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.  

Ham Radio -- How To Build Stable Oscillators

Spasibo Vasily!  

Wow, thanks a lot Todd.   There is some great wisdom in your video.  You clearly demonstrate that it is possible to build your own stable LC VFOs.  Sure, for many the arrival of the synthesizer chip put an end to this kind of project.  But some of us still want to fully homebrew all the stages in our rigs, and not be dependent on mysterious chips and software written by others.  

I really liked the way Todd acknowedged the tremendous contributions of Wes, and Roy, and Rick and others. 

Of course, all of Todd's recommendations are right on the mark.  I have been following most of them (but I do fall short and occassionally use a Manhattan pad or two).  Todd even gets into the mysterious and arcane practice of boiling (three times!) toroidal transformers.  I do have a preference for air-core coils, but that boiling sounds like fun. 

One thing that Todd and Brad might also want to consider:   tuning linearity.  Too often LC VFOs end up having the frequency spacing very close at one end of the dial and very broad at the other end.  "Bob's Electron Bunker" provides some great tools for alleviating this problem:

https://soldersmoke.blogspot.com/2022/09/the-cure-for-frequency-bunching-up-in.html

Thanks again Todd! 

Will KI4POV on QSO Today with Eric 4Z1UG

I really liked Eric's interview with Will KI4POV:  

https://www.qsotoday.com/podcasts/KI4POV

Will has appeared on this blog and podcast before: 

https://soldersmoke.blogspot.com/search?q=KI4POV

There were a lot points in Eric's interview with Will that resonated with me: 

-- Will told about how his very understanding and perceptive wife KNOWS when a homebrew project is not going well.  Yea, we have the same situation here!

-- Will mentions the wisdom of Wes Hayward, Doug Demaw, and Pete Juliano.  

-- Eric mentioned that there is a bit of his own blood in most of his homebrew projects. One slip of he screwdriver is often enough.  My projects also often have a bit of my A+ in them.  This adds soul to the new machine. 

-- Will spoke of S-38s and HW-8s.  I have both these devices here with me in the Dominican Republic. I  have used both of them here.

-- Will mentioned the magic that comes when you listen with a receiver you built yourself.  Yes. 

-- NanoVNA.  Yes, very useful.  

Lots more great stuff in this interview.  Thanks Eric and thanks Will. 

KE5HPY Builds a QRP Transmitter

 

FB Chuck, very cool.  Please send us more reports on this rig.  

Chuck has been on the blog many times, with many projects: 

https://soldersmoke.blogspot.com/search?q=KE5HPY

73  Bill 

-------------

Bill/Pete:

 

Thought you would appreciate a recent project inspired by the fabulous EMRFD.  This started as a test bed W7ZOI universal tx to evaluate my stock of RF BJTs and employ some FT-243s in the shack.  That was interesting by itself but the 16-32 dBm output (choice of device really matters!) did not reach the intended targets using my 40m dipole.  So, add a W7EL RF PA and a nifty, clean 7W emerges after damping output from Q2.  The final is pleasantly efficient and needs only a modest heatsink to survive key down for 60 seconds.  KFS then reported S7-9.  Success.  Time to box it up and go XTO, add a meter output at 30dB down and an RF driven LED indicator.  Left room to add an ATtiny85 CQ keyer but ran out of time.  Had to move house and knock down my 40-6m antennas.  That was the most painful part of moving.  So this rig sits while I find a new place to hang antennas.  Eventually, the TX will get a RX mate when it is possible to box up a 40m DC RX with Si5751 and OLED display. Am still trying to solve how to mount an OLED display cleanly in an aluminum box. First, I have to reconstruct my workbench.

 

Keep up your good work, and that is no April Fool’s joke. 

 

73,

 

Chuck KE5HPY

Old Tricks, Lore, and Art -- Freezing and Baking our LC VFOs -- An Example from Cuba

Pavel CO7WT explained why Cuban hams used a process of thermal endurance to improved the frequency stability of their homebrew rigs: 

  --------------------

I'm CO7WT from Cuba, I started my endeavor in ham radio with a islander board.

They (FRC, like ARRL but in Cuba) made a print of a PCB to build the Islander, with component numbers and values, making construction fool proof, I think it was on the 90 or end of the 80...

Mine was built with scraps from an old KRIM 218 Russian B&W TV as Coro's explain, later on I get the 6bz6 and 6be6 tubes for the receiver (this worked better than the Russian parts) the VFO was transistorized, made with Russian components. A friend CO7CO Amaury, explain me a trick: thermal endurance:

For a week put a crust of ice on the VFO board by placing it in a frosty fridge during the night. Put them in the sun by day. This indeed improved stability, this was an old trick.

By thermal endurance I mean improving thermal resistance vs tolerance, meaning that tolerance doesn't vary as much with temperature changes.

 It's crazy, but it worked!!

I remember that my vfo was on 7 MHz, with Russian kt315 as normal Russian transistors and capacitors, nothing 1-5%, 20% at most, it ran several khz in 5-10 min, mounted on a Russian "Formica" board (no PCB) and wired underneath.

After that treatment to the complete board with components and everything, including the variable capacitor; I managed to get it to "only" noticeably in the ear after 30-40 minutes.

To me it was magic!!

Basically, what I'm describing is just "thermal annealing", but Cuban-style and with more extreme limits.

In a refrigerator you could easily reach -10 c and in the sun for a day in Cuba 60-80 celsius at least.

In Cuba in the 1990s-2010s many designs of DSB radios proliferated, both direct conversion and super heterodine (using an intermediate frequency)

At first tubes and then transistors, mostly using salvaged parts, so it was common to find 465/500 kHz (if common Russian) 455 khz and 10.7 Mhz with or without "wide" filters since narrow filters for SSBs were not scarce: they were almost impossible to get.

Not only that, crystals, ifs, PCBs, transistors, etc.

Then, around the 2000s, Russian 500 khz USB filters began to appear (from Polosa, Karat, etc. equipment from companies that deregistered and switched to amateur radio) and that contributed to improving... Even though at 7 MHz 500kc if is very close.

I made many modifications with the years mostly from 1998 to 2004 ish... better filters in front of the first RX stage (same IF described between stages) improved selectivity and out of band rejection, remember we had on that days broadcast as low as 7100 khz

Tx part was a pair of russian 6P7 (eq. RCA 807) in paralell, etc.

The Jagüey and others is one of those evolutions...

 This is something I remember...

73 CO7WT

----------------

This is not as crazy as it sounds.  We can find versions of the same technique in the writings of Roy Lewellan W7EL, Doug DeMaw W1FB, and Wes Hayward W7ZOI.  I found this 2007 message from our friend Farhan VU2ESE: 

I think the word 'annealing' is a bit of a misnomer. the idea is to thermally expand and contract the wiring a few times to relieve any mechanical stresses in the coil. after an extreme swing of tempuratures, the winding will be more settled.
this techniques owes itself to w7EL. I first read about it in his article on the 'Optimized transceiver' pulished in 1992 or so.
but all said and done, it is part of the lore. it needs a rigorous proof.
- farhan

https://groups.io/g/BITX20/topic/copper_wire_annealing/4101565?p=,,,20,0,0,0::recentpostdate/sticky,,,20,1,860,4101565,previd%3D1193595376000000000,nextid%3D1194269624000000000&previd=1193595376000000000&nextid=1194269624000000000

And here is another example of coil boiling: 

https://www.qsl.net/kd7rem/vfo.htm

-----------

I can almost hear it,  all the way from across the continent:  Pete N6QW should, please, stop chuckling.  Obviously these stabilization techniques are not necessary with his beloved Si5351.  Some will see all this as evidence of the barbarity and backwardness of LC VFOs.  But I see it as another example of lore, of art in the science of radio. (Even the FCC regs talk about "Advancing the radio art." ) This is sort of like the rules we follow for LC VFO stability:  keep the frequency low, use NP0 or silver mica caps, use air core inductors, keep lead length short, and pay attention to mechanical stability.  Sure, you don't have to do any of this with an Si5351.  Then again, you don't have to do any of this to achieve stability in an Iphone. But there is NO SOUL in an Iphone, nor in an Si5351.  Give me a Harley, a Colpitts, or a Pierce any day.  But as I try to remember, this is a hobby.  Some people like digital VFOs.  "To each, his own." 

Thanks Pavel. 

My Manhattan-style Termination Insensitive Amplifier Production Line

 

You gotta love the name, right?  It sounds like some sort of psychological condition.  Perhaps someone who just doesn't care  if his girlfriend breaks up with him, or is indifferent to getting fired.   

But no, we know that that's not what it means. 

I recently had to make three sets of TIA amps for my new 15-10 rig.  First, I decided not to use the boards provided by Todd of Mostly DIY RF.  You can see one of these boards above the tin shears in the picture above.  Note how compact it is.  Even though you would need two of these (one for receive, one for transmit) to get what you need for a bilateral rig like the BITX,  using these boards (as I did on my 17-12 rig) saves you a lot of space.   But this time I wanted to build a rig that is TOTALLY DIY RF.  So out came the tin shears and the super glue. 

First I decided on the Manhattan pad placement.  I used a pattern that had worked on previous rigs. Pete is right -- I use a lot of TIAs (but no, I have no tattoo of the circuit anywhere on my anatomy!).  I scaled it down a bit, thinking that I could come a bit closer to Todd's compactness.  

Knowing that I would need three sets,  I first made three boards.   Then it was just a matter of soldering in the components:  I did resistors, then capacitors, then, finally, the transistors.   In this way I was able to put together the three dual TIA amps in a couple of morning build sessions.  It was kind of tight and I had to be careful to avoid wiring errors or unintentional shorts.   But it worked. 

I like the TIA circuit.  It lets me select the gain of a stage by simply using two resistor values from W7ZOI and K3NHI's chart.  And with this circuit I know that it will look like 50 ohms both ways.  This is really important on bilateral rigs like this.  

I don't think there is anything wrong with using BITX-like bilateral circuits or TIAs or LC VFOs.  This is all for fun right?  I just like using these circuits.  

My friend Pete is right in pointing out that the bilateral concept did not originate with the BITX -- it has been around for a long time, going back at least as far as the Cosmophone.  But I think Farhan's BITX definitely moved it into the solid-state homebrew mainstream.   Three cheers for Farhan for doing that.  

F6CRP's FB Homebrew Receiver

I like F6CRP's homebrew receiver.  I like the way he presents it (block by block) and I like the inclusion of the W7ZOI IF board. The JF3HZB VFO is quite cool (even though it is digital),   We have posted about this VFO several times: 

 https://soldersmoke.blogspot.com/2022/05/who-is-jf3hzb-creator-of-that-nice.html

Denis has a very nice station and workbench: https://www.qrz.com/db/F6CRP

He also has some very nice videos on his YouTube channel: 

https://www.youtube.com/@radiorider8249/featured

Thanks Denis! 

Jerry KI4IO (Wizard of Warrenton) Describes His ALL ANALOG Phasing Transceiver -- Bob Crane FDIM interview #3 (audio)

Wow, this one really resonated with me.  Jerry had me won over when, early in the interview, he described his decision to dispense with the Si5351/Arduino combo:  "I said the hell with this digital stuff!"  I hear you Jerry.  I feel your pain OM.  

Jerry then goes on to describe a rig with bits of circuitry from some legendary sources:  The Ugly Weekender transmitter.  SSDRA and EMRFD.  W7ZOI's 1968 Direct Conversion receiver.  

Jerry discusses the "presence" of the direct conversion receiver.  And he decries the pernicious effects of AGC.  (Indeed, real hams MANUALLY control the gain.) 

The Wizard of Warrenton then shares some important tribal wisdom:  After building that new piece of gear, leave it on the bench for a couple of weeks.  Beware of "radio infatuation" (what a great term -- we will have to include this in the lexicon).    Jerry points out that while at first, the new rig will seem just perfect, with time time the need for improvements and modifications will become apparent. 

Jerry also has connections to India and Nepal (where he helped Father Moran).  See: https://www.qrz.com/db/KI4IO

Here is W8SX's interview with Jerry: 

http://soldersmoke.com/KI4IO23.mp3

Thanks Jerry!  Thanks Bob! 

Retro QRP Rigs of the 1960's, 70's, and 80's -- Video by Mike WU2D

It is time to put aside (again!) all of the heated ideological arguments about the power level that defines "low power."  Just sit back and enjoy this wonderful trip down QRP memory lane. 

Mike's description of the simple, single-transistor QRP transmitter was really nice.   I recently made something similar: https://soldersmoke.blogspot.com/2023/02/first-qso-with-high-school-receiver-100.html  And Mike does a nice plug for our beloved Michigan Mighty Mite.  Go CBLA! 

The modular idea:  words to live by my friends. 

40673!  TT2!  And G3RJV's PW Severn - indeed, bow your heads!

Wow, the Ten Tec Power Mite (or Might!) -- I still want one.  Same for the Argonaut -- what a great name (sounds like a "magic carpet), and with SSB to boot!  I want to join the Argonaut cult! 

I have both the HW-7 and HW-8 (the HW-8 is heading to the Dominican Republic).  This video makes me want to fire up the HW-7.  Maybe on 40.  

My 40 meter homebrew rig (Digi-Tia) has in it the filter from that old Yaesu FT-7 rig.  The filter was given to me by Steve "Snort Rosin" Smith.  https://soldersmoke.blogspot.com/2015/05/bitx-digi-tia-build-update-2-installing.html  

Thanks to Mike for including me in the credit roll at the end.  What a great group of people -- it is a real honor to be listed with those folks. 

Technology and Methods from Wes Hayward W7ZOI

Great stuff.  Lots of wonderful articles filled with wisdom to ponder. 

 http://w7zoi.net/oldtech/ponder.html

Thanks to Tony G4WIF for spotting this gem and alerting us.  And thanks to Wes for all of this.  

SolderSmoke Podcast #243 -- HI7/N2CQR, uBITX mods for 10 meters, High-School Direct Conversion Receiver Project Launched (Success!) Mailbag

 

DC RX and one of the PTO boards we built as demos last night. 

February 10, 2023

SolderSmoke Podcast #224 is available. 

http://soldersmoke.com/soldersmoke243.mp3

Video here: (32) SolderSmoke Podcast 243 (video) Hi7/N2CQR, uBITX, Success with High School Receiver Project - YouTube

Pete N6QW had technical difficulties this morning.  He insisted that the show must go on.  Pete will be back for the next episode. 

 

Travelogue: 

Bill in the Dominican Republic for all of January.  

HI7/N2CQR  Eastern tip of the island. uBITX and dipoles. 

20, 17, 10.  CW and SSB.  SSB was tough and I had reports of RF getting into the signal.

Went to CW. 

Worked VWS Mike KA4CDN, and Walter KA4KXX on 20CW.

Finally moved up to 10 CW.  Lots of contacts. Even though uBITX very QRP on ten.

I am modifying the uBITX now.  

Copper tape shielding to keep RF out.

 Low power out not the fault of the IRF-510s.  The problem is the 2N3904s.

Will replace with 2N2222 in To-18 cans.

Dean KK4DAS putting KD8CEC software into Arduino.  I gave up.

Who sent me this orphan uBITX?

SolderSmoke Shack South in final phase of construction.

 

SHAMELESS COMMERCE DIVISION:

Patreon!

Bezos Shopping!

 

DC Receiver Project

Local High School radio club. 

Simple:  Like Herring Aid 5 and Wes’s original.

Farhan’s four stages:

BP Filter, Diode Ring, PTO, AF amp. 

Simple Colpitts PTO SURPRISINGLY STABLE.

Simple and easy.  No chips.  No complicated circuits.

Guys have helped test out the design:  Rick N3FJZ, Walter KA4KXX,

Daniel VE5DLD, Stephen VK2BLQ and others. 

First session last night:  We demonstrated build of the PTOs.  

They worked (thank God).

 

Open Circuits book.

Envelope Detection Controversy

Save the Antenna – Book “Losing the Nobel Prize” K1JT

 

MAILBAG

--Dean KK4DAS 10 meter DSB!  Tiny SA ULTRA! FB

--John AC2RL on Elmer W3PHL DSB guy

--AC3K reports inventor of Fender Stratocaster guitar was a ham: W6DOE

--AF8E was doing POTA.  I worked him. He said my rig had presence. FB

--Alain F4IET FB DSB rig with mic in Cigar can!

--Daryl N0DP worked him on SSB.  He is homebrewing

--Steve N8NM was in for repairs but is on the mend.

--Rick G6AKG working with sub-harmonic mixers and logic chips

--Paul HS0ZLQ Built DC receiver but looking for something else to build. No DSB!

--Steve AB4I – Coherer, Jagadish Chandra Bose, and Marconi

--Eldon KC5U    Worked VK5QD right after me and mentioned SolderSmoke FB

--Todd K7TFC is building the DC RX.

--Tony G4WIF and Ian G3ROO using automotive relays for antenna switching. FB.

--Dave WA1LBP Great to hear from my fellow Hambassador (Okinawa)

Older post comments:

--Scott VO1DR was also in CF Rockey’s class! (Blog comment)

--Aurora Aug 4, 1972: Twelve people shared memories.  (Blog comment)

--Will WN1SLG Googled novice call and was led to my Novice log.(Blog comment)

DC Receiver: 100db Gain? Diplexer? VFO in a box?

Here is a progress report on Direct Conversion Receiver developments. Dual Tuned Circuit, Diode Ring with Diplexer, PTO VFO from Farhan's Daylight rig, two stage 49 db BJT AF amp with a transformer. It works very well. I discuss: Shielding of the VFO -- necessary or not? Why brass in the PTO? Do we really need 100db in a receiver, especially with ear buds? Sourcing the AF amplifier's transformer. Using W7EL's diplexer. (I think it has solved my Radio Marti breakthrough problem). Developing a DC RX circuit that can be built by students. I end with a bandsweep of 40 meters that includes CW, FT-8, SSB, and AM

Adding a Diode Ring to the Direct Conversion Receiver, And How the Diode Ring Works

I take a look back at Wes Hayward's classic DC receiver from the November 1968 QST.

I then try to describe how diode ring mixers work ("the particular go of it") using Alan Wolke's excellent YouTube description as my base.

I present some drawings that I did that use the "crossed diode" diagram as the start.

I also discuss interference from Radio Marti's 250 kW transmitter on 7335 kHz in Greenville NC.

Finally, we listen to the receiver a bit.

Alan Wolke's Diagram

Wes Hayward's 1968 DC Receiver

A Bout of Direct Conversion-ism in Northern Virginia -- DC Receivers Under Construction

There I was, minding my own business,  when suddenly I was dragged into the construction of Direct Conversion receivers. 

Here is a video about my latest effort.  But I feel the urge for more simplification -- I may go back to the seminal DC receiver designed by Wes W7ZOI and presented in the November 1968 issue of QST.  It is on page 15 here: https://worldradiohistory.com/Archive-DX/QST/60s/QST-1968-11.pdf

An Especially Good (Old) SolderSmoke Podcast

February 22, 2008    

-- We were in Rome.  

-- I read a 1931 QST ad sent to me by my fellow "Hambassador" David Cowhig, WA1LBP; David was in Okinawa when he sent it. 

-- I describe Wes Hayward's comments about Pat Hawker, G3VA. 

-- I talk about getting on the air with my HW-8 (after fixing it!), re-tubing my Drake 2-B, and putting up a 30AWG antenna in Rome. 

-- I describe meeting up with Roman hams (including amplifier manufacturer I0ZY!) and visiting the local radio club.

-- The Science Museum in Florence, Italy. 

-- DSB from Rome with my NE602 rig. 

-- Tony Fishpool and Graham Firth's Test Gear book. 

-- An important corollary to Murphy's Law. 

-- Listening to SolderSmoke from safari, under the Southern Cross in South Africa. 

-- Ron Sparks calls in from Dubai. 

You can put on a playlist of all the SolderSmoke podcasts here: 

(12) Videos of the SolderSmoke Podcast - YouTube

 

New Video: Farhan's Presentation on the "Daylight Again" Analog Transceiver

LOTS of tribal wisdom in this presentation by Farhan VU2ESE. 

For more info, go to: 

https://www.vu2ese.com/index.php/2022/08/04/daylight-an-all-analog-radio/

Mike Caughran KL7R's Last Podcast

 

Mike KL7R (SK) during a visit to the AL7FS shack.

This was Mike Caughran KL7R's last podcast. He died in a car accident shortly after we made this program. January 13, 2007. Mike's oscillator work. Michigan Mighty Mite. Lasers, diodes, and Einstein. Laser communication experiment. W7ZOI-KL7R QSO on SKN.M0HBR's feedback amps.The new comet. Saturn, Jupiter and calculation of c. 17 meter QSOs. New SPRAT CD. MAILBAG: China enigma, VE4KEH, M0DAD, GU0SUP, M1CNK, K4AHU, KD4EDM, KG9DK, AA6KI, VA7AT ON5EX

---------------------

Mike's Obituary from the February 2007 ARRL Letter:

Mike Caughran, KL7R, SK: Well-known low-power (QRP) and homebrewing
enthusiast Michael S. "Mike" Caughran, KL7R, of Juneau, Alaska, died January
22 of injuries suffered in an automobile accident in Hawaii. He was 51.
Caughran may be best known as one-half of the team -- with Bill Meara,
N2CQR/M0HBR -- that created and produced the weekly SolderSmoke podcast
<http://www.soldersmoke.com/>. "I think people were drawn in by Mike's
friendly voice and manner," Meara commented on a memorial page for KL7R
<https://kiwi.state.ak.us/display/mc/Home>. A member of ARRL and the Juneau
Amateur Radio Club, Caughran also wrote articles for the Michigan QRP Club's
T5W newsletter and he was an active ham radio contester. "Mike was one of
those people who you instantly like because of his honest, straightforward
and humble way of talking and expressing ideas," said Mike Hall, WB8ICN, who
edits T5W. "His co-hosting of SolderSmoke provided me hours and hours of
enjoyment." Caughran was an IT professional with the State of Alaska.
Survivors include his wife and son.

"Experimental Methods in RF Design" LADPAC Software Available FREE!

We've frequently said that is pays to check the W7ZOI web site.  Tony G4WIF did just that and pointed us in that direction, noting that the LADPAC "Ladder Package" software is now available for download from that site. 

Homebrewers will really want to have that package on their computers.  There are all kinds of useful programs in that package:  software for designing crystal filters and feedback amplifiers, a program that allows you to think systematically about receiver gain distribution and dynamic range, and many other useful things.  

You can get the program here: 

http://w7zoi.net/emerrata.html

Also on Wes's site is this May 22, 2022 picture of Farhan VU2ESE with EMRFD co-author Bob Larkin, W7PUA. 

Thanks Wes! 

Receiver Dynamics -- How Good is my Receiver?

OK , so I've finished building my new 17-12 Dual Band SSB Transceiver.  I am now testing it out on both bands.   A big question I have is this: how good is my receiver?   Did I get the gain distribution right?   Is it generating too much noise?   Are any of the stages too vulnerable to distortion in the presence of large signals?  

These kinds of questions are at the heart of receiver design.  Many of us have for years just thrown together amplifiers oscillators and mixers, and have been pleased if we could copy signals on the ham bands.  But could we have been doing it better?   

This is a very complicated issue, and unfortunately much of the literature is plagued by jargon and unnecessary complexity.  Rarely do we find something that goes from the general to the specific and explains what it is we are trying to achieve:   We want the receiver to be sensitive, but we don't want it to be so sensitive that it distorts with strong signals.  It will make some noise, but we don't want the receiver's internal noise to be stronger than the noise coming in from the antenna.  The "front end" stages are very important because any flaws there will be amplified by the follow-on stages and will "cascade" down through the receiver.  Bandwidth is very important. 

This morning I found (again!) a document that defines terms in a very clear way.  Be sure to check out the footnotes mentioning Dave Newkirk and Wes Hayward!  FB!  Here it is:

https://www.nsa.gov/portals/75/documents/news-features/declassified-documents/cryptologic-quarterly/Receiver_Dynamics.pdf

Exorcism Completed! Getting Rid of the Spur in my 17 meter SSB Transmitter using a TinySA (video)

To re-cap:  The problem became evident when trying to "net" or "spot" my transmitter onto my receive frequency.  Around 18.116 MHz, I could hear at least two tones in the receiver as I moved the transmitter frequency.  I needed to get rid of the extra tone. 

First, thanks to all who sent in suggestions.  They came in literally from around the world, and this is a demonstration of the IBEW in action.  I used or at least tried all of them.  They were all good ideas. 

Following Vasily Ivananeko's pseudonymous suggestion I rebuilt the carrier oscillator (apologies to G3YCC).  I used the carrier oscillator/buffer circuit from Farhan's BITX20.   

Henk PA0EME said I should look at the signal level at the input ports of the NE602 mixer.  Henk was right --- the VXO input was far too high.  I lowered it, but the problem persisted. 

At first, I thought that the spur in question was so small that it would not show up on the air.  I could not see it in the TX output using my TinySA spectrum analyzer.  That was good news and bad news:  Good that it was not showing up on the air, bad that I could not see it in the TinySA and use that image in the exorcism. 

At first I thought that the spur was being caused by the 10th harmonic of the carrier oscillator and the third harmonic of the VXO.  This seemed to fit.  So, following VK3YE's sage advice, I built a little 69 MHz series LC trap (using a coil sent by AA1TJ, on a board CNC'd by Pete N6QW).  That trap succeeded spectacularly in crushing the 10 harmonic.  Look at these before and after shots on the TinySA: 

Before Trap

After Trap

Spectacular right? But guess what?  The problem was still there.  

I scrutinized the situation once more. I realized that the spur would be more visible if I put the TinySA on the input of the transmitter's PA (a JBOT amp designed by Farhan) as opposed to putting it on the output.  Watching the spur and the needed signal move in the TinySA as I tuned the VXO, I realized that they were moving in opposite directions.  This indicated that the spur was the result of a carrier oscillator harmonic MINUS a VXO-generated frequency (as the VXO frequency increased, the spur frequency decreased).  Looking at my EXCEL spread sheet, I could see it:  8th harmonic of the carrier oscillator MINUS the main output of the VXO. 

To confirm this, I plugged the values into W7ZOI's Spurtune program.  Yes, the spur popped up and  moved as predicted.  

For further confirmation I shut down the carrier oscillator by pulling the crystal from the socket, and then just clipped in a 5.176 MHz signal from my HP-8640B signal generator (thanks KB3SII and W2DAB). Boom!  On the TinySA, the spur disappeared.  Now I at least knew what the problem was:  a harmonic from the carrier oscillator.  

Following good troubleshooting practice, I turned off the gear and went to bed.  When I woke up, an idea came to me:  Before launching into a lot of filtering and shielding, just try running the carrier oscillator at a lower voltage, seeing if doing so might reduce the harmonic output.   I disconnected the carrier oscillator board from the main supply and clipped in a variable voltage bench supply.   Watching the signal on my TinySA, I watched as the spur completely disappeared as I reduced the voltage from around 13V to 10V  (see video above).  The main signal frequency level did not change much.  I tested this by listening for the hated extra tones.  They were gone.  Exorcised.  

Key lessons: 

-- Spur problems are difficult to troubleshoot.  Armstrong's superhet architecture is, of course, great, but this is definitely one of the pitfalls.  Single conversion makes life easier.  IF selection is very important. Choose wisely! 

-- When looking at the TinySA as you tune the rig, pay attention to which way the spur is moving.  This provides an important clue regarding the combination of harmonic you are dealing with. 

-- The TinySA is a very useful tool.  It seems like it is easier to use than the NanoVNA (which is also a fantastic tool). 

-- It can be fun and rewarding to re-visit old projects.  In the years between original construction and the re-look, new test gear has become available, and the skill and experience of the builder has improved.  So problems that once seemed insurmountable become fix-able. 

-- Thinking through a problem and thinking about possible solutions is very important.  It pays to step away from the bench to think and rest.  Rome wasn't built in a day. Here's a rough block diagram that I drew up (noodled!) while trying to figure out this problem: