Chitika: troubleshooting

Showing posts with label troubleshooting. Show all posts

I was really happy to get this encouraging message from Mark, K6HX. Mark is a real wizard -- he has been deeply involved in the production of many of Pixar's wonderful animated films. And his blog -- Brainwagon -- is always a good read. Mark offers good advice for software and hardware troubleshooting. Thanks Mark!

Hey Bill and Pete:

Just finished listening to your latest SolderSmoke on my commute
yesterday, and thought I'd drop you a line to let you know that I'm
really enjoying the "dynamic duo" format that you've adopted. Having
different ideas and different perspectives on the show, but with both
of you showing such great enthusiasm really makes the show a pleasure
to listen to. (Incidently, your audio for this last podcast seemed
much better to me, a couple of episodes seemed to be plagued with much
different levels between Pete, who was booming, and Bill, who
frequently seemed to be quite low. Whatever you did, keep it up!)

As a guy who does mostly computer/software engineering, I'm especially
liking Pete's continual, good natured prodding of Bill to get with the
program and use more gadgets like the Arduino, the AD9850 and the
Si5351. :-) But what's most valuable to me is when you guys engage
in the back and forth of debugging problems like your recent amplifier
feedback issues. And what I realized (and might come as some comfort
to Bill) is that most of the skills which you guys have developed to
understand and debug radio projects apply equally well to software.

Stop me if this seems familiar:

If you want to learn to program, you do it by programming. Pick a
simple project and try to get it working, then build on your success.

Don't try to learn it all at once. Making a computer blink an LED is
a good start.

Make use of the resources of the Internet community. Look at what
other people are doing, look at their designs, and enlist their help
when necessary.

Keep notes about what works and doesn't. Make an archive of all the
code you write. Examples that work can be helpful to create new code
that works.

Don't just poke the program with a stick, hoping it will work if you
prod it the right way. Develop a theory of why it works, and test
that theory. If the theory is not born out in practice, then don't
leave that code lying around in your program.

Don't get too wedded to your idea about why a program may not work.
Test your assumptions, even the ones that you are sure of. Often
those hide the worst bugs.

Think about modularity. Build simple routines/modules that you can
reuse to build bigger programs.

Build on the shoulders of giants: using tested modules of other people
isn't cheating. But eventually you may need to understand what is
inside these black boxes, so keep working on developing your skills.

Share your enthusiasm with others, via the Internet, Youtube or social media.
-------------------------------------------------------------------------------------------
See Bill, you've already learned a lot of the lessons you need to be a
programmer, you just learned them all with respect to radios. They
will serve you well if you decide to take the plunge into tinkering
with programming. :-)

On some of the ham radio related Facebook pages, I've been a little
annoyed lately that so many hams seem to lament that "nobody builds
anything anymore". Ironically, I suspect these are the same sort of
people who decided to pile onto Bill's amplifier project and skewer
him for its audio quality. If we want more experimentation in ham
radio, we are going to have to tolerate a little more failed (or at
least, not totally successful) experiments. But even beyond that, I
supect that there is quite likely more people (in absolute numbers)
doing homebrew now than in any time in decades. It's an incredible
golden age for homebrew. We have great books out like EMRFD, great
mailing lists, vendors to sell us amazing parts at incredibly low
prices, and the Internet to share and learn. People like you two are
part of this. What are all these complainers doing to get people to
build stuff?

I have to really thank you, Bill in particular. While I've still not
gotten all the way to building my own transceiver, you got me back
into amateur radio, fueled my interest in beacons, QRSS, WSPR and
homebrew in general. And Pete's approach to radio seems to be the
wedding of electronics and software that I find in sync with my own
ideas. I look forward to doing more projects, and hearing about
yours in the weeks and months to come.

Well done, sirs.

Mark (K6HX)

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htmOur coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmokeOur Book Store: http://astore.amazon.com/contracross-20

You guys really have to listen to this. This is culturally important. And it is a great follow-up to SolderSmoke 173.

In this 1965 radio broadcast, Jean Shepherd describes his teenage struggles with parasitics and other technical problems in his homebrew 160 meter transmitter.

He describes the sound of parasitics on a signal, saying that they sound as if the signal is being attacked by "debauched erotic locusts."

He really nails it in describing the scornful, dismissive tone that many hams use in telling their fellow radio amateur that there are problems with his signal. ( I have recently been on the receiving end of this kind of treatment.)

He observes that no one is more worried, "than a man who has built something and can't get it to work." Indeed.

During a date with a girl from his high school, he is so obviously pre-occupied with his transmitter trouble that she tells him that something is wrong with him and that his mother "should take him to a doctor."

And he describes the joy that comes when you figure out the problem and get the thing to work.

The REALLY good stuff begins at about the 25 minute point.

http://ia310115.us.archive.org/2/items/JeanShepherd1965Pt1/1965_01_29_Ham_Radio.mp3

Shep was quoting from King Lear: "O, that way madness lies; let me shun that; No more of that." In other words: "BASTA!" That is what I have said about my 40 meter troubles. My BITX 20/40 is now a BITX 20.

EXCELSIOR!

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htmOur coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmokeOur Book Store: http://astore.amazon.com/contracross-20

SolderSmoke Podcast #173 is available:

http://soldersmoke.com/soldersmoke173.mp3

7 March 2015

Bench Report:   Pete's Progress on the Let's Build Something Rig:
http://www.jessystems.com/LBS_Detail.html
Ben's cool case for his LBS rig
Bill's Tale of Woe: QRO troubles with the BITX 40
    -- QRO amplifier taking off on 40 (but not 17)
    -- Criticism and public humiliation on 40
    -- Troubleshooting
    -- Suggestions from Allison
    -- A sad realization about my VFO frequency selection
    -- Exorcism needed
    -- Pete suggests a digital solution
    -- Wow, my 'scope has an FFT! Almost a spectrum analyzer!
    -- Some thoughts on trouble shooting
    -- On the meaning of "BASTA!"
The Spring 2015 Issue of Hot Iron http://www.walfords.net
More on Pete's KX3
Encouraging other hams to build

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htmOur coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmokeOur Book Store: http://astore.amazon.com/contracross-20

Oh man, I was struggling yesterday. I guess I had been lulled into a false sense of security by the phenomenal ease with which I had put my BITX 17 on the air, then added a 120 watt amplifier, all without any sign of the dreaded feedback and parasitic oscillations that had plagued almost all of my previous projects. So when I decided to add the low pass filter and the switching/relay arrangements needed to use the amplifier with my BITX 20/40 rig, I kind of expected a similar trouble-free experience.

WRONG! And you know what? I think guys on 40 and 20 are a bit less forgiving and collegial than the folks on 17. As I struggled to exorcise the transceiver, I'd make some changes then hopefully go out onto the airwaves and call CQ, looking for a signal report. Well, I got them. Many were not accompanied by call signs. I'd be in contact with someone who was trying to help, and -- as we were trying to figure out what it might be -- we'd be bombarded with harsh, sometimes angry, anonymous commentary: "YOU'RE 20 kcs WIDE!" "Are you on AM?" "You have a CARRIER!" One fellow scornfully told me "That little QRP rig of yours is not ready for prime time." Ouch. (I didn't realize we were on prime time. Isn't this AMATEUR radio?)

Others would answer my CQ by announcing that I was "on the wrong frequency." Others would respond (off frequency) and tell me I was distorted -- I'd ask them to tune me in, then they would say, "Oh yea, you are OK -- you were just on the wrong frequency." Some of these guys seemed to be under the impression that there are "channels" on 40 meters. It was a real disheartening mess.

Then came the saving grace. I got the e-mails that appear below. WOW! My faith in ham radio was renewed! In the 18 months that I've been running the BITX rigs, I've never once worked another station using a homebrew rig. But Rick and I were 3/4 of the way there yesterday. And he was using a direct conversion receiver of his own design, with a PTO in an enclosure made from "flattened out tin-plated food tins." Fantastic! It was as if the radio gods had arranged all this to pull me out of the depths of parasitic despair! Thanks Rick! A video of his receiver picking up my BITX 20/40 appears above.

Pete and I will talk about the actual troubleshooting in the next podcast. I am HOPING to have it fixed by then. I may have to sacrifice some chickens to Papa Legba."

................

Bill,

I'm a long-time SolderSmoke podcast listener, and today one of my ham radio dreams came true.

I was listening to 40 meters today on my homebrew direct conversion receiver, and I heard your call. At first I didn't believe it was you, but there you were.

At first I just sat there dumbfounded, just listening, but soon realized that I should make a video of this "rare DX" (rare DX for me hi hi), and post it on YouTube for you to review.

My apologies for the low audio in the video. I was using my iPhone and its inboard mic leaves a lot to be desired, but the best audio of you is at 0:13, 0:50, and again at 2:12 into the video.

Heard you on 7.16 MHz, Sunday 2-22-2015 at 10:15 a.m. local east-coast time (15:15 UTC).

I'm located in Manchester Maryland (North - Central Maryland). My homebrew 40 meter rig is a PTO tuned direct conversion receiver with all discrete components. My antenna is a simple wire dipole about 6 feet above the ground just outside by workroom window.

Below are links to the YouTube video of your QSO , and the schematic the DSB transceiver that you were received on. The rig is one that I designed, based on the published works of many home-brewers from the web. I call it the Lakeside 40 (in homage to Peter Parker's Beach 40 transceiver).

So far I only completed the receiver section, and hope to complete the transmitter sometime this summer so I can use the rig at Lake Marburg (at Codorus State Park in PA), thus the "Lakeside" in the rig's name.

http://youtu.be/emsKg5n5-0c

http://www.remmepark.com/circuit6040/lakeside40.gif

73
Rick - N3FJZ

Bill,

Yes, what a coincidence with the PTO! That's the same WA6OTP PTO design
I based my PTO on.

I created a webpage tonight(very much a work in progress) so you can see
the details of how I constructed my PTO in the Lakeside 40, as well as
my rendition of a BITX 20. Click the [Permeability Tuned Oscillator], or
[My rendition of a Bitx 20] links on the left of the page.

The webpage is here:
[http://www.remmepark.com/circuit6040/index.html]

The ground plane for the Manhattan construction (and RF tight enclosure
for the PTO) are made from flattened out tin plated food cans, and the
coil-form for the PTO is cut from Masonite wall panel material with my
scroll saw.

Don't get discouraged from the less than enthusiastic response from the
others about your signal, pay them no mind; I'm sure they simply didn't
realize the significance of what it represented. To me, your signal was
the most perfect signal I have ever heard. It was perfect because I
know (from your pod-casts, and my attempts at homebrew) what it took for
it to be produced. Its existence, and the fact that I successfully
received it on my little homebrew rig too, represents the fundamental
core foundation of Amateur radio; experimentation, building equipment
with your own hands from scratch, expanding ones knowledge in the radio
art, and most important, having fun and enjoying the excitement that
comes from using gear that *you* built.

I cannot put into words how significant hearing your signal was for me
today - thank you! My biggest regret is that I didn't have a means of
transmitting yet on 40 meters, and my Bitx 20 is not ready yet,
perhaps in the future we can have homebrew to homebrew QSO's
where we can fine-tune our designs and tweak things (however we'll have
go above 7.175 MHz, or 14.225 MHz since I only hold a General ticket at
the moment).

Rick
N3FJZ.

Rick's PTO

A De-Soldering Primer

Wayne Burdick, N6KR

Removing resistors and other parts from double-sided boards is easy and

fun. After years of careful analysis of my own technique I have documented

the process. I start with technique #1, below; if that doesn't work, I try

#2, etc. Good luck!

1. Turn the board over. With one hand behind your back, a wry smile, and

the confidence of a pet surgeon, simply heat the lead in question and

listen for the pleasant sound of the component hitting the work bench.

2. Well, that *would* be too easy, wouldn't it. Staying with the solder

side for now, locate a large solder sucker (the larger the better; it

should frighten smaller pets when brandished). Heat each joint and deftly

suck out the solder with a single satisfying Thwop! Listen for the part

hitting the bench.

3. Didn't fall out, eh? No problem: rummage in that tool bin for a shiny

new roll of solder wick. Crack open a beer, too, and take a generous swig.

Wedge that wick in between the lead and pad, heat until you see the solder

flow nicely onto the wick, and pull it out of the way just in time to see a

beatiful, black annular ring around your component lead. Nudge each lead

with your iron and keep your fingers crossed.

4. OK, so you've got a tough customer: small lead, hole just barely

larger, and a bit of off-color solder that can't be bothered with any of

the usual techniques. Have another sip of that brew. Vigorously flip the

board back to the component side. Now grip the lead professionally with

your most elegant long-nose pliers and hold on tight. Give it a playful

yank, then pray. Should pop right out.

5. Damn. Finish the beer and get out your brutal, 8" electrician's

long-nose. Grab the component with gusto this time, buster, then tip the

board up at a 45. Turn up your soldering station to max and heat that baby

up on the backside. Pull down hard with the pliers.

6. No go? Hmmmm -- let's get serious. Put the board up directly on its

edge and hold it in place vertically with your chin. Since your iron is

suspect by this time, test it for several seconds on the nearest exposed

skin. (Doing it by accident is just as effective.) Heat the joint with

*feeling* this time. Lunge and parry. Don't worry about the pad, traces,

or other parts--this is war! With maximal chin pressure exerted to hold

the offending board in place, pull the lead out, out, Out!

7. OK, so you "...couldn't get hold of it...," blah blah blah. Fool!

You must risk everthing at this stage. Insert a small screwdriver under

the part, and white-knuckle that soldering iron on the obverse. Pry and

heat until it pops. (Note: It is important to keep in mind the concept of

"kick-back" should you succeed at this. PC boards are likely to

wobble, flop, slip, then fling out of your grasp once the offending little

monster finally lets go, taking test leads and soldering station with it.)

8. So, what kind of inept dweeb are you, anyway? Give up! Clip the part.

Leave some lead to grab onto and repeat #6 and 7. If your face has turned

red it is best to shield the work from veiw with your body, then steal a

quick look behind you to be sure noone is suppressing a giggle as they

watch this humiliating display.

9A. The lead came out but you STILL have some solder left in the hole?

Gads. Find another part that you can sacrifice. Press its helpless

lead into the depressingly small pit you made in the center of the pad.

Heat the base of the lead until you achieve Punch-Through. Yank and Heat,

Yank and Heat. Evetually the solder will give up in disgust and the

sacrificial component lead will slide smoothly, signalling victory.

9B. To your left is a hand drill; to your right is a #60 bit. You know

what you must do.

10. Now—you brute!— now that you've overheated the pad, broken the trace,

cracked the component, gouged the board, pitted the tip, blistered the

skin, wasted a beer, and irrefutably proven once and for all that you

should have taken up gardening instead, NOW maybe you'll learn the color

code!

;)

N6KR

Thanks Wayne! Been there! Done ALL that! This brought to mind the time I soldered in a 16 pin logic chip on a double sided board... UPSIDE DOWN. TRIBAL KNOWLEDGE MY FRIENDS.

Pete and I congratulated Colin on the First Sigs heard by his BITX (sort of like First Light for a telescope.) He is clearly following the advice offered by Farhan in the original BITX20 article: Take a break when the receiver is done; sit back to enjoy the sounds of success. I told Colin that having a small error in the build, then finding it and fixing it, well, that's icing on the cake OM. This also shows the benefit of having an oscilloscope. Here is Colin's report:

Hi Pete and Bill,

I really enjoyed the latest SolderSmoke! I think you two have got a winning formula, humour interspersed with valuable technical knowledge. Some podcasts are just too serious, there's nothing wrong with having fun in your hobby!

Progress is slow here, as always, but each week I have managed to move a little bit further forward. This week I aligned my BITX band pass filter and made a rough measurement of my crystal filter using the DDS signal generator that I built last week.

My oscilloscope is a Tektronix 465, older than me I believe! Of course there is no fancy signal level readout like the modern digital scopes, so I had to just peak the injected signal through the crystal filter and measure the frequency using a frequency counter connected to the IF amp. I followed the BITX ver 3 build instructions and my results seemed to match very closely to the Indian kit. I'm going to set my BFO at the -20dB from peak level as suggested in the ver3 instructions, I guess I can fine tune the setting later.

At first I had no signal making it out of the last RX IF amp, I traced the signal right through to the base of the first transistor but then the signal was lost. I had thought that band conditions were poor when I tried my BITX in RX last week when in fact it turns out that I'd made a small mistake building the IF amplifier that follows the crystal filter! I had wired the 4k7 resistor in the wrong place! I made the circuit good and hey presto, lots of signal coming out of the amp!

I was eager to give the receiver another try. On Fridays work finishes at 1pm, so a great chance to try out my rig during daylight hours. I hooked up the rig to a random piece of wire and I was amazed by the great noises coming from the speaker! I hadn't even set the BFO but voices were just leaping out. Man that rig has a lot of AF gain! I obtained a switched 10k log pot which I intend to use for power on and AF gain so hopefully the volume control will be OK. As a side note, it was nice to hear HF0YOTA down in the CW portion, I'm guessing that it is youngsters on the air station, I must do a search on the call later.

73, Colin M1BUU

So the little signal generator has already earned it's keep. I guess I can would have been scratching my head for a while without it!

I received a very nice message from Preston Douglas. Conveniently, he is an attorney, and I have asked him to stand ready to defend me in court should I ever be accused of manipulating the markets for Drake 2-Bs (and perhaps the market for SSDRAs).

Can any out there help Preston with his SX-110 455 kc IF can?

May 20 at 3:38 PM

Hi Bill,

I enjoyed #160, even though I heard those talks, live at FDIM.

I thought you'd be amused by what I overheard in the flea market on Saturday in Dayton. I was looking at a Drake 2B and Q multiplier being offered by a lady who said they were her father's. They looked to be in pretty clean shape, though of course there was no way to know what was going on under the hood. She was asking $200 for both, and said she was open to reasonable offers. Now, I already have a 2B and haven't found any need for the Q multiplier. And I had flown out to Dayton from NY, so would have had to ship the pair of boxes home--probably should have bought them anyway and sent them home by UPS for that kind of money.

Anyway, there were two other guys looking at the 2B. One said to the other that these were among the best receivers of the tube era, but that the prices had become inflated by this guy who does the Soldersmoke podcasts talking up the virtues of the 2B. Couldn't help smiling at that.

As to the Hallicrafters SX-110 on the repair bench. Well, I worked out a deal with a professional tech guy to trade him my non-working HP 8640b sig gen for some bench time on the 110. He found that the first IF transformer that I was having so much trouble aligning was non-working. He had no replacement, so he bypassed the whole transformer with a cap to get signal to the next stage. This is, of course, not a satisfactory solution. And nobody has that IF can to sell. I did read on another radio repair guy's web site that he, too, usually stops working on a set with a bad IF can because repair is so labor intensive.

Frankly, I don't accept that. I mean what's inside there? A couple of coils and some open silvered mica leafs. So, I plan to remove the can, open it, and fix it. According to the Internet, the built-in caps on these cans become defective and need replacement by modern capacitors. Or, maybe a wire is broken off. Before I do anything, I am going to see if that transformer is really unable to peak at 455. Anyway, maybe I'll get some time to mess with this radio over the holiday weekend.

One of the guys (or was it you?) recently said he builds 'em, makes a few contacts to prove they work, and then puts them on a shelf. Then he builds another one. It's like that sometimes.

PRESTON DOUGLAS

FIXED! Following up on suggestions from Tony Fishpool and from Roy Morgan, I put a 10 ohm resistor between the two supply lines and put 100 uF caps to ground at either end of the resistor. I can now operate the receiver at high AF gain (no problem running a speaker) without the KLUDGE of two power supplies. The RX sounds great. I will soon match it up with the equally awesome Tuna Tin 2 for 1976 QRP EXTRAVAGANZA.

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Thanks to all who responded. This morning I got a significant clue: Following up on Tony Fishpool's suggestion, I separated the power supplies: I ran the RF amp, oscillator and mixer base bias off a small 12 V battery, with the mixer collector circuit and the AF amps running of the bench 12V supply. The AF oscillations completely stop under these conditions. So the feedback is probably taking place via the 12 V supply lines. 73

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The Herring Aid 5 is a direct conversion receiver (scroll down for details). It is a minimalist design from 1976 using parts available at Radio Shack stores.    One of the parts no longer carried by Radio Shack is a 10K-2K ohm audio transformer. Following NORCAL's 1998 design update I ordered an equivalent Mouser part (Xicon 42TU002-RC).   I had been running the receiver with simple RC coupling instead of the transformer.

Yesterday the Mouser part arrived and I put it into the circuit. An increase in AF gain was immediately apparent, but the thing went into AF oscillation as soon as I turned up the AF gain.

I tried beefing up the AF decoupling.   But I think the real problem is just the presence in the middle of the board of a rather large (1 inch x 1 inch) audio transformer.    I moved it around a bit to get it away from the toroid of the preceding stage. This helped a bit, but it still breaks into oscillation if I turn up the AF gain.

Any suggestions?  Or is this just part of the minimalist 1976 lifestyle?

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Sure, this receiver is not "state of the art." But that's the whole point. I wanted to finish the receiver project that I couldn't finish back in 1976.

I tried to stick as close as possible to the original design and parts. NORCAL came up with an updated schematic in 1998 with parts that are more readily available. But Designer Jay Rusgrove was shooting for something that could be built with all the parts coming from Radio Shack.   I think that is probably one of the factors that attracted me to the project way back when. That's why Jay went with varactor tuning (no hard-to-get variable caps!). And that's why he used coils that were wound on Radio Shack 10uH RF chokes (no need for hard-to-find toroidal cores). In this sense there is some common ground between the BITX rigs and the Herring Aid 5.

I stuck with the RF-choke as a coil idea for the VFO, but went with the NORCAL-prescribed toroids for the front end and mixer coils. (I may go back and try to use chokes in these circuits, but I'm not sure my junk-box will yield the kind of RF chokes that Jay used).

I wish I had known a few things when I was building this back in 1976: More knowledge about how to wind the coils would have been a big help.  I wish I had realized that I could use a SW receiver to get the oscillator on the right frequency. I guess this was in the days before Ugly and Manhattan building techniques, but it would have been nice to know that there was no need to actually etch a board for this project (I did!).

The coils really are a bit tricky. Jay didn't use any trimmer caps, so I guess you had to just hope that the front end coil and cap resonated somewhere near 40 meters.   As for tuning the oscillator, Jay recommended scrunching and un-scrunching the turns on the RF choke. Yikes! Give me some trimmer caps!

I also found that you have to watch the level of the RF going from the oscillator to the mixer.   Too much, and the receiver is deaf. Too little, same result.    You need to experiment a bit with the number of turns on the pick-up coil from the oscillator.

The warnings about the pitfalls of that single BJT mixer were right on the mark: Lots of AM SW breakthrough. But I kind of like the background music.   Strong RFI from local FM broadcast stations was another story (WMZQ is a country music station!). I reached into my junkbox and found a low-pass filter from a Heathkit DX-60.    I just put that between the antenna and the receiver and the country music was GONE!

I really love this little receiver. I have it playing 40 meter CW as I type. It sounds great.   I feel the urge to built a Tuna Tin 2 and put both of them on 40.

In the original Tuna Tin 2 article, Doug DeMaw notes that Jay Rusgrove was thinking of doing a companion receiver and says that he was thinking of calling it the "Clam Can 5" !  There were jokes about receivers for hams with "tin ears" and about there being "something fishy" about these rigs.

Thanks to Doug DeMaw and Jay Rusgrove and QST for bringing us these little circuits.

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I know, it is just a little Direct Conversion receiver. Getting it going is no great technical achievement. But this little receiver gave me such trouble as a teenager, it has been in the back of my mind for a long time. Finally, yesterday afternoon it started picking up signals.

I felt a bit bad about insinuating (a few days ago -- see below) that QST may have made an error in the 1976 schematic. They didn't. So it was kind of spooky when I heard that first call-sign coming through the speaker: It was W1AW! It was as if they were saying: "See, the schematic was correct!"

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Opposite "sense" winding and resulting phase shift

My second attempt at building a Herring Aid 5 (the first was 1976) continues.

I thought I had discovered an error in the schematic that (I hoped) explained my failure to get this simple receiver running (scroll down for details). But Dex, ZL2DEX, in New Zealand spotted something that got QST off the hook and put all the blame back on me:

I had failed to check the rotational sense of the windings. The schematic called for 4 turns over the Radio Shack choke. So I just went ahead and wound them. I didn't pay any attention to the direction of the winding. I then hooked it up in accordance with the phasing dots in the diagram. And it didn't work. So I switched the coil connections around. And it worked. Aha! I thought! QST messed up! It wasn't my fault.

Dex brought me back to reality. He noted that I probably wound the coils with the wrong rotational sense. I confirmed this. I rewound the coil following the rotational sense of the choke. I hooked it up following the phasing dots of the schematic. This time the oscillator started right up. So the problem wasn't an incorrect drawing of the phasing dots. Instead it was my failure to remember that phasing is more than just the top or the bottom of a transformer's winding. Rotational sense is also important. That's why "phasing dots" are sometimes referred to as "sense dots."

This doesn't come up very often, because most of the toroidal transformers we make are bifilar or trifilar -- the windings are always in the correct sense because we twist the wires together before putting them on the coil. When we look at those phasing dots, we are focused on getting the proper tops of coils connected to the appropriate bottoms of other windings. We don't pay any attention to the sense of the windings. Thanks to Dex for bringing me back to my senses :-o

Grob's Basic Electronics has this definition for those phasing dots:

"	Used on transformer windings to identify those leads having the same instantaneous polarity."

This morning I did a little experiment to confirm all this: I took a toroidal core and wound a little transformer. Using a dual trace scope, I looked at the input and output wave forms. Sure enough, when the windings are in the same rotational sense, there is no phase shift.   But when that secondary is wound in the opposite sense, you get a 180 degree phase shift. I know this is very basic, but it was fun to re-learn it and to confirm is.

But I still don't have the little receiver running. I think there are a few problems. That single BJT mixer stage needs a lot of RF (2.5 volts p-p) from the oscillator.   Also, I think the 10 uH chokes that I am using are not the same as the chokes used in the original Herring Aid design. So when I build transformers on these chokes, they don't work very well.

But I will keep at it. It has been 38 years... I can wait another week or two.

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During the summer of 1976, at the age of 18, I made an audacious attempt to join the ranks of the true homebrewers. I tried to build a receiver. It was the Herring Aid 5 from the July 1976 issue of QST, a 40 meter Direct Conversion receiver intended for use with the famed Tuna Tin 2. As I have recounted (perhaps ad nauseum), I never got it to work.   My recent encounter with the ORIGINAL Tuna Tin 2 (Mojo was transferred to my BITX17, and it definitely works better now) got me thinking about this painful experience.   I decided to try again.

There is an updated NORCAL schematic for this rig. I found it (and some good articles) on the NJQRP club page.   In the original, designer Jay Rusgrove, WA1LNQ, used only parts that could be found at Radio Shack stores. In the days before the internet and Mouser, this was a good idea.  Instead of toroidal ferrite and iron powder coils, Jay built his coils around Radio Shack solonoidal 10 uH chokes.

The NORCAL version dispensed with the Radio Shack chokes, and used toroids. But I wanted to try to find out what went wrong 38 years ago. So I dug up some 10uH chokes.

I know that my problem was that I never got the oscillator working. I remember being able to hear signals with my "almost" receiver when I put my HT-37 in "CAL" mode and tuned through 40. I was so close! The Herring Aid was picking up RF from the HT-37 and using that in lieu of the LO energy that obviously wasn't coming from my Herring Aid VFO. But WHY didn't that oscillator work?

Today I started with the VFO.   Again, it didn't work!   But now I have decades of troubleshooting experience under my belt. So I poked around a bit. Then I decided to look closely at the phasing.

Take a look at the schematic(above) and the picture (below). L7 is the 10uH choke. L6 is 4 turns wound over it (or adjacent to it). Now, here is the key question: Look at the phasing dots. How would you guys connect those coils?   For me, the schematic indicates that the TOP of L6 should go to the Zener and the BOTTOM of L6 should go to the drain of the JFET.   The TOP of the choke should go over to C5, and BOTTOM of L6 should go to ground. Right? Or am I reading the phasing dots wrong?

Well, the oscillator was not oscillating in this configuration. Then I did something that I might not have known to try back in 1976: I reversed the phase of L6: I put the top of the coil to the Drain of the JFET and the bottom of the coil to the Zener. Bingo. The joy of oscillation. Now it works. (The picture below shows it as it is when the oscillator is working well.)

So, is there an error in that diagram? Was this not all my fault?

Aha! I just looked at the schematic of the NORCAL version. Check out the dots! I think that was the problem!

The transmitter was working fine on 40, but was horribly unstable on 20. In the past, this kind of thing would really drive me nuts, but experience has made me more patient. I know that "taming the beast" is part of the homebrew process.

I knew that layout was part of the problem: I had significantly less room on the board with this rig than I'd had with the BITX17: the additional bandpass filter and low pass filter, and the associated relays, used up a lot of copper clad real estate. So by the time I built the PA chain, the inputs were too close to the outputs.

The fact that the rig was stable on 40 but not on 20 led me to believe that this was not a problem of insufficient decoupling. Instead, I thought that I was getting additional inductive feedback at the higher frequency.

I noticed that the instability disappeared when I put the 1X scope probe on the input to the first amp in the RF chain (Q14). That was an important clue. Looking closely at the circuit, I realized that the base of Q14 had a long lead (several inches) up to the low pass filter. I had experienced problems with this lead on the BITX 17 project and had cured it with a relay at the low pass filter -- this relay took one end of the lead out of the circuit on transmit, preventing it from becoming a little radiator. I used that mod in this rig, and figured that that cured the trouble. Wrong. The other end of that lead was still connected to the input to the RF power chain. It was picking up enough RF to send the PA chain into oscillation.

I put a SECOND relay at the other end of the line. That took it completely out of the circuit. And the instability disappeared. I fired up the rig and worked California on 20. Very satisfying.

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From "A Simple SSB Transceiver" by Ashhar Farhan:

"What if your transmitter is unstable? Don't curse your fate. All transmitters start out as unstable beasts. Relax." Farhan goes on to provide some good pointers on how to tame the beast.

I've had very good luck with the PA in the BITX -- very little cursing of fate on this project.

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Good news on the BITX. I think I have solved the low frequency oscillation problem in the power amplifier. I tried running the PA off a separate power supply -- the oscillations disappeared leading me to conclude that the feedback was taking place via the power supply lines.   I put a 22 uF cap to ground from the top of the PA's RF choke. With this cap in place I can dispense with the separate supply kludge. The amp is stable.

This morning I also resolved a different stability problem. I'm using a relay for T/R switching. One set of contacts controls the DC power, the other set was supposed to disconnect the receiver input from the antenna/lowpass filter when on receive. But I had positioned the relay too far from the LP filter and RX input, so I ended up with this long piece of coax that was hanging off the PA output terminal and carrying lots of RF on transmit. Yes, this led to oscillations. I thought about repositioning the relay, but I think part of the problem is that even if optimally positioned, the long unshielded contact levers inside this relay would be radiating a lot of RF and causing stability problems.   So instead I put a small reed relay very close to the PA out and RX in connections. It carries the signal to the receiver when in R mode, and disconnects the RX when in T mode, without any long coax lines or unshielded relay levers.   It works.

I still have a few things to do:
-- I need to build a proper speaker amplifier so that I can dispense with the amplified computer speakers KLUDGE.
-- I need to get a 3 pole double throw switch and some crystal sockets so that I can switch crystals from the front panel.  Three rocks will cover all of 17 meter phone.
-- I have to build a case for this rig. I'm thinking wood, with tin or aluminum sheeting glued to the inside (for shielding).

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htmOur coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmokeOur Book Store: http://astore.amazon.com/contracross-20

I found a quote from Doug DeMaw that I wanted to share. This one seems appropriate as I struggle with unwanted oscillation (and as Halloween approaches). From the January 1986 QST:

"Self -oscillation occurs not only in the low-frequency and high-frequency spectrum, but it often takes place at audio frequencies! I have actually heard the transistors "screeching" when strong audio oscillations were taking place in a homebrew transistor power amplifier. On one occasion I could see a bluish glow coming from within the transistors (visible through the ceramic heads of the devices) during a period of instability. Needless to say, the transistors self-destructed."

I've been having some instability problems with my BITX 17 IRF510 final. But I think I have the problem identified. I was getting low frequency oscillations (around 100 KHz). Tonight tried putting the IRF510 on a separate power supply. The oscillations ceased and I am getting a nice clean 3 watts out. So I'll go back and beef up the decoupling on the power supply lines.

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htmOur coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmokeOur Book Store: http://astore.amazon.com/contracross-20

Thanks to the manual provided by Jim and the HV test gear provided by Alan Wolke, I was able to finish the troubleshoot on the broken Tek 465. It is the HV multiplier, U1432. The cathode voltage is supposed to be -2450. It initially tested at -1000. The manual calls for a jumper to be removed to take the HV Multiplier out of the circuit. As soon as I did that, the cathode voltage went to -2500. Bingo.

Now I have to get a replacement for U1432. Any carcasses laying around?

Thanks guys.

Chitika

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Overheard at Dayton: Drake 2B Market Manipulation! (& Help needed with 455 kc IF can)

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Stopping the AF oscillations in the Herring Aid 5

Direct Conversion Receivers, AF Transformers, and Motorboating

Some notes on the Herring Aid 5

Herring Aid 5: Working after 38 years!

Herring Aid: It was NOT the dots! Rotational Sense and Phasing

38 Year HB Mystery Solved? Was it the phasing dots?

BITX20/40 Update #6: 20 Meter Exorcism

Words of Wisdom (on Amplifier Stability)

BITX Build Update #14 -- STABILITY!

Yikes! Screeching Transistors Throwing off Blue Light!

Tek Troubleshooting Triumph

AHMED HASSAN MOHAMMED

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