to get a few more up this year.