Wednesday, November 15, 2017

21st Century Homebrew SDR SSB Transceiver Project

Roll Your Own SDR SSB Transceiver

 

N6QW Moves Totally to the Dark Side of the Hobby!

 

11/20/2017 ~ First Transmit Test and More Listening Tests

 
 
 
The transmit concept works with my front end board. The Modem Transformers are also now a proven concept on transmit. I need to find a way to adjust the Microphone gain and to look in more detail the output SSB Envelope. But this is getting exciting.
 
 
73's
PeteN6QW
 

11/19/2017 ~ Block Diagram of the SDR Front End

 
 

11/18/2017 ~ We are 98% there ... Listen to the Video

 
 
 
 
 
This video is a great leap up from where we started. I think we have some positive trends going here. My next task is to get it t work on Transmit and then we can see if we can make a Transceiver from these two boards.
 
73's
Pete N6QW
 
 

11/17/2017 ~ The Problem Appears to be Fixed

Aside from installing a new Codec board and taking a tip from Hans Summers g0upl, today the 600 Ohm to 600 Ohm Isolation transformers arrived and were installed. That cured the hum problem and I will make another video to demonstrate the improvement. The Trick is to separate the grounds. Thanks Hans!
 
 
 
Shown above are the two Isolation transformers (sold as Modem Transformers from Jameco Electronics -- Triad Transformer is the Manufacturer-- about $6 each). Phasing is important and that is why you see the dots (as supplied) on the transformers. Hard to believe that what you see above is the front end, the quadrature LO, phase splitter  and the I & Q Detectors. The audio amp (2N3904/LM-386-3) is also on this board.
 
In passing I do know that the I & Q is working very well. After modifying this board and the Teeny 3.5 board to add the isolation transformers I powered up the unit --and all I was receiving was USB -- Inadvertently I had the I & Q reversed.
 
The two black wires going to the ADE-1's is actually a chunk of shielded cable from a pair of defunct Sony Walkman earbuds. I made it extra long just in case I did that. I will now trim the wires and tidy things up. On either side of the J310's RF amp stage I will be adding a couple of relays on the RF Amp to use this circuit as the Rx RF Amp and as the Tx RF Pre-Amp just like in the Simpleceiver Plus V2.0. I purposely left space on this board to do that. You still need to have the isolator installed on the audio output out of the Teensy 3.5.
 
Can't wait to get this working as a transceiver.
 
73's
Pete N6QW

11/16/2017 ~ Some Progress on Fixing the Whine Burble Noise

 
Part of the problem was the Teensy Codec Board. I had a second board and the above video shows the improvement. We are not out of the woods yet. There is still a bit of background hum which may be resolved with the addition of the 600 Ohm to 600 Ohm Isolating transformers on the front end output similar to what Hans Summers has done with his QRP Labs receiver board. I already have a small fortune in hardware so a few more bucks almost seems like pocket change. The flies in the face of my 1st station which cost me $20 in 1959. I had to mow a lot of lawns to amass $20.
 
73's
Pete N6QW
 
With a large Tip Of The Cap to Charlie Morris ZL2CTM who has done some pioneering work in building SDR SSB Transceivers as evidenced by his superb videos on You Tube --I decided to try my hand at replicating Charlie's work. ZL2CTM has most kindly provided me a great deal of assistance and supplied the all important sketch code and many photos and schematics that he used.
 
Charlie has been successful with his rig. But I have not been so lucky. I simply cannot put my finger on the root cause but in hopes of those more skilled at this SDR stuff will immediately know the answer. View the video and "Tell Me What You Think".
 
The main issue is the terrible background noise that is present on the audio output. If the "whine and burbling background noise" could be resolved --this would be one heck of a rig.
 
By way of background the rig consists of a front end comprised of a pair of J310's configured as a DGM RF amplifier, a 40M Band Pass Filter, a homebrew ferrite core balun signal splitter, two ADE-1's as the I & Q Detectors and a SN74AC74 that is used as the divide by 4 quadrature LO. Also on the main board is an audio amplifier using the 2N3904 and LM386-3.
 
The SDR board has the Teensy 3.5, the Audio Codec Board, the Si5351 and some relay switching so the Line In and Line Out I & Q can be routed to/from the board. For a Display I am using the 1 inch square OLED.
 
After connecting everything up and listening -- it was awful and a terrible whine and burbling noise was evident which called for a disciplined trouble shooting process. The first thing I did was hook up the front end as a Direct Conversion Receiver and routed the output of the I & Q Detectors to the Audio amp (1 channel at a time). The sound was crisp, clear and no evidence of any problems. While the SDR board was bypassed, I was using the LO signal from the Si5351 and the OLED for reading the frequency. Thus the clean signal was not impacted by any OLED noise and what also was evident -- nothing was coming through the Si5351. The outlier was the Teensy 3.5 and the Codec Board.
 
Steve Hartley g0fuw sent me an email about an event in the UK called YOTA which also had a link to a video about the event. (YOTA = Youngsters On The Air). After seeing what these youngsters were doing -- they probably have the answer. The problem is this "oldster" doesn't! Help????
 
I did pose the problem on the PJRC Forum (Teensy gang) and even contacted the head guru at Teensy -- aside from one response from the forum which was not helpful nothing else has been heard other than to sell me another piece of hardware while helpful did not totally resolve the issue. Help????
 

 
 
 
This project has been a frustration to me personally as I just don't know enough about the Teensy 3.5 to lay a finger on the problem. Perhaps it is not a bad device --but I upgraded to a Teensy 3.6 and the results were worse --an important clue that the problem is a Teensy hardware issue.
 
Has anyone reading this blog been successful with the Teensy 3.5 -- ZL2CTM has had good luck but he too is scratching his head.
 
 
73's
From the Dark Side
Pete. N6QW

Wednesday, November 1, 2017

Simpleceiver Plus Version 2 SSB Transceiver

V 2.0 of the Simpleceiver Plus SSB Transceiver

11/13/2017 ~ Last Posting on the Simpleceiver Plus SSB XCVR

 
 
Thanks for riding along but now it is time to move on --Perhaps Part 15 Low Power Neighborhood FM radio stations using a Arduino and Si5351 in an FM Mode much like VU2ESE. It is a whole new world out there. I can only hope the readers have enjoyed this project as much as I have.
 
 
73's
Pete N6QW

11/12/2017 ~ A Few More Photos Before Painting JuliYellow

Note new email address as of 11/12/2017:  n6qwradiogenius@gmail.com

 
 
 
 
An approach for indicating USB/LSB --The Red Square. Works for Me. So far have had a bout 10 contacts and the Rig is doing exceptionally well.
 
Pete
 
N6QW

11/11/2017 ~ On the Air QSO with KC6FZY.

The Simpleceiver Plus SSB Transceiver is nearly complete and the documentation will ultimately shift to my website http://www.n6qw.com. Most likely there will be no more posts about the project as I have been politely told -- enough Pete! Despite that input this rig is one of the better ones I have built.

 
 
 
73's
Pete N6QW

11/09/2017 ~ First QSO with the Simpleceiver Plus SSB V2.0

The wiring of the V2.0 was completed today and the very first QSO was coast to coast with WA3RSL, Frank in Appomattox, VA. The QSO was at 1445 PDT on 7188 kHz. Frank was running  a Yaesu FTdx3000 with an ACOM 1000 and a 5 element wire beam. On this end I was running the V2.0, the intermediate amp and the SB200. The Pout was close to 800 Watts and my usual antenna was the droopy dipole. WA3RSL was of course 5X9+ and I also got a 5X9 report --including a comment on the nice sounding audio.
 
 
Top View of the Simpleceiver Plus SSB V2.0

 
This is the Simpleceiver Plus V2.0 SSB Transceiver prior to painting and finishing off the case.
 
 
This project has turned out to be one of the best transceivers I have ever constructed -- and the circuitry is so simple. Stay tuned for more reports of on the air QSO's
 
73's
Pete N6QW

11/08/2017 ~ Simpleceiver Plus V2.0 Construction Photos

 First look at the front panel layout of the Simpleceiver Plus V2.10 SSB Transceiver being boxed up. Work remaining includes building the Low Pass Filter and the power relay switching wiring plus build the back panel. If we can get the LPF built we can do some on the air testing. I am impressed at the sensitivity and how good it sounds.

 This posting will now show some details of the V2.0 Build as we progress through the process. By way of review the V2.0 build consists of two PC boards which are stacked one above the other. Here is the breakdown of the two boards
 
 
Bottom Board. This is the main board consisting essentially of the following elements: The 40 Meter Band Pass Filter, The RxTx Mixer (ADE-1), The 9.0 MHz IF Amplifier block (two sets of J310'c configured as a Dual Gate MOSFET), The Product Detector/Balanced Modulator (ADE-1), The Audio Amplifier and The Microphone Amplifier. The IF Amplifier Block is relay switched so that the signal is passed through the block in the same direction on both transmit and receive. This one board forms the basis of the transceiver and all this circuitry is packed onto a board 4 X 6 inches.
 









The last photo show the board with all of the circuit blocks starting on the lower right side with the band pass filters moving to the lower left hand corner with the Surface Mount 2N3904 Microphone amplifier. The first photo shows the PC board on the bed of the CNC Mill. Noteworthy is that much of the wiring is routed underneath the PC Board which is mounted on the base plate using 1/4 inch aluminum pillars This really cleans up the wiring and helps with unintended coupling and feedback paths.
 
The top board is mounted on spacers that are about 1.25 inches above the main board. This board has the mounting space for the Si5351, The RxTx RF Amp Stage which again is relay switched to change the signal path so that is passes through the stage in the same direction on both transmit and receive. Following that stage is the EMRFD transmit driver block and finally the IRF510 final amplifier. Not seen is the aluminum plate that is 3 X 4 inches by 1/16 inch thick and forms the basis of the heat sink. This plate is mounted to PC board which has the cutout so that IRF510 is directly mounted to the plate. The overall box size now is about 4.375 inches wide by 8 inches long and 3 inches high.
 
The following photos show the top board and the component parts.
 

The above photo show the top board starting at the upper left corner with the space where the SI5351 will ne housed and below that is the relay switched RxTx amplifier stage consisting of two J310's configured as a Dual Gate MOSFET. In the lower right hand corner is the EMRFD Driver Stage with the IRF510 directly above that circuit block. If you look closely you will see the cutout in the board where the there is access to the heatsink.



 
 
 
The above board is the blank board hot off the CNC Mill. Additional work involved the removal of material where the IRF510 will penetrate the board. That was done on my manual mill --yes I have two of them. The heat sink is mounted to the PC Board and electrically connected so that it is actually a shield. 

 
The above photo show how the Si5351 is affixed to the board and was taken prior to the installation of the Driver and Final stages.
 
I will take some additional photos as the construction progress. I am still noodling the front panel as I need to pay attention to the "ergonomics" of how the controls are arranged. Keep in mind that panel size will be 4.375 inches wide and 3 inches high. That is about 13 square inches and that must accommodate two large real estate items -- the large tuning knob and the display.
 
A question was asked about V1.0 and V2.0 and a comparison of their performance. I was delighted to see that both perform well and are essentially equal. The V2.0 in reality makes the rig be a compact package.
.
Stay tuned!
 
73's
Pete N6QW

 

11/04/2017 ~ Simpleceiver Plus V2.0 First Transmitter Test . Take note a 2nd video was added to document the improved receiver performance with the one capacitor change  (10NF) to the Drain on the 2nd IF Amp stage


We started of the day by building a surface mount version of our Microphone amp circuit that was originally developed for the LBS II transceiver.

The squares I milled out were 0.15 X 0.15 inches and the assembly is as shown above. Noteworthy this was designed over two years ago. This really works well!

Thus after building the microphone amp I hooked everything up and the output was low and the sound was garbled. Well if you look at the photo above -- there is a wire going from the 10 K surface mount resistor to ground as the SMD resistor straddles two squares. If you forget to include that wire then you get low output and garbled speech. I also found that by taking the output off of the drain of the of the second J310 Combo versus the junction of the 68 and 470 PF caps --more output and the instability issue I noted in the earlier video was in part from too low of a battery voltage. No instability with a higher voltage and the 10 nF connected to the drain.

You can see the transmitter testing here.

 
 
 
 
About another week and we should have board #2 completed ready for air testing.
 
73's
Pete N6QW

11/03/2017 ~ Simpleceiver Plus V2.0 Inhaling RF.

Today was a great day as we got the receiver portion inhaling RF. I will do a bit more of peaking and tweaking and then build the microphone amplifier to test out the transmit function. We are about a week away from having a complete 2nd transceiver.


73's
Pete N6QW

11/02/2017 ~ More Progress Photos and Notes

As of 1600 Today!
This afternoon I finished off the Audio Amp stage. The Finger Test (no not that one) produced a loud hiss on the output --thus this stage is working. Tomorrow's work plan is to add the two cables for the LO and BFO and with an outboard 2N3904 RF amp I will see if the receiver circuitry is working.
 
I also must modify the Arduino sketch for the 9.0 MHz IF but that is but a 5 minute effort.
 
Following that series of tests will be the building of the single transistor (2N3904) microphone amp stage that will reside in the island square area of the lower left hand corner. Virtually all of the power wiring and the controls for the audio amp and audio output plus the microphone input will be run underneath the PC Board. This sure makes things a lot neater.
 
The steps after that is to cut the top board for the RF circuits, TR & Control Relays and the LPF.
 
Still noodling the Front and Rear Panel layouts  but the color scheme will be Juliano Blue.
 
BTW I have seen some CNC Mills advertised for sale that can be had for about $300. Since I have most of the circuit board patterns stuffed in the computer cutting new boards is a short piece of work. Christmas is coming --Time to either give yourself a present or to share with your family your Christmas Wish List.
 
On a sad note, once again I know that as usual this year my XYL will get me another SUV present (Socks, Underwear and Vitamins).

73's
Pete N6QW
**********************************************************************************
Today I added to the wiring and a couple of notes about impedance matching. The GQRP Filter has a Z in/out of 500 Ohms and so we will need to match that impedance of the two stages. On the output side of the 1st stage we have a 2 dB pad with an output of 50 Ohms --so a match from 50 to 500 Ohms is a 10:1 match. This easily done with a 6 Turn and 19 Turn transformer wound on a FT-37-43 Core. 6^2 = 36 and 19^2 = 361 ----361/36 = 10:1. Thank You Mr.Boyer.

On the input side of the 2nd stage we have 2.2K and so we must match 500 to 2.2K or a 4.4:1 match. This again is easily done with a 9 Turn Primary (500 Ohm side) and a 19 Turn Secondary (2.2K side) Thus 9^2 = 81 and 19^2 = 361 . 361/81 = 4.45 : 1. Thank You again Mr. Boyer.

 
 
 
 
Noteworthy is that I used some 1/4 inch aluminum pillars to elevate the board above the base plate and made penetrations through the PC Board so the wiring would pass underneath the board. Look closely and you will see the two SPDT relays that are used for routing the signal through the IF Amplifier block for Transmit and Receive which was successfully demonstrated in the V.1 Prototype.
 
I also used my standard color code for wiring.
 
  • Red wires for circuits powered at all times --IF Amplifier block
  • Orange wires for those circuits powered only on receive -- Audio Amplifier
  • Yellow wires for circuit powered only on transmit --Mic Amp, Relays and Transmit chain
  • Black wires for grounds
That is it for now -- if I get a chance to add the parts for the audio amplifier we may get to test this on receive later today.

73's
Pete N6QW

So OK many of our builders are still in the process of collecting parts for the Direct Conversion Receiver version (that was three configurations ago). But just in case you are ready for the next (and final) iteration of this project here we go.
 
Version 2 -- What is it? V2.0 is the Simpleceiver Plus SSB Transceiver Architecture with the following changes:
 
  • A GRQP Club 9.0 MHz Crystal Filter is used in place of the homebrew 12.096 Four Pole Filter. This gives the advantage of acquiring the matching crystals for the BFO and with a 5 MHz Analog VFO you can have a two band rig (20 meters or 80 Meters). The only change required is the appropriate matching Band Pass and Low Pass Filters. A couple of relays and a toggle switch will put you on either band. So a big plus here. Or you can leave it on 40 Meters.
  • Compacting the rig in physical size. I have used two 4 X 6 inch PC Board and fit all of the circuitry on these two boards which will then be stacked upon each other. The main board has the Band Pass Filter, the RxTx mixer (ADE-1), the IF block module comprised of two amps and the filter with the relay switching network, the ADE-1 Product Detector/Balanced Modulator, the Microphone Amplifier and the Audio Amplifier. 
  • The upper (second) board will have the RxTx RF Amplifier, the driver stage and the IRF 510 Final, Low Pass filter and the TR relay switching scheme.
  • The Si5351/Arduino/Display will be mounted to the front panel.
  • The finished size should be about 4.5 Inches wide, about 9 inches deep and about 3 inches high. This is not a miniature rig but certainly small and will be painted Oasis Blue
Here are some photos of the work in progress: The grid in the lower left hand corner is for the Microphone Amp and the grid in the lower middle is for the Audio Amplifier. There are some blank spaces on the board where the switching relay will be installed
 


 
 
73's
Pete N6QW