Archive for July, 2010

Feeding the WA5VJB cheap Yagis

July 30th, 2010

The WA5VJB cheap Yagis are a great way to get on VHF/UHF without spending a fortune on commercial antennas.  While it is practical on the UHF/microwave bands to use a copper driven element, it is less practical on the 144 and 222 MHz bands.  I know that McMaster carries copper and brass rods, too.  But, I also like to have a coax connector at the feedpoint.  Since I am in the process of building what amounts to a “super cheap Yagi” (note that’s not a “super-cheap Yagi,” the hyphen matters; will report on this in the future), I figured I would share my feedpoint for aluminum driven elements.

While wandering through the electrical aisle of the local big box hardware retailer about six months ago, I discovered the Thomas and Betts ADR6-B2 (try the ADR6 for a drawing of a similar part) grounding lug.  This looked like a good candidate for the cheap Yagi feedpoint, especially costing only $1 for a pair.  In order to fit an SO-239 flange-mount connector to the ADR6-B2, I cut off the portion of the lug with the bolt hole and drilled my own hole (#43) and tapped it 4-40.  I did the same to the other piece.  I did not cut off the lug on the second one, but I should.  Then, I soldered a short piece of wire to the center conductor of the SO-239 jack and added a lug to it.  Here are the parts so far:

Then, I assembled the whole mess on the J-shaped driven element (dummy used for photos) using two 3/8″ 4-40 screws and a lock washer.  Note that the ADR6 lugs are installed on opposite sides of the element.

And, after installing on the wooden boom, it looks like this:

It’s not quite square and some mechanical strengthening is in order before it goes up in the air.  But, this is a considerable improvement over what I’m using now.  Ty-wraping the coax to the boom will provide considerable relief to the connector and it’s attachment.  More details will be forthcoming on the antenna, if it works.  Stay tuned!

More on the TS-930S PA

July 29th, 2010

I put the “troublesome” TS-930S back on the bench again yesterday to investigate its PA instability some more.  A few points are worth mentioning:

  1. The instability onset power gets lower with increasing frequency.  That is, at 7 and 14 MHz, the instability onset is at about 60 watts output.  At 28 MHz, that drops to 40 watts.
  2. I was able to increase the onset power slightly by increasing the resting bias of the MRF-422/2SC2510A pair from 1.1 A to 1.5 A.  I don’t know if that was a real effect or just a coincidence, though.
  3. I tried adding 0.001 uF, 0.1 uF, and 4.7 uF capacitors shunting the 28B line to ground to remove RF that I observed on that line during transmit.  I don’t have a good measurement of the amount of RF, yet.  But, I know that it’s the same frequency as the transmitter because it varies as I change bands.

I still need to find that Helge Granberg article from RF Design to locate the references.  Still counting my lucky stars that I haven’t destroyed anything in the course of these experiments.

An Evening of R/C

July 27th, 2010

It’s been over a year and a half since I flew the airplane, but interest from the young and impressionable prevailed.  We also piloted the newly-repaired boat, went swimming, listened to some 80s rock music, and had the best ice cream.  It was a good way to spend a Sunday evening.

Brookside Gardens

July 24th, 2010

Last night, Sarah suggested that we (finally) make the short trip from our home to Brookside Gardens.  To our mothers:  we are sorry we haven’t brought you there, yet.  We enjoyed ourselves and I took some pictures, none of which are particularly remarkable—just wide-open aperture and low ISO (Nikon D40 : 35mm : f/1.8 : ISO 200).  But, I thought the site needed some color.

Travel with Radios and Antennas

July 23rd, 2010

Every now and then, there is a question on one of the e-mail lists or forums about traveling by air with radios and antennas.  In my experience, most travel headaches can be minimized by adhering to a couple of simple rules:

  1. Make it easy for the security (and Customs, if international) inspectors. Pack everything neatly so it’s easy to search, even if you’re not present (checked baggage).  Label everything.  Include documentation and instructions on how to quickly disassemble things if needed.  Be courteous if searched.  This is not the time to “educate” inspectors about amateur radio.
  2. Carry your radio and computer as hand luggage. I think everyone knows this by now.
  3. Put antennas into a sensible container and check them. I’ve heard of golf club carriers, ski bags, fishing rod carriers, and cardboard boxes.  I use a 4-inch thin-wall PVC drain pipe that’s about 48 inches long.  It has a black rubber cap on one and a drain plug on the other.  This may have problems in the automatic baggage-handling systems of some airports like O’Hare.  The sporting equipment bags are better because the airlines know how to handle them.  It makes sense to use a carrier that might be similar to other baggage going to your destination.  But, in reality if you just call it your “ski bag” or “golf bag” at the counter, the agent will never ask what’s in it (aside from the usual security questions).  Also ensure that this bag is acceptable on all your flights, including island hoppers.
  4. Keep as low a profile as possible, but don’t be weird or break the law. Practice moving fluidly with all of your gear.  Expect to be questioned and prepare for it.

If the trip is international, every country is different.  So, it’s helpful to have either a resourceful, intelligent local fixer or at least to discuss your plans with someone who has been there before.  However, most countries that receive a lot of tourists and have relatively easy reciprocal licensing requirements will not pose any problems.

Noting Differences: Tektronix 464s

July 21st, 2010

Through the usual twists of fate and my inability to pass up a good deal on high-quality used/vintage electronics, I ended up with a pair of Tektronix 464 100-MHz oscilloscopes that were not quite fully functional.  To be correct, one actually belongs to my father, but until it’s working it’s essentially mine.  I did the first check out tonight and noticed something curious when I looked at the nameplate on the backs of the scopes:

Aside from the fact that the first one has Option 4 (increased EMI resistance—in other words, increased PITB factor when assembling/disassembling), what else is different/interesting?  After I noticed it, I was not surprised that one of the units had Option 4…

CW DX pranks

July 21st, 2010

One of the perpetual frustrations of being in a rare (in ham radio terms) location (or just having a big signal from an exotic location) is handling the ensuing “pile-up” of stations calling you, separating them so you can hear them and keeping them from interfering with your signal.  The sought-after (“DX”) operator must maintain control of the pile-up or pandemonium breaks loose.  A tried and true technique for controling a pile-up is to spread callers out in frequency above the DX operator’s frequency, which should remain clear, except when the DX is transmitting, of course.  This is called “working split” and on CW (Morse code mode), the DX operator indicates this condition by appending “UP” to his calls.

For unknown reasons, this concept is lost on some operators, who call repeatedly on the DX’s frequency much to the consternation of everyone else who is trying to make contact.  Sometimes, it’s an honest mistake and after some “helpful” operators send “UP UP UP UP” a few times (also on the DX’s frequency), the offender catches on.  But, in just about every pile-up these days, there’s always one or two operators at the shallow end of the pool of clue.  Tonight’s JT5DX pile-up on 20 CW (listening from the mobile on the way home from work) was no exception.

I’m never sure whether to laugh or hang my head in shame when this happens…but, now and then one of the other operators in the pile-up will answer the poor clueless soul impersonating the DX and give him a contact!  It shuts them right up and is usually good for a laugh.  I do feel a little bad every time I hear it…but, if they don’t get it when the pile-up police send “UP UP” and the DX sends “UP”, how can you explain it to them?!

K8GU/M (or how convert your 1999 Ford Escort into a real head-turner)

July 21st, 2010

When we got married, the Escort I was driving had gone to my parents in exchange for a larger vehicle with an automatic transmission and a 6-cylinder engine (all three points nods to Sarah, although I admit that it was a much better ride for the kind of driving we did).  With the transfer of the Escort, my HF mobiling days were on hold, although I kept the gear.

In order to finance a DSLR a couple of years ago, I sold-off some ham gear I wasn’t using, notably the HF mobile equipment.  I didn’t manage to sell the tri-magnet mount I borrowed from N8ET for the 2004 MnQP and a rather dismal attempt at WiQP.  This mount had an interesting life, which included being destroyed at 75 mph on I-94 north of the Wisconsin Dells.  I drop-shipped a replacement to N8ET, but had the good fortune of finding similar donut-shaped magnets and some heavy adhesive vinyl at Ax-Man Surplus.  So, with a little epoxy and elbow grease, I fixed the mount while I was still in Minnesota.  It lived to ride again in several QSO parties before my futile efforts to sell it.  I raised the requisite capital for the DSLR before the mount sold.  So, I kept it.

When we moved the DC area, it quickly became apparent that we were going to have to relinquish our delightful position as a one-car couple and the Escort returned to our lives, probably to the chagrin of my father and delight of my mother.  Dad later passed along a Yaesu FT-5100 and mag-mount VHF/UHF mobile antenna which I promptly installed.  But, I really longed for HF CW in the car like the good old days.  So, a few weeks ago, I plunked-down $30 for some knock-off Hamstick-type HF antennas for 20 and 40 and put the Yaesu FT-840 back in the car.  (Astute observers will note that I have a 100% Kenwood fixed station and a 100% Yaesu mobile station.  The IC-290H and the DJ-580T are anomalies that I permit to persist in my life for various reasons.)

There is nothing like listening to JAs via long-path on the way to work…and getting funny looks from the other commuters at the same time.  A car full of teenagers waved once.  Friends and relatives have called it everything from “a space ship” to “a hunk of junk” (thanks, Rachel).

Exceeding Tolerance

July 20th, 2010

I read IEEE Spectrum via my Google Reader (and, as an IEEE member, in hard copy).  One of the disappointing things about Spectrum is that it’s written predominantly by people who are science and technology writers, not actual scientists and engineers.  Therefore, it’s a little more sensational than what I’d like (I can read that stuff in Wired).  But, I digress.  I was pleased, however, to see an article today entitled Low Tech Fixes for High Tech Gizmos.

The author wistfully lists all of the things she’s fixed with duct tape and hot-melt glue…

This is really anecdotal evidence of the fact that many non-catestrophic device failures are due to failures of tolerance.  That is, the device (or some of its components) are operating outside their expectations in the design.  This is especially true of mechanical tolerances in low end injection molded consumer devices.  As manufacturers seek to save more, tolerances get tighter.  Cleaning, replacing batteries, disassembly/reassembly, etc, are all examples of the same class of repair.

I just repaired a toy boat for Sarah’s cousin’s son tonight.  It had dead batteries and a gear was pressed too far onto the motor shaft causing the motor to stall.  It’s a good reminder to look for the tolerance failures, even if that sounds like obvious advice.

IC-290H dial frequency offset

July 5th, 2010

Some time back, I had the good fortune to stumble across a broken IC-290H at an attractive price.  The IC-290H is a synthesized mid-1980s 25-watt 2-meter all-mode transceiver.  Since I had been contemplating a radio to use as the IF to my W1GHZ transverters for 903 through 3456 (yeah, still need to build/integrate all of these), I jumped.  The problem was described as an offset of some tens of kHz between the dial frequency and the actual transmit and receive frequencies.  Since the IC-290 lacks a user community like the TS-600 and TS-700 (my other 2-meter all-mode radio), I went to Google and then posted a quick inquiry on the Stanford VHF e-mail list to see if this was a common problem.  Google produced nothing and the VHF list produced the usual “get the Service Manual” response.  Since I already had the Service Manual thanks to the previous owner, I was set.

The synthesizer (“PLL”) in the IC-290H has at its heart a VCXO (shown above).  The control voltage biases varactor diodes D2 and D3 in a tank circuit with crystal X1 operated between the series and parallel resonant frequencies (as a very high-Q inductor).  Contributions to the control voltage come from the microprocessor (red dot), the receive incremental tuning (RIT, blue dot), and an overall bias of -9 V derived from 5 V using DC-DC converter IC2.

In the “PLL Adjustments” section of the Service Manual, the VCXO adjustments are outlined, checking the synthesizer output with a frequency counter.  I noted that as I changed rotated the VFO encoder on the front of the radio and the digits changed on the display, the output frequency of the synthesizer changed accordingly.  Similarly, the RIT caused the frequency to shift.  Neither of these things were surprising since I could tune in different stations before.  In USB mode at 145.998.5 MHz, the synthesizer should output at 134.250.0 MHz.  I read it at 134.230.21 MHz, clearly the source of the almost 20-kHz offset.  I nudged potentiometer R2 (against the vehement warnings of the Service Manual) and the output didn’t change.  For good measure, I swept R2 over its entire extent with no change.

R2, it seems, controls amount of the available -9 V bias applied to the varactors.  I checked the -9 volts line.  Zero.  Who stole the bias from the cookie jar?  The 5 V line was sagging down to 4.23 V.

I removed IC2, which is in a metal can that resembles an overgrown Mini-Circuits mixer and has only “DP-1” stamped on the cover in black ink.  For kicks, I drove this little guy with 5 volts into no load and got well over -100 V out.  Did this punk destroy other parts in my synthesizer?  I put this question to Dad, who happened to be here over the weekend.  He suggested that it might require a load to produce a regulated output.  Good thinking.  Nothing on the synthesizer board appeared to be charred.  So, my theory was unlikely and I proceeded.

Without IC2, the 5 V line bounced up to 4.95 V.  And, the output side (connected to L6) showed a DC short to ground.  If you trace the circuit from the output of IC2 to one of the legs of R2, nothing should show a DC short.  I looked for bridged solder traces.  None.  Taking the divide an conquer approach, I removed R10 (green dot), to isolate the entire RF portion of the circuit.  Still shorted.  So, this left the following three suspects:  two 0.1 uF ceramic disk capacitors and a 10 V, 100 uF electrolytic.  Since electrolytic capacitors, especially older ones, have a bad reputation for causing problems, I interrogated it first (C20, purple dot).  Bingo.

The only 100 uF capactor I had on hand that even came close to fitting was a 50 V unit from a previous repair.  I squeezed it in—it’s the big brown one against the edge of the case in the center of the photo below.  Note IC2 “DP-1” in the lower right corner.

So, I plugged the radio into a power supply and antenna.  And, low and behold…it was about back on frequency.  So, I completed the synthesizer and RIT adjustments in the Service Manual and put it back together.  It actually receives WA1ZMS/B on 145.285.0, which, Doppler notwithstanding, is GPS-locked at 145.285.000…   Stay tuned for the low-drive transverter IF modification in the next few months once I start building them again.