Farhan's sBITX -- Combining SDR with the Traditional Superhet

Here is Farhan's amazing presentation to the virtual 2021 FDIM event.  There is a lot of tribal knowledge in this video.  Lots of old and new technology.  I was especially intrigued by Chris Trask's Kiss mixer.  Farhan's discussion of simple Arduino-based speech equalization and compression made me think that I have work to do in this area. And of course, Farhan's whole discussion of how to bring SDR into -- literally into -- the circuitry of a uBITX is really cool and very educational.   

Bill N2CQR Talks to Dean KK4DAS about the Simple SSB Group Build

Dean KK4DAS visited the N2CQR SolderSmoke shack.  We talked about a lot things including chess, Mars, and AI.  Dean is an amazing guy -- he used to work at NASA's Jet Propulsion Laboratory and a couple of times  actually spoke with Richard Feynman. We also shot a video about the Vienna Wireless Society's group build of Pete Juliano's Simple SSB transceiver (video above).  

This group build all started with Dean's build of Pete's rig.  He built his early in the pandemic, while on furlough from work,  thus the name "The Furlough 40." That makes all of this very much a quarantine effort. As we have learned, dark clouds often do have silver linings. 

For more details on the group build, check out Dean's blog:
https://kk4das.blogspot.com/

And here is the Vienna Wireless Society's Group Build page: 

https://drive.google.com/drive/folders/1cQMGPfG1aAZyksIa9fIkS90TjX2_TMuv

Thanks Dean!  And three cheers for all the Vienna Wireless builders!

Over the Waterfall into the Dark Side: Hodgepodge SDR

This one's for Pete. My effort to add features and modes to my Hodgepodge transceiver took a dramatic turn when I connected the rig to my computer via an RTL-SDR dongle. Woohoo! A Hodgepodge waterfall! Check it out.

The dongle was modified for direct sampling at HF. In the box with the dongle I have one amplifier stage, consisting of a 40673 dual gate MOSFET and one parallel tuned circuit, now tuned to the Hodgepodge IF of 11.998 MHz. I tap the the Hodgepodge's BITX40Module at the output of the first mixer, just before the crystal filter. This was a lot of fun. I can even check my own signal on transmit! This is like having the best of both worlds.

Putting the Quarantine Hodgepodge Rig on CW (Video)

Putting this rig on CW posed a real Hodgepodge challenge: What did I have laying around that would let me do this? Then I remembered: Years ago I built a little 750 Hz audio tone generator. So I pressed that into service. I also needed a sidetone so I built a little RF-actuated circuit that turns on a piezo buzzer when I go key down. And I put a little DC monitoring device (recommended early in 2020 by the Ham Radio Workbench podcast) between the power supply and the rig. There is more to do! Stay tuned.

Update from the Wizard of Wimbledon -- "Always listen to Pete"

In a recent podcast, Pete mentioned that Leo Sampson (the young Brit who is rebuilding the sailing yacht "Tally Ho") should seal the deal with his girlfriend.   Well, it seems that "life coach" should be added to Pete's already impressive list of abilities (homebrew hero, pasta chef, guitar player, etc.)  A while back Pete gave similar advice to Jonathan, M0JGH.   This morning, Jonathan reported in, confirming that Pete's advice was completely correct.  A "mixing product" arrived early in the lockdown. Congratulations to Jonathan and his remarkably radio-tolerant wife.  It seems Leo should be shopping for a ring. 

--------------------------  

Dear Bill and Pete

I hope that you and your families are staying very well during these extraordinary times.

I wanted to thank you both for the reminiscent shout-out during the last podcast, whilst you were suggesting that Leo Sampson of sailing yacht Tally Ho should "seal the deal" with his girlfriend. If our case study is indicative of his future prospects, he absolutely should do! Not only are we happily married but we welcomed a bubbly baby girl into our family at the start of lockdown. (I note that hams refer to children as “harmonics”, but wouldn’t mixer products be a more appropriate metaphor?) 

Apologies for my radio silence of late. Circumstances have allowed me the rare and special opportunity to take more of a lead with parenting, and so my soldering iron has only been wielded for maintenance purposes rather. Your discussion about the intrigue of distant voices emerging from homebrew rigs has whetted this CW addict's appetite to build something for SSB or even DSB, and likely for one of the higher bands...

I feel that I should briefly stick up for the art of CW, though. As a keen amateur musician the ability to communicate through rhythm will always hold a special charm, particularly when you consider that many of my regular EU chums on 40 and 80 are easily identifiable by their “distinctive fists”. I recall a true WW2 spy story in which a double agent, I forget which, was rather unwell but still had to be carried into the radio tent to send his CW whilst lying on a stretcher, otherwise the Germans might notice the absence of this distinctive fist and realize that the game is up!

73 from Wimbledon

Jonathan

M0JGH

Quarantine Hodgepodge Rig -- Part 1 (Video)

More videos to follow.  I have added features, and a transmission mode.  Stay tuned.  

A Problem with the San Jian PLJ6-LED Counter

I had hoped to use this handy and cheap little frequency counter to add some glowing Juliano Blue to the frequency readout on my Quarantine Hodgepodge rig.   I've used these boards with my BITX20, my HA-600A,  and with my DX-100/HQ-100 rigs.  But guess what -- these boards do not work with the BITX40 module board that is the heart of the Quarantine Hodgepodge.  And the reason why is interesting. 

Here is what happens:  First, you plug in the IF frequency of your rig.  In my case 12 MHz.  You connect your VFO output to the signal input on the PLJ6.  You power up the PLJ6.  You then have to select one of two IF frequency options.  One of these options ADDS your IF frequency to whatever it detects at the signal input.  In my case, for a 7.2 MHz signal it would detect a VFO signal at 4.8 MHz. If it were to ADD this signal to the IF freq,  it would readout 16.8 MHz.  And it does.  But obviously that is wrong.  So you go to the other option -- this one SUBTRACTS the designated IF frequency FROM whatever it finds at the signal input.  So here we get 4.8 - 12 =  -7.2   Almost perfect right?  But here is the problem:  The PLJ6 can't handle negative numbers!  So it displays 000000.  Not helpful. 

Here is the manual: 

https://www.mpja.com/download/35057tebasic%20manual.pdf

I didn't have this trouble with any of the other rigs because none of them required the use of negative numbers.  My BITX 20 for example had an IF of 11 MHz and has the VFO running a bit above 3 MHz -- so the PLJ6 just adds the IF to the VFO signal and Bob is my uncle.  Similar problem-free addition takes place with the other rigs. 

I found some discussion on this problem on the internet.  Here is one: 

https://groups.io/g/BITX20/topic/bitx40_and_plj_6led_frequency/4330098?p=,,,20,0,0,0::recentpostdate%2Fsticky,,,20,2,0,4330098 

Some of the respondents didn't seem to understand the problem.  Others hint that the ability to handle negative numbers was as some point in the code for the PLJ6 device,  and may somehow be accessible, but no further info is provided. 

I have already worked up a possible solution, but I'm interested in how you folks would approach this problem.   Any thoughts or suggestions?  I will reveal my solution in the days ahead.   

My Current Rig: The Quarantine Hodgepodge

 

As I continue to Stay In The Shack,  last week I was looking for something to do. This is what I came up with.   

Left to right: 

-- Speaker

-- Ramsey-kit QAMP20 modified for 40. I now have two MTP3055V MOSFETS in there.  

-- BITX40 Module with a solidified VFO from a Galaxy V (note the knob from a Drake 2B!)

-- Power supply 

It puts out about 15 watts SSB.  I was bracing for attacks from the 40 meter waterfall police, but no, everyone said it sounds great.  I had four very nice contacts yesterday.  It was fun. 

Still to do:  Possibly a San Jian frequency counter to give some Juliano Blue glowing numerals for the frequency readout.  This would be a step up from the Juliano Blue sticky note and  corresponding piece of black electrical tape that currently serves as the frequency indicator. 

Our Editorial on the U.S. Election

In our last podcast we took a few minutes to share with our listeners our views on the U.S. election and who we think they should vote for.  Here is the text of what we said.   We stand by every word.

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

Just days before a very important U.S. election we feel obligated to express our opinion and to let our listeners in the U.S. know who we think they should support.

Some of you will think this is inappropriate -- we disagree.  Several of the long-running and more recent themes of SolderSmoke are wrapped up in this election:

SolderSmoke is all about global community, the International Brotherhood of Electronic Wizards.  Trump just rejects the idea of global community. He is all about building walls, imposing travel bans, rejecting refugees, circling the wagons, and blaming our problems on foreigners.  This is one of the reasons we oppose him.

SolderSmoke is all about Science and Technology. Trump is anti-science.  He is a climate change denier. That's another reason we oppose him.

Speaking of science, since the onset of the pandemic we have been urging SolderSmoke listeners to protect themselves, their families, and their communities by following the advice of doctors and scientists.  We urge them to socially distance, and to wear masks. We even invented an acronym in support of this -- SITS – “Stay In The Shack.”  Incredibly, Trump has been pushing in the opposite direction:  He ridicules the use of masks.  He calls our leading doctors "idiots."  He stages super-spreader events at his rallies and at the White House. Look, more than 200,000 Americans have been killed by this thing.  I know five people who have buried close relatives.  Yet Trump STILL treats this virus as some sort of political hoax.  This is one of the many reasons we oppose him.

We are both military veterans.  We have both been offended by the way Trump -- who is a draft dodger himself -- has disparaged those who have gone into harm's way for the United States.  We remember what he said about John McCain.  His scorn for veterans and service members is another reason we oppose him. 

There are many other reasons to oppose Trump, but those are the ones we feel are most relevant to SolderSmoke. 

Election day is Tuesday.  PLEASE, for the good of the country and the world, get out there and vote against Trump. Wear your mask and stay safe as you do so, but get out and vote.  Especially if you are living in Florida, North Carolina, Georgia, Pennsylvania, Wisconsin, Michigan, Arizona, Texas, or Omaha, Nebraska, please help vote Trump out of office and please urge your friends and relatives to do the same.

The Bitsy -- Homebrew Double Sideband from Scotland

 

This is such a beautiful project:  it involves DSB, homebrew, troubleshooting, George Dobbs, SSDRA, J310s, a box kite,  and ham radio nostalgia.  I was struck by how similar the Bitsy looks to some of my own DSB creations (but the Bitsy is nicer).  I'm really pleased to find a DSB project coming out of the UK -- when I was there, DSB was kind of frowned upon by spectrum preservation zealots.  I say there is plenty of room for the very few homebrew DSB rigs that will ever grace the airwaves with their presence.   Thanks John.  Have fun with all your projects.  73  Bill 

Hi Bill

In the early 80's I built and experimented with Direct Conversion Receivers and had a lot of fun with them. I came across a 40M DC cw transceiver by the late Rev. George Dobbs in a Practical Wireless magazine and decided to build it. Whether I was just lucky I'm not sure but it worked first time and I had several cw contacts with it. It was called “The PW Severn”. I then discovered DSB and looked into modifying the wee rig. I gave George a phone, no internet in those days, and explained what I was proposing to do and if there was any advice he could offer. His reply was ,  “it should work so try it and see, any problems get back to me”. It worked and I had a lot of fun with it. I used to take it portable and with a box kite to support a long wire and worked all over Europe.

It was after reading and learning about circuits and home brewing I wondered if I could design and build a DSB transceiver of my own. I had plenty of articles and most importantly a copy of Solid State Design, now well thumbed.

So the “Bitsy” was born. It is an 80M DSB transceiver. The PA produces about 2 watts. I took what I thought was the best for each module and built it using six circuit boards which I designed and etched myself. Nowadays I use the Manhattan method for one of circuits. It is much easier and quicker.

Like most home brew projects, the fun is in the building and the wee rig lived in a box for several years. Probably over 30. My doesn't time fly. I came across it again while looking through my boxes and decided to give it an airing. Expecting it to work on power up I was quite shocked when it produced nothing on both receive and transmit. After staring at it for a couple of minutes I unscrewed the lid and studied the wiring for a dry joint. Nothing so I switched on my Digital Multimeter and Oscilloscope. I soon found out that the output from the VFO was missing. The VFO uses one FET and two PNP Transistors for the buffers. The scope soon proved that the FET was faulty. I used an MPF102. These are hard to get so I replaced it with a J310. While I had the VFO out I also replaced the 9.1v zener diode, which provides a regulated voltage for the FET, with a 78L05 connecting the centre pin via a 580ohm resistor to earth. This gives me a 9.3v regulated supply for the oscillator. It is now back in full working condition.

With the Covid 19 epidemic I, like a lot of the Amateur Radio fraternity, am spending a lot of time in the shack and looking for new projects. I am buying back my old FT200 which was my first rig. An old friend and lapsed amateur has still got it and agreed to sell it back to me. It is still in a good condition for being nearly 50 years old and just needs some TLC. When it is finished it will take pride of place beside my restored Heathkit SB104A. And they say nostalgia is not what it used to be!!

John Forsyth

GM4OOU

SolderSmoke Podcast #224: Mars. Spurs. Bikes. SDR. NanoVNA. Antuino. MAILBAG

SolderSmoke Podcast #224 is available:

http://soldersmoke.com/soldersmoke224.mp3

1 August 2020

--The launch of Perseverance Mars probe with Ingenuity helicopter.

--China’s Tian Wen 1 on its way – radio amateur Daniel Estevez EA4GPZ is listening to it! 

--Sci Fi Books:  Mars Trilogy by Kim Stanley Robinson.  No skip on Mars :-(

--We have some sunspots!  SFI now 72 and the Sunspot number is 23. 

Bill's bench: 

--Conquering Ceramic Spurs in Q-31   Roofing filter -- sort of 

--NE602 for a Q-75 converter – Gilbert Cell. 

--Measuring low power levels out of NE602.  Antuino better than 'scope . 

--NanoVNA   Really cool stuff.  SDR in there. 

--Building a 455 kc LC filter from QF-1 rubble. Using LTSPICE, Elsie... 

--Reviving my bicycle AM radio – The “All Japanese 6”

--Understanding L Network impedance matching. 

--Bill’s new resistor kit from Mouser. Thanks to Drew N7DA. 

SHAMELESS COMMERCE:  PATREON, AMAZON SEARCH.  THANKS

Pete's Bench: 

--Lockdown Special 

--BPF work on SDR Rig

--I U W I H 

Mailbag:

VK3HN Summit Prowler 7

VK2EMU “The Stranger”

SM0P  HB uBITX in Dubai

AE7KI  Worked him in VK from London

ON6UU  EA3GCY’s 4020 rig

KA4KXX A Simpler Mighty Mite

W9KKQ M19 DMR

KD4PBJ Radio Schenectady

W3BBO 12AU7 Regen

KE5HPY Another 12AU7 regen

N5VZH Ne602 Converter

KY3R Wall Art

G4WIF  Spectrum Analyzer in your pocket

W2AEW  Talks to UK Club

KK0S Sent 455 Kc IF cans

KL0S Making 9Mhz filters

VU2ESE  Diving into simple SDR schemes

Dean KK4DAS  Amateur Radio Astronomy

A 75 Meter AM Quarantine Converter for the Q-31 Receiver (video)

A while back Fred KC5RT sent me a nice collection of parts, including some 6 MHz crystals.  I had been thinking of making a converter to put ahead of my Q-31 receiver.  When Fred's 6 MHz rocks arrived, I knew that The Radio Gods Had Spoken (TRGHS).  

I found some NE602 chips in the junk box.   I used an Altoid-sized box for the case.  The toroids are from W8DIZ.  I use trimmer caps from KC5RT to resonate the input and output circuits.  

Hooray!  Now I can listen to 75 Meter AM on the Q-31.  I may have to build a transmitter to go with this contraption.  

Thanks again Fred. 

Paul Taylor's Quarantine "Summit Prowler 7" and some Radio Archaeology

Paul Taylor VK3HN has really outdone himself in this video (above) and blog post. He describes coming across a somewhat mysterious homebrew SSB exciter with some cryptic markings on it. Paul eventually figures them out.  We still don't know who the builder VK3WAC was -- can anyone find him in their logbooks? 

As Paul goes through the description of the transceiver he built around the mystery exciter, he mentions a number of hombew heroes including Farhan VU2ESE, Peter DK7IH, Eamon EI9GQ (I have to get his book!), and Don W6JL.  Also,  our beloved SSDRA book plays a prominent role in the story. 

Paul's video is really beautiful -- at one point the camera pans the landscape and we see kangaroos in the field.  It is also refreshing  -- as we suffer in the heat of the northern hemisphere summer -- to see Paul and his friends out on the summits in their winter coats and hats.  

It looks to me as if Paul built this rig during the current emergency, so I will list it as a Quarantine rig.  Every dark cloud has a silver lining, and Paul's rig has added a bit of silver to the dark COVID cloud.  Thanks Paul. 

https://vk3hn.wordpress.com/2020/07/26/something-old-something-new-a-four-band-5w-50w-ssb-cw-transceiver-summit-prowler-7/

ANOTHER 12AU7 REGEN! W3BBO's Quarantine Receiver

Hi Bill,

I was really impressed with Chuck KE5HPY’s 12AU7 Quarantine Regen!  A very nice build and my hat is off to him!  It caught my eye, as I also built a 12AU7 regen during this period, my first “Hollow-State” unit in sometime. 

It would be interesting to find out what other construction projects fellow hams have involved themselves with during this trying time.

Keep melting solder!

73 de Bob W3BBO

  

KE5HPY's 12AU7 Quarantine Regen -- FB!

Bill and Pete:

Thanks for upping the frequency of your podcasts.  Each one is a welcome note to break-up the COVID monotony.

Following on to Bill’s 31m rx, I am pleased to have a new regen on the air and performing well.  This started as the 12AU7 Hartley circuit found on the web; however, the original circuit needed some further work IMO.  I made a number of modifications – outboard 30 MHz LPF (to remove our local Spanish FM station), inductive antenna link, variable cap for antenna coupling adjustment, up to 24V on the plate, extra by-passing, NE5532 audio section vs LM386 and a switched cap for a lower “band”.  It’s still a starved triode oscillator/audio amp and it has that regen presence.  Best DX is Singapore (BBC) and Madagascar although it’s ideal for easy listening on 19-60m to Romania, Greece, Cuban music, Spain, etc.  As Bill said, there is still plenty worth listening to on a homebrew AM rx.  40, 30 and 20m copy OK, but bandspread is tricky! Adjusting regen is good for +/- 1 kHz, kind of a poor man’s BFO adjustment.   I heard a TI station calling CQ on 20m and called him back on my Icom for a QSO. 

By the way, this rx has some serious vintage mojo – Hammarlund varicap, National coil form, Millen dial and an RCA tube.  The all-star team plays great together! It’s a kick seeing the filament glow while putting RF through recycled parts made decades ago.

73,

Chuck

KE5HPY

A Quarantine Mighty Mite

'Tis a thing of beauty. 

Bill/Pete:

    I just decided here over the COVID period to head back to basics here and build a Michigan Mighty Mite with a Color burst crystal I had here. And wouldn't you know it, it works!  Here's a couple of pictures, it's not pretty at all. Needs to be mounted on something. 

Don KC9ZMY

Q-31 Receiver Filter Fix with the NanoVNA

The picture above shows my problem. As predicted by the Murata data sheet and as warned by R.A. Penfold, that nice 455 kc ceramic filter has a significant response at around 640 kc.   This caused me to hear Brother Stair twice as often as I should have.  Clearly a spur exorcism was called for. 

Click on the picture for a better image.  As noted last time, my first idea was to build a series 640 kc trap LC circuit and put it ahead of the ceramic filter.  But I had trouble getting the desired high Q.  So I then thought about putting a wider 455 kc filter ahead of my 12 kc filter.  I would, of course, need one that did NOT have the 640 kc spur.  I found a 455B filter in my junk box.  I used the NanoVNA to look at its response.  No spur at 640 kc!  Yea!  

Next I put the two filters together, 455B first, then the 12 kc filter.  Success!  You can see on the NanoVNA that there is no spur at 640 kc. 

With close to the desired termination impedances, the passband at 455 kc looked pretty good.  I just put 1500 ohm resistors in series at the input and output of the dual filter combo. 

It worked.  Spur exorcised!  I no longer hear each SW broadcast stations at two spots on my dial.  

The Ceramic Spurs (not a rock group)

Paul Taylor VK3HN's magnificent AM receiver was the inspiration for my Quarantine-31 Shortwave Broadcast receiver.  Like Paul I decided to make use of ceramic filters at 455 kHz for selectivity.  I started with the +/- 3 kHz filters that Paul used, but I found them kind of narrow for SW listening.  So I went with some wider ceramic filters that Bruce KK0S had sent me.  But I misread the specs that Bruce sent.  I thought they were 10 kHz wide filters. I realized later that they were +/- 10 kHz -- really twice as wide as I needed.  So I went back to Mini-Kits in Australia and got some +/- 6 kHz filters.  12 kc wide should be just about right, I thought. 

The bandwidth was right, but I started noticing a problem:  I could hear strong SW broadcast stations at two places on my dial.  This brought to mind an admonition from R.A Penfold, author of "Short Wave Superhet Receiver Construction" (1991 Babani Publications).   He advised keeping a few standard 455 kc IF cans in the circuit because, he warned, the ceramic filters have spurious responses, spurs that the IF cans can help knock down.  

Penfold was right.  Look at the filter response curve on the right (above).  There is a nasty spur at around 640 kHz.   This was the cause of my problem. Here is why: 

Suppose I was tuning Radio Marti's big signal on 9805 kc.  My VFO would be running at 9350 kc. 

9805-9350=455.  Great, but... 

With that spur at 640 kc, I could tune down to 9620 kc on my dial.  My VFO would be running at 9165 kc. 

9805-9165=640.  Bad.   That 640 kc difference product would make it through to my detector and AF amp.  I'd have Radio Marti showing up in two places.  I didn't like this. 

I thought about putting a series LC circuit tuned to 640 kc at the output of the ceramic filter.  This looked like a possible solution, but on the bench it looked like I would have trouble getting a circuit of sufficiently high Q.  

So rummaging around in my junk box I found an old Murata CFM455B filter.  This filter is quite broad, but it does not have the spur at 640 kc.  I could use it as a kind of roofing filter just ahead of the +/- 6 kHz filter.  Putting it there would allow me to avoid having to build additional matching circuits for the 455B filter.  

+/-6kc filter upper left,  455B wide filter to the lover right. 

I'm happy to report that this fix works.   The 6 kc filter provides the needed selectivity, and the broader 455B filter knocks down the 640 kc spur. 

Beware the Ceramic Spurs!  

Q-31 with can for first IF amps and filters open

Jerry's Sproutie: A Short Wave Receiver (and a Limerick) by Jerry KI4IO

Jerry KI4IO is a really talented homebrewer;  I've called him the Wizard of Warrenton:  

https://soldersmoke.blogspot.com/2015/07/the-wizard-of-warrenton-jerry-ki4io.html

and 

https://soldersmoke.blogspot.com/2019/05/fdim-interview-with-ki4io-homebrew.html

Warrenton Va. is not far from me (and is the birthplace of Cappucio the Wonder Dog).  Once we are done with the pandemic I hope that Jerry and I can get together to talk about homebrew radio.  

Like me, Jerry recently turned his attention to the shortwave broadcast bands. He too went the homebrew route, but his receiver is a regen.  It is based on the Sproutie by Dave AA7EE. 

Here is Jerry's article detailing the project and the results: 

http://soldersmoke.com/KI4IORX2.pdf

Jerry had been scheduled to talk about antenna tuners at FDIM this year, but the pandemic caused the event to be canceled.  He shared with me a Limerick that he was going to include in the presentation.  Obviously we have similar feelings about automatic antenna tuners. 

In days of old

when hams we bold

and BALUNs weren't invented

We adjusted our C

and fiddled with L

and reflected power was prevented

KI4IO in his shack Feb 2020

Replacing Electrolytic Caps in my Drake 2-B (Video)

Every dark cloud has a silver lining. Here is a very small silver lining for this terrible COVID-19 situation:  I had time to do a proper replacement of the electrolytic capacitors in my Drake 2-B. 

Three cheers for Hayseed Hamfest LLC for providing the replacement capacitor.  
Go to their website to find capacitors for many other old rigs: 
http://hayseedhamfest.com