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

Finishing up (?) Version 2 of my 15-10 Transceiver (Video) -- An Annoying Residual Carrier Problem

Front panel is on. RF PA is installed. Balanced Modulator problem fixed (?) Rig is on the air with about 3 watts, working lots of DX.

But there is an annoying amount of carrier that is still getting through. It is only about .5 watts with sidebands of 100 watts PEP, but it annoys me, and it makes the setting of the carrier frequency in relation to the filter passband very critical: If I set the carrier a bit too far from the passband I get improved carrier rejection (from the filter), but I also lose the lows in both received and transmitted signals -- the RX just doesn't sound as good. I see it in both of the 15-10 rigs (IF of 25 MHz). There is less of it in the 17-12 meter rig (IF of 21.4 MHZ), and none of it in the Mythbuster (75-20 meters) (IF of 5.2 MHz). I am now wondering if this might be a consequence of my using a very high (25 MHz) single conversion IF in the 15-10 rigs. What do you folks think?

From my log: March 7, 2024 PUT VERSION 2 of the 15-10 RIG ON THE AIR! 10S 1528 OK2RZ Jiri – said I was 57! 15S 1539 S52WW 58 Damian. 15S 1602 SP1NQH Stev said I am big signal! 10S S58N 1726Z 10S S58N 1726Z 10S S57S 1728Z 10S IK4GRO Lauro 1735Z 10S W0CJV 1825Z Ft. Collins Gary 10s 2000Zish KK7TV Gary in Randy. Asked what software/microcontroller I was using. 10S KJ5MFF 2015Zish a middle school in New Mexico. KI5MFF control op sent picture

 

Using the RF Power Amplifier of the BITX40 Module

 

PA shematic from the BITX 40 Module

Click on the diagram for a better view

C.F. Rockey W9SCH (who alerted us in SPRAT 22 to the chicken sacrifice option) spoke of transistors that exhibit "quantum mechanical necromancy."  Rockey explained that when this happens, "The transistor simply turns up its toes and dies. Not even an Atomic Physicist can tell you why!"  

This often (very often!) happens with homebrew power amplifiers.  So when we find a good one, many of us stick with it, using the same power amp circuit in rig after rig.  I have done this with the power amplifier from the BITX40 Module. 

Mythbuster (75 & 20 Meter) version (early)  

Click on image for a better view. 

https://soldersmoke.blogspot.com/2021/08/mythbuster-video-13-rf-power-amplifier.html

Same amplifier built into Version 2 of the 15-10 Transceiver 

Click on image for a better view. 

In the build for the 15-10 transceiver you can see some changes.  I used an RD06HHF1 instead of an IRF-510.  I used an 8.1 volt zener diode instead of the regulator chip. I set the bias at around 5.5 volts DC on the gate of the RD06.   I used a smaller, metal can driver transistor (it works fine). I changed the input/output physical configuration between the pre-driver and the driver stages (I think it was kind of goofy the way I had it in the Mythbuster).  Finally, you can see how I used a small piece of copper tape (with conductive adhesive) to shield the line going from the driver transformer to the gate of the RD06.  The wire was too small to use a bit of shielded coax, but I think the copper tape and the copper clad board beneath it work just as well. 

Farhan provided me with some fascinating background on this circuit: 

Bill,

I just saw your post on the bitx40 power amp. The credit must go to Wes for this, it is from the Lichen transceiver described in 6.9 of the EMRFD. I merely copied it with some modifications for it to work with junkbox components.

It bears mentioning that at that time I didn't have a way of generating two tone signal or measuring the IMDR. Those came later when I built my own spectrum analyzer based on Wes and Terry White's spectrum analyzer. It was sheer luck that I picked this power chain that already had careful gain distribution.

For the output, the original build used and LPF with inductors wound on a ballpen shell and TV baluns cores instead of toroids. Again, it was incredibly lucky that they worked at all. 

- f

Innovation and a Dual Band Sweep with Version 2 of the 15-10 Transceiver

Here are a couple of videos on Version 2 of my 15-10 SSB transceiver.  In the video above I try to show the advances and innovations that have been made since the start of my BITX construction adventure back in 2013.  

 The video below shows the receiver in action this morning on 15 and 10 meter SSB.  I think it sounds pretty good. 

Click on the image for a better look

Farhan asked what the passband of the 25 MHz crystal filter looked like.  I sent him this.  I think it looks very good, and shows that it is possible to use an IF this high.  This permits us to not only set up the transceiver for dual band coverage (in this case 15 and 10 meters), but it also allows for a lower frequency VFO (in this case around 3.5 MHz) with a resulting increase in VFO stability.  

SolderSmoke Podcast #250 Dean KK4DAS joins Pete N6QW and Bill N2CQR

SolderSmoke Podcast # 250 is ready for download: 

http://soldersmoke.com/soldersmoke250.mp3

VIDEO VERSION: (1707) SolderSmoke Podcast #250 -- With Pete N6QW, Dean KK4DAS, and Bill N2CQR - YouTube

Intro:   Welcome to Dean KK4DAS.  For 2024 Pete and I hope to jazz things up a bit by bringing in fellow homebrewers to talk about their projects.  Dean is our first victim.  Welcome Dean. 

Some good news:  Several new homebrew receivers are inhaling:  Armand WA1UQO in Richmond has an amazing looking regen.  Scott KQ4AOP in Tennessee got his DC RX working.  Mike AG5VG in Texas has been homebrewing BITX 20s and BITX 40s.  All are on the blog.  

Pete's report: 

-- Recent blog entries on filters,  SSB rig architecture, and of course digital VFOs. 

-- Phasing measurements, quadrature, and the Seeed Xiao RP2040

-- Error in QST article on early SSB transceiver.  ANOTHER ERROR!

--LC VFO on blog!  FB Pete!  

Dean's report:  

-- Tales of woe on the homebrew sBITX

-- Help from Farhan.  

-- Ground Bounce.  FFT Hallucinations.   Wisdom files.

SHAMELESS COMMERCE DIVISION:   

-- Whenever you are tempted to buy something from AMAZON, just start at the Amazon symbol on the right side of the page.  We get a cut from Bezos, and it doesn't cost you anything.  

-- You can try to do the same thing with E-bay.  We are finding a lot of great parts there. 

-- If you see a SolderSmoke post on Facebook,  please Like and forward. 

-- Become a patron!  Go to the Patreon page.  We put the money to good SolderSmoke use. 

-- Visit Mostly DIY RF and buy a PSSST kit!  

Bill's bench:  

-- Building yet another BITX dual bander.  15-10 again. Tried to use a 25 MHz filter left over from the earlier project, but I had to build another.  Built a new VFO using the variable cap and anti-backlash gear recommended by Pete.  Was a bit tough to get the receiver sounding good.   Had a diode ring as the second mixer, but went back to a singly balanced mixer. 

-- 10 meter AM -- Thanks to Jerry Coffman K5JC for mod. 

Other topics: 

--Counterfeit chips.  Why? 

MAILBAG: 

Wes W7ZOI 

Jim Cook W8NSA  Transoceanic BFO

Grayson KJ7UM -- Vintage Computer Museum

Chuck Adams --Glad to hear that Chuck is doing well.  

Frank Harris  K0IYE --  NO CHIPS!!!! 

ED DD5LP  Antenna software

Eldon KC5U  10 AM We  made a contact

Joh DL6ID  10 AM   

Phil   W1PJE of MIT   10AM   Where is L5? 

Bob WP4BQV now in UK 

Dino Papas KL0S in Wilmington   Reverse Polarity protection. 

AA7EE Dave Richards  Liked Armand's receiver

Rogier PA1ZZ  

Jonathan-san W0XO  Listened to my ET-2 CW Whoop,whoop

Nick M0NTV  Great videos from Nick the Vic

Will KI4POV  Working on his own SSB rigs.  

John West -- Who is the South American ham who made his capacitors and heat sinks? 

Ed KC8SBV  Working on DC receiver, experimenting with FETs 

Mike WN2A great contributions.  Si5351 sole source danger! 

Nick N3FJZ -- watch out for dead bands when testing receivers! 

Don KM4UDX encouragement from new Prez of VWS

Dave K8WPE Likes QF1 Cap backlash.  Says I'm getting soft! 

Dave WA1LBP My fellow Hambassador, from Okinawa USMC Sergeant with a workshop. 

First Light! First Signals received on Version II of Homebrew 15-10 Transceiver

Ianis S51DX in Slovenia was the first call sign heard. Some peaking and tweaking remains to be done, but the receiver is working.

Congratulations to Scott KQ4AOP who got his Direct Conversion receiver working yesterday, And congratulations to Armand WA1UQO who got his regen receiver working. I think all of us are following Farhan's advice and are taking some time to just listen to the receivers we have built ourselves.

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.  

Yet ANOTHER Homebrew 15-10 SSB Transceiver (Video #1)

A homebrew 15-10 SSB Rig for the Dominican Republic:

This is my second build of this rig.

I am using a 10 pole crystal filter that I built for the first build, but did not use. I am also using the tuning capacitor from a Galaxy V's oscillator -- I like the anti-backlash gears and the reduction drive. This rig is built on a pine board covered with adhesive copper tape. It has been built stage-by-stage on copper-clad boards using the Manhattan construction style.

The structure of the rig is basically that of a BITX rig -- the RF and IF amplifiers are Termination Insensitive Amplifiers.

Soon the receiver will be completed. I will then build the stages needed for the transmitter portion of the transceiver.

I will take this rig with me to the Dominican Republic.

Clock Chimes from Japan - Contact with JA0LBE

This contact with Masa was a lot of fun.  2300Z January 14, 2024.  15 meters was obviously in great shape.  Suddenly I started hearing clock chimes.  The sound seemed to be coming from my rig.  Then I looked at my watch and realized we were at the top of the hour.   Masa-san's clock chimes were being picked up by his microphone.  The microphone was in his I-pad, which he was using to connect to his ham radio station.  Very cool. 

This email came in from Masa: 

兼子政彦 <>	Sun, Jan 14, 7:54 AM (20 hours ago)
to me

Hello Bill

Thank you very very much for your Email attached the video of our QSO.

Your homemade transceiver is working excellent! I was very surprised to watch the video. I checked transmitting of your equipment is very good this morning. And this evening I understood receiving was also very very good. Congratulations on your homemade equipment.

I have tried remote operation for several months. But I’m afraid my transmitting is not good.

Thanks for your video, I could tell following things. Thank you so much l appreciate it.

My remote signal has almost no blinking up,I felt.

There are about 2 seconds latency on my transmitting.

Most important thing I realize is English conversation over the phone is very difficult for me. I need to learn intonation and pronunciation of English much more.

Again thank you very much for your Email,I appreciate it.

Have a nice day. And good night from Japan.
73!

JA0LBE, Masa in NAGANO

QF-1 Variable Capacitor Problem -- What Should I do?

For years I have been heartlessly slaughtering innocent Heathkit Q multipliers, just to get these variable capacitors. Dean KK4DAS has joined me in this mayhem. And recently Wes W4JYK has also started hunting down QF-1s.

I am sorry to report that my love for this variable capacitor has taken a hit.  The capacitance is perfect.  And it has a reduction drive built into the shaft.  But I have found that that reduction Drive has a form of backlash. It is really just a dead spot that you find when tuning in a signal. Turning in one direction, all is good.  But when you then try to turn in the other direction, you have to turn the shaft a bit before the cap blades begins to move (see video above).  This makes tuning SSB signals a bit difficult. 

What should I do? Should I pull out a Dremel and cut off the reduction drive, then use a better (external) reduction drive to move the vanes? Any other ideas?

These are the kinds of problems that homebrewers face...

 

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

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! 

Crushing Spurs with Better Bandpass Filters

PA3AKE's passband (on screen) an mine (on NanoVNA) 

While I was away in the Dominican Republic (3-9 August 2023),  I was thinking about spurs.  While there I watched Nick M0NTV's video about mixers.  The video was all great, but I was especially taken by the way he used a spectrum analyser to evaluate the output of various mixers.  This made me think that I should do the same thing with the output of each of my dual-band BITX rigs. 

I was especially worried about the output from my 17-12 rig.  The IF is at 21.4 MHz.  The VFO runs around 3.5 MHz.   So if you add the IF and the carrier oscillator signal you get to 12 meters.  If you subtract them you get to 17 meters.  But you need some good bandpass filtering to sufficiently knock down the unwanted output from the mixer.  And the BP filter should be sufficiently narrow to take out any remnants of the carrier oscillator signal. I had taken the easy way out and had used simple dual-tuned-circuit (DTC) filters.  I started to wonder if these simple BP filters would be enough to knock down the 12 meter signal while on 17 and the 17 meter signal while on 12.  I pulled out my NanoVNA to look at the passbands: 

Here is what the 17 meter DTC filter passband looked like. The cursor is at 29.6 MHz and you can see that near the 12 meter band it is only providing about 21 db of attenuation.  That is not enough. 

And here is what the 12 meter filter looked like. Here the cursor is at 18.150 Mhz and shows about 25 db of attenuation at this frequency.  Again, not enough.  

The results are as you would expect: I could see 24.9 MHz signals in the output when I was on 17 meters, and I could see 18 MHz signals in the output when I was on 12 meters.  The spurs weren't strong, but they were there.  I knew that more robust BP filters would help.  

At first I used the circuits prescribed by Martein PA3AKE.  He used larger toroidal cores, I used smaller T-50-6 (yellow) cores.  The results were very similar.  See the first picture on this blog post. 

The results were really good.  See pictures below.  I was using a TinySA with the signal fed through a 50 ohm 30db attenuator.  I was putting a 1 kHz signal in to the mic input.  

This picture shows the 12 meter output and the now non-existent 17 meter spur.  The cursor is at 18.142 MHz:    

This picture shows the 17 meter signal and the now non-existent 12 meter spur. The cursor is at 24.993 MHz.   We can see some second harmonic signal getting past the LP filter -- I will fix this.  

Then Farhan commented on Martien's filters, noting that they are all in the "LSB" configuration.   You can see from the charts below how they would be really good when you are trying to use the "difference" output from your mixer while knocking down the sum output,  but not vice versa.     So I built new USB filters for 12 meters,  and for 10 meters in my nee 15-10 rig.  I got better results on the two "sum" bands in my rigs (10 and 12 meters) 

15 Meter Homebrew SSB Rig As Heard in Mexico City

 19 August 2023. Ralph XE1RK recorded part of our QSO and played it back to me. Thanks Ralph!

I was running about 75 watts to a hex beam aimed Southwest.

Working Indonesia and Chile with new 15-10 Homebrew Transceiver

Conditions were good this morning, and the Radio Gods continue to favor homebrew rigs.  I got on 15 meters SSB with the new 15-10 dual bander and quickly worked YH0AD in Jakarta (about 10,000 miles).  A few minutes later I talked to YB2MVD; he was a bit further east on Java.  I shot a video of the QSO with YB2MVD.  He said I was 59.  

I then switched to 10 meter SSB (same rig) and worked CE4PS in Chile (5,000 miles).   

TRGHS. 

The antenna for all these contacts was my K4KIO Hex Beam.  I was running about 75 watts from the .1kW CCI amplifier. 

First Contacts with 15-10 Rig -- Two Atlantic Crossings

 

I was just testing it, working (as usual at this stage) on final amplifier stability.   Then I heard ON5WO calling CQ.   I could not resist.  I worked him, but had to use a test lead to manually key the .1 kW amplifier.  Minutes later I worked OH6RM.  He very diplomatically said that I had "highly unusual audio."  This was probably due to earlier efforts to shift the carrier oscillator to improve carrier suppression. (I will fix this.)  

I will continue to work on the rig; It should look a bit better when I am done.  But hey, it works!  It has already crossed the Atlantic. Twice!  

Martein's Bandpass Filters - PA3AKE

Above you can see the really nice 15 meter filter that I built using data provided by Martein PA3AKE. 

https://martein.home.xs4all.nl/pa3ake/hmode/bpf_all.html 

Before I built Martein's filter, my bandpass had been inadequate.  Looking at the signals coming out of the diode ring mixer in my 15-10 rig, I realized that when I was on 15, there would also be an output on 10.  And vice-versa.  These outputs would have to be knocked down by the bandpass filters.  I had been using simple dual tuned circuit filters. But when I looked at the filter shapes of these filters in NanoVNA, I could see that On 15 the 10 meter signal was only down about 20 db.  And on 10 the 15 MHz output was also down only by about 20 db.  That's not enough.  Take a look: 

Before,  with the dual tuned circuit filter

After with Martein's Filter 21.5 Mhz

AFTER with Martien's filter 21.1 MHz

While the earlier filter had provided only about 20 db of attenuation at 28 MHz, Martein's filter provided at least 68 db of attenuation.  That is really nice.  And the passband is nearly flat at 1 db attenuation. 

I built mine using some of the guidance provided on Martiens site.  I did use T80-10 toroids (I got them from kitsandparts.com).  And I did not use copper clad boards.  

One of the charming features if Martein's filters is the total lack of trimmer caps:  Martein recommends tuning the filters by simple squeezing the coils (to increase inductance and decrease frequency) or by spreading out the turns a bit (to decease inductance and increase frequency).  I did the later when NanoVNA showed that I didn't quite have all of the 15 meter phone band on the flat portion of the curve. 

I also like the way Martein provides the values for BP filters for all of the HF ham bands.  Very useful. 

Next I will build one for 10 meters.  And I will probably go back to my Mythbuster and 17-12 rigs and build Martein's filters for these rigs.  

Thanks Martein!