SDR on a Breadboard -- But Isn't This an Old-Fashioned Fantasy?

Nice video, but I'm afraid it is a bit of an old-fashioned fantasy.  It would be nice to think that our beloved analog mixers and direct conversion receivers still have a place in the SDR world.   That may have been true a few years ago when we were using soundcard-based SDRs.  But today we just put an Analog to Digital Converter at the antenna, do "Direct Sampling," create a digital stream, and sent it to the CPU for processing, right?   

Sometimes we think that we can show younger people how our older tech (Direct Conversion receivers) is STILL relevant in the age of SDR radio.  But I can just hear them scoffing at this notion, pointing out that I,Q-to-soundcard front ends have gone the way of the dinosaurs, and all we need now is an ADC and a CPU.  

But hey, I am an HDR guy.  Am I missing something here?  

Hodgepodge: Tablet SDR with a Bluetooth Mouse (video)

I continue to find things in the shack that I can connect to the Hodgepodge.  Here it's an old Android tablet with a Bluetooth mouse.   

The waterfall is pretty, but this addition just shows why SDR is really TOO easy.  The modified RTL-SDR dongle is doing direct sampling, so there is not even any phasing circuitry to tinker with.  All the filtering and sideband selection is happening in software inside the 40 buck Android tablet.  The results look nice, but I don't find it very satisfying -- all I did was connect some cables.  So it's back to HDR for me. 

Kevin AA7YQ (Montana Smoke Jumper) Launches his SDR/HDR Build Blog

 

Earlier this month I posted a note from Kevin AA7YQ describing his effort to design and build a nice transceiver that mixes the best of SDR and HDR.   Kevin has launched a blog in which he will describe the project in more detail.  He is looking for constructive feedback and suggestions.  Check it out: 

http://aa7yq.blogspot.com/.

Thanks Kevin. 

Nick M0NTV's Really Useful SDR Transceiver (video)

Even though I am more of an HDR guy, I really liked Nick's SDR rig.  I like the modular approach, with all the modules inside a transparent plastic box (see below).  Don't worry about the shielding Nick -- I had the same concern about my BITXs in wooden boxes, but they worked fine. 

Nick really did a great job on the video.  The bloc diagram was especially useful, both on the hardware and on the software.  Very cool.   It is nice to use this phasing approach,  with the digital magic happening at audio frequencies.   I fear that soon FPGAs and direct digital sampling will take the hardware fun out of these rigs.  We already have a bit of that with the RTL-SDR dongles. 

Very cool how the Teensy takes care of the 90 degree audio shift.   I had to do that with chips in my phasing receiver. When I first saw Nick's bloc diagram, I was looking for the audio phase shift network -- then he explained that that was in software, in the Teensy. 

Nicks arrangement for switching the filters is very nice.  

Thanks Nick!  

 

Pete N6QW and Steve G0FUW Talk to RSGB About Homebrew (Video)

Wow, what an unexpected treat!  Here we can watch Pete N6QW and Steve G0FUW talk to the Radio Society of Great Britain about homebrew radio.  Steve talks about kits and scratch-built rigs.  I really liked seeing his early rigs and his description of how building these rigs helped him become a more advanced homebrewer.  I also liked his mention of George Dobbs as a guiding light in the QRP and homebrew world. 

Pete focuses on SDR and provides a really great description of this approach to homebrew.  I was struck with how great it is that, after a lifetime of HDR building, Pete is willing to embrace this new technology. He talks about it as part of "a learning journey."  As always, he sets the example for us all.   

Thanks to Pete, Steve, and RSGB. 

QCX SSB -- But How Much QCX Remains?

Hack-A-Day carried a very nice video describing recent efforts to turn Hans Summers' amazing QCX CW monoband transceiver into a multi-mode, multi-mode (including SSB) rig (see above).   This is project will greatly interest QCX and SDR fans.  

But I wondered how much of the old QCX is still there after the modification.  Not much, it turns out.  

Here is the bloc diagram of the QCX.  It is essentially a phasing rig, using the same principles as my venerable HT-37 transmitter and my version of KK7B's R2 receiver: 

Yesterday Paul VK3HN sent me the schematic of the new multi-mode, multi-band version:  

Notice how different it is.   I thought that perhaps the new rig would keep something of the I-Q circuitry of the QCX, but it does not.  This is not a criticism, just an observation.  

But here is something that harks back to a topic we've been debating on the blog and podcast.  Notice that the top diagram is a bloc diagram.  There is a lot of circuitry in most of those boxes -- lots of resistors, capacitors, inductors, and transistors.   There is a schematic diagram under that bloc diagram.  But look at the second diagram.  While it looks like one, that one is NOT a bloc diagram. That IS the schematic diagram.  Most of the circuity has been sucked into the chips.  

While many will prefer the rig described by the second diagram, I remain an HDR guy, and don't really like seeing the circuitry disappear into the ICs.  But, to each his own.  This is all for fun.  Congratulations to the guys working on the new rig. 

N6ORS's Hot Mustard Phasing Board. And how Phasing Works.

Keith N6ORS is a prolific homebrewer and a frequent contributor to the SolderSmoke blog.  Many of you will remember his MINEX rig.  And who can forget his SDR creation,  called (by him!) "Satan's Digital Radio"?  Well, Keith is at it again, this time working on a phasing rig. 

HI Bill,

Its been a while.  Lately I've been working on a phasing transceiver

that fits in a tiny can.  Its called Hot Mustard. You need hot mustard

when you hamming. I finished the phasing board, its 10 poles , 5 in each

phase branch. here is a pic.  Building the cpu board

next. I'll document this one for a change hihi.
73,

Keith N6ORS

A while back I did a little diagram that -- for me -- explains how phasing cancels one of the sidebands.  It appears below.   I think Keith's board is for the 90 degree audio phase shift.   You can see how, by changing the shift from you can affect the degree of sideband suppression.   I guess by going from -90 to +90 you could completely switch sidebands.  

This diagram shows a direct conversion receiver with the VFO tuned to 7200 kHz.  There is a signal at 7202 kHz and another signal at 7199 kHz.  In a simple direct conversion receiver, BOTH these signals would produce audio tones in the receiver output.  You'd hear both a 2 kHz tone and a 1 kHz tone. Assume you only want to hear the 1 kHz tone resulting from the 7199 kHz signal.  Phasing lets you do this. Here's how: 

-- First split the VFO signal into its "normal" output and an output that lags by 90 degrees (-90) 

-- Consider the output from the top (normal) mixer to be your reference signal. 

-- Because of the lag in the VFO signal going to the bottom mixer,  the output from the bottom mixer will have the 1 kHz signal 90 degrees ahead of the reference signal (+90) while 2 kHz tone will be 90 degrees behind the reference signals (see "scope view") above.  This is a consequence of the mixer math.  

-- Now, in the bottom signal path, shift BOTH audio tones by -90 degrees (in relation to the top reference signal).  I think this is what Keith's board is doing. 

-- With this -90 degree shift, the 1 kHz signal on the bottom path will be IN PHASE with the 1 kHz signal at the top.  But the 2 kHz signal in the bottom path will be 180 degrees OUT OF PHASE with the (top) reference signal path. 

-- The two signal paths are combined before going to the audio amplifiers. The 1 kHz signal is reinforced while the 2 kHz signal is "nulled out."  

The same principle can be used on transmit.  Instead of two receive mixers, you have two balanced modulators.   Both are putting out upper and lower sidebands.  Instead of the VFO you have the carrier oscillator.  By using the same phase shifting techniques you can reinforce one of the transmitter's sidebands while nulling out the other. 

SolderSmoke Podcast #221 is available -- Quarantine Rigs, Phasing, SWL, Parts Suppliers, Mailbag

Q-31.  "Roll-bar" on cap.  Note RGS316 coax between stages. Country markings on tuning dial

SolderSmoke Podcast #221 is available: 

25 April 2020

http://soldersmoke.com/soldersmoke221.mp3

Obviously no travelogue.   QUARANTINE.  SITS.

Good news:   Lawyers at Dewey Cheatham and Howe report that SolderSmoke will NOT be taken off the net for brazen promotion of the S-38E receiver.

Also some good news on the FT8 vs. FT-FAKE issue.  That report itself was fake.  

PETE’S PROJECTS:

Phasing SSB

And what’s this about a tube CW rig?

Dean KK4DAS builds Pete’s Simple SSB rig. Quarantine Rig: The Furlough 40.  See: https://kk4das.blogspot.com/

SHAMELESS COMMERCE DIVISION:  NEW AMAZON LINK IN THE UPPER RIGHT SIDE OF SOLDERSMOKE BLOG. .

BILL’S BENCH:

QUARANTINE PROJECT:    Q-31 AM SW Receiver.  April 4 through April 19.   15 days of fun.   Learned a lot. 

Need to pay attention to total gain.  Need to measure.   Not always easy.  My resistor-based technique.

AM detection can be more difficult than SSB/CW detection.  Germanium diodes make a big difference.

But…I don’t have to build a BFO, because these signals bring their own beat frequency.

455 CAN BE PROBLEMATIC AS AN IF – image response, making impedance matching transformers tough at those low frequencies.   But WIDE filters available.  

LM386 AF chip make a LOT of audio.  Hard to reproduce these great results. 

Great stuff you can listen to on 31 meters (9.4 –10 MHz):

n  DX WaveScan

n  WRMI Rock and roll

n  VORW music show

n  Radio Nacional De Espana (Madrid)

n  China Radio International  soap operas and Confucius philosophy lessons.

n  China Radio International Chinese Lessons.

n  Radio Greece

n  Radio Republica (France)

n  Radio Havana Cuba

n  Radio Saudi Arabia

n  WBCQ – They advised listeners to fix up an S-38 during quarantine! !!!!!!!

n  WWV

SHOPPING BAG -- THINGS TO GET:

-- Great source for hardware (screws, nuts, bolts and more):  McMaster-Carr   https://www.mcmaster.com/ 

-- Thermax RGS316 coax.   Great stuff.   Thanks Jim  In some ways better than Belden 1671A https://soldersmoke.blogspot.com/2012/03/murphys-whiskers-shaved-with-belden.html

-- Copper Clad board:  Pete’s boards use CEM 1. CEM 1 is low-cost, flame-retardant, cellulose-paper-based laminate with only one layer of woven glass fabric.

https://www.ebay.com/itm/18-pcs-Copper-Clad-Laminate-Board-Single-Sided-4-x-6-CEM-1-060-2-oz/311756276147?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

-- BEST TEST LEADS: https://www.ebay.com/itm/BEST-TEST-LEADS-PERIOD-Hand-Soldered-MINI-CLIP-Version-32-16AWG-Ultra-Flexible/233519356767?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

NEED/WANT: 

-- Thermaleze magnet wire.  First encountered in QRP GUYS EFHW tuner kit.  Very FB

http://www.amidoncorp.com/thermaleze-coated-magnet-wire/

Resistor kits

NP0 cap kit

Replacement Iron for XTRonic 4000 Iron.

RIGOL PROBES Why do we burn through so many of these?

MAILBAG:

-- Eric 4Z1UG Episode 300 Special

-- Farhan working on ventilators. Special thanks to Dr. Gordon Gibby KX4Z. 

-- Jonathan-San working out of new shed in Seattle

-- Grayson reminds us of the Fran Lab: https://www.youtube.com/channel/UCMLgHbpJ8qYqj3CkdbvC0Ww

-- WRMI likes SolderSmoke

-- Peter VK2EMU continues to build his amplifier.  But it is NOT for 50 MHz.  It does have 6 different meters on the front panel.  But it is not a 6 meter rig!

-- Rich K7SZ – “now look what you’ve done”   Fixing up an S-38

-- Rich WD3C  Provided some great SWL links:

https://www.short-wave.info/ if you move the green dot to your location it will predict what the signal strength would be at your location and will also allow you to search by station, language, frequency, etc. 

Thomas Whitherspoon, https://swling.com/blog/  Another, https://shortwaveschedule.com/ and of coarse https://www.hfunderground.com/board/index.php all the pirate broadcasters show up here. 

-- Paul KL7FLR amazing S-38E diagnosis from afar. Paul's toroid tool (more to follow on this). 

Pete's Quarantine 6V6 Rig

"Sideband Suzy" and the History of SSB

Farhan alerted us to a very interesting presentation on the history of single sideband:  It was in episode 81 of Bob Heil's "Ham Nation" show.  It starts at minute 22:

https://www.youtube.com/watch?v=xSF0WBdK1IQ&feature=youtu.be

Two things really caught my attention:

-- Note how OM Carson, way back in 1915, had figured out how to get rid of the carrier, but needed some way of eliminating the unnecessary sideband.  He did it by using his antenna tuner as a filter.  FB OM!

-- In the early days of SSB, when it was an exciting new technology, hams had regular "sideband dinners."  At these events an award was presented.  Kind of like an Oscar or an Emmy I guess.   The award was the "Sideband Suzy" (see above).    Kind of a classic figure...  but half of Suzy was missing!

Renewed Hope for Divide by 2 I and Q

An anonymous reader posted this interesting message in the comments section yesterday.  Very interesting.   A potentially important tip that may help in the quest for 90 degree phase shift with divide by 2 Flip Flop circuits.  What do you guys think?   And who is that masked man?

I wanted to make a comment regarding your Frankenstein R2 Clock divider, but did not come around to do it until now and fear if I were to put it below the appropriate post, it would be so many pages away nobody sees it. Please forgive me for posting this here if my assumption is wrong. I had a play with two edge-triggered JK - Flip Flops (74HC109 & HC107) and tied the J and K to the appropriate rails to use them as T- Flip Flops. Because of one being positive, the other one being negative edge triggered, this behaves as a divide by 2 IQ clock generator. The HC107 has an inverting clock input, so as with the other design, some kind of inverter is involved. And as Bill has reported, I initially measured the Phase shift on the scope to be off. But while playing around, I realized this was a function of the signal level. I could tune the phase shift by adjusting the signal level of the driving clock! When the clock and power supply levels were almost equal, the phase shift was very close to 90° and pretty stable with frequency (tested with 1-10Mhz). Later I thought about it some more and suspect it might have to do with the exact time the inverter "flips" on different signal levels in relation to supply voltage level. Aside from the exact cause, I believe one could vary the supply voltage of the gates with the same effect on the phase shift as with varying the signal level. I hope my observation helps to somewhat make the advantages of divide by 2 IQ clock generators more accessible.