Listen to Latest SolderSmoke Podcast

Tuesday, April 17, 2018

N1AW's uBITX -- Cardboard Panels, and the Mic in a Sharpie

On Sunday night at 7 pm local on 7.277 MHz BITX users gather.   This week was the debut of my uBITX.  I was able to make only one contact before we were over-run by the Rookie Roundup, but that contact was a good one.  Above you can see N1AW's FB uBITX.   The front and back panels are made of cardboard.  The mic holder is from a re-purposed Sharpie marker.  FB Al.  Thanks for the contact.  

Sunday, April 15, 2018

Carpentry and Socketry for the uBITX

Yesterday I decided to spend some time at the bench -- I wanted to get the uBITX boxed up.  My basswood box had arrived from Amazon on Friday.  It was time for what George Dobbs G3RJV called "socketry."  

First, the back.  I figured I would need five connectors back there.   Connectors for 12V DC, speaker, and antenna would be needed right away (it is my preference to have the speaker connector on the back of the BITX).  Looking ahead, I might want to also have a jack for T/R control of my linear amplifier, and a jack for 24 VDC if I want to go wild and put more voltage on the drains of the IRF510s. So I put two extra holes in there.  

Basswood is SO easy to cut.  I put the LCD in the center of the front panel, and opted to put the board close to the front of the board.  This avoids the need for jumpers to connect the Raduino to the LCD, and it keeps the lines to the front panel controls and connectors very short. I mounted the board on the spacers that came with the BITX, drilling holes the bottom of the basswood box.  It all fit quite nicely. 

I would need to put two jacks on the front panels:  key jack and mic jack.  And I'd need two controls: main tuning and AF gain.  I used hole saws to cut holes big enough to accommodate the four items. 

The controls and jacks were then placed on two small pieces of copper clad board.  These then went on the front panel.  

Wiring up the uBITX was  easy.  I just followed Farhan's instructions.  I did the wiring AFTER placing the boards and controls in the box -- this helped me keep all the wires at their optimum length (not too long, and more important -- not too short!).  If you do it this way, put a cloth over the boards so you don't drop solder blobs on the uBITX. 

Farhan's uBITX fired up nicely as soon as I applied power.   The receiver really sounds nice.  I hope to make some contacts with it today. 

Three cheers for Farhan! 

Saturday, April 14, 2018

Boxing up my uBITX -- Question for the Group

Our friend Rogier and I are involved in an East Coast -- West Coast uBITX launch project -- we plan to assemble our uBITXs together (more or less, via Skype) and then get them on the air. 

As has been my recent practice, I have opted to put my uBITX in the same kind of wooden box that I used for my three scratch-built BITX projects.  See above. 

Now, due to Farhan's wizardry the uBITX is considerably smaller than the box.  This is, of course, a good thing. It leaves room in the box for many bells and whistles.  

But here is my first box design question

Should I put the uBITX board to the front of the box so that the LCD can be connected to the board DIRECTLY via the connector on the Raduino board (no jumpers needed), or should I put the uBITX board to the back of the box so that I can stick the PA heat sinks out the back?   In the later case I'd have to use 4 inch jumper cables to connect the LCD to the Raduino.  This use of jumpers seems to increase the possibility of noise from the display. 

What say the Knack Wizards?  Back of the box with LCD jumpers, or front of the box with no jumpers but heat sinks inside the box? 

Sunday, April 8, 2018

AMAZING 1999 Video on the Invention of the Transistor at "Hell's Bells Laboratory"

Thanks to Armand WA1UQO for alerting me to this.  I really liked the book -- "Crystal Fire" -- that this 1999 video is loosely based on. I'm also a fan of the narrator,  Ira Flatow, whose melodious voice is heard each week on NPR's excellent "Science Friday" radio show. 

A few observations and thoughts on the video: 

-- I liked the irreverant Calypso song "Hell's Bells Laboratory."  It looks like those folks had a lot of fun.  And wow, Shockly's secretary was named Betty Sparks.  TRGHS. 

-- I have the same big Variac on my bench.  And I have one of those "third hand" devices.  

-- I'd like to build my own replica of the point contact device with the triangular piece of lucite and the gold foil. 

-- While Shockley seems to be the real bad guy in this story (he seems to have all the bad characteristics of David Sarnoff,  Lee DeForest, and Steve Jobs),  I liked the his use of "physical intuition" to understand devices and the problems they were meant to solve.  

-- The image of the two Japanese founders of Sony working in the late 1940's in a bombed out department store was very powerful.   

-- Although I came on the scence a bit later, I WAS one of those kids who used a transistor radio and an earphone to surreptitiously listen to rock-and-roll music. 

-- "More transistors are made each year than raindrops fall on California."  Hmmm.... 

More info here:
Extra interviews:

Friday, April 6, 2018

Solder Haze -- Sing Along with N8NM and Jimi Hendrix

Back when some us were thinking of new names for the podcast, Steve, N8NM thought of Purple Haze by Jimi Hendrix and came up with this set of lyrics (listen to the video above to get the tune). 

Solder Haze, all in my brain
Making rigs, some don't work that great.
They're acting funny, but I don't know why
Kill some birds for that Legba guy.

Solder Haze, all around.
Don't if I should turn the bias down.
Or maybe I should raise the Vcc
Oh, it's a FET, that would make it Vdd.

Solder Haze, all in my eyes
Don't know if it's day or night.
You got me blowing, blowing my mind
Come tomorrow,  I won't be to work on time. 

Pete, WB9FLW took a more, well, defiant line.  He came up with new name for the podcast that sort of captures the shocking level of indignation that this completly bogus story generated.  Pete suggests that we simply call the new show: "FLUX YOU"

Thank you gentlemen.  You are both, in a way, poets.  And Hendrix would, I think, approve. 

Now, will the Wizard of Newbury Park pull out his guitar and get to work on this?   

Monday, April 2, 2018

REPRIEVE! SolderSmoke Saved by a Loophole!

First, let me thank the many, many MANY, loyal listeners from around the world who wrote in with expressions of support and sympathy.  Special thanks to our UK listeners who were notable in their indignation for they saw as a blatant example of US litigiousness "gone mad."  One loyal British listener went so far as to pledge to immediately end his patronage of the Birmingham Vaping business known as SodderSmoke.  We found this quite, well, suprising.   But we were chuffed, nonetheless.  Thanks OM! 

The expressions of concern were really quite touching.  One listener asked if he should  -- in an effort to keep us out of hot water -- destroy his SolderSmoke coffee mug.  With fans like that, well, what can I say?  

In responding to the legal crisis, our listeners displayed ASTOUNDING creativity in their crafting of alternative names for the podcast.   

Buck seems to have a real "knack" for name-smithing. He wrote: 
The easiest would be Solder Haze - it's a simple scan & replace.  But
if the trademark trolls grabbed 'haze' too...
Some other ideas:
Eutectic Point
The Solder Wick Chronicles
The Joy of Soldering
Fahrenheit 368

John suggested the rather toxic  "LeadVapors," but we feared that that one might lead to even more trouble, perhaps even with the EPA.  (But, no, wait -- no worries there!) 

Gary suggested SolderSuckers.   I briefly thought of the many people who wrote in (see above) but concluded that that one just sucked.  No. 

A number of listeners suggested legal counterattacks and fund-raising effots.  (We did get one unsolicited donation!)   One fellow suggested fighting fire with fire by having us trademark the phrase "Chicks dig it" and then just letting the money roll in. 

One devoted radio amateur said that he "informed his club and launched a letter writing campaign."  Thanks OM!  Keep those cards and letters going... 

There were, unfortunately, many disparaging comments about California, and "pot-heads," and "California pot heads."  But hey, Dudes...  they don't mind.  They are not going to let you harsh their mellows. 

Stewart tried to claim that there is some sort of UK rule that says that things like this can't be carried on past noon local time in Britain.  Ha! I said.  We are no longer bound by Imperial edicts.  

Similarly, Peter in Australia complained that the story reached him on April 2, rendering it null and void.  Sorry Peter, these are UTC operations my friend.  Time to wake up and join the rest of the world!

Well, let me get to the point:   The beloved name of our podcast and blog has been saved by a loophole.  You see, any legal challenges of this nature launched and announced on April 1st of each year are HIGHLY likely to be found, on even casual examination, to be be null, void, and totally bogus. 

So no, 





But we thank you for your support.  And, to make it official:  APRIL FOOL!  73  Bill 

Sunday, April 1, 2018

NO MORE SMOKE: Lawsuit Leads to Podcast Changes

We mentioned on the last podcast that we had some difficulties that led to a long delay between Podcast #202 and #203.   We couldn't go into detail, and we are still somewhat limited as to what we can say, but we thought that today we should bring you all as up-to-speed as we can with what has been going on.  

First, an apology.  Some of what we told you was, in retrospect, kind of misleading.  Pete's computer didn't really crash.  Sure, he did have to reconstruct a lot of files, but his original computer was just fine.  The problem was that it had been taken by court order as part of the legal mess we find ourselves in.   

Here is the deal:  We got hit with a "violation of trademark" lawsuit.  It seems that one of the new agricultural industries that has sprung up recently in California has taken a very aggressive legal stance in protecting their "rights."  Part of this effort is a proactive filing for trademark protection for any product name that could in the future be related to their product.   So apparently anything with "smoke" in the name was scooped up by them.  They also claim to forsee the possibility of a "solder-scented recreational product." We also suspect they are in cohoots  with the new electronic cigarette "vaping" industry.   We  have heard that they are working with a "vaping" company in Birmingham, England that calls itself "SodderSmoke."  (As you may have heard, the word has a different connotation in the UK.)  They are using this British Vaping thing to bolster their claim that we are violating their trademark.  

Pete feels terrible about all of this.  The fact that he is located in California was what allowed the LA lawyers to take us to court in that state.  And we have been advised that we do not have much of a chance in this matter.  You see, marijuana has become a very important product in Pete's state. And "vaping" with e-cigarettes is also very big out there.  So there is big money and big cultural forces behind this effort.  We a tiny small fish caught in the net of big new industries.  

Pete wants to fight this (you know how he is) but I think we will have to just give in and move on.  Look, STARTING TODAY they are threatening to sue us for ONE MILLION DOLLARS every instance in which we use name of the podcast that you have all come to love so much.  I am scrambling to expunge the title from all the blog files.  Just look at the header on the top of this blog page. 

So at this point we find ourselves in search of a new name.  We turn to you, our loyal listeners, for ideas.  We hope to come up with something that will remind people of what we once were, of the good times we had under the old name.  Please send us your suggestion.  PLEASE DO NOT use the e-mail address that has the old name in it.  That would just make the lawyers and the "farmers" rich.   Instead, send your suggestions to

Bill and Pete


Saturday, March 31, 2018

Yet Another Household Item Useful to Homebrewers: Toilet Bowl Cleaner for PC Board Fabrication


We have already been using Desitin ointment for heat sink compound, kitchen breadboards for radio breadboards, Scotchbrite pads for polishing, nail polish varnish for toroidal core coating and Olive oil as a field-expedient lubricant. (Am I forgetting anything?)   But I must say I was a bit taken aback by KV4QB's mention of his innovative use of the dilute hydrochloric acid in toilet bowl cleaners in his PC board fabrication process.   Good one DuWayne!   Eric Guth went the extra mile be suggesting a recycling of the liquid. 

This was a really interesting QSO Today interview.  Listen here: 

Saturday, March 24, 2018

SolderSmoke Podcast #203 Winter, Transceivers, Antennas, DC RX, uBITX, Mixers, 'fests, MAILBAG

N6QW in 1959. Building an SSB transceiver
SolderSmoke Pocast #203 is (FINALLY!) available:

24 March 2018

--The reasons for our delay. 
Winter, Computers, College, Family Trees, Lawyers....

-- Winterfest 2018 
-- Pete launches 2018    THE YEAR OF THE TRANSCEIVER
-- SDR -  Satan's Digital Radio?  
-- Direct Conversion Receiver Projects
-- Mixer Musings 
-- A Thailand Troubleshoot 
-- Nor'Easter knocks out Bill's Moxon -- An appliance replacement? 
-- Homebrew Electret Mics.  Seriously.  
-- uBITX Build with Rogier
-- Civilized Crystal Testing
-- Baofeng! 

N6ORS's SDR rig
Mike Rainey's DX-100

Sunday, March 18, 2018

Haunted by Hallicrafters At Winterfest

I was on the verge of not going to the Vienna Wireless Society's Winterfest Hamfest this year.   We had just returned from a long trip.  I was tired.  Armand WA1UQO bailed due to a family obligation. But, since this is about the only hamfest that regularly attend, and because it is only about 5 miles down the road, I went.  

As soon as I got there I started wondering if I should have stayed home.  Here's why:  Hallicrafter S-38s.   Just about everywhere I turned, there were S-38s.  I had never seen so many of these EVIL  AC/DC trandformerless widow-makers.  I watched in horror as innocent hams reached into their wallets and bought these little monsters.  "Does it work?" asked one victim. "Well," said the seller, "it hums like crazy when you turn it on."  Yea, I'll bet it does.  (The guy bought it.) 

It was kind of a Hallicrafters day.  I even saw an Hallicrafters TV!  See above. 

Nothing big followed me home.   I got a couple of nice variable caps (one with a reduction drive).  A Radio Shack speaker.   Some coax.  A project box of BITX40 size.   A Weller soldering gun  slightly less beat up than the one I've had since age 13. 

I got to meet Richard Choy of Midway Electronics.  He has a business out in the Shenandoah Valley and is selling a neat little 2 watt CW transceiver kit.  Go to for more info. 

Oh yea, I got a kick out of this ENORMOUS BFO.  I almost bought it for Pete (who is so fond of tiny little oscillators).  This is a real Boatanchor BFO.  I wonder how many Si5351s you could put in that box? 

Thanks to VWS for putting on the 'fest.  In spite of the S-38s, I had fun.  

Monday, March 12, 2018

WA1UQO's Discrete Ceramic DC Receiver

Armand writes: 

The attached picture is your DC receiver. A little tweaking left to do as the range right now is ~ 7.44Mhz to 7.032Mhz. I used one of Farhan's trifillars and a couple of air coils that you gave me last year.  Listening to the Wisconsin QSO party as I type. 

FB Armand!  The receiver looks great.  I hope others will follow your lead and build this simple little receiver for 40. 

Wednesday, March 7, 2018

Homebrew Your Own Electret Microphones

Don't be such a microphone appliance operator.  Whip up some of your own electret material and turn it into a mic.  Imagine how the audio adjustment guys will react when you tell them you are using a special, tailor-made,  homebrew electret material that gives added PRESENCE and BRIGHTNESS and SPARKLE.  Wow.  Minds will be blown.  A cottage industry could be launched.  

I realize that I tried to fool you guys with a bogus story about making your own Rochelle Salt mics using Tartar sauce.   But on this one, I'm not kidding.  Check out Hack-A-Day's excellent article:

Monday, March 5, 2018

Great Video on Crystal Motional Parameter Measurement

Who out there can save us from further Dishal distress?  Who has one of these fantastic bits of old test gear and is willing to donate it to the cause of accurate filter building?  

Thanks to Tore LB4RG for alerting us to this gem.  

Friday, March 2, 2018

Moxon Destroyed

The north-east region of the U.S.  is experiencing a very strong winter storm.  These storms are called "Nor-Easters"- that describes their track up the coast.   Here, we had wind gusts at 71 mph -- that was around what we had with Hurricane Sandy.  But no rain or snow down here -- it is a different story in New England. 

I was on the air, having a nice chat with Ivo OP2A on 17 when suddenly my SWR went way up.  I knew immediately what had happened.  I stepped outside and saw what you see above. 

Oh well, we had a good run.  It went up there on July 20, 2014.  Not bad for some fiberglass poles from Amazon, some scrap lumber and some wire from Steve Silverman (thanks Steve).  

To tell you the truth I was kind of hoping this would happen.  I'll replace it with a Moxon or a Hex that covers at least 20 and 17.   

Thursday, March 1, 2018

N6ORS and "Satan's Digital Radio"

Hey Bill,

I just finished testing the new rig.  Better sit down for this......
Its an SDR (Satan's Digital Radio). Actually its an estension of an
earlier experiment You might remember the 'Franken SDR". The Franken sdr
worked so well I thought I would make a companion for it and built a QSE 
(quadrature sampling exciter) and an amplifier chain to go with it. The rig
used G3PLX's fantastic SDRTX software for the transmit and DB0JBJ's
wonderful HDSDR software for receiving. The original idea was to make
a small rig for Digital comms, but I decided to add a Mic for voice, also
there is a 'Hardware" audio Phaser already in the building stages 
(you can calm down now).

A few specs. The RX is fantastic , -135 noise floor and the audio is
so clean that it copies wspr signals to -33db. The transmit is 
12 watts and the phasing audio sounds so nice that my wife says 
"thats your terrible voice exactly."So if you catch me on Sunday night
 and i dont sound 'yellowee' enough and you justdont like that 
no-crystal-filter sound just say  "Hey , Dont phase me bro"

See Ya on the bands,
Keith N6ORS

Monday, February 26, 2018

Dragnet Goes After TV Repairmen in 1951

Detective Friday goes after a vicious new kind of crime:  Crooked TV repairmen who overcharge their customers.  These monsters unnecessarily replace (or say they do!) transformers, when all that is needed is a new 5U4 tube.  Oh, the humanity!   

And the reporter they were working with pretended to be a salesman for a new company dealing in rosin-core solder!   

No kidding.  I really thought this was a joke.  They were serious.  Just click on the video above to listen.  

Or scroll forward to the 1:32:59 point on this link.  Lots of tube talk.  This one's for you Grayson!

Sunday, February 25, 2018

Soldering Fingers (and SWR Bridges) in Norway

Tore Bonderudt√•jet LB4RG tells us that he is a SolderSmoke listener, and that the old tradition of hams soldering their fingers together continues to be practiced in Norway.   Here are some pictures of his latest efforts.  This is an SWR bridge project.  Thanks Tore!  Careful with the fingers OM! 

Tuesday, February 20, 2018

N8NM's "20 Dollar Bill" DC Receiver

Steve N8NM wrote: 

I call it "The $20 Bill" because it contains about $20 in junkbox parts and complies with Bill's discreet component, hardware defined radio ethos.
73 - Steve N8NM

I replied:  

Excellent Steve.   Very nice.   

Your post caused me to fire up my DC RX -- I was listening on 40 earlier today.  I think the world needs MORE 40 meter direct conversion receivers.  

Too bad about the regulator IC chip.  We need to get you an 8 volt Zener so that you can bring that receiver into a state of discrete component purity.  


73  Bill N2CQR 

Monday, February 19, 2018

A Wonderful Troubleshooting Story -- Thailand, Mixers, a Simpson 260, Microwaves, and some Black Tape

My old friend was really fortunate to have had such a good Staff Sergeant instructor at Signal School, someone for whom the mixer trig was obviously not enough.  And our old friend obviously also benefitted greatly from having had a dad who set him up with a Simpson 260 and some handmade experimental glass diodes. Wow.  It all came together with some black tape in Thailand... 


Enjoyed your latest blog. I remember your asking about mixers years 
ago.  I received much the same explanation from a Staff Sergeant 
instructor at Ft. Monmouth in 1967.  His example was a mixer with 
diodes, noting the need to have them forward biased by the LO supply.  
We worked out much the same waveforms as shown in your Blog and 
the concept became part of my 'intuitive' knowledge.

A few years later I was fighting 120hz hum on the baseband of an IWCS 
microwave system feeding USAF command at the Korat Air Base in
Thailand. The hum was pretty high level and causing inter-modulation 
problems on the 60 channels of signal sideband suppressed carrier 
being applied to the microwave system.

We ended up with a couple of DCA DoD employees being flown in to help, 
to their credit they were prior service and darn good at what they did.  
After three days of testing all parts of the microwave system with a 
very long distance and long duration phone call to the manufacture in 
Calif, they still had not found the trouble.

I had stayed working with the DCA guys all of the time, during the 
testing I noted the hum seem to lessen in strength with someone standing 
directly behind the radio bay.

I went around to the back and took a close look, Yep! the mixer diodes 
for the baseband order-wire were glass and exposed.

Put a length of black tape over them and the hum went away.  Not the 
power supply problem everyone was fixated on, it was diode photo 
sensitivity.  I guess we could have just turned off the florescent 
lights too.

When I was 10 years old my father showed me how to use a Simpson
260 to check diodes and early transistors*. We were on the floor of the 
living room with sunlight streaming in.  I saw the forward resistance change
a lot when the glass diode was in sun light vs shade. It was this memory 
that prompted me to try the black tape.

All the MW systems in SEA later received a MWO to change out the 
order-wire board and I found that the assembly was a non-standard part 
of the microwave system just for military use.  Civilian deployment of 
that microwave system had no need for the order-wire.

Thanks for the quick trip, for me anyway, down memory lane and the 
memory of being an electronics tech hero for all of two minutes. The DCA 
guys made me buy the first round at the club.

73  from an old friend....

Sunday, February 18, 2018

HB2HB QSO with KC1FSZ and his Al Fresco Scratch-built BITX

I had some good luck on the ham bands last weekend.  First, I was called by Bruce KC1FSZ -- this time he was on his Al Fresco scratch-built BITX-on-a-board.  FB.  The next day, I called CQ on what seemed like an empty 17 meter band.  I heard someone come back -- it sounded like DX.  I had to swing the Moxon a bit -- oddly, I thought, to the south-east.  FR5FC was calling me from Reunion Island.   TRGHS. 

Here's a follow-up message from Bruce: 

Hi Bill:

Great to catch up with you on 40m yesterday.  I was using the Peppermint II which is a scratch-build of the BITX-40 for the most part, although I did my own digital VFO/BFO and made a few other modifications in order to be able to use it on 80m.  It took about 8 months of noodling to get the thing to work, but it was a great learning experience. 

As discussed, I’m working on a 24V power supply (LM723 + 2N3055) and a push-pull IRF510 final so that I can get some more power.  

I got a few more Williams-Sonoma Peppermint Bark tins off of EBay so I’m ready to start boxing things up as soon as the linear is working. 


Bruce KC1FSZ

Saturday, February 17, 2018

KD4PBJ's Acorn AM Broadcast Band Regen

From Chris, KD4PBJ: 

This is my AM band regen I built during December and early January. 

It uses a 955 acorn tube and is a really hot performer! I can pick up dozens of stations with only a 20 ft piece of wire thrown out my shop window and tied to a nearby tree limb 5 ft off the ground. This is from rural Tennessee where we have no local AM’s. 

It uses a velvet vernier I bought off eBay back around 1999 or 2000 and had saved for a special project like this. 

I’m running filaments off a 6V lantern battery and plates off a type 415 45V battery. 

A nice ham/machinist I met on the Time Nuts list who lives in San Francisco made my insulated shaft couplings. I got the Delrin rod cheap off eBay. He cut them to length, center drilled for 1/4 inch and drilled each end for 2 setscrews.

Wednesday, February 7, 2018

Understanding Switching Mixers (as in the Ceramic DC RX)

W3JDR's Comment on my post about the DC RX mixer got me thinking.   He was right -- my explanation of the mixer action wasn't quite complete, especially as far as switching mixers are concerned.  I remembered that I had written about this in the SolderSmoke book.  Below you can see the part of the book in which I discuss switching mixers.  Realize that the two diodes in F5LVG's mixer play the same role as the two gates in Leon's circuit.  It will be worth your while to sit down with Leon's circuit diagram, his frequency chart,  and a ruler and really go through this so you can SEE and really understand how the two gates (or switching diodes) generate sum and difference frequencies.  


I guess I still yearned for clarity and intuitive understanding...  Time and time again, as I dug into old textbooks and ARRL Handbooks and promising web sites served up by Google, I was disappointed. 
Then I found it.
It was in the Summer 1999 issue of SPRAT, the quarterly journal of the G-QRP Club.  Leon Williams, VK2DOB, of Australia had written an article entitled “CMOS Mixer Experiments.”  In it he wrote, “Generally, mixer theory is explained with the use of complicated maths, but with switching type mixers it can be very intuitive to study them with simple waveform diagrams.” 
Eureka!  Finally I had found someone else who was dissatisfied with trigonometry, someone else who yearned for the clarity of diagrams.  Leon’s article had waveform diagrams that showed, clearly, BOTH sum and difference output frequencies.

Switching mixers apply the same principles used in other kinds of mixers. As the name implies, they switch the mixing device on and off.  This is non-linearity in the extreme.
Not all mixers operate this way.  In non-switching mixers the device is not switched on and off, instead one of the signals varies the amount of gain or attenuation that the other signal will face. And (as we will see) it does this in a non-linear way.  But the basic principles are the same in both switching and non-switching mixers, and as Leon points out, the switching circuits provide an opportunity for an intuitive understanding of how mixers work. 

Let’s take a look at Leon’s circuit.  On the left we have a signal coming in from the antenna.  It goes through a transformer and is then applied to two gate devices.  Pins 5 and 13 of these gates determine whether the signals at pins 4 and 1 will be passed on to pins 3 and 2 respectively. Whenever there is a positive signal on gate 5 or on gate 13, signals on those gaps can pass through the device.  If there is no positive signal on these gates, no signals pass.  Don’t worry about pins 6-12.

RF A is the signal going to pin 4, RF B is the “flip side” of the same signal going to pin 1.  VFO A is a square wave Variable Frequency Oscillator signal at Pin 5. It is going from zero to some positive voltage.  VFO B is the flip side.  It too goes from zero to some positive voltage. 
Look at the schematic.  Imagine pins 5 and 13 descending to bridge the gaps whenever they are given a positive voltage.  That square wave signal from the VFO is going to chop up that signal coming in from the antenna.  It is the result of this chopping that gives us the sum and difference frequencies.  Take a ruler, place it vertically across the waveforms, and follow the progress of the VFO and RF signals as they mix in the gates.  You will see that whenever pin 5 is positive, the RF signal that is on pin 4 at that moment will be passed to the output.  The same process takes place on the lower gate.  The results show up on the bottom “AUDIO OUTPUT” curve. 
Now, count up the number of cycles in the RF, and the number of cycles in the VFO.  Take a look at the output. You will find that that long lazy curve traces the overall rise and fall of the output signal.  You will notice that its frequency equals RF frequency minus VFO frequency.  Count up the number of peaks in the choppy wave form contained within that lazy curve.  You will find that that equals RF frequency plus VFO frequency. 

Thanks Leon!  

F5LVG's Glue-Built Mixer Transformer

One thing I forgot to mention:  In Olivier F5LVG's DC receiver article back in SPRAT 100, he casually mentioned building a transformer for his mixer by taking two inductors of the appropriate values and GLUING THEM TOGETHER.   What a great idea!  I had to try it.  I did.  Picture above.  It worked in my Ceramic DC receiver, but the trifilar transformer from Farhan in India worked better.  Perhaps the coupling was tighter.  But hey, it worked.  Three cheers for Olivier.    

Sunday, January 28, 2018

Building the Ceramic Discrete Direct Conversion Receiver #4 -- The Mixer

I think the most important stage of a direct conversion receiver is the mixer.   This is the stage that takes the RF energy coming in from the antenna and -- in one fell swoop -- turns it into audio.

It is important to understand how this happens.  I go into this in some detail in the SolderSmoke book.  To summarize: 

1) You have two signals going into a non-linear device.  The way in which the smaller signal passes through the device -- how much it is amplified or attenuated -- depends on the instantaneous value of the larger signal.  We are not just adding the two signals together.

2) The waveform that comes out will be a complicated repeating waveform.  We know from Fourier that any complicated repeating waveform can be broken down into sine wave components.

3) When you analyze the complicated repeating waveforms coming out of the mixer, you will find that the sine wave components include a frequency that is the sum of the two inputs and another that is the difference between the two.

So lets suppose we have a non-linear device.  We send in a signal from our oscillator at 7061 kHz. Coming in from the antenna we have a signal at 7060 kHz.   The non-linear device will produce outputs at 14121 kHz (sum)  and at 1 kHz (difference).  We are interested in the difference frequency.  We can HEAR that one.  We feed it into our audio amplifiers and we can copy the Morse Code coming in.  It will sound like a 1 kHz tone going on and off as the operator at the distant station presses his code key.  (We don't really have to worry about the 14121 kHz signal -- it is easily eliminated by filters and would never make it through our audio amplifiers.  And in any case we could not hear it.)

What can we use as a non-linear device?  In this receiver we will use diodes.  Diodes are  extremely non-linear devices. They can be used as on-off switches, with one of the signals determining if they are on (conducting) or off (not conducting).  When used like this they are "switching mixers." In essence, a larger,  controlling signal from the VFO will be turning the diodes on and off. Thus the signal coming in from the antenna will be chopped up by the switching action of the diode being turned on and off.  This is non-linear mixing at its most extreme.  It will definitely produce the sum and difference products we are looking for.

We could build the mixer with just one diode. You could apply the VFO signal to the diode to turn it on and off, and then feed the signal from the antenna into the same diode.   You would get the sum and the difference product out the other end.   You will see very simple direct conversion receivers intended for use in software defined radio schemes using just one diode. But this kind of circuit has a couple of serious shortcomingsq: it is susceptible to "AM breakthrough" and it is "lossy."

The circuit we are using addresses these problems by using two diodes.  To reduce loss, one conducts during half of the oscillator signal's cycle, the other during the other half.  Here LTSpice is ueful. You can model this mixer and see in the simulator how each of the diodes handles half of the oscillator RF cycle, with both contributing to the AF signal we want at the output (the difference frequency).   (The schematic above is from LTSpice but it is not ready for simulation.  For this you should replace the variable resistor with two fixed 500 ohm resistors, and add two oscillators -- one with the weak incoming RF signal and the other the strong local oscillator signal.)

The AM breakthrough problem is also addressed by the use of two diodes.  Here's the problem:  If you are on 40 meters, there will be strong shortwave AM broadcast signals coming in from your antenna.  Some will be so strong that they will get past your front-end filtering.  If you were using just one diode, that diode might demodulate the AM signal -- the AM carrier would mix with the AM sidebands and you would have an undesired audio signal heading for your AF amplifiers. Many of us have experienced this -- you are trying to listen to ham radio SSB signals, but you can hear China Radio International playing in the background. 

The two diodes take care of this easily. Look at the way an AM signal would reach the diodes. The carrier (and its sidebands) going through the top diode will be 180 degrees our of phase with the signal going into the lower diode. But the output of the diodes are joined together.  They will cancel out.  We say that for the RF signal coming through from the antenna, the circuit is "balanced."  That signal -- in this case the undesired AM signal -- will cancel out at the junction of the two diodes.

But to understand this circuit you must see what is NOT cancelled out.  The signal from the VFO is hitting each diode with the SAME polarity at the same time.  Look at the 1k variable resistor. So the signal from the VFO will NOT be cancelled out at the output.  Nor will the mixing products produced in the diodes.  That last sentence is the key to all of this.  The sum and difference products that result from the mixing of the signal from the antenna and the signal from the VFO SURVIVE.  They are not cancelled out.

We can easily select the one we want.  An RF bypass capacitor connected from the output of the mixer to ground will get rid of most of the VFO signal (7061 kHz) and most of the sum product (14121 kHz) while passing the audio to the AF amplifiers. 

When I built this detector I used a trifilar toroid out of a box of them that Farhan left with me back in May. I used two of the windings  secondary and one of the windings for the primary.  You might want to make a more simple transformer using an FT-43 type core.  I recommend W8DIZ as a source. 

I hope this explanation helps, and I hope I got it right.  Let me know if you see any errors in my explanation.  Tinker with the circuit when you build it.  You should be able to get it going.       

Complete Schematic

Sunday, January 21, 2018

Mike Rainey and Heavy Metal AM Phone

Michael Rainey AA1TJ wrote:  
I can tell you exactly what's going on here. I'd just received a license upgrade from "Novice" to "General." My new license granted radiotelephone privileges and I was eager to try them out.

In the early 1970's no self-respecting amateur radio operator would dream of using amplitude modulation (AM) on wavelengths above 10m. It wasn't illegal, rather, it was frowned upon due to bandwidth issues, among other things.
But in my excitement - and in the time-honored spirit of, "don't ask permission, ask forgiveness" - I tuned my clunky, Heathkit DX-100 to the 40m radiotelephone band and began calling CQ on AM. Everyone that I contacted was very polite, but to the man they all mentioned how "odd" it was to hear an AM signal on 40m. I eventually took the hint, but not before I'd figured out that yakking on a microphone wasn't my thing after all. Morse telegraphy was my first and enduring love.
I think Michael's next phone transmitter was that voice-powered rig that he used in an attempt to cross the Atlantic with the only power source being his vocal cords. But even there, he was using his voice to send Morse.  

C'mon back to radiotelephone Mike.  There is more to life than dots and dashes!

Saturday, January 13, 2018

SolderSmoke Podcast #202 Cover-Rig, SKN, Pete's Vector Boards, uBITX, K1BQT rig, MAIL

SolderSmoke Podcast #202 is available:

13 Jan 2018

Opening music from Shel Silverstein and Dr. Hook and the Medicine Show.  
On the Cover of the Rolling Stone or  On the Cover of SPRAT magazine.
Travelogue and Weather Report
-- Bill's trip to the Dominican Republic.  SWL on the beach.  Return to the ice box.  
-- Dramatic events in California. 

-- Reading Chinese Sci Fi with lots of radio in it.  "The Three Body Problem" by Cixin Liu

Straight Key Night.  IN QRP MODE THANK YOU.  With nephew Jeffrey.  Annual event -- worked Jim W1PID  friend of Mike Rainey.  

Steve Murphy and Jeff Damm on QSO Today.  FB. 

Oh your rig is homebrew?  "It must be propagation." 

ER Reading about G3UUR

Hams avoiding 60 meters due to 100 watt limit.  SAD. 

Bill's Bench:    Continuing series on the Ceramic Discrete DC receiver.   Described  the oscillator and the AF amp.  Next we will do the Mixer.   The most interesting stage. Nephew John Henry and niece Helena visiting today. 

Pete's bench.  uBITX adventures.   
The K1BQT IC transceiver. 
The Vector Board building technique.  See

Paul KA5WPL  Looking for project with his son.  Sawdust.  Thanks again  Steve Silverman.

Chris Waldrup OM PBJ thanks for the gift

Pete in contact with Sven Johnson
Chuck KE5HPY sent us picture of fashion model with boatanchors in background  Grayson recalled 73 magazine covers...

Pete WB9FLW        Bilateral  SBE-33 ad  "with inherent stability"  That's the best kind!
Bruce KK0S experimenting with AF amps for the DC receiver

John KE5ETX Attempting CBLA

Designer: Douglas Bowman | Dimodifikasi oleh Abdul Munir Original Posting Rounders 3 Column