Archive for April, 2010

Knitting Electronics

April 29th, 2010

Sarah is a knitter.  She started when I was in graduate school.  It was a sort of support group for all of the other wives and girlfriends of grad students, postdocs, and faculty.  When we moved, several others also moved to various places and the group keeps in touch loosely via e-mail and (electronic) social networks.  The unofficial leader of their group moved to Switzerland while her husband was on sabatical there this year.  Knitting is to her what building and repairing electronics is to me—she always has multiple projects, buys more yarn than she needs for a project, etc, etc.

Sarah remarked yesterday that her friend in Switzerland had e-mailed an urgent plea for suggestions on some eight different projects.  “Gee, ” I thought, “this sounds like my problem.”  I was reminded also that one of my SuperDARN colleagues calls the portion of a radar build in which we construct the phasing cables and wire antennas “the knitting circle.”  Everyone sits around with a sharp knife, connectors, crimpers, or a solder iron, making up cables and chatting like a group of knitters.  Let’s extend this a little farther…

It occurred to me that it is socially acceptable to knit in coffee shops, during lectures, on mass transit, on airplanes (politically-incorrect jokes about knitting Afghans aside), and even during church services.  What are the barriers to knitting electronics in public?  A few thoughts came to mind…

  • Soldering is incompatible with the public sphere.
  • Knitting is inherently tidy by virtue of the yarn being continuous, unlike discrete components which are tiny and hard to contain.
  • Knitting is socially “understood” whereas building electronics in public might elicit the bomb squad.
  • Most of my projects (e.g., TS-930) are too heavy to schlep around.

Ok.  That settles it.  I guess I’ll have to settle for drawing block diagrams in my little black notebook.

Candy Deliveries

April 28th, 2010

I’m fond of telling visitors to our home that I stock more electronic parts than a RadioShack.  That used to mean something.  But, I digress.

I took delivery of a used Cushcraft A50-3S 6-meter Yagi antenna yesterday (tnx, W8RU).  And, today a package arrived from Dan’s Small Parts and Kits.  Dan’s is a good place to pick up some unusal semiconductors.  In fact, he probably has the largest stock of thru-hole dual-gate MOSFETs left in the world.  I ordered a lifetime supply of piston trimmers and BF981s, in addition to a few other odds and ends for my VHF+ adventure.  As I use some of this stuff, it will get written up here—reminds me, I owe a schematic for the 6-meter RX converter.

Tomorrow, I expect to receive the remaining components (mostly miscellaneous carbon composition resistors) to build the TX section of the 6-meter converter from Mouser, in addition to some TS-930 spare parts purchased to make the shipping worthwhile.  Enough shopping!  It’s time to build some stuff.

Common Loon in DC

April 27th, 2010

Friends from Champaign-Urbana, Matt and Robert (aka Common Loon), are on tour this spring and stopped by DC a little over a week ago.  Finally got the pictures out of the camera—erm, off the card—last night.  (Nikon D40 : ISO1600 : 50 mm : f/1.8 : 1/15)

Notes on the ham exams

April 26th, 2010

I really like reading KB6NU’s blog.  He is a good writer and he has a positive enthusiasm for amateur radio which balances some of the other outlets I peruse.  But, a recent post (largely sourced from a guest) left me scratching my head.

It’s more or less billed as the foolproof guide to passing the FCC’s Amateur Extra examination for the highest class of license.  I tend to look at the ham exams as having two components:  necessary information to bootstrap your ham operating career (to the next level) and trivia questions that for most purposes amount to hazing.  There is considerable overlap between the categories and once a question loses relevance to the point of being 100% hazing, it should be removed.  Although I was not happy about it at the time, this is why the Morse code requirement was dropped.  (I might add here that the Morse code exam should have been retained for the Extra, but I have my opinions.  Mode-specific examination should also include the “sound card modes” and SSB.  But, I digress.)

So, where is this going?  The point is that anyone who is an active ham should be able to pass the Extra with minimal study.  You need to know the rules and how to hook up your station.  Some of the math formulas are important to help diagnose problems or set up your station.  The rest are trivia and can be memorized.  It’s not rocket science (or brain surgery, as rocket scientists like to remind each other; don’t ask what the surgeons say).

Ok.  Done ranting.

50-MHz RX converter (Day 1)

April 26th, 2010

This is going to be short with a few pictures.  The schematics will follow once I get things into a final form.  As anyone who follows the blog knows, I have recently acquired a VHF habit.  I have endeavored to do this at reasonable cost.  Thus, the “transverters” series begins…

One of the first things Dad won at a hamfest after we got licensed was the 1993 ARRL Handbook.  Between us, we’ve read the thing cover-to-cover a few times.  OK, that was mostly me.  I ended up swiping it at some point a few years ago and I still read it now and then.  One of the objects of my interest since the very beginning has been the chapter full of VHF projects.  I was always frustrated as a new ham that the 6-meter transmitting converter article was not a complete transverter.  This is my story of building a 6-meter transverter based on the transmitting converter in the 1993 ARRL Handbook.

The Handbook calls for a 22-MHz LO, resulting in a 28-MHz  IF.  I elected a 24-MHz LO using an inexpensive (< $1) computer crystal instead of the $15-$25 custom crystal.  We’re talking most of the cost of the project going into the crystal.  The 24-MHz LO put the IF at 26 MHz.  For the non-engineer (or non-ham) readers who’ve made it this far, this is just arithmetic:  22+28=24+26=50.  26 MHz (28 MHz) is the frequency to which we are tuning our existing receiver, 50 MHz is where we wish to receive, and 24 MHz (22 MHz) is the oscillator frequency we need to mix with the 50 MHz signal make it show up at our receiver (26 or 28 MHz).  The designs are functionally equivalent except for some tighter filtering requirements when the IF and LO move closer together.  No big deal for this design, though.

After noting two important failures in the wiring (before the walls in the photo above were installed), the oscillator jumped to life and I tuned it for maximum smoke (peaked it).

As an aside, this picture reminds me that if I had a modern digital oscilloscope, I could have a soft copy saved to insert into this post.  Ah, analog!

While the LO chain was straight out of the ARRL Handbook, except for the 24-MHz crystal, the RX strip was completely of my design.  I don’t have the schematic in electronic (or paper, for that matter) form, yet.  But, it consists of a 2-resonator preselector filter (lifted from Experimental Methods in RF Design), a TUF-3 diode ring mixer, and a diplexer mixer IF-side termination (from the 144-/220-MHz transverter article in the same edition of the Handbook).  I had an SGA4586 MMIC amplifier board soldered-up from another project; so, I tacked that on the front end.  This final step was mostly because I was in a hurry to meet the weekly landline sked with my folks.

I hooked the whole mess up to my 10-meter dipole and FT-840 to have my first tune about 6 meters.  The preamp did not appear to work, so I shunted it.  (This was not surprising since I just found it on my bench in some unknown and unrecorded state.  Plan to build something better.)  Last night, thunderstorms were in the area, so I didn’t want to leave it connected for long.  I had cleverly shunted both the preamp and the preselector, so I was getting a fair bit of static crashes from the 2 MHz image, as well.  But, I heard the W3APL beacon on 50.064 (actually 26.0725…the LO is not exactly on 24.000 MHz).

This morning, I realized my error and put the preselector in line, shunting only the preamp.  I peaked the preselector on the beacon signal.  It is handy to have a local beacon.  If I ever live somewhere without them, I think I’d almost just install a set of them for the sole purpose of helping experimenters align their gear with minimal test equipment.  Although, the HP8640B is reasonably-priced, even with option 002.  Should probably pick one up at some point.

More on this adventure to follow…

Computer Projects

April 24th, 2010

Worked on a couple of computer projects this afternoon:  1. Finally requested a username/password from Verizon so I could do authenticated SMTP through their server and thus end my relationship with gmail.  I did not think this was working earlier, but now it is after fixing a couple of lines in the Postfix file.  2. Thinking about IPsec VPN for home to use the iPod Touch from the road.  Ideas solicited.  3.  Still fighting with the mod_rewrite error in Omeka.  Would like to get this working.  More later…


April 17th, 2010

Something noteworthy that I should have added to the previous post, but that could deserve it’s own:  I’m all caught up on radio repairs, which means I’ll have more time to operate!  And, I can return to the business of building transverters (or repairing test equipment—Dad’s Tek 464 and my HP 8405A).  NN3W told me yesterday he’d give me $10 to repair his TS-930S when I got done with mine.  I told him I wouldn’t take the screws out of the case for that…

TS-930S repair notes (17 April 2010)

April 17th, 2010

This is just a quick note summarizing my repair of the 5-million S/N TS-930S.  Both the fragile MRF-485 drivers and the hardy MRF-422 finals were toast.  The power supply pass transistors (2N5886s) were also dead.  Two electrolytic capacitors in the PA bias network over-voltaged and exploded.  Original cause unknown, but certainly exacerbated by a slipped probe when setting the driver bias previously.

I almost wrote this one off and parted-out the goodies from this radio to finance a new radio.  But, when I saw the price of a used Orion or properly-configured K3/100, I realized I could repair this one a lot of times and save my money for my newly-acquired VHF+ habit and the eventual, mythical, first tower.

To begin with, I got the power supply working again with my last set of spare 2N5886s.  Should buy a half-dozen more of these to keep on-hand.  With the PA disconnected, I set the 28B line at 28.5 volts.

Now for the big job:  I tore-down the entire PA board, cleaned it, and cleaned the heatsink.  Replaced all of the bias resistors with new carbon composition types from Mouser.  Replaced the MC1723 regulator IC in the PA bias with LM723.  Replaced all electrolytic capacitors in PA.  Replaced drivers with MRF-485MP-HB (matched-pair, high-beta) from RF Parts.  Used all-new mounting hardware and mica insulators.  Replaced finals with 2SC2510A-MP, also from RF Parts.  This part is essentially the Toshiba version of the Motorola MRF-422, but at about 1/2 of the price and a little higher beta.  Yes, I know the higher beta may cause instability if run at full output or poorer IM if run at lower power.  But, I was in a thrifty and experimental state of mind.  Performed the PA bias alignment according to the Service Manual.

I fired the radio up into a dummy load on my bench (which is in the basement, two floors away from the shack—note to self:  this was a dumb idea).  No output on CW.  Check ALC—pegged.  Check Ic meter (PA collector current)—pegged.  The radio wasn’t groaning (or popping/stinking) like a circuit drawing too much current.  So, I figured it was in the current transducer circuit.  Righto!  This circuit contains a beefy 0.5-ohm cement resistor bolted to the power supply heatsink—basically they use the voltage drop across this resistor to estimate the current.  One of the sensor leads from this resistor read 0 volts.  After a good deal of tracing and troubleshooting, including inductors on the power supply board, I tracked it down to a bad trace near the connector on the power supply board, which was easily shorted with a small piece of wire.

That fixed it right up.  The radio made slightly more than 100 watts on CW and about 55 in TUNE mode, just as it ought to.  Next, I noted that the PA and P/S fans did not come on while I was transmitting, even though the heatsinks had become appreciably warm to the touch.  So, I hard-wired the P/S fan to the 8-volt line in the fan case (see the W6NL mods for more details).  In the case of the PA fan, I hard-wired a 7812 regulator (with an appropriate capacitor–0.68 uF/50 volts) to the 28B line on the power supply and brought 12 volts out to the fan.  So, both of the fans run all of the time now, which is a better arrangement.  Plus, I now have a regulated 12-volt source easily accessible inside the top portion of the radio.

I put the radio back together and took it up to the shack.  Made a few QSOs in the Michigan QSO Party and it seemed to be working great.  However, I did hear a little popping on the second radio.  I don’t know if this is a symptom of poor isolation in my station (need to follow the K9YC directives for SO2R bonding) or a power spike or IM problem on the radio.  Probably should make some measurements on those things.

Wanted: Good QSL Card Design

April 17th, 2010

I got a stack of cards from my bureau sorter the other day and that got me to thinking about my QSLing practices, which are lackluster at best.  (For the non-hams who may be reading this, “QSL cards” are postcard-like cards that serve as written confirmation of a radio contact.  The “QSL bureau” is a sort of mail co-op that combines outgoing and incoming international postcards to save money on the postage—a big deal if you exchange hundreds or thousands of cards every year.)  Although, I do respond to all of the direct cards, I’m way behind on the bureau cards.  I need to develop a better system, one part of which is combining all of my logs into one computerized database.  But, that’s an aside.

One of the fascinating things about receiving cards is looking at the design features.  My personal (“home station”) card, shown at top in the photo associated with this post, is long overdue for an update.  So, I am particularly interested in what’s out there. It seems that the advent of widespread digital printing capability has blown-open the market for full-color cards.  There are some times when I wonder if that is such a good idea—some hams and their stations are not that photogenic—at least clean up your shack and smile for the picture.  And, then there are the cards that are completely irrelevant to ham radio and the operator’s location—like bikini girls.  Seriously?  DXpedition photo cards are usually pretty good, though.  My favorite came from 6V7P/ON4HIL—a Senegalese man with portable broadcast receiver wearing a stocking cap and aviators with a cigarette hanging lazily out of the corner of his mouth.  I’m leaning toward a plain one-color card.

So, I went shopping around the usual suspects to look for my latest card in the one- and two-color cards sections.  Wow…it’s been a while since I’ve seen any stateside QSL cards…anything that’s not a plain “computer” card like the PJ2/K8GU card shown above is UGLY:  Eagles with talons extended or sitting on top of the globe, J-38s, D-104s, giant ARRL diamond logos, etc…they look bad.  So, I am on a quest for a good card and someone to print it for me.

Here are my requirements:  mega-multiple-QTH flexibility, multiple QSOs, computer or hand label, capable of mailing as a postcard, and attractive single- (or possibly two-) color design.

Now, back to finishing the repair of the last broken TS-930S.