Category: Canada

Daniel VE5DLD’s FOUR FB Saskatchewan SolderSmoke Direct Conversion Receivers

Daniel VE5DLD is a teacher in Regina, Saskatchewan, Canada. Back in early 2023 several lucky students joined him in building the SolderSmoke Direct Conversion receiver. We had asked people to build the receiver — we wanted to test the design before asking the local high school students to build it. Daniel and his students came through for us, and ended up having far more success than we did. Congratulations Daniel! Welcome to the Hall of Fame.

Daniel wrote:

Hi Bill! Yes, I had my own DC Receiver that I use every so often for fun and 3 built by my students. All working. We didn’t get any video because we just finished the school year and the kids left, but I’ve kept in contact with them and they told me they have been able to receive signals from their homes. The kids developed excellent troubleshooting skills gained large amounts of confidence in their ability to fix things. Over the next year, my students told about fixing their gaming consoles and fixing problems in their parent’s electronics. They are certainly no longer afraid of opening something up to see what is going on! And that’s what makes me the most happy! Yeah, you can just recognize myself and only mention that 3 students were able to build DC receivers.

And yes, the Michigan Mighty Mite was a fantastic gateway to home brewing!

Thanks for thinking of me and my students!

73
Daniel D.
VE5DLD

On June 19, 2023, Daniel wrote:

We got everything going and all 3 students now have receivers capable of inhaling RF. We 3D printed some knobs and hot glued them. We took one outside but didn’t hear any signals. Mid afternoon is not good for 40m. We will try again later this week and I’ll bring my KX3 to make sure there is a single for them to listen. This issue on that last radio was an improperly installed J310. The angle is was installed hid the problem well! Here are a few pictures of the completed rigs.

Back in 2015, Daniel built a Michigan Mighty Mite. I was pleased to be reminded that I had sent him the crystal. Go CBLA! For more info on Daniel’s transmitter see:
https://soldersmoke.blogspot.com/2015/10/saskatchewan-mighty-mite-video.html
Thanks Daniel! 73
___________________________

Join the discussion – SolderSmoke Discord Server:

https://discord.gg/Fu6B7yGxx2

Documentation on Hackaday:

https://hackaday.io/project/190327-high-schoolers-build-a-radio-receiver

SolderSmoke YouTube channel:

Wayde VA3NCA Receives SSB, CW, FT8, and CHU Canada on his SolderSmoke Direct Conversion Receiver

Above you can watch and listen to Wayde’s receiver as he tunes across 40 meters. It sounds good, even though Wayde is thinking about some improvements.

It was highly appropriate that Wayde’s first reception report should be of CHU Canada, the Canadian time signal on 7.850 MHz, a bit above the 40 meter band, but clearly in tuning range for an unmodified SolderSmoke direct conversion receiver. CHU is probably unique in the world in that it is transmitting the carrier and JUST ONE SIDEBAND. It transmits only the upper sideband. This makes it clearly detectable by our receiver. As Dean pointed out to Wayde, all he had to do was “zero beat” the carrier with the PTO signal (tune to the point where they are on the same frequency and the audio tone disappears). Because there is only one sideband, the direct conversion receiver can demodulate it very well. If there had been two sidebands, this would have been a standard AM signal, and our little receiver — which does very well with SSB and CW — would have been unable to demodulate the signal without distortion. (For an explanation of why this is, see: https://soldersmoke.blogspot.com/2022/12/but-why-why-cant-i-listen-to-dsb-or-am.html Warning — this is kind of in the “advanced course” category.)

Here is an overhead shot of Wayde’s receiver:

This is a really nice build. The use of what appears to be a kitchen cutting board harkens back to the early days of radio when young hams took the cutting boards from their mothers’ kitchens and used them as bases for rigs. This is origin of the term “bread board.” Frank Jones continued in this tradition by building most of his rigs on wooden boards. Wade’s DC receiver continues in that tradition.

Wade was able to decode some FT8 picked up by this receiver and recorded on his phone:


Congratulations Wade!

—————————-

For more information on how you too can build the receiver:

Join the discussion – SolderSmoke Discord Server:

https://discord.gg/Fu6B7yGxx2

Documentation on Hackaday:

https://hackaday.io/project/190327-high-schoolers-build-a-radio-receiver

SolderSmoke YouTube channel:

Mr. Carlson Makes a Thermatron Power Supply for a BC-348

When I was 14, I had to make a power supply for a Heath HW-32A. Mine ended up working, but it was nowhere near as nice as Mr. Carlson’s BC-348 supply (shown in the video above). I didn’t have a sand blaster, nor a drill press, nor much of anything else, really.

But hey, don’t real boatanchor hams use Greenlee chassis punches? What’s with the drill press and the hole saws?

Note that Mr. C takes care to make sure that the rectifier tube is in the proper angle FOR OPTIMAL VIEWING. That’s some serious attention to detail OM. And whoa, DELICATE SURFACE MASKING TAPE from 3M? Respect! Also, era-specific looming material.

His point about the importance of the cardboard washers in the power transformer was really useful. I hadn’t thought about that.

Here are the two previous BC-348 videos:



Thanks Paul!

Wilson Cloud Chambers – I Want to Build One

Wow, I’ve been wanting to build a Wilson Cloud Chamber for a long time, ever since I read about one back in the 1970s in C.L. Stong’s famous book “The Amateur Scientist.” Now this fellow Jim Messier comes along with this amazing video that features a cloud chamber that he built for a few bucks at age 13. I am feeling the pressure. No pun intended.

Back in the day, a reasonable excuse for not building this device was that it was hard to find the dry ice you needed for the cooling. No more! Now, at least in this area, you can get dry ice at your local supermarket (bring thick gloves or else you can burn your hands on this stuff). The heat is on. Well, actually the cold is on.

I wrote about cloud chambers before on this blog:

You can get the entire C.L. Stong book for free courtesy of KE5FX here:

All of this was sparked by a visit to Jim Messier’s amazing YouTube channel, “Our Own Devices.” There is a lot of great material there. Check it out and subscribe: https://www.youtube.com/@CanadianMacGyver
Thanks Jim!

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!

SolderSmoke Podcast #247 — Hating on the IC-7300, Pete Goes FT-8 with a KWM-1, Bill’s 15-10 Rig, MAILBAG

Bill’s 15-10 Rig — Click on image

SolderSmoke Podcast #247 is available:

Audio Podcast: http://soldersmoke.com/soldersmoke247.mp3

Video: (482) SolderSmoke 247 — Hating on the IC-7300, Pete goes FT8 (with a KWM-1), Bill’s 15-10 rig, Mailbag – YouTube

Bill’s Bench:

The 15-10 Dual Bander.

n 10 pole crystal filter at 25 MHz.

n G3UUR, Dishal, AADE and all that..

n Testing woes. Looked bad. But it was a bad test cable. Duh.

n VFO (Colpitts) at around 3.5 MHz.

n Buffer blues: Bad J-310s. Beware!

n Variable cap from a Heath Q Multiplier

n A bit of a black art – competing goals. Freq coverage, etc.

n BFO needed an amp to turn on the diodes in the balanced modulator

n TIA amps. SIX dual direction TIAs. 18 transistors.

n On a pine board (like Frank Jones)

n Will use the N6QW all discrete AF amp.

n Maybe an RD16 in the final?

n Will build a second one for the DR.

Shameless Commerce: Mostly DIY RF and the PSSST kit. Todd K7TFC reports: “The P3ST is on track for Lee Deforest’s birthday release (August 26th). I’m going to send out another newsletter on July 4th, and I’ll give some details on P3ST development.” Results of Todd’s Survey.

Pete’s Bench

n FT-8 on the KWM-1!

n Presentation to the ham club.

n Why the Icom 7300 is the anti-thesis of homebrew.

MMAILBAG:

— SPRAT 195 Summer 2023, in the mailbox. A happy day at N2CQR

— Armand WA1UQO sent a wonderful book about Faraday and Maxwell… And told me Jim K8OI was heading to our area. I met Jim at the VWS Field Day event. FB. Thanks Armand.

— Tony G4WIF sent Father’s Day greetings.

— Alvin N5VZH asking about electrolytics for his 2-B. Hayseed Hamfest!

— John AC2RL replacements for the IBEW. We need to start over!

— Steve “Snort Rosin” Smith WB6TNL was in the area. Sorry I missed him.

— Joh DL6ID helping us to track down origins of a homebrew receiver Grayson saw in Berlin.

— Grayson KJ7UM was in Europe visiting his wife’s relatives. But I think he is back in the USA.

— Walter KA4KXX sent a QRP HB family portrait.

— Wouter ZS1KE sent info on surface mount soldering.

— George Zaff KJ6VU Ham Radio Workbench – re-runs! Recommended audio processor. Let me know how it sounds.

— Michael AA1TJ Great to hear from him.

— Alan Wolke W2AEW on the toroids he used in Diode Ring video. Thanks Alan!

— Dean KK4DAS, AI and SWR meter project And new lexicon word: Hamsplaining.

— Bob N7SUR — Let me know we are semifinalists in the Hack-A-Day prize!

The 15 – 10 rig from above — Click on image


Canadian Build of the Direct Conversion Receiver — Do This in Your Town! (Video)

This is so cool. We have been getting reports from Daniel VE5DLD up in Regina, Saskatchewan, Canada. Daniel is a teacher and he has been building the receiver with a group of students.

They have been doing very well. They may end up having more success than we have had here.

This morning Daniel fired up his build of the receiver and it was inhaling 40 meter signals. You can hear the CW and the FT8 and you can also hear shortwave broadcast signals just above the 40 meter frequencies. Congratulations to Daniel! He is now one of very few radio amateurs who has homebrewed a receiver. I think his students will soon do the same.

Daniel’s students have built several of the boards and appear to be on the brink of full success.
Their PTOs look very nice.
The AF amps were the most challenging of the boards. Theirs look great. Excellent soldering.
We want the receiver project that we carried out at our local high school to serve has a model for others. After all, we got our inspiration from Farhan in Hyderabad. We want to see this kind of homebrewing continue. All of the information on this receiver is on our Hack-A-Day.io page:
https://hackaday.io/project/190327-high-schoolers-build-a-radio-receiver

We strongly encourage others around the world to find ways to use this project to teach analog electronics. We think the circuit strikes the right balance between simplicity and usefulness — when they are done, the students will have a useful receiver capable of worldwide reception.


Please let us know if you are building this receiver; we are especially interested in the use of this receiver in student-focused group-build projects.

Troubleshooting an Intermittent with Mr. Carlson. And Troublesome Tube Re-Branding.

This is a really great video on how Mr. Carlson (VE7ZWZ) did troubleshooting on a tube-type receiver. The problem was an intermittent. They can drive you nuts, but Mr. Carlson show us how to stay sane.

— His use of ordinary observation at the start of the process is very important. He notices a flickering glow in the voltage regulator tube. The flickering coincides with the intermittent noise that he is trying to fix. That is an important clue.

— He also can see that the grid of one of the AF amplifier tubes is getting way too hot: grid emission. That is another important clue.

— He checks the grid voltage on the AF amplifier and finds that it is way too low. It is fine on the other side of the resistor that carries the voltage to the tube. But it is close to zero at the grid. This means that the mica capacitors on the grid are suspect.

— He uses some fairly esoteric test gear — a homemade device and an an old Heathkit signal tester — to check his diagnosis. They confirm that the mica caps are the problem. He replaces the caps and the problem is gone. A very satisfying troubleshoot.

Mr. Carlson presents us with a lot of good info:

— 6K6 tubes were often in fact 6V6 tubes. And 12AX7s were often 6VJ8s! Manufacturers were deliberately re-branding tubes. So we shouldn’t be surprised if some of our solid state devices turn out to be a bit different from what was promised. This practice goes way back.

— I liked Mr. Carlson’s final sensitivity test on the receiver — he just waved his hand near the antenna connection and we could hear the receiver respond. Excellent.

— Mr. Carlson is very negative about the use of polystyrene caps in oscillator circuits. But we these simple and cheap caps being used to good effect in oscillators in India.

— The leaky and bad micas were a bit surprising. Carlson speculates that their proximity to heat-producing resistors might have caused the trouble.

Finally, it is interesting to hear the Canadian pronunciation of radio words: Solder with the L pronounced (as in the UK). Farad with the second A long and the final D emphasized (I say it just as the first two syllables of Michael Faraday’s last name).

Thanks Mr. Carlson.

Mr. Carlson’s Grand Receiver Restoration Project — Your Input Sought (video)

Mr. Carlson (VE7ZWZ) is launching a series of videos on the restoration of some old boatanchor receivers. I have been working on an old HQ-100, so this all resonates well with me.

He asked for viewer input on which of these receivers he should work on first. I voted for the SP-600 because I wanted to see how difficult it really is to change out the infamous Black Beauty capacitors. My second choice was the R-390, but I warned Mr. Carlson that he might need a chassis crane for that one. No kidding. Really.

I look forward to watching the series. Thanks in advance Mr. Carlson.

The NCDXF/IARU Beacons (very useful website)

So there I was, innocently checking the lower end of the tuning range on my now 17 meter SSB Barebones Barbados W4OP receiver. I had it tuned to the bottom of the 17 meter phone band. All of a sudden I hear YV5B in CW. It was obviously a beacon transmission.

I had forgotten about these beacons. Some quick Googling brought me to a very up-dated web site:


The site shows exactly which station is transmitting at any given moment. There is also a very handy map display giving beam headings and distance from your location.

So far, I’m only hearing YV5B and VE8AT. I hope to hear more once the Coronal Mass Ejection is behind us.

Check it out. Leave your receiver on 18.110 MHz. Let us know what you are hearing.

Three cheers for the NCDXF and the IARU!

A Christmas Story: Mike AA1TJ Builds Receiver for 486 kHz, Listens to Fessenden Commemoration (Audio)

Mike’s 486 kHz receiver

As if being able to get home on Christmas Eve 2021 and then catching the Webb Telescope launch was not enough, Santa had another gift for us: Michael Rainey, AA1TJ, the Homebrew Hero of the Hobbit Hole, was back at it, melting solder. Mike threw together a regen receiver that allowed him to receive a transmission commemorating Reginald Fessenden’s historic first transmission of phone signals. I was really pleased to once again be able to read about an AA1TJ radio adventure. Thanks Mike! Here is what Mike heard: http://soldersmoke.com/AA1TJ 920km.mp3
Mike wrote:

My chum, Peter/DL3PB, recently told me that Brian/WA1ZMS would broadcast a commemoration of Reginald Fessenden’s mythical (operative word) 1906 Christmas Eve AM transmission. Doesn’t that sound like fun?


True to form, I began scratch-assembling my receiver yesterday afternoon just as Brian went on the air. Then again, a two-transistor regenerative radio for 486kHz isn’t exactly rocket science. In any case, I was up and listening inside of a half hour.

What did I hear? Static. Just static. As a sanity test I quickly tuned down to 371KHz to find my favorite non-directional beacon, “GW,” beaming in loud and clear from Kuujjuarakip.

Kuujjuarakip?

Kuujjuarakip is a tiny settlement of mostly Inuit and Cree inhabitants located up on Hudson Bay. The villages are primarily accessible by air and water so a robust radio beacon is an obvious necessity.

Satisfied that my receiver was working properly, I re-tuned to 486kHz. Back to static. On the bright side, at least there were no commercials. I continued listening intently until Vic called me to dinner. After the dishes were done I slipped back down to my underground radio shack for one last try.

I heard it right away. Beneath the static I heard a weak, out-of-tune, solo violin playing, “Oh, Holy Night.” The signal strength varied wildly with ionospheric propagation. When the signal finally climbed high enough above the noise I ripped out the bipolar transistor audio amplifier stage, connecting my headphones directly to the junction field effect transistor detector output terminals. Of course the audio was far weaker now, yet I could easily follow the tune until it eventually faded away. Not bad for an estimated 15 watt ERP AM signal from a distance of 920km. And on 486kHz, no less, just a hop-skip-and a jump from the old 500kHz Maritime CW band; where countless ship radio operators went to send their last SOS.

Returning to the house, I emailed my reception report and included a short recording that I had made of it. Brian replied just after midnight; apparently, equally as stoked

“Yours’ is the best DX ever given your regen RX! Way to go! I just love it.”

He went on to tell me that he was born and raised in Vermont, but he’d been working as a radio scientist down in Virginia since 1990. Told me his heart was still here in the Green Mountains and he was touched to learn his meager signal had found its way back there on Christmas Eve. All in all, a night to remember.

If you’re still with me I hope you’ll listen to the short NPR story in the provided link. It originally aired on the supposed 100th anniversary of this event. It’s not just about radio history. It’s about belief, memory and the myths we lug around in our heads. I thought it was well done.

Cheers,
Mike

Listen to what Mike heard. He says he “merely connected the mic input line of my computer across the headphone terminals. Some of the noise in the recording, – certainly the higher frequency stuff – is a byproduct of the computer. The headphone audio with the computer switched off was much more pleasant.” Here it is: http://soldersmoke.com/AA1TJ 920km.mp3

NPR story (audio and text)

VE7SL’s Beautiful Single Tube Transmitter and Single Tube Regen Receiver

Just stunning, in their simplicity and beauty. Really amazing work. Kind of reminiscent of my ET-2, but with tubes, and much nicer construction. More details here:

RECEIVER: https://qsl.net/ve7sl/neophyte.html

TRANSMITTER: https://qsl.net/ve7sl/neotx.html?fbclid=IwAR3cM6tSRjyTsNouHWVz_buuzz4C9O-IwQbdZM5dekkle69ZW7-JBQcHTVI

Three cheers for Steve VE7SL! I’ve been linking to his blog for several years, but somehow I missed this magnificent red rig.

Steve’s online notebook: https://www.qsl.net/ve7sl/

Steve’s blog: http://ve7sl.blogspot.com/

A Step Closer to the Elser-Mathes Cup? Ham Receives Signals from Mars

That is the antenna that Scott Tilley VE7TIL used to receive signals from the Chinese spacecraft Tianwen-1 in orbit of Mars. In a recent SpaceWeather article, Scott comments on the importance of SDR receivers in these deep space reception efforts.


I’ve been watching the Elser-Mathes cup for a long time. I dedicated my book “SolderSmoke — Global Adventures in Wireless Electronics” to my kids, Billy and Maria, noting that they were both possible future winners of this most prestigious award. Scott Tilley’s work has put us a step closer to an award ceremony for some intrepid radio amateur.

Here is a good article on the Elser-Mathes Cup:

Scott was in the news last year for finding a zombie satellite:

HP8640B Internal Frequency Counter Fixed (More Repairs Pending)

The HP8640B is a complicated machine. Above you see just one sub-assembly, and the page from the manual that describes it. This is what I’ve been working on. The little spring “tine” fell out of one of those discs behind the two control knobs. So I had to open this thing up, find the spot from which the tine had fallen, and glue it back in.

I used Gorilla Super Glue, followed 24 hours later by a dab of JB Weld “minute weld” dual epoxy. One of the other tines was about to fall out, so I went ahead and gave all the tines in this assembly the glue treatment. ( I bought some “Weld On” acrylic cement but the warnings on the label were quite sobering. So I left that can sealed up.)

This morning I put the thing back together. This is not easy. At one point a spring popped and a tiny metal part that is probably irreplaceable seemed to fly away into the black hole that is the shack’s carpet. I had just about given up hope when I found the thing sitting right in front of me on the bench. TRGHS.

The HP8640B fired up right away without trouble and the internal frequency counter is working fine.

As I noted in the last SolderSmoke podcast, a very nice community devoted to the HP8640B has developed around the world. Here are some of the notable participants:

Bill at Electronics Revisited is a very nice fellow with lots of experience on the HP8640B. He offered to sell me a replacement unit for the assembly pictured above. If you have an ailing HP8640B and are looking for someone to work on it for you, Bill is the guy you should talk to: http://www.electronicsrevisited.com/ He also very kindly offers to answer any questions you may have about the HP8640B.
Here is the e-bay page of the fellow in Bangalore who makes the brass gears. Mine are on the way!
https://www.ebay.com/usr/engineeringideas?_trksid=p2047675.l2559
Marcus VE7CA has a great site devoted to the HP8640B: https://www.ve7ca.net/TstH86.htm
BH1RBG in China has a nice site describing his adventures with the HP8640B: https://sites.google.com/site/linuxdigitallab/home/hp8640b-20v-power-supply-down
K6JCA has a good blog post about fixing the tines and the gears:
http://k6jca.blogspot.com/2018/09/repair-log-hp-8640b-rotary-switches-and.html
Steve Silverman (who gave me this HP8640B) found a really useful history of the device:
http://hpmemoryproject.org/timeline/bob_devries/some_memories_05.htm#part_05_chapt_09
And of course special thanks to Dave VE3EAC who alerted me to the falling tine problem and put me on the path to a successful repair.
The gears should be here in a few weeks, so that will be another opportunity to work on this HP8640B. Also there are some tines in the attenuator assemby that might reinforce with the glue treatment.

HP8640B — Fault Found! A very TINY and Hard-to-Fix Fault

I’ve been troubleshooting the internal counter in my HP8640B signal generator. The generator itself works fine. And the counter works fine for all signals coming in on its “external” port. But the internal counter stopped working properly above 16 MHz. So I started digging into the manuals and the schematics, re-familiarizing myself with the digital logic behind pre-microcontroller frequency counters. NOTE: If you are working on one of these, be sure to be using the correct version of the manual and schematic. At one point I found a really nice high def copy of an HP8640B manual (for one used in a Patriot Missile System!) only to discover that MY A8A3 board was significantly different from the one in this manual. BAMA provided a manual that matched my device: http://bama.edebris.com/manuals/hp/8640b/

Every dark cloud has a silver lining. Here, the silver for me came from opening up the HP8640B. What an impressive looking piece of gear. It looks like something from the Apollo command module, or perhaps from a nuclear weapon. “The RF source is a 256 to 512 MHz cavity-tuned oscillator that is mechanically tuned…” There is phase lock circuitry. The are AM and FM modulators and a really useful array of attenuators. There is a frequency counter with an external port and an internal frequency counter that measures the original 256-512 MHz signal, then divides down to give a very accurate readout of the output frequency. This is the kind of device that would generate a cult following. Count me in!

Also, I’ve sometimes lamented the lack of VHF test gear on my work bench — the HP8640B could really help me move me into the VHF range.

I started the troubleshooting with some observations and noodling. At what frequency did the internal counter stop working? What did the readout look like when it stopped working? What device failure could lead to these symptoms? I was aided in this by suggestions sent in by readers of my previous blog posts. Thanks guys.

I was just getting ready to start some intrusive testing on the logic devices in the internal counter when Dave VE3EAC sent me this:

—————–
I think you might be overthinking the failure mode here. I had a similar problem with my unit and it was one of my early Covid-fix-it projects. There is an assembly that controls the bands on the front. It has the famous gears that crack. On the back side are two sets of rotary switches that control a lot of stuff. The switches are of a very unique HP design and offer a lot of advantages over traditional switches EXCEPT they fail in an unusual manner. A PC board has all of the interesting wiring and very tiny double leaf springs short tracks together as needed. The springs tend to break away from the plastic posts on the rotating plate and not make the needed contact. Very carefully examine the insides of the 8640 and your bench top to see if any have fallen out. These are difficult to buy or fabricate. The disk is designed to be rotated 180 and use a new set of posts to locate the springs. Use a small dab of epoxy to set in place. The totally mechanical repair fixed my unit that also would not read above 16 MHz. There are a number of web pages that give great detail of this repair. Also it is worth while to replace the Delrin gears if they are cracked. Replacement brass ones are available on eBay and they will permanently fix the gear problem.
—————

I had thought about the problem being in the frequency range switch, but I had sort of tested for this by slowly rocking the switch through various positions as I watched the display. A dirty rotary switch will usually allow the circuit to intermittently work as you rock the switch. But this didn’t happen. And the HP switch felt quite sturdy, so I focused on the circuitry.

When I got VE3EAC’s message, I carefully flipped the HP8640B over and for the first time opened the bottom of the compartment. The bottom view is much more impressive than the top view:

The switches that VE3EAC wrote about are just below the ribbon cable near the center front. I could see the little springs that he was discussing on the switches. They appear MUCH more delicate than the rotator on a standard rotary switch. And I didn’t see any of them lying around below the switch. But when I tried to flip the HP8640B over, something in there moved and caught my eye. I pulled out some tweezers and pulled this out:


Wow. That little spring contact fell off the switch. That was preventing the HP8640B internal counter’s time base from changing as I went above 16 MHz. It is ironic that such a big and solidly built device such as the HP8640B should be laid low by such a TINY part.

This gets me back to my original question: Discretion or valor? Getting that spring back onto that switch will not be easy. VE3EAC sent me this K6JCA link describing how to do this. Yikes, it even requires the purchase of a special tool!
http://k6jca.blogspot.com/2018/09/repair-log-hp-8640b-rotary-switches-and.html
I’m going to let the HP8640B sit there with the cover off for a while. It will be taunting me, challenging me to fix it, to make it work the way Hewlett and Packard intended. It may take a while, but I think I’m going to have to accept this challenge. I’ve become real fan of the HP8640B and it would be a shame to leave it wounded like this.

Mr. Carlson’s Lab Attacked by Dangerous Canadian Snow Static! (Video)

Even when describing something as simple and basic as snow, Mr. Carlson is electronically awesome. This video made me realize that in the event of an EMP, his will probably be the only lab to survive.

 The SolderSmoke Daily News took up the topic of snow static back in 2011. Be sure to read the comments, especially the one from KC7IT about the QUARTER INCH ARCS that woke him up in the dorm at MIT. Check it out:

https://soldersmoke.blogspot.com/2011/10/snow-static.html#comment-form

 I’ve got to get one of Mr. Carlson’s 2020 calendars!

Mr. Carlson’s Lab Attacked by Dangerous Canadian Snow Static! (Video)

Even when describing something as simple and basic as snow, Mr. Carlson is electronically awesome. This video made me realize that in the event of an EMP, his will probably be the only lab to survive.

 The SolderSmoke Daily News took up the topic of snow static back in 2011. Be sure to read the comments, especially the one from KC7IT about the QUARTER INCH ARCS that woke him up in the dorm at MIT. Check it out:

https://soldersmoke.blogspot.com/2011/10/snow-static.html#comment-form

 I’ve got to get one of Mr. Carlson’s 2020 calendars!