New Technology for 2020 -- A New SDR Transceiver

Out of Adversity Comes New Ideas!

Then it occurred to me … a different mousetrap.

February 13th, 2020 ~ Leading Edge SDR

This is a photo of a rig from the Radioberry SDR reflector where a ham is using his SDR to communicate with OSCAR - 100. Firstly the Radioberry board is quite advanced and it is a new favorite of the "extreme end" techie types of our hobby. 

Secondly many of the Radioberry boards are being run with a Raspberry Pi4 and here is another example of the rapid technology infusion into our rigs! Keep in mind it is only the second month and 45 days into  2020. 

My post of yesterday regarding conventional radios versus SDR seems to be in tune where the hobby and hardware are going. Today's board type SDR rigs are small, extremely powerful, feature rich and yet at a cost we can at least drool over. Just think an RPi4 with all of the bells and whistles is around the $60 to $70 range. The Radioberry board I think is around $300, so for less than $400 you can be talking to the satellites or having an on the air emperor (small e) "love fest" on 75M.

The Hermes Lite is another board similar to the Radioberry and can be run directly from Quisk. An added bonus of the Hermes Lite -- within Quisk is software to turn your Hermes Lite SDR into an advanced Vector Network Analyzer. Try that with your regen receiver...

So rather than resist SDR like many did in 1959 about transitioning to SSB, do the research and start small by learning about SDR and its benefits. Without hesitation I say that in time you will want to see the waterfall spectrum of signals and you will want to be able to invoke the digital filtering.

My good friend Bill, N2CQR in our latest podcast SS#217 spoke about a very capable hardware audio CW filter from the 4 States QRP Club which he will add to his uBitx V3. 

I am anxious to hear about his experience with this filter. That said, Quisk comes standard with CWL and CWU options as well as 5 digital filters ranging from 200 Hz to 1 kHz. Quisk is a free download and runs on a $35 Raspberry Pi3. The Quisk software will also run a host of SDR boards including homebrew rigs like my RADIG V1 and V3. 

Ad nauseum you can see more about this at http://www.n6qwradiogenius.us

We live in the Golden Age of Homebrew Fabrication!

73's

Pete N6QW

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February 12, 2020 ~ SDR vs Conventional?

I can well remember the on the air discussions of transitioning from AM to SSB. The year was 1959 and there were many new SSB transceivers showing up on the scene including homebrew rigs. Some of those homebrew rigs mostly transmitters  graced the pages of the ARRL Handbook -- one even using a McCoy 9 MHz crystal filter. That was well before the ARRL became an advertising conglomerate dedicated to only selling ham gear.

The discussions were heated and there were complaints of the "Donald Duck" sounds coming out of the speakers on 75 and 40 Meters. The illuminati of  1959 saw it was only a matter of time before there would be a mass exodus to the then new form of SSB communication.

While to many homebrewers there is a sense of connection to the past by building a conventional analog transceiver complete with a homebrew filter, the SDR approach today in 2020 is the SSB of 1959.

I recently bought a Tech Special KWM-2 as a Christmas present to myself. It did not take much work to get it on the air. But there are things still needing attention. I am amazed at the frequency stability of the Collins PTO. That was something done right and endures to this day. My KWM-2 was built in 1962 (pull the crystals and look for the date code) and the S/N is in the 12XXX range --certainly before Nam. So something 60 years old still working is a very good sign.

But yesterday, after replacing a flaky 3.8 to 4 MHz heterodyne crystal I wished I was using my SDR RADIG V.1. Here is why -- two 6 Land hams were having a QSO on 75 Meters --it was around 5 PM. One ham was using a homebrew SSB transmitter (with LC Filter Components for his SSB Filter) and was built in 1947 and the other was using a FLEX 6XXX series. 

Well they were not on the same frequency --split by about a kHz -- My RADIG with the Quisk software has a built in RIT and I would have liked to look at the spectrum of the 1947 Transmitter. 

When they finished I called the guy with the 1947 Transceiver but he was operating with a separate Rx and Tx -- he seemed to have a problem "zeroing" us and he kept moving his transmitter VFO. I do not have the remote VFO for the KWM-2 and there is no "Record" capability as there is with my RADIG. So a bit frustrating and while operating the 1962 KWM-2 in 2020 is cool, I can see where in 2020 the SDR transceiver, especially a homebrew one, is the ticket.

Out here on the left coast, I also note that many hams operating the various 75M/40M nets and round tables simply shut off their receivers and use the web based SDR receivers in Utah and California. In fact many of these nets today, are only possible because stations while using perhaps conventional rigs for transmitting use the web SDR receivers for receiving. An often heard comment : "I can't hear you direct; but you are 5X9 on the Utah SDR receiver."

This does not look anything like a KWM-2 but sure outpaces it with capability.

There is also a significant cost differential for the capability -- about $11K (in todays dollars) for a KWM-2 versus about $300 for a RADIG complete.

My "new" KWM-2 acquired as a Tech Special seen above. So far have replaced three bad tubes, four electrolytic capacitors, one bad crystal and a severely out of tolerance 2 watt resistor. The value is supposed to be 820 Ohms -- it read once out of the circuit 2.7K Ohms. This resistor was in the screen circuit of the 6146's. There was a dramatic change in less bias voltage required once this resistor was replaced. In fact the Bias pot setting now is more in line with the other KWM-2 I have.

73's

Pete N6QW

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February 11, 2020 ~ RADIG V.3 Block Diagram

For those who like to follow the circuit block modules this is how it was done. 

Interesting note as many of these pieces are bought off the shelf and simply connected together. The Sound Card, Sound Dongle, HDMI Display and either the Raspberry Pi3 or the ASUS Tinker Board are off the shelf as is the Arduino Nano, Color  TFT and the Si5351. Other bits would include the keyboard/mouse and the headset microphone.

The "build hardware" is the bi-directional amp which can be just a simple pair of J310's that are relay steered as the Rx RF AMP or the Transmit Pre-Driver. The Driver stage is a 2N2219, and the IRF510 is the standard implementation. The USB to I2C is a build but you will need to contact Cecil Bayona to purchase the programmed microcontroller. You will also need to build the Band Pass Filters. 

The most critical build part is of course the RADIG board which has but a few components such as the 74AC74, the two ADE-1's which can be gotten as free samples. and the RF splitter (FT-37-43 core) and the two modem coupling transformers.

I am thinking of buying the 28.224 MHz Packaged Oscillator ($1.14) and testing that concept as that would reduce the hardware count (Nano, Color TFT and the Si5351) and gives you the digital operation on WSPR, JT-4 and FT-8 on 40Meters. Will keep you posted.

73's

Pete N6QW

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February 10, 2020...

Just finished testing 20M using the 20M BPF and resetting the LO so it would tune 20M ( about 56 MHz). I used the 20M FT-8 signals.

Spent a bit of time yesterday exploring some facets of the RADIG V.3 and will now share those with the blog readers.

1.  My website dedicated to the use of SDR   http://www.n6qwradiogenius.us spends much time on the loading of Quisk onto a RPi3 and/or ASUS Tinker Board. There are now images available that make loading of the basic software much easier. I will need to update that website so that some of the drudgery is eliminated. There are also new versions of Quisk from N2ADR that will work with Python 2 (soon to reach EOL) and the new Python 3. Jim's new software likewise makes things much easier to implement Quisk.
2. I mention many times in the videos and the blog about the setting of Quisk to a center frequency. A bit of explanation as it involves an initial data entry and not simply moving the cursor with the mouse. That said once the center frequency is set in Quisk you can freely tune frequencies either side of the CF simply by moving the mouse
3. There is a Quisk functionality where you can manually enter a "specific frequency" in this case our center frequency. There is a block on the Quisk dashboard where this can be done and is shown in the photo below. Once entered that is the "center frequency" and appears in the very middle of the screen. From there you can tune 24 kHz either side. Noteworthy, the same center frequency must be set on the LO feeding the RADIG Board. These two must initially match! The Arduino / Si5351 is not tuned but Quisk is! While the UNO Color TFT display may show 7.200 MHz, the actual frequency being generated and fed to the 74AC74 is 4 x the display frequency! However with some high end sound cards that range can be extended to 48 kHz either side for a total of 96 kHz; but you also will need to make an entry on the Quisk configuration "Sound Tab" as the default is 48 kHz. I have such a card made by Creative Labs called the Xfinity V. The only negative is the weird connectors on Line Out (uses RCA) but 3.5 mm stereo on Line In and is an odd shape
   

   
4. The RADIG V.3 has opened up possibilities for a "compact "digital only" SDR rig. I have a 5" inch HDMI screen and if you couple that with the fixed crystal oscillator to cover FT-8, JT-4 and WSPR with perhaps some CW thrown in for good measure this could be an ideal in the field digital radio.
5. I have on order from China; ( I think any goods from there have to go through some quarantine process) but won't be here for several weeks, two DC to DC converters from Mean Well. With an input of anywhere from 9 to 18 Volts DC they output up to three amps at 5 VDC apiece. I also have some Micro USB power cables in transit to me. The plan is to cut off the standard USB side and fit the wire ends to the DC to DC converter to power the RPI3 or ASUS Tinker Board from 12 VDC. At  3 amps this will now even power a RPi4 but you will need a USB C to Micro USB adapter plug. The second DC to DC can supply power to the 5" or  7" HDMI or even charge a cell phone out in the field. 
6. All this effort with the power supplies is to simplify powering any RADIG as right now there are several "Walwarts" plugged into a power strip and it is a mess of wires. Final configuration -- one simple connection to a bench 12 VDC Power Supply or to one of those Talent Cell Batteries (bigger amp version) as suggested by N2CQR.

73's

Pete N6QW

February 9, 2020 

Much progress today as I better understood the concept of the "Center Frequency". The Uno and the Quisk must initially be manually set to the same frequency and once done you can "tune" the Quisk software 24 kHz in either direction from there/

A bit of FT-8 (once the setting of the center frequency for both at 7.070 and then the Quisk tuned to 7.074 USB).

An additional thought crossed my mind ... If you wanted to operate only FT-8 and WSPR exclusively with this rig then it might be possible to revert back to the early Soft Rock days. FT-8 is on 7.074 and WSPR on 7.038600, which means they are located 35 kHz apart. If you set the LO to 7.074 - 0.0175 the Center frequency of 7.0565 kHz will operate both digital modes along with JT-4. 

Now if you take 7.0565  X 4 = 28.226 Mhz, and use a fixed crystal oscillator operating at that frequency all you would need is the RADIG board (plus front end Rx RF amp and the Tx chain), the Raspberry Pi3, no sound card for audio; but a sound card for I and Q and the USB to I2C to toggle between transmit and receive. A small 7 inch HDMI display would make for a compact rig. CW operation might even be possible.

Bonus News: Digi-Key sells a 28.224 MHz Packaged Oscillator that when divided by 4 = 7.056 MHz that would give a spread from 7.032 to 7.080 MHz and the price  is $1.14. It is a SMD part but you can make it work. All you need to do is connect a source of 3.3 VDC plus ground and take an output and connect to the RADIG Board.

Digi-Key Part Number	631-1278-ND

This is exciting news!

I have also determined that with the USB to I2C control board installed, once you hit Spot or PTT, then +5 VDC appears on Pin #3 of the USB to I2C. So we now can have the RADIG go into transmit. [A programmed microcontroller that will work in this circuit was recently purchased from Cecil Bayona, K5NWA in Springdale, Arkansas.]

That said I was unable to communicate with the Si5351 directly -- Now I know it can't be done! A bit of further "internet snooping" and it appears the way the 570 and the 5351 develop the PLL multipliers they are incompatible insofar as just connecting some wires and hoping it will spit out RF regardless of which device is used. 

I do have a 2nd SDR Kits interface board (unbuilt) and that may be the shortest distance between two points. But this investigation shows that you could make the Arduino Uno and Si5351 drive the RADIG Board albeit a bit "klunky". 

I noted that on the posted you tube video of the first sharing of this project that there were 25 Thumbs Up and 0ne thumbs down --out of about 222 viewings. If you really didn't like it then tell me the "why" and perhaps I have overlooked something.

So for that one person, you must lack "Knack Skills" and are simply envious! Or perhaps are Republican, attend all emperor (with a small e) rallies and live in the Midwest.

73's

Pete N6QW

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February 8, 2020

Sometimes you get lucky and remember things from the past. Based on yesterday's discovery, I pondered how to turn on the PTT of the RADIG V.3 from the Quisk Software via USB. I even thought of the possibility of controlling the Si5351 from Quisk and eliminating the Arduino Uno and the Color TFT. One step at a time Grasshopper!

About 3:00 AM my brain awoke me and said check the box of old SDR parts from the Soft Rocks you built about 10 years ago. As the Soft Rock SDR radios were being developed there was a separate USB to I2C adapter kit being sold by Tony Parks. 

The schematic looked like this...

So there it was, a way to tap into the USB and trigger the PTT plus accept a pair of CW paddles. But also a couple of all important ports to control SDA and SCL originally on a Si570 but perhaps would work with the  Si5351. 

Now what is in the ATTiny 45 (or 85) is a code as stated set to control a Si570. I just don't know if that will work with the Si5351; but the firstly important piece is the PTT control. That I do know works as that is what is being done with original RADIG V.1.

There is a variant of this schematic as used on the Ensemble Soft Rock that has an Opto-isolator on the output and it looks like the schematic below. This seems like a good idea...

I did find that box this morning and this is what I found...

TRGHS --- here it is built for me (by me). I just need to match the wiring with the 1st schematic above and evaluate the Opto-isolator addition for the switching, checking initially the activation of the PTT. When you hit the Quisk Spot button do you in fact get an output on pin #3. That is the most critical piece to make this into a transceiver.

Later I can evaluate can I control the Si5351 with this same interface board. Baby Steps.

Stay Tuned for the excitement.

73's

Pete N6QW

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February 7, 2020...

So OK, I smoked a Teensy 3.5 (Not the 4.0) and I think the Codec board maybe gone too. These were used with the ZL2CTM SDR evaluation rig. I have another Codec board but need some 32 pin headers to mate the board with a second Teensy 3.5. So basically nothing will happen with this approach for a bit until new headers arrive in abut a week. But the new RADIG V.3 Board is working just fine.

Then today I thought about something from the past. Early Soft Rock users were kind of stuck with crystal control. You got one crystal and with the sound card you could cover about 48 kHz of the band. This was the V6.2 Crystal version. Having only a small slice of the band kind of sucked. Thence the V6.3 which used a Si570 under software control and you no longer were anchored to 48 kHz. Search for WB5RVZ to get the full dope on this history.

Thus my idea --suppose you used the Si5351 in place of a crystal and then use Quisk to tune the 48 kHz slice --all run with a Raspberry Pi or ASUS Tinker Board. 

Off to the races and --yes it works!

I also have been looking at how to use this RADIG on transmit. My original RADIG used a USB Synthesizer kit that is supplied from a company (SDR-Kits) in the UK. Basically the kit contains the ATTiny 45 microcontroller and the RF device is a Si570. That controller works flawlessly!

The programmed Microcontroller can be purchased from a ham here in US (Cecil Bayona). Thus you could actually partially build what is on the schematic so that you would have the PTT and CW paddle controls. But you still would need the Arduino for the Si5351.

I am not certain if the code set for the Si570 and Si5351 are the same; but a further experiment would be to substitute the Si5351 board in place of the Si570. If this works then a huge step up the ladder and you could eliminate the Uno or Nano and the display as everything would be under control of the Quisk software.

Stay tuned my hammie friends for more to come.

73's
Pete N6QW