It's been quite a while since I fiddled with the RXTX.  I had gotten it to working - sort of - and then I fabricated an enclosure for it.  Quite stupidly, after mounting the board in the enclosure, I decided to add some more holes for additional switches, etc.  Adding holes involved drilling, deburring, and filing.  This is NOT something you do with the board still installed.  A bad senior moment!

Upshot was that, after powering up the board, I got nothing.  I suspect I more shorts than a pump and dump stock scheme.  The board has not been able to receive since then and my limited troubleshooting expertise has not served me too well.

I decided to take the time to build up my troubleshooting infrastructure beyond just a single DMM.  I had fun building the 4SQRP HF Multi Tester, which gave me a frequency counter, a crystal tester/RF generator, an AF generator, a Noise Generator, and a dummy load.  I also took a flyer on a PC-USB Oscilloscope from a Chinese outfit (you may have seen them on ebay) and it turned out to be a surprisingly nice buy at $224 delivered.  After some time, I screwed up my courage to try and troubleshoot the RXTX and encountered numerous issues where the testing suggested a hugely faulted circuit.

An example of the kinds of issue I am having was yesterday's test of the RX antenna path.  I injected a 40 mV 7 mhz sine wave into the antenna (with a dummy load connected) and started tracing it through the bandpass filters.  Signal looked good until we came out of L3, when it disappeared and there was a faint (~7mV) 28 mHz signal where I was expecting the injected signal.  At that point, I was at a loss, although T3 looked like a possible suspect. 

I also tried injecting a 1kHz signal into the op amp and found that I could see the signal at the ring/tip outputs when power was off; when power was switched on, the signal at ring and tip disappeared.

All I can be sure of is that, at least, my LO and the divider chain are working: I am getting healthy 7.0559 mHz signals that are almost perfectly in quadrature.  Nothing else seems to work as one might expect.  See below (sig was actually square.  I was just too lazy to switch the probes to 10x):

While the potential for a great deal of learning is there if I c0ntinue to beat my head against this wall, I am afraid that - having apparently mucked up quite a bit of the circuit - I am likely to travel so many wrong paths that I will "learn" a lot that I will have to subsequently unlearn.  At least I have begun to build up a modest test bench that should serve me well in the future.

Being a glutton for punishment, I am close to ordering another kit from Tony and starting all over again. 

 de robby wb5rvz

For the moment, I am unable to proceed with my project. My laptop is in the shop for rework of the thermal seal and a thorough cleaning.

Seems the addition of two sound cards (both USB), a USB mouse (can't stand those touch pad thingies), a USB-to-serial port adaptor, and SDR programs that push the CPU to places it has not gone before have all conspired to produce serious overheating in the laptop. The machine's reaction to such overheating is as elegant as it is drastic: an immediate shot-off (OFF, not DOWN)!

At first, I did not recognize the problem as overheating. I naturally thought it was a software problem (BTW, how many programmers does it take to screw in a light bulb? Answer: none. That's a hardware problem). I suspected software because the problem manifested itself initially while using the SDR program and, subsequently, showed up again (and again) in the early stages of booting up the computer. However, there was no real pattern. Sometimes it would crash to black (not blue) just before I could successfully login; other times, it would crash before the initial stream gobbeldygook as the system tried to load drivers, etc. In each case, it was a "crash to black", with all functions immediately turned off: fans, disks, screen, everything.

Suspecting OS issues, I decided to try the copy of Knoppix (a Linux distribution) I had lying around and, sure enough, Knoppix could not boot either.

The light finally dawned when, after taking a 45 minute sanity break, I came back to the computer (now cooled off) and successfully booted it up and was happily operating until, 10 or so minutes into the heavy lifting: crash to black. A quick check at the back where the fan exhaust comes out and I knew we had an overheating problem.

Off to the web for some advice. I quickly discovered that my laptop (Toshiba A75 S211) apparently has a reputation of overheating! After a few years of use, the thermal paste dries out and begins to exhibit properties more closely resembling those of glue, rather than those associated with heat transfer. The remedy involves nearly complete disassebbly of the computer and some serious cleaning and thermal repasting. Judging this to be beyond my meagre talents, I consigned the device to the hopefully more competent care of the local CompUSA tech repair center.

When I get the machine back, I shall have a great thermal test jig (my project) for its shakedown cruise.

On the software side, while I really like WINRAD, I am gravitating toward the M0KGK SDR software. WINRAD does not implement a transceiver. KGKSDR allows you to transceive with only one soundcard. Rocky needs two to transceive. I have only one soundcard capable of the full 96KHZ. If I use two, I am forced to the lowest common denominator of 48 KHZ.

In any event, the timing of this hiatus was appropriate. I have a house full of visiting grandkids, so I am completely occupied with their antics.

Does anyone reading this know how to get baby formula out of a cordless phone handset?

73 de robby wb5rvz

We have RX! See the final measurements in “WorkingRX_Measurements.pdf” in the files section.

I have done the initial TX tests and they are encouraging. See "RX_Works_NowTestTX.pdf" in the files section.

There appears to be some light at the end of the tunnel.

73 Robby WB5RVZ

Got some suggestions from several helpful experts and went back to the board. Touched up some solder joints as suggested, reinstalled the U8 chip, and retested.

Still no signal evident in Rocky (no oscilloscope here). Rocky is same as last time (spikes). Relevant voltages (dc WRT ground):
VCC: 4.92
U5
- pin 3 (clk): 2.93 from LO
- pin 5 (Q): 2.32
- pin 6 (/Q) 2.33
U6
- pin 5 (Q): 2.25
- pin 6 (/Q): 2.28
- pin 9 (Q): 2.25
- pin 8 (/Q): 2.28
U7
- pin s 1 & 15 (RX Mute): 0.05
- pins 6&11, 3&12 (from T4 Secondaries): 2.32
- pin 7 (1A) 2.32
- pin 9 (2A): 2.32
U8
- Pin 3&5 (from T4 SEC CT): 2.33
- pin 1: 2.19
- pin 7: 2.19

Back to the group for more suggestions.
Detailed results are in "RX_Test1_7_24_2007.pdf" (http://www.softrockradio.org/files/RX_Test1_7_24_2007.pdf)

I guess my natural pessimism has been rewarded. AE5BK and I tested the assembled board yesterday. Great smoke test - no smoke.

That was the good news.

The bad news is there appeared to be no signal in the I and Q lines. I did not have the courage to test the TX side, figuring if I can't at least get the receive up, I do not want to tackle perhaps even worse problems on the TX side.

I ran the voltage tests that have been suggested in the many trouble-shooting messages on the Yahoo Softrock Group and most seemed to be in line, albeit a shade on the low side. The resistance tests - as mentioned earlier - were OK.

We hooked up the antenna to a 40m buddy dipole tuned to 7.015 mhz and used Bill's Audigy SE USB external soundcard. Power was via a 12VDC regulated 1A wall wart.

Fortunately, Bill brought his scope along and we were able to trace through the LO and RX paths. I am set up for the 7.015 MHZ center frequency (the 28.06 MHZ Xtal). We saw that signal pretty well coming out of Q14.

The divide-by-4 seemed to work and we were getting signals into the two LO inputs of the mixer (U7). The square waves were - at least on Bill's scope - pretty ragged and ugly looking traces.

Nothing, however, seemed to be coming down the RX path. The 40m band was not helping us; we checked the antenna, etc. setup using Bill's known, good Softrock 40 RX. The spectrum display from that RX looked like a 1950's flattop haircut. No cw to be found.

Switching to my board, Rocky showed the all-too-common central and outlying spikes of inherent noise. Looked like no RF was making it in to the mixer. The RX Mute was - as it was supposed to be - low, so RX was enabled. The LO signals were coming into the mixer. The mixer outputs to the Op Amps did not show up on the scope, although there was some DC voltage on those pins.

We decided to go back to the drawing board and call in the elmer reserves. I have a sneaking suspicion I will need to revisit my favorite area (where there be dragons!), specifically, L4 and T4.

At least I am learning more!

The details of the test results are uploaded in "Initial testing of RXTXV6_2_ 40_30M.pdf"

The board is done. (See CompletedBoardTopAndBottom.PDF)

I got sidetracked for a couple days with some medical issues and the project went into a hiatus.

Now, however, the board is finally stuffed. The toughest part was, as I had suspected, the inductors and transformers.

With the transformers, the challenge here was to:
 Direct the wires into the appropriate holes (T1’s physical “footprint” almost obliterates the view of the holes
 Avoid shorting the wires due to their close proximity,
 Don’t lose track of the different windings’ leads

For the multiple windings’ leads, after identifying each set of matching leads with the ohmmeter, I slipped short lengths of different colored insulation over them to keep them sorted out (in addition to the 1/8” leads in the center set called for in the notes). Still, the challenge of getting those leads all into the correct holes and not shorting against each other was always there.

I found that a sewing machine needle was of great help in threading th4e windings through the binocular coils. That #30 wire just does not provide the stiffness needed to get through the holes unscathed/unbent.

A couple of times, I had sufficiently weakened the leads in the scraping/tinning process, broke the lead(s) off right at the coil, and had to rewind it. L1 was especially stressful: it just about took the entire toroid to hold those 47 turns. One must make sure to take this one on in a quiet, distraction-less environment. I did not do that and, as a result, I lost count of the turns twice and had to restart or backtrack the process each time.

I got a shock when I read a post on the reflector that suggested that T1’s secondary winding required 34 turns. I had wound it with 24 turns. I checked my notes and the schematic and, sure enough, 24 turns were required. I raised the issue in the reflector and Tony quickly straightened me out. In a Homerian (as in Simpson) moment, I had failed to note that the 34 turn T1 was for the 80/40M kit; mine is the 40/30M kit! DOH! Just goes to show you how spooked I get on this subject.

After the inductors, the additional components (Q2 and the SOIC chips on the bottom of the board) went relatively smoothly. I don’t know what we did before solder wick!

Now I’ll go over all of the joints with the scope again and begin to run the tests from the notes. There has been a very good discussion on the Softrock Yahoo Group regarding tests and measurements which I intend to put to good use.

More later

After a long weekend of planned, strategic inactivity, I got back to the project and installed the crystals and more of the transistors.

The crystals.
My kit actually had three crystals: a 28.06 HZ, a 28.224 MHZ, and a 40.5 MHZ. One of the 28.xx mhz (28.224) crystals was in a short stubby case.

The builder's notes were silent as to which to use, but I guessed (hopefully correctly) that I was being given a choice of center frequencies:
- 7.015 MHZ (28.06/4) - tall case
- 7.056 MHZ (28.224/4) - stubby case
- 10.125 MHZ (40.5/4) - tall case

I used the two crystals whose cases were both tall cases (28.060 and 40.5) to give me, if my guess is right, a small slice of the 40M cw subband and another slice spot in the middle of the 30M band.

The tricky part that one might overlook is the need to install the crystals so that they were "slightly raised above the board". The only other thing of note was the fact that the board is now really starting to get crowded.

The Transistors.
Q1, Q7, and Q8 were a straight-forward process. Did I mention that the board is getting crowded?

Q3, Q5, Q6 and the TO220 Heat sink.
You really have to read the notes very carefully. The step where you bend the leads at right angles away from the flat side of the transistor was important, as was the need to bend them such that the transistor, when placed in its spot, had its case end "very close to the heat sink mounting hole in the board". I missed that part and had to go back and redo the bending and mounting. Also one must note that the requirement is to tack the transistor in by soldering one hole from the top side of the board.

Heat sink assembly and stacking was pretty straight-forward. The sil (from the cores bag) did not fit well; it did not fit neatly in the footprint of the heat sink, but, rather, hung out on one end and was a tad short on the other. This was true regardless of the orientation of the sil.

The board is now getting pretty crowded (see "Xtals_ Qs (1,7,8,3,5,6)_and HeatSink Installed.pdf").

Coming up next, winding and installing the inductors. I do not look forward to it, but it's gotta be done.

Now that we were into the sensitive components, I made certain to use my anti-static mat and wrist band, grounding to the ground connection on my soldering station. I got an excellent deal on a Welleman grounded tip soldering station for 19.95 from our local electronics store (Tanner Electronics) and not so good a deal on a ESD mat and integrated wrist band from Radio Shack.

After a little 4th of July celebration (but not too much), I completed the mounting of the NPN and PNP transistors (Q4, Q9, Q10, Q11, Q12, Q13, and Q14), The 5 volt voltage regulator (U4), and the shunt and the ground contact on JP1.

You really need some good eyes/magnification to identify the NPN and PNP transistors. I found it helpful to divide the seven transistors into two stacks (5 X “3904” NPNs and 2 X “3906” PNPs) and then mount all from the first stack and then move on to the remaining 2 in the second stack.

After soldering the shunt wire and the ground test point onto JP1, I brought out the DMM and ran the two tests for DC power resistance to ground. The notes say that the 5VDC to ground resistance should be “slightly more than 800 ohms”: result was 814 ohms. The 12V DC to ground resistance was supposed to be “greater than 10 K ohms”: result was 1 megohm.

I believe I can call that a qualified success. I am a little nervous about how much over 10K the 12V reading was, but, in an earlier correspondence with Tony K9YIG, he did not seem too concerned by a measurement of that magnitude.

Now, it’s on to the crystals and more of the FETs. I am cautiously optimistic. The successful interim tests were a morale booster. Frequent, interim, quality checkpoints are, IMHO, a much more intelligent way to take on a construction project as opposed to the approach that waits until a grand end-of-project smoke test. Kudos to Tony.

The current board is shown in "BoardAsTested.pdf"

Flash! Once more, just after posing a question or a doubt, I find that the Yahoo Softrock group has the answer. Today, Tony responded to another ham who was at the same point I am at and had the same concerns over the high resistance on the 12V DC-to-ground. Tony's response:
"Your measurement is probably good. The reading is across a number of electrolytic caps and should be high. Sorry if the way I stated it caused some concern."

Fine business!!

All resistors and Diodes are now installed on the board. Things are getting crowded, but all still seems to be going smoothly. I am looking forward to that point in the process where I can take some test readings along the DC voltage busses. Not exactly a “smoke test”, but I look forward to the feedback opportunity presented thereby. It also represents the pause before the storm of inductor winding and placement, a task for which I feel so woefully unprepared.

There were few challenges – beyond the tedium – in installing the resistors and diodes. One has to keep alert in placing the resistors into the holes and avoid missing the silk screened circle and stub (O--) designating the correct hole placement. Similarly, one has to be alert on correct polarity for the diodes.

I do not yet have the heat sink for Q2, so I cannot know whether I installed the three resistors (R22, R23, and R24) so as to avoid any real estate challenges once Q2 and its heat sink are brought into the picture.

All’s well so far. Now, on to the transistors (Q4, Q9, Q10, Q11, Q12, Q13 and Q14), U4, JP1, and the initial tests.

The current state of the board is in the PDF "BoardWithResistorsAndDiodes.pdf".

OK - progress at last. I have installed the Capacitors, beginning with the SMT 1206 caps on the bottom of the board and then to the top and its ceramic and electrolytic caps.

I really enjoyed the tutorial videos on SMT soldering at http://www.sparkfun.com/commerce/present.php?p=BEE-7-SMDSoldering . They are highly recommended.

The bottom went pretty well. In one case, I got a little sloppy/shaky while soldering a SMT cap and managed to get a glob of solder into one of the lead holes for R48 adjacent to the cap's pad. No amount of wicking could get that plug out. Fortunately, I discovered that heating the hole up with the iron and then hitting the hole from the other side with a blast of canned compressed air blew that slag right out. A word of caution, though. That slag comes out of the hole like so much schrapnel - eye protection is essential.

The top went easily. At first, I'd just mount one component, bend its wires, go to the underside and solder/snip, repeating the process for each component. Then, things picked up as I began to mount multiple components, bending back their wires for structural integrity, and then solder/clipping on the underside.

I am perhaps being overly cautious, but, especially given my eyes and their advanced state of disrepair, I am using the magnifying glass/microscope to check all solder joints as I go along.

The electrolytics had some very close lead holes and I had to wick up bridges on a couple.

I have uploaded a pdf file (CapsInstalled_BottomAndTop.pdf) with pictures of top and bottom with the capacitors installed.

Now, bouyed by the confidence built in this first stage, I'll move on to the resistors and the diodes. Can't get too cocky, though. I know this can't be as easy as it has been so far.

OK, as promised, here are the enhanced builder's notes.

The file is named: RXTXv6 Construction Manual.pdf (at the time of writing this comment, I see no way to upload the additional file - hope I find one).

I started with Tony's notes and "steppized" them, adding graphics where it seemed appropriate. I will follow these notes as I move through the project.