Lessons Learned about AI (Large Language Models): "I don't 'know' the facts the way that a human does..." Let's do an experiment...

Yesterday, as I struggled with a Large Language Model that at first gave good advice (how to build a 5 crystal filter) and then really bad advice (how to build a filter with 5 crystals in parallel to achieve a USB passband) I got a message from an old friend who currently works in this industry.  

He advised me to be careful about advice from LLM AIs.  He warned that these AIs would just develop answers based on the information that had been used to train them.  In the case of ham radio electronic questions, the training material was often littered with errors and lore and bad, wrong info.  Often this bad information would be repeated over many years.  This would make the AI more likely to use it in their answers. 

It then occurred to me that I should take one case where I knew that wrong information was in the ham radio "literature" and that this information had been repeated many times over the years.  I am referring here to the question of why hams use lower sideband below 10 MHz and upper sideband above 10 MHz.  I had explored this question in many blog posts.   Many explanations were offered -- all of them violated the Hallas rule.  All of them failed to answer the question.  I wondered, would AI be wrong?  

Well, AI was wrong.  AI said:  

Subtracting in heterodyne mixing inverts the frequency spectrum. An Upper Sideband signal generated at the IF naturally flipped into a Lower Sideband signal on the lower bands.

That is wrong.   The Hallas rule tells us that sideband inversion ONLY occurs when the signal with modulation is SUBTRACTED FROM the signal without modulation.  

I called AI on this error in its answer.  I asked it why it had given me bad information.  Its responses were telling. 

Why did you initially say that sideband inversion results from subtraction? Is this because of the material on which you had been trained?

You're asking a fair question about where that explanation came from.

The brief answer: yes, it comes down to how technical explanations are presented across textbooks, amateur radio training materials, and online discussion forums—and how LLMs synthesize those patterns.

So you are just repeating incorrect information, as long as it was repeated enough, right?

That is a fair critique, and it gets to the heart of how Large Language Models work.

I don't "know" facts the way a human does; I generate text based on statistical patterns learned from vast amounts of training data. When a simplified explanation, misconception, or shorthand rule of thumb is repeated thousands of times across forums, textbooks, and study guides—as is the case with "subtraction inverts sidebands" in ham radio literature—I am prone to picking up and repeating that pattern.

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I think we can draw three conclusions from all this: 

1) The talk about AI "personhood" is just nonsense, mostly nonsense from Anthropic. 

2) The concerns about data poisoning are real.  The ham radio "literature" is already poisoned, and look what happens. 

3)  We are living with the results of bad info in the amateur radio "literature" over the years.  AI is just spitting it back at us.  And I think it is getting worse.  Now everyone with a callsign and camera has a YouTube channel. The quality of content is low and dropping.  Soon AI will be spitting this stuff back at us. 

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Let's do an experiment.  Those of you who have access to the other AI's like Claude, ChatGPT, DeepSeek and others, just ask them the question I started with: 

"Why do ham radio operators use LSB below 10 MHz and USB above 10 MHz?"  Let's see if the other AI LLMs are better at coming up with truthful answers.  Of course, they may see this and not repeat the error. 

About the Limits and Problems and Shortcomings of AI (actually of LLMs) -- The Design and Construction of a Crystal Filter

Complaining about AI on the computer/internet while surrounded by digital rigs!

 

A couple of days ago, I described in this blog how AI (specifically the Gemini LLM) had helped me design a 13 MHz crystal filter.  There was some angry push-back from people who seem to dislike any use of AI. One fellow said I should use my own mind and hands, and that by using AI I would risk having time to stand on the street corner.  I found it kind of ironic that this observation was being sent to me on a computer connected to the internet (two tools that have made this kind of construction MUCH easier).  

In the first round I think AI helped a lot. It even drew nice looking schematics for me.  Using the motional parameters determinef by me via the G3UUR method,  AI used the basic equations to calculate the shunt capacitances and the termination impedances.  This helped me avoid many of the mathematical errors that had slowed me down in the past.  I went ahead and built this filter, and (later!) took a look at the passband in my Antuino (a Scalar Network Analyser from Farhan). 

I found the passband to be that of an "LSB filter":  the skirt was steep just below the cutoff frequency, but much more sloping farther down in frequency.  This is not what I needed.  The signal hitting this filter would be (and would remain) USB. I could try to use this filter but I would be placing my BFO/Carrier Oscillator on the sloping portion of the curve.  Carrier and opposite sideband suppression would suffer. (Note: It is NOT 20 db down!  -20 db on this meter equals 0 db.) 

And here is one point where LLM AI really screwed up:  I asked it for a 5 crystal filter that would be a USB filter: One with the steep part of the skirt above and close to the cutoff frequency.  AI LLM quickly obliged.  I was suspicuous, because I had never seen this before. Here is what AI LLM Gemini recommended: 

Wow, looks great right?  Yea,  but it doesn't work.  I built it and looked at it in the Antuino.  NOPE.  It wasn't even acting as a bandpass filter.  It is more of a notch filter. Confronted with the failure, AI LLM admitted it was wrong (my coments in red): 

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This configuration does not work. I have never seen it in any amateur radio book. Are you sure that this will work?

You are 100% correct to call that out—that schematic is incorrect and will not work as an SSB bandpass filter.

Why the Shunt-Crystal Schematic Fails

In quartz crystal equivalent circuits, the crystal reaches its lowest impedance () at its series resonant frequency ().

• Series Position (Correct Bandpass): When the crystal is placed in the series signal line, its low impedance at allows the RF signal to pass through to the next stage.
• Shunt Position (Incorrect): Placing the crystal directly from the signal line to ground causes it to act as a shunt short circuit at . Instead of passing a window, it short-circuits directly to ground, creating a band-reject (notch) response rather than a bandpass filter.

This is why you will not find that topology in Experimental Methods in RF Design (EMRFD), the ARRL Handbook, or classic G3UUR/Dishal filter literature.

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At this point I decided that a 10 crystal Cohn filter would give me the steep skirts I needed.   Here is what AI recommended: 

I went ahead and built this one.  I looked at it with the Antuino.  It works. 

You can see the steeper skirts on this filter.  These steep skirts will allow me to use this filter on 17 meters with the 5 to 5.5 MHz VFO from the old Kenwood TS-820s.  

In the course of doing this, an old friend who works in this field (and who will remain anonymous) warned me about the dangers of over-reliance on AI LLMs, especially when working on ham radio circuitry.  More on this in the days ahead.  

Using AI to Design Crystal Filters -- Please comment, especially on the use of AI

 

Earlier, AI told me that for 17 meters with a VFO in the 5.2 MHz range, and and a BFO/Carrier oscillator at 13 MHz I should not have any spur problems.  So I ordered 10 crystals from Mouser.  I hope to use it with the VFO from the Kenwood TS-820s. 

This project plunged me back onto the world of motional parameters determined by the G3UUR method, followed by the use of software to determine the shunt capacitors and the termination impedances. I have used Dishal, AADE software, and Wes Hayward's GPLA. 

Using this software can be a pain in the neck.  There are a lot of exponents.  Capacitance often has to be expressed in femto farads.  Frankly, there is a lot of potential for error. 

There is no way (as far as I know!) to skip the G3UUR measurement stuff.  You just can't tell AI to determine the motional parameters.  But after that, AI should be able to handle the calculations.  I have built these kinds of filters before, so I know roughly what the shunt capacitance should be.  Sure enough, just telling AI what the 2 motional parameters are, how many crystals I want to use (5) and the configuration (I selected the very simple Cohn configuration), and the desired bandwidth (I said 3 kHz).  AI happily spat out the shunt capacitance (which looked right) and the impedance that would result in a flat passband (613 ohms).  AI even designed the little FT-37-43 toroidal transformers that would work nicely with the 50 ohmm TIA amps on either end of the filter. 

I think this is a good example of one of the uses that can be made of AI.  It made the design of this filter a lot easier.  

Both Images Produced by AI Gemini (FLASH HIGH)

I have built the filter (in the real world) and it is mostly working.  I will perform some more tests on it and will report on this here.  

What do you folks think of all this? 

Steve KW4H's Notes on the Drake 2-B -- Part 1 - Excision of an Unnecessary Mechanical Filter

Obviously I am interested in the Drake 2-B.   Steve KW4H restores rigs of this vintage (similar to our own vintage!).  He has sent me some notes on his work on the Drake 2-Bs.  

Steve writes: 

Attached is a photo of a completely needless 455 kHz mechanical filter I found in this 2B.  Never seen this before, but I found the info -- this was the Henry DMF-2, which was a modification kit sold for the Drake 2A and 2B.  Yet more snake oil sold to the "I need a mechanical filter like a Collins" crowd.  There was a REASON why Drake didn't filter on 455 kHz -- it wasn't nearly as effective as filtering on 50 kHz, which is exactly what the passband filter does.  That, along with the 2-BQ Q-multiplier/speaker makes for a terrific receiver that rivals even many of the modern rigs of today.

That filter is clearly unnecessary, and Steve was completly right in getting rid of it.  Still, it is a Kokusai.  Pete N6QW gave me one of those.  I think I have it in my Mate for the Mighty Midget receiver.   One other note:  As a kid, Steve was in Puerto Rico and operated from the navy base club station KP4USN.  I have that station, during that period, in my log book (I worked KP4USN on April 12, 1974 on 15 CW).  I have to dig up the QSL card to find out if it was Steve, or one of his friends.  

Filters: Crystals, LC, Mechanical, SAW, etc.

I thought this was an interesting look at filters and crystals.  And even mechanical filters.  Remember:  Those little SAW containers became the lapel pin symbols of the FMLA.  

 I know there are readers who object to anything produced using AI.  This video is in that category.  But those who object would presumably have accepted the videos or other content found through the use of a search engine, right?  Perhaps those who object to this kind of material should just turn off their computers, wait for the next delivery of QST or 73 Magazine (!) and hope that no AI tools were used in their production. Also, I would point our that reading this blog is entirely optional. 

Farhan Talks LARCSet (CW & SSB) at FDIM (with a Lot of Homebrew Wisdom)

Watch the presentation here: https://www.youtube.com/watch?v=MefojjQ84YY

Farhan made it to FDIM 2026  (he must hold the "distance travelled" record!). We thought he might be talking about the latest version of the digital SDR sBITX, but NO!  Farhan talked about the entirely analog LARCSet, a 30 dollar SSB/CW monobander.  And in the process he shared a lot of good homebrew history and wisdom. I took notes on the video of his presentation: 

-- Farhan recounts his discussion with Steve Hartley, President of GQRP.  Farhan said he started to talk about SDR projects, but Steve steered him away from all that.  Farhan said he realized that the homes of GQRP members are often small, and projects need to fit into took boxes that are pulled out as needed.  There is often not even enough room to mount a screen.  Analog rigs just fit better.  

-- Farhan talked about the beauty of analog.  He also shared some info on the recent timeline of analog rigs, going back to 1976 with the IARU gift kits made available by W1VD.  Farhan very kindly mentioned the DC receiver that Dean and I are promoting.  He talked about the 2003 BITX 20 rig, and the subsequent uBITX.  Farhan talked about the cleanliness of all-analog rigs.  "SDR's are a mess!" he said. "With SDRs it is difficult to avoid hash." 

-- Farhan said he had trouble measuring the phase noise of the VFO in the LARCSet.  He consulted with Wes W7ZOI.  Wes told him this was NOT a measurement problem; VFOs have almost no phase noise.  The level is even lower than that of crystal oscillators.  Of course, crystal oscillators are more stable, but they also have more phase noise.

-- He noted that almost no recent homebrew design does not rely on an Si5351.  This, he said, is "not a healthy situation."  Indeed.   

  --  Farhan talked a bit about how Indian regulations seemingly require a deviation from the completly open source ethos.  Indian regs require companies to have assets.  So the PC board layouts have to remain proprietary.  

-- Farhan talked about the sharpness and shape of the BP filter in the LARCSet.  I remember talking to him about the shape of my BP filters in my dual banders -- I had to rebuild the filters.

-- On the crystal filters that form the heart of SSB rigs, Farhan noted that cheap low Q crystals often introduce a lot of loss in the filters (that may explain my problem with some styles of computer crystals). 

-- A member of the FDIM audience asked about the Sharpie written frequency readout on the LARCset that Farhan showed to the group.  Farhan told them that this was the only frequency readout used in the rig. 

  -- With the LARCSet, Farhan used varactors to vary the frequency.  But the varactors he used were cheap but horrible.  They varied the frequency as the rig hearted up.  The LM386 was the source of heat.  He also noted that the cheap varactors, while cheap, did not provide linear frequency readout. Farhan said the varactor scheme was still not perfect; he offered a PTO solution that could be used instead.  Three cheers for the PTO! 

-- Farhan said the LARCset was really an SSB rig, but when coming to FDIM he said he felt obligated to present a rig that included CW, "or they would throw me out of the room."  Farhan described a scheme to generate CW based on what was done with the Atlas rigs. 

-- Farhan said the LARCset might even work on 2 Meters.  Hmmm.  

-- On tuning, Farhan said he used a very large tuning dial (he said it was like a steering wheel) and then recommended the use of a smaller control that could serve as an SSB "clarifier." 

-- Farhan pointed out that homebrew rigs are never really done; even decades later, they can still be modified.  

Watch the presentation here: https://www.youtube.com/watch?v=MefojjQ84YY

Hiss, Filters, QRM, and Hearing Loss: Do we need AF filters in direct conversion receivers?

L6 is the 88mH toroid

Messages on Discord about the need to knock down higher frequency audio response in the SolderSmoke direct conversion receiver got me thinking.

I agree with Rick Campbell and others on the benefits of hearing a "wide open" direct conversion receiver. But Rick and others have built DC receivers with 3 kHz low pass AF filters. This made me ask myself a question: Is an audio filter in a direct conversion receiver a good idea?

And I started wondering if perhaps I was being too dismissive about the complaints about high frequency audio -- I had been attributing them to newcomers who were just unaccostomed to radio noise or "static." But maybe there was more to it than that. Maybe a big part of the problem was in my head, specifically in my ears. So this morning I did an experiment. I took an online hearing test. First, without my hearing aids: As expected, it showed significant high frequency loss. (It was as if the US Army had installed a 3 kHz audio low pass filter in my head!) Then I put my hearing aids in and retook the test: This time I passed the test and showed no loss. I then listened to the DC receiver with my hearing aids in. Now I could hear what builders on the Discord server were commenting on: I could hear higher frequency hiss, and, more importantly, stations that were producing 4-5 kHz sounds on my speaker were audible and annoying.

So I went back to Wes Hayward's November 1968 QST article. In his receiver, he has a low pass AF filter using an 88 MILLIHenry coil and a couple of capacitors to ground. I had a few of the coils (given to me years ago by a NOVA QRP club member) so I built it. With my hearing aids in, I noticed an immediate improvement. I then did what one of the Discord builders did and put the filter in with a switch that would let me make "with and without" comparisons. The filter definitely cuts down on any AF above about 3.5 kHz. And it doesn't seem to do damage to the desired signal. This is useful. I left the W7EL diplexer in the circuit.

This filter won't solve the image or "opposite sideband" problem inherent to simple DC receivers, but it will help with signals or noise that are producing tones above about 3.5 kHz in the receiver. I think this is especially important in countries in which there is a lot of SSB crowding on 40 meters. The UK, for example, has an allocation from 7.0 to 7.2 MHz. In the US we go from 7.0 to 7.3 MHz. That is a big difference.

So the answer is probably yes, an AF filter in a direct conversion receiver is probably a good idea, especially if you can switch the filter out of the receiver. You can live without these filters. Not having the filter keeps the receiver very simple, and lets it sound really great. But having the filter in there does help reduce interference and high frequency hiss. So I think this is a useful add-on mod for builders who see a need to cut down on the kind of interference that a lack of this filter causes.

In 2019 W7ZOI noted: "Another unusual element is the 88 mH toroid used in the audio low pass filter at the detector output. A viable substitute would be a 100 mH inductor with radial leads. The muRata 19R107C (from Mouser) should work. Bourns also offers a variety of similar parts."

A Homebrew Crystal Filter Shaped Like the Desired Passband -- by Andy KB7ZUT

 

Over on our Discord channel, some of those who have successfully built the SolderSmoke Direct Conversion Receiver are starting to experiment with Double Sideband and even Single Sideband.  Andy KB7ZUT is experimenting with QER filters.  He recently wrote: 

My second attempt at a SSB crystal filter using the QER topology.  I think laying out the crystals to resemble the filter profile you want should help 😏

I think the Radio Gods would be pleased Andy. 

Here is a free invite to our Discord server: 

Join the discussion - SolderSmoke Discord Server:

https://discord.gg/Fu6B7yGxx2

Update from KK4DAS on the SolderSmoke Direct Conversion Challenge: BP Filter Added to Circuitry -- Full Video on BP Filter Soon

Dean now has the PTO, the Diode Ring, and now the 40 meter bandpass filter.  Dean fires up his signal generator and, using his 'scope we see audio coming out of the mixer.  FB.  

Dean says he will have the complete build video for this stage soon.  Thanks Dean. 

 

SolderSmoke Shack South -- with Mythbuster II and AN762 .1 kW Linear

This is the current operating table at HI7/N2CQR.   

The box up on top is my Mythbuster II -- like the original Mythbuster, but without the circuitry for 75 meters. Below it is the 15-10 I rig with dial from Pericles HI8P (SK). 

The shiny box with the heatsink is my new AN762 .1 kW linear from CCI. Most of this amp was assembled in Virginia, but I did the relay work and "socketry" here in the DR.  It seems to work fine.  I use it with the little box to its right which houses the Low pass filter board from a Ten-Tec Delta (Pete advised me to buy this back in October 2023). 

Out on the terrace in the upper right you can see the bottom of the 16 foot fishing pole that is holding up my 20-15 1/4 wave groundplane antenna.  I have already crossed the pond many times with this combination. 

A 40 Meter Direct Conversion Receiver from M0NTV -- With some SolderSmoke Comments

Nick's video appears above. 

First, let me say FB Nick.   It is nice to see you making use of the AGC amp designed by Wes and Bob,  using the board from Todd's Mostly DIY RF, using a mix of homebrew pads and Me-Squares  from Rex, and finally the Franklin Oscillator that we spent so much time talking about on SolderSmoke.  

But here are some comments:  

-- I still don't think you need that RF amplifier in front of the mixer. And I suspect you would be better off without it.  We did not use one in our high school 40 meter project, and never missed it.  In fact, on one version of the high school receiver I even put in a simple 10k pot as an attenuator (no RF amp).  Even up on 20 meters, I do not have an RF amplifier ahead of the diode ring mixer on either of the Mythbuster rigs I have built.  Nick,  maybe experiment a bit more and try the receiver just going from the BP filter into the mixer and see what happens.  

Note that Wes W7ZOI DID NOT have an REF amp ahead of the diode ring mixer in his original 1968 40 meter Direct Conversion receiver (the one that launched the solid-state DC recevier revolution): 

-- The Franklin oscillator is an interesting, but complicated circuit.  The gimmick is, well, gimmicky.  Here is the thing:  You can achieve similar levels of stability using simple conventional, single transistor oscillators.  We dispensed with the variable capacitors, and used PTO--style variable inductors. They worked fine.  This Franklin oscillator still does seem to drift a bit, right?   I would ground the board to the inside of the metal box.    

I would also try putting all the stages on a single ground plane.  This might help.  

Bill N2CQR Builds Yet Another Mythbuster Transceiver

 This one is for 20 meters (no need for 75) and will go to the Dominican Republic.

6 crystal filter at 5.2 MHz. VFO from old Yaesu FT-101 Termination Insensitive IF amplifiers using boards from Mostly DIY RF No RF amp ahead of the mixer. First mixer is homebrew diode ring. Bandpass filter has 4 LC circuits. Steep skirts. Low insertion loss. Bal Mod/Product detector has two diodes (singly balanced) Carrier osc is crystal controlled and homebrew. Audio amp starts with a 2N3904 amplifier followed by an LM386 board. Transmitter portion will be done next.

The crystal filter as seen on the Antuino

Filter on the blank board. 

Bandpass filter (-20 db = 0)

VFO box, carrier osc, Bal Mod/Product Detector, AF amps

The Antuino looks at the Crystal Filter

Woebot -- An AI-Based Therapy Bot for Us?

 

This was on 60 Minutes last night.  Of course it made me think of our many "Tales of Woe."  Perhaps this could be of use to us.   But I wonder how the bot would react to our typical problems: 

"I am feeling bad about myself becasue my RF amplifier keeps going into oscillation.  What should I do?"

"My opposite sideband suppression is inadequate because my filter skirts are too wide. What is your advice?" 

"My LC VFO drifts slightly and my SDR-using friends taunt me about this.  I feel dejected.  What should I do?"  

"The Raspberry Pi in my SDR rig is hallucinating and I can't find the needed wisdom files. Is there a support group for this?" 

"I have discovered spurs in the output of my transmitter.  They are 60 db down, but I still can't stop thinking about them.  What should I do?"

I can't help thinking that if Jean Shepherd had access to something like this, his Heising modulator trouble might not have spoiled his date with the girl from his school.  

What do you guys think about the Woebot?  

SolderSmoke Podcast #251 Aurora! CBLA, Winterfest, Legal Action Against SolderSmoke, HB sBITX, SDR, Raspberry Pi, Rounded Passbands, MAILBAG

Aurora Picture by Dean KK4DAS

SolderSmoke Podcast #251  4-1-2024

Audio: http://soldersmoke.com/soldersmoke251.mp3

Videos: Podcast 251 Aurora! CBLA, Winterfest, Legal Threat, sBITX, SDR, RaspPi, Rounded Passbands, MAILBAG (youtube.com)

Travelouge:  Dean goes to the North Pole to see Aurora. 

A CBLA Call to Arms! 

Winterfest.  Lots of goodies.  MXM Industries 40 meter transceiver. 1 dollar. 

Jean Shepherd. Recording of Bill talking to Shep in 1976. 

 https://soldersmoke.blogspot.com/2024/03/listen-to-me-talking-to-jean-shepherd.html

Legal Trouble: Could put us out of operation for a while.  We need listener input. 

November 2023

December 2023

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Pete's Bench

Homebrew SDR (based on Zl2CTM’s original design) and how good it sounds.

Raspberry Pi Zero W is now working on FT-8 with digital adapter.

Ferrite Cores at Digi-Key (a replacement for the FT-37-43 where  you buy 100 and the price is 21 cents/each)

ADE-6 –great specs in HF but more expensive than the ADE-1

For Pete's recent blog posts, go to this site and click on "Archive" in the right column: 

https://n6qw.blogspot.com/2024/03/march-31-2924-happy-easter-to-those-who.html

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Dean's Bench 

sBITX progress, McGyver-ing a lifted pad, replacing crystal on the CODEC board, sBITX success! See: 

https://kk4das.blogspot.com/2024/03/homebrew-sbitx-tx-modules-pa-lpf-and-mic.html

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Shameless Commerce Division:  Please use the Amazon link on the blog to start your Amazon purchases. And please consider using Patreon to support the podcast and blog.  We try to send extra content to our Patreon supporters. Mostly DIY RF --  Boards, Kits and Pete's PSSST

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Bill's Bench

More trouble with the 15-10 rig.  Rounded passbands in 25 MHz filter. See figure 4 in both links: 

https://www.arrl.org/files/file/QEX_Next_Issue/Nov-Dec_2009/QEX_Nov-Dec_09_Feature.pdf

https://www.networksciences.com/pdfs/tutorial.pdf

Experimenting with Balanced Mixers and Product Detectors. Paul VK3HN  Suggests the MC1496 chip; Walter KA4KXX points to SSDRA circuits

But it is on the air!  Using the PA from a BITX40 module and an RD06.  

Put an OLD dial from Pericles HI8P on 15-10 version 1.  Soul in the new machine.

Pericles' Dial on the 15-10 Rig 

Mailbag: 

Grayson KJ7UM's Hollowstate video. 

Mike WU2D's amazing 10 meter DSB transceiver. 

Jack AI4SV (Dhaka Jack) liked video of recent QSO with AzoresDSB rig

Mike AA1TJ and Dave AA7EE on backwaves and 100 uW QRPpppp

Dave G3UUR  on my curved passband problem

Alan W2AEW heard my only QSO with the MXM indsutries SupeRX/TX40

Wes W7ZOI, Mike WN2A, Walter KA4KXX. Farhan VU2ESE on passband, 

Ramakrishnan sent article about Charles Proteus Steinmetz.  Beautiful. 

Justin AC8LV built a receiver!  FB. 

San Francisco QRP:   KDOFNR TouCans Rig, and N6ASD Zinc-Oxide TX

Frank KC8JJL -- Another guy who heard first ham sigs from a homebrew rig. 

Nate KA1MUQ's homebrew thermatron superhet

Dino KL0S sent info on the PAL CB VFO I picked up at Winterfest. Airborne! 

Bob W8SX will be once again doing SolderSmoke interviews at Dayton.  Thanks Bob

Peter VK2EMU  Always good to hear from him.

Tobias Feltus -- Wisdom teeth removed, wondering if he will get sBITX hallucinations...

Rick WD5L continues to work on his Herring Aid 5

Ciprian YO6DXE wants to learn CW. No alerts from his FB Blog!

Todd K7TFC -- Likes CW, says it eliminates the Blah-Blah-Blah 

F1BFU's Amazing PSSST VFO

How to Feel Bad about Carrier Suppression (and How to Get Over It)

Version 2 of the 15-10 rig continues to give me trouble.  But I guess it is "good trouble" because I am learning from it. 

You see, after you build an SSB rig, one of the critical alignment steps is the placement of the carrier oscillator/BFO frequency in relation to the filter passband.  (The IMSAI Guy has a good video on this -- see above.)  You want to place this oscillator somewhere on the downward skirt of the passband curve.  This will add to the carrier suppression already done by your balanced modulator.  There will always be some carrier remaining from the balanced modulator -- putting the oscillator frequency on the downward skirt of the filter passband adds to the suppression the carrier remnant.  

But you can't overdo it.   If you place that carrier oscillator frequency too far down on the skirt, you will start to cutoff the low audio frequencies in your transmit and received signals.  You will notice that your once beautiful sounding receiver suddenly sounds tinny and high pitched.  Yuck. 

So you go back to the books and the websites.  You look at the passband promissed by the Dishal software you used to design the filter.  See below:  

Click on the image for a better view

Surely with a passband as nice as that one, you will be able to find the sweet spot where the carrier is suppressed and your audio remains pristine.  

But I couldn't do this with the 15-10 rig.  I was forced to compromise: I had to accept less than optimal carrier suppression for less than optimal low frequency passband coverage.  And here is why:

Click on the image for a better view

The curve above is a much more realistic picture of what my filter passband actually looks like (see NanoVNA picture below).  The curve above is from the AADE software.  I found out that the Dishal software DOES NOT factor in important things like Q or ESR.  Dishal treats all crystals as "loss-less radiators."  So when you get up to 25 MHz where Q is important, AADE and other programs will show you that your passband has become curved.  And you can see how this curvature makes it difficult to get the kind of carrier suppression and audio response we want.  

What my filter looked like in a Nano VNA

Click for a better view

Look, the rigs work OK.  The receivers sound good to me.  The carrier is so far down that no one can hear it.  I have to remind myself that we are using 'SSB-SC" -- suppressed carrier, not eliminated carrier.  I've worked a lot of DX with these rigs.  But still,  I would like to improve the situation.  It kind of bothers me.  Homebrewers will understand. 

I have been experimenting with different balanced modulators.  I started with the simple two diode, single transformer, singly balanced design from Farhan's BITX20.  It works fine.  But I think I get a bit better suppresson from a doubly balanced diode ring.  I may try an NE602 Gilbert Cell.   I may also try to build a higher Q 25 MHz filter using low-ESR surface mount crystals from Mouser.  Stay tuned.  

Thanks to W7ZOI, VU2ESE, WN2A, KA4KXX, KK4DAS, N6QW, W2AEW, and G3UUR for all the good advice and encouragement.  Please put any additional ideas in the comments below.  

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