AA9IL's Sputnik Tube, Altoids Tin Transmitter

November 24, 2023

Hello Bill

I have just built an tested a 20 meter “Sputnik” transmitter. It uses two Soviet era “rod” tubes and is fixed tuned to 14.060 MHz.  I was able to compress the design to fit in an Altoids tin. The plate tuning capacitor was replaced with a fixed capacitor value closest to the variable for peak power out. Plate voltage is 90 volts and I key both the oscillator and PA via the B+ line. Power output is around 200mW and my first test transmission from the Chicago area was picked up 864 miles away on the east coast via the Reverse Beacon Network. It was definitely Joy of Oscillation and Joy of Transmission!

73, Mike

AA9IL

EN52

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Mike's rig has been heard by many Reverse Beacon Network stations: 

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November 29, 2023

Bill: 

I started a QSO with AC2C in Ellicott, MD who responded to my CQ but the band dropped (20m)

But that’s a good start and I’ll keep at it!  So, yay!

73 Mike

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Here are some earlier blog post on rigs using Soviet rod tubes: 

https://soldersmoke.blogspot.com/search?q=Sputnik+tubes

Other Workshops: Genius Girl Fixes (Re-builds!) Old Tractor

This is amazing.  I put it in the "other workshops" category, but when you watch this you will see that she re-builds this tractor with NO WORKSHOP AT ALL.  It seems to be done at roadside and on the front yard of her house.  With some very basic tools. 

I would be a complete mess if I tried this.  And I would fail to get it going. 

I have posted about Lin's projects before.  See:  https://soldersmoke.blogspot.com/2022/04/the-next-time-you-hear-someone.html

Here is her channel: https://www.youtube.com/@LinGuoErOfficial

Video on Discovery and Restoration of the Apollo Guidance Computer

I've probably posted before about CuriousMarc's efforts to restore the DSKY Apollo Guidance Computer.  But this Wall Street Journal video sums it up and adds detail about where the computer they worked on came from:  the guy in the video found it discarded in a junk warehouse that he bought in the 1970s!  Those of us who scour those under-the-table parts boxes at hamfests will appreciate this find, and the ensuing restoration. 

Some Short-Wave Listener QSL Cards

Click for a better view

I haven't received many, but I always like QSL cards from shortwave listeners.  Someone out there is listening!  

The top one is from recent contact. It arrived from Hungary via the W2 QSL bureau.  Here is Tamas HA00001: 

https://www.qrzcq.com/call/HA0002SWL

https://www.c3.hu/~ha0khw/ha00001.html

The middle one is from my youth.  in 1975 Nick in Moscow USSR heard my contact with OD5IO.   I didn't remember the contact with Lebanon.  It turns out that the operator was K4NYY (who is now a silent key.  See https://www.qrz.com/db/K4NYY/?mlab=). 

The bottom one pre-dates me by more than twenty years.   It comes from Berlin in 1936. W5AIR was heard working EI7F on 20 meter CW.   Does anyone have any info on this SWL? 

Over on The SWLing Post blog,  readers posted this info: 

Klaus WernerNovember 25, 2023 at 1:12 pm On the German SWL card, it would probably need some serious digging into records.Consider, it’s dated 1936, about 3 years before the nazis started WW2 (which included tough restrictions on all radio listeners, including death penalties for listening to and spreading enemy news).The name STOLP is fairly common in Germany.Interesting, the Bernauer Strasse in Berlin was well known during the cold war as there was a border crossing to East Berlin used for exchanging spies (I believe).
13dka

November 26, 2023 at 8:32 amDE 2518 /F was Willi Stolp, the DE number popped up in listener contest lists in “CQ” 1936 and 1944. There is an Excel spreadsheet that lists him as DE 2518 /G (/F stands for Berlin, /G for Silesia) with a (inaccessible) link to the DARC district Chemnitz, which may indicate that he survived the war and became a regular ham. That’s all there is to find out so far, there is a ham with the same name but since the name isn’t that rare it may not be the same guy.

A FREE Book from the Early Days of Ham Projects with Transistors: The CK722 -- The Device that Got Pete Juliano Started in Homebrew

 

Pete N6QW sent this amazing book to me this morning.  Pete wrote: 

"The book was the size of a Notebook and had a gray cover. I built some of the projects like the CPO. If you had a CK722 then you were there."

You can get the book for free here: 

 http://n4trb.com/AmateurRadio/RaytheonTransistorApplications/Raytheon%20Transistor%20Applications.pdf 

The impact of the CK722 on Pete Juliano, on ham radio, and eventually on SolderSmoke was quite profound. Back in 2015,  I wrote about this on the blog: 

I knew Pete had a lot of experience with transistors, but I didn't realize just how far back this experience reaches.  Pete writes, "The March 2015 issue of QST  had an article about a 1953 transistor transmitter project which was really advanced technology since the transistor was only invented about 5 years before that time...  About 1953 at the age of 11, I built my first solid state audio amplifier using the venerable CK722 from Raytheon. The transistor did look a bit strange in that cool blue cube shape with a red dot on the side to identify the collector. What a joy and surprise to me that it worked the first time power was applied...  It  was the CK722 that in large measure started me on a life’s work and engagement in a wonderful hobby. That CK722 path also led me to designing and building a QRP solid state version of the Collins KWM2 which I call the KWM-4."  I asked Pete why an 11 year-old kid in 1953 felt compelled to build a solid state audio amp.   The answer is very cool:  Pete's father had introduced him to crystal radios at age 8.  Pete wanted an amplifier for his crystal set, but his dad was worried about him building high voltage tube gear.  So that's how Pete got his VERY early start with transistors.

We are really lucky to have Pete Juliano sharing his vast tribal knowledge with us.

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You can see a complete set of SolderSmoke posts about the CK722 here: 

https://soldersmoke.blogspot.com/search?q=CK722

Wikipedia has a nice article on the CK722.  The design contest Raytheon sponsored would be the kind of contest we could really get into!  https://en.wikipedia.org/wiki/CK722

Thanks Pete.  And thank you Raytheon! 

Other Workshops: A Twin Cylinder Solenoid Electric Motor and some Very Cool Craftsmanship

This project caught my eye for a couple of reasons:  

First, it is the product of a very cool metal shop and a very skilled craftsman.  It is fun and inspiring just to watch Maceij build this motor.  We see great precision in the metal cuts, speedy tap and die work, and some great PC board technique.  The use of an open flame on the heat shrink material was, well a bit courageous. 

Second, this is a far more sophisticated version of the trivial electric motor that my son Billy and I built 17 years ago (I still have it!), following up on inspiration from Alan Yates VK2ZAY (see below).   With Alan's device we turned on power to the commutator by just sanding away the insulation on one side of the enameled wiring.  Maceij takes a much more sophisticated approach, with carefully milled switches and opto controllers turning on and off power at the right time to each of the solenoids.    

 

Maceij's YouTube channel has many other projects, many like this one:  https://www.youtube.com/@maciejnowakprojects 

Thanks to HackaDay for the heads up. 

On my Second Day on 10 meter AM, I Worked K5JC -- the Creator of the Mod that I was Using (Video)

See video above.  This happened on my second day on 10 meter AM. I was using the little GE CB radio that I had modified for 10 meters. I had lucked out. First bit of luck: the CB that I bought (for parts!) at a hamfest turned out to be just the thing I needed for a quick and easy mod. The GE box had what is called a Hygain board and -- most important -- a PLL02 chip. Second bit of luck: I stumbled across an article by Jerry K5JC on how to put this particular kind of device onto 10 meter AM. Boom, Bob was my uncle, and I got on 10. Then, today, the miracle happened. I heard Benny K5KV and I gave him a call. He asked about my rig. I described the mod to the GE CB. Benny seemed kind of surprised, and for good reason. You see, Jerry K5JC (the guy who created the mod that I was using) had just broken squelch on Benny's rig! Benny told him to get on 10 and soon I as in contact with the guy who had created the mod that I was using. The Radio Gods Have Spoken. Thanks Benny and thanks a Jerry. This was all really cool.

Think of odds of this happening: On my second day on 10 AM, running just 4 watts, I just happened to contact Benny K5KV in Texas who just happened to be in 2 meter range of Jerry K5JC, who just happened at that moment to be breaking squelch on Benny's 2 meter rig. TRGHS.

Bill's Fortune Cookie

 TRGHS (The Radio Gods Have Spoken)

Mr. Carlson's ART-13 Transmitter (with Dynamotor)

Here we have a really cool video from Mr. Carlson.  In it he reveals (admits!) to what we already know:  HE IS A HAM RADIO OPERATOR.  FB Mr. C!

You can see that he is a true ham, with a true case of THE KNACK, when you see his reaction to the inside view of the ART-13.  He seems to gasp as he notes that there is a lot of "RF goodness" in that box.   There is a vacuum relay, a bread-slicer capacitor, there is even a variometer. And lots of good, big THERMATRONS.  Only a true ham, a true Knack victim can recognize this RF goodness. 

The Dynamotor that goes with this transmitter is really interesting to me.  I have been hearing these things whining in the background (audible noise, not a signal defect) on many early morning (Saturday 3885 kHz) of the Old Military Radio Net.  I can often hear the dynamotor of Buzz W3EMD as he transmits from Rhinebeck, New York.   It was great to see the inside of this device.  

Back in 2017, Hack-A-Day took a look at Dynamotors: 

https://hackaday.com/2017/07/04/retrotechtacular-dc-to-dc-conversion-rotary-style/

There are several good ART-13/BC-348 pictures on W3EMD's QRZ page:

 https://www.qrz.com/db/W3EMD   

I was especially taken by the handwritten frequency chart on the front panel of the ART-13.  This reminded me a lot of the handwritten readout that I have been using on various rigs, including (most recently) the 15-10 SSB transceiver. I hope Paul focuses on this paper-and-pencil frequency chart;  it is nice to step away a bit from the glowing numerals of San Jian. 

Mr. C points out that the ART-13 was the transmitter that was paired up with the BC-348 receiver.  He will be working on both in the weeks ahead. 

Thanks Mr. Carlson. 73 OM. 

Bill N2CQR Goes Citizen Band

 10-4 Good Buddies! 

The Grid Leak Detector -- Follow-up from Yesterday's Post on the Whole Earth Catalog's "Hippy" One Tube Receiver

Click on image for a better view

When I first looked at it in the Whole Earth catalog circuit, I thought it was a regen.  But a commenter correctly questioned this conclusion.  I remembered the grid leak circuit (WN2A provided more info in the comments).  This morning I found a Wikipedia page that explains it all very well.  I especially like the description of how this detector works both with small signals in the "square law" range of the tube, and with larger signals in the linear range of the tube.  The history of the discovery of the need for the large resistor is also very interesting.  I remember building FET amplifiers and finding that they would -- after time -- shut down.  This would happen as charge built up on the gate.  I had neglected to include the normal 100k ohm resistor (that would "leak" this charge to ground).  Once I put this resistor in, the amp worked fine.  

Here is the Wikipedia article:  

https://en.wikipedia.org/wiki/Grid-leak_detector

Whole Earth Catalog Part II: More on SWL (and a Hippy One-Tube Receiver)

Click on image for a better view

Lee McKusick was correct about many things, but of course we were a bit disappointed by his focus on store bought gear.  But the 1971 Whole Earth catalog made up for this by publishing the schematic for a very simple single-triode receiver: 

Click on image for a better view

There is a follow-up article on grid leak detectors here: 

https://soldersmoke.blogspot.com/2023/11/the-grid-leak-detector-follow-up-from.html

From the Last Whole Earth Catalog (1971) -- Short Waves -- Part 1

Click on image for a better look

Having recently returned from San Francisco, it seemed somehow appropriate for me to take a look into the Last Whole Earth Catalog  (1971).   I picked a copy of this book up some time ago.  There is some radio stuff in it, a lot of it on shortwave listening.  Above is one article. I'll post more in the days ahead. 

It was around 1973 that I gave my cousin's husband Mike an S38-E shortwave receiver.  It is a wonder that he survived.  He did report electrical shocks.  

SolderSmoke Podcast #249 -- Travel, Pete's 6BA6 rig, Books!, VFOs, SDR, Computers, Spectrum Analysers, Transistor Man! MAILBAG

New VFO for 15-10 Transceiver

Schematic below

SolderSmoke Podcast #249 is available:  http://soldersmoke.com/soldersmoke249.mp3

There is also a video version of this podcast: https://youtu.be/5xyaYivtOhw

Travelogue:  

HAPPY VETERANS' DAY TO PETE AND GRAYSON AND TO ALL THE OTHER VETERANS WHO ARE LISTENING. 

Trip out to San Francisco. Sticker placed on the corner of Haight and Ashbury:  See picture below.  Note other sticker.  Really Groovy! 

Cuban Cacharreo! Andy CO2AFV's Knack Story  https://soldersmoke.blogspot.com/2023/10/a-cuban-knack-story-and-pandemic-sits.html

Bill's DXCC-100.  DONE.   

Tribal Wisdom:  W1REX on HRWB https://soldersmoke.blogspot.com/2023/11/listen-to-rex-w1rex-lots-of-tribal.html

Pete's Bench:

Pete's 6BA6 rig

Pete's 6BA6 Rig

Pete Re-invents the Shirt-pocket SSB Rig

Pete's remake of the ShirtSleeve Transceiver

Pete Builds Two Computers 

Pete Adds a Second Band to his Homebrew SDR 

 

SHAMELESS COMMERCE DIVISION:  

BEZOS BUCKS ARE BACK!  PLEASE  BUY THERE! >>>>>>>>>>>>>>>>>>>>>>>

Mostly DIY RF:  Work proceeds in the Oregon Silicon Forest on P3ST kit development. Todd is confident the P3ST will be released on December 18th.Many other kits available now:  https://mostlydiyrf.com/ 

Sign up for the newsletter:  https://mostlydiyrf.com/subscribe/ 

Bill's Bench: 

Rebuild of the 15-10 VFO (for improved Dial Spread) (with yet another QF-1 capacitor) https://soldersmoke.blogspot.com/2023/10/dial-scale-linearity-spreading-out.html

Why Building for 10 meters is harder: https://soldersmoke.blogspot.com/2023/09/why-building-for-10-meters-is-harder.html

Copper Tape shielding of 15-10 rig. 

Crushing Spurs with Better Bandpass Filters (see blog post) https://soldersmoke.blogspot.com/2023/09/crushing-17-and-12-meter-spurs-with.html

Another 15-10 rig in the works... for SSSS.   Boards are accumulating... 

More problems discovered with the Herring Aid 5 Receiver . Lots of SS blog posts  Comment from Rick WD5L.  ) https://soldersmoke.blogspot.com/2023/10/a-big-error-discovered-in-1976-qst.html   Did you try to build one?  Did you succeed or did you fail?  Please let us know. 

The Basil Mahon books (blog posts) https://soldersmoke.blogspot.com/2023/11/basil-mahon-is-author-for-us-he.html

The Sunburst and Luminary book of Don Eyles (blog posts) 

The Art of Electronics by Horowitz and Hill (blog posts) 

Spectrum Analysers:  Tiny SA Ultra https://soldersmoke.blogspot.com/2023/09/the-tinysa-ultra-spectrum-analyser-video.html  and Polarad 632C-1; George WB5OYP gave me one of these spectrum analysers  (I NEED a manual! Does anyone have a manual or a schematic? )  : 

Polarad 632C-1

Stabilizing the EB63A (with Pete recommended LP filters from e-Bay. 

MAILBAG:

TRANSISTOR MAN T-SHIRTS!  Thanks to Roy WN3F! 

Todd VE7BPO on AF amplifiers.  Thanks Todd.  

Wes W7ZOI -- Always a privilege to exchange e-mail with Wes. 

E-mail from Jay Rusgrove W1VD. About the Herring Aid 5. 

E-mail from Eamon Skelton EI9GQ!  Amazing! 

HB2HB with Denny VU2DGR https://soldersmoke.blogspot.com/2023/09/hb2hb-contact-with-denny-vu2dgr.html

Nick M0NTV on diode matching for ring mixers: https://soldersmoke.blogspot.com/2023/10/does-matching-matter-diode-matching-for.html

Paul Taylor VK3HN on the new Elecraft CW rig. 

Dean KK4DAS fixed the noise in his Hallicrafters SW receiver.  A long battle, finally won. 

Dean also in contact with G3UUR. 

Ramakrishnan VU2JXN helping me set up a backup of blog on WordPress.  

Mark KA9OOI noticed that SS podcast archive appears gone.  In fact just temporarily relocated to http://soldersmoke.com/podcastarchive.html

(SS PODCAST Archive temporarily relocated to http://soldersmoke.com/podcastarchive.html) 

Andreas DL1AJG - Crystal radio video. https://soldersmoke.blogspot.com/2023/10/building-crystal-set-videos.html

George N2APB on the Herring Aid 5

Grayson KJ7UM experimenting with Varactors and Thermatrons! 

Thomas K4SWL on Mattia's DC receiver. https://soldersmoke.blogspot.com/2023/10/mattia-zamanas-amazing-direct.html

Bob Weaver of Dial Bandspread Linearity  fame.  Electron Bunker

Mike Bryce WB8VGE QRP Hall of famer -- he too couldn't get the Herring Aid 5 working. 

Kirk NT0Z wrote about the Wayback machine.  But this former ARRL staffer he also tried and failed to get the Herring Aid 5 going.  Way back when... https://soldersmoke.blogspot.com/2015/03/kirks-herring-aid-tuna-tin-and-regen.html

New 15-10 VFO with schematic

Dial Bandspread (Before)

At corner of Haight and Ashbury

Listen to Rex. W1REX. Lots of Tribal Wisdom in this Ham Radio Workbench Interview

 

https://workbench.libsyn.com/hrwb-193-building-projects-with-rex-harper-w1rex

This week's Ham Radio Workbench podcast features an interview with Homebrew Hero Rex Harper, W1REX of QRPMe fame. (The bulk of Rex's portion starts at about 1:26:30.)

I really liked this talk with Rex.  His enthusiasm for homebrewing is really inspiring -- it is very reassuring to know that there are others like us. Rex clearly has The Knack.  

I got a kick out of Rex's story about the outhouse at Dayton.  FB OM.  

Here is the video of the mojo transfer ceremony in which shared some of the Tuna Tin 2's mojo with my BITX 17.  Thanks again Rex!  

And thanks to George and the gang out at Ham Radio Workbench. 

Basil Mahon is an Author for Us -- He explains Faraday, Maxwell, and Heaviside

 

Armand WA1UQO has sent me two of Basil Mahon's books.  They are both really great.  He is a wonderful writer who has the rare ability to present not only the people who made the discoveries, but also the technical details of the discoveries themselves.  There is so much to learn from Basil Mahon's books.  I put a link to one of them on the column to the right >>>>>>>>>>>>>>>>>>>>>>

I bought his book on Maxwell so I can read it on a long flight our to California.   

PERSONAL:

Born May 26, 1937, in Malta;  married Ann Hardwick (a teacher of chemistry), April 1, 1961; children: Tim, Sara, Danny. Education: Attended Royal Military Academy, Sandhurst, 1955-57; Royal Military College of Science, B.Sc., 1960; Birkbeck College, London, M.Sc., 1971. 

Check out his career: 

British Army, career officer, serving with Royal Electrical and Mechanical Engineers in Germany, Aden, and United Kingdom, 1955-74, retiring as major; Government Statistical Office, civil servant, 1974-96. Consultant and trainer on censuses and statistics, including work for clients in Russia, Estonia, Croatia, and Republic of Georgia.

And his thoughts on writing: 

Basil Mahon on writing: "To me, the joy of writing is simply the chance to give readers the joy of reading—to share one's thoughts and passions with them, hoping to leave them with a feeling of pleasure and well-being. By the time I came to write The Man Who Changed Everything: The Life of James Clerk Maxwell, careers in the army and the civil service had given me plenty of practice in writing instructions—where crispness and clarity were the cardinal virtues—so the big test was to try to hold fast to these qualities and to entertain the reader at the same time."

https://www.encyclopedia.com/arts/educational-magazines/mahon-basil-1937

From the Netherlands, Manu Joseph explains why he loves Mahon and Forbes' book on Faraday and Maxwell: 

Thank you Armand, and thank you Basil Mahon. 

Building a Crystal Set (Videos)

Andreas DL1AJG in Germany sent the above video to me.  Andreas is the fellow who ran the course in which his university-level students built direct conversion receivers.  

I like the presenter's technique.  But it would have been cooler if he actually used a chunk of Galena or Iron Pyrite, with a cats whisker.  (I still have some of the Iron Pyrite that Mike KL7R gave me many years ago.)  I think that all radio amateurs should (as a rite of passage) actually poke a crystal with a cats whisker in search of a signal. Like here: 

 Thanks Andreas!

Apollo Core Rope Memory -- CuriousMarc Takes it on (video)

Here is another amazing Apollo video from CuriousMarc (AJ6JV).  Thanks to Bob KD4EBM for alerting me to this. We have recently been discussing the "Apollo rope memory" as I read Sunburst and Luminary by Don Eyles (ex K4ZHF). In this video Marc and his colleague Mike get ahold of some actual Apollo memory modules, develop a device that allows them to read it,  and they discover a design error.  Wow.  

My analog HDR head hurts after watching this.  Even Marc says he was approaching his limits in explaining all this.  

I had not heard of the bug they discovered in the Apollo 11 software just a month before launch, and how they had to climb into the Saturn V to fix it.  Amazing.  

Thanks Marc, thanks Mike and thanks Bob. 

Mattia Zamana's Amazing Direct Conversion Receiver

Thanks to Ed KC8SBV for sending me this awesome video.  It looks like Mattia built this receiver way back in 1995.  The tuning indicator is very cool, and I had not seen a similar indicator before (could this be a way for us to escape the clutches of the San Jian counters or the Arduinos?)  The Italian ham magazine articles are great, and you can follow the rig description even if you can't read the Italian.  The pictures in in the attached drive are also very good.  

WB9ZKY used Google Translate to get English versions of the articles.  Thanks Chuck! 

https://www.dropbox.com/scl/fi/kil3osilchqlyk8afim2r/part1.pdf?rlkey=9ubgaqb8t4k91d1a10su9mw1p&dl=0

https://www.dropbox.com/scl/fi/t2790qatf5riepyqh5oj1/part2.pdf?rlkey=bhs77gkcchziakh7ngjbpuaz7&dl=0

I have been in touch with Mattia via YouTube:  He reports that he has done other electronic projects, but he considers this to be the most interesting.  He does not have a ham license -- he has a Shortwave Listener license.  His father was a ham:  I3ZQG. 

This is one of the rare cases in which the builder should -- I think -- be issued his ham licence purely on the basis of this build.  

Mattia writes:  

Jul 25, 2023 ITALIA

Self-built Direct Conversion Radio Receiver for the Amateur Bands 80 - 40 - 20 - 15 meters. This direct conversion receiver for the hf radio amateur bands was designed and built by me way back in 1995. Later, in 1996, it was published in two parts on RadioKit Elettronica magazine. What you hear in the video was received with a simple antenna made from 4m long wire inside the house. By connecting the receiver to a suitable antenna tuned to the various bands, the reception is truly excellent and no different from commercial professional receivers. This is undoubtedly the project that has given me the most satisfaction in my activity as an electronic hobbyist. For those interested in making it, here is the pdf of the project (italian language): https://drive.google.com/drive/folder... Here, instead, there are some photos: https://drive.google.com/drive/folder...

Mattia Zamana

A NETFLIX Series with Boatanchors and Direction-Finding -- All the Light We Cannot See

Looks good.  November 2, 2023. 

Bringing a Faulty Herring Aid 5 Receiver Into the Light -- Fixing the AF Amp Schematic Error (video)

I picked up this old homebrew receiver in March 2023 at the Vienna Wireless Society's Winterfest Hamfest.  It is a Herring Aid 5.   I was surprised to see that the builder (who was he?) got the windings on the VFO transformer right.  Later, I learned that he had also substituted MPF-102s for the original Radio Shack FETs called for in the QST article. This allowed him to overcome the PC board layout problem at Q5 (VFO).  With an MPF-102, he was able to get Q1 working by kind of shoe-horning the leads into the proper holes.  FB OM.  Whoever he was, he seemed like a really competent builder.

The Hamfest Herring Aid 5

But then I started wondering:  Did he also overcome the big problem in the audio amplifier?  You see, there is an egregious error in the QST schematic.  Between the collector of Q3 and the base of Q4 (the two AF amplifiers) they have a 10uF capacitor to ground.  That would send most of the audio to ground. This is clearly a mistake.  Not only does it not make any sense, but this cap to ground does not appear in the PC board drawing, nor in the photograph that went with the QST article.  I included this cap in my 2014 built of the Herring Aid 5, but with it, I found the receiver to be exceedingly deaf.  When I clipped that capacitor out of the circuit, my 2014 Herring Aid 5 sprang to life.  Did this hamfest Herring Aid 5 have the error capacitor?  Would it too be brought into the light by clipping one lead?  

Sadly, the erroneous third capacitor was there, and it was wired into the circuit.  The receiver worked,  but just barely.  It was very deaf.  You could not hear 40 meter band noise, and you could barely hear strong CW signals.  Builders may have thought that this was normal with such a simple receiver. 

3 10uF caps. The center one is an error.  I have clipped it out

In the video above you can see what happens when I cut the lead to the mistake capacitor.  Suddenly, you can hear band noise, and CW signals.  The receiver comes to life -- for the very first time!  

This was an error that echoed through the decades.  As far as I know there was never a published errata.  The erroneous capacitor is there in the 1977 ARRL book entitled Understanding Amateur Radio.  In 1998,  NORCAL QRP redid the Herring Aid 5.  Incredibly, THEY INCLUDED THE OFFENDING CAPACITOR in their new and improved schematic.  

NORCAL's 1998 Schematic included C14

I'm fixing up this old receiver a bit.  It was nice to have it playing 40 meter CW yesterday.  Better late than never.  

This morning I was feeling kind of guilty about paying so much attention to a receiver from 1976.  But then I opened the paper and read about the recent find of a DeLorean car.  Heck if a DeLorean from the early 80's is worthy of attention, so is a homebrew receiver from the late 1970s. 

DIAL SCALE LINEARITY -- Spreading out the Frequencies for the 15-10 BITX Rig

Click on the image for a better view

The 15-10 Rig has been performing very well, pulling in a lot of DX contacts on both bands.  But there is one thing that has bothered me:  The way the transceiver tunes.  It can be a bit difficult getting an SSB station tuned in properly.  At first I thought this was caused by a lack of lubrication on the variable cap that I've been using (out of an old QF-1), but it turned out that this was not the cause.  The problem is something that Pete Juliano has lamented several times:  LC style analog VFOs have a tendency to have the frequencies "bunched up" at one end of the tuning range.  In other words, the tuning range is far from linear.  I was having trouble tuning stations on on the portion of the band where the frequencies were bunched up.  I did some quick measurement and found that on this side of the capacitor's tuning range, one turn of the dial would move the frequency about 100 kHz -- that is far too much.  On the other end of the capacitor moved  only 22 kHz with one turn of the dial (as I recall this is close to the recommended 20 kHz per dial rotation).  Clearly I had a lot of the dreaded bunching up.  This was what was making tuning difficult. 

I had built a pretty standard Colpitts FET VFO.  I had a 6.6uH coil, and a 9-135 pF variable cap in series with a 68 pF fixed cap.  I was pleased that the VFO worked, and I put it in the circuit.  Only later did the bunching up shortcomings become apparent. 

I decided to build another VFO, this time paying attention to DIAL SCALE LINEARITY. 

I turned to the excellent Bandspread Calculator on Bob Weaver's Electronic Bunker web site:  http://electronbunker.ca/eb/BandspreadCalc.html

I plugged in the frequency range that I needed and the values for my variable capacitor.  I calculated Cs which was the combined capacitance of the feedback and coupling capacitors.  Finally, I had to make a decision about the nature of my variable cap:  was it a Midline-Center Cap or was it a Straightline Capacitance cap.  I consulted with Bob and he suggested that it might be somewhere between the two.  I got out some graph paper and measured it -- it looks to me like a Straight Line Capacitance cap, with the capacitance varying linearly with changes in in the rotation of the shaft. 

It looked fairly linear, so I selected "Straightline Capacitance."  Bob's calculator predicted a much better dial scale linearity (see the picture at the top of this blog post). 

I then built the oscillator stage in LTSpice using the values called for by Bob's calculator: 

It worked well in LTSpice: 

So I built it in the real world.  I didn't have the exact values for the padder and trimmer caps, so I use values that were close. 

Using the frequency counter in my Rigol 'scope, I again measured the frequency change for each movement of the shaft. 

Here are the results: You can see that the bunching up has been largely eliminated.  Frequency change for a 20 degree (not %) movement at one end of the capacitor's range is essentially the same as it is on the other end of the range. 

I will continue to play around with the padder and trimmer cap values to get this VFO where I want it.  I may also have to opt for less frequency range in order to get closer to the desired 20 kHz per dial turn value.  I will also have to play around with the additional capacitance that will be switched in to move the VFO down a bit to the range needed for the 10 meter band. 

The bottom line here is that Bob's bandspread calculator is very useful in figuring out how best to avoid the dreaded bunching up of frequencies that can -- sometimes -- come with the use of analog LC VFOs.  The display of Dial Scale Linearity that appears at the end of each calculation is really brilliant, and allow for an instantaneous look at how changes in the various parameters will affect the linearity of tuning.  This is a really wonderful tool for the homebrewer. 

Thanks Bob Weaver!