3D printed project boxes

 I have been busy with some other things that have kept me away from electronics projects for quite a while.  Now I can get back to them, but realize I need some boxes to put them in.  I have 3D printed some simple ones a while ago,  I will redo the design to make them fit the way I have been building my projects now. Most of my designs use modules that I etch or route.  For these I buy copper clad boards that are usually 100 mm wide.  This is one of the standard widths availibale cheaply through eBay or other suppliers. One standard size I use is 100 x 70 mm.  Going with that as a default I designed a clam shell case, that has two identical parts, that you join together with a few screws.  I want to be able to simply add modules without having to drill holes in the case. 

 To do this I designed the case half with slots to slide the modules in vertically.  After printing a set of these I decided to also design another without the slots to use as a top, which makes it easier when trying to aligning multiple modules. 

 I decided on 7 internal slots for modules, along with slots on the ends for front and rear panels.  I also made versions in three heights,  mixing different height versions I could get an inside height from 40 to 80 mm. in 10 mm steps.

I also made a set that fits one of the standard 50 x 70 mm perf boards I use sometime.  This one only has 4 internal slots long with the ones on the ends.

I made the mounting holes to fit 3 mm screws.  They are tight but I was  able to self tap without too much problem.  Depending on printer settings and filament I might have to run a drill bit or a tap through the holes to clean them up.

For those interested I have added the .stl files to the dropbox I have for the storage boxes from a previous post.

https://www.dropbox.com/sh/webi4nhd1a6kd6f/AAArBUSR40y3TQSZBHt8w-Cja?dl=0

Farhans' DAYLIGHT Radio

 Unfortunatly I was not able to make it to FDIM this year, but was able to watch the streamed presentations.  All of themwere good, but the one tht interested me the most was Farhans' DAYLIGHT RADIO.  The design is interesting because the input and ouput impedances of the different stages were not all designed to be at 50 ohms. This can make the design a little easier in some cases.

Farhans' design is for an all analog system including the VFO.  Not sure if I will go that way or use a micro-controller and a SI 5351 instead.  There are some ideas  I want to try that would require the micro-controller.  But if everything is in modules, they can be swapped out with the analog stages as desired.  If I went with the Analog VFO I still have enough parts to use one of the small frequency counter boards I built up years ago.

http://kv4qb.blogspot.com/2015/03/dl4yhf-frequency-counter-re-package.html

Farhan resently uploaded a hard-copy of his presentation to his  web site.  https://www.vu2ese.com/index.php/2022/08/04/daylight-an-all-analog-radio/  This has a lot of good information about some of the considerations that went into the design.

Lets start with the AF Filter and amplifier.  Farhan has a nice desription in his presentation so I will just ashow his schematic. Everything is the same except I am using  seperate opamps for the AF amplifier, and the product detector.  Because of this I  shorted the unused opamp  + input  to the common reference used by the AF amplifier, and the - input to the output . This is left to float,  and as just a precaution to prevent any possible instability of the unused opamp from affecting the AF amp.

I laid out the board using through hole components, but I might make another using MUPPET style, or shrink it down even more and use SMD components.

I will etch the board using Toner Transfer, but since I also have a CNC I can use it to pre-drill all the holes.  Then it is very quick to align the toner image to the board using the holes as s guide.  This makes the whole process very quick and easy. 

Since the board is fairly siimple I decided not to bother with doing a silk-screen . If wanted I could just print  it on a laser printer, and iron this on the same way as you apply the toner image for etching.

This board turned out pretty nice, so now I can finish the layout of the product detector and balanced modulator board, and get them built.

With as long as it takes to get some of the  components these days, it is nice to have several home brew projects going. at the same timr.  And speaking of home brew, I have a two gallon batch of beer ready to bottle..  Thats always handy to have on hand when it takes toooooo long for the electronic components to arrive.

VWS DC Receiver Low Noise Amplifier

Getting back to working  on the VWS DC Receiver, I decided to combine the AF mplifier and the low noise amplifier on the same board to cut down on size.  Because I have been thinking about having separate Low Pass filters for SSB and CW, I will put them on another circuit board instead of with the LNA.

To better match the low impedance of the of the Low Pass filter, the LNA uses a common base amplifier feeding a common emitter stage.  To provide power supply decoupling, Q2 and the associated components are commonly called a cpacitance multiplier.  This provides a capacitance value to the input stage of approximatly the value of  C3 times the gain of Q2.

This configuration along with the LM-386 stage has over 90 dB. total gain, therefore a separate gain adjustment is added to prevent possible overload distorton.  

I decided to make the board MUPPET style, instead of using through hole.  To reduce the board size I installed the resistors vertically.  I

etched a board using toner transfer, and dipped it in some 'liquid tin' to provide a better soldering surface than just bare coppper.  One of these days I will try one using the CNC router to see if there is much of a difference in the quality I can get.

Waiting on an assortment of inductors, that seem to be taking forever to get here so I can finish the LowPass filter board.

VWS Direct Conversion Receiver Project

I have been working on several projects, most of them not related to electronics.  The main electronic related one has made me look back on some code I wrote 6 years ago when I first started learing C++  and the Arduino IDE.  Still wonder what I was thinking of, and how did I ever get anything to work.  Looking at some of the code made me think it was written in a write-only languge.  Almost as bad as looking at some of the things written in FORTH.  

I had been following the Vienna Wireless Society makers group and their Simple SSB transceiver.  They finished that with around 10 units up and running. Many built by members that had no building expereience.  I had started to build a version of this, but they had mostly finished with the project when I started joining their Zoom meetings.  I had some ideas of how I would like to change this, and then other things came up that postponed  my doing this.  They just started a new project, to try to get more of their club members into home brewing (electronic kind not liquid kind).  This one is a Direct Conversion Receiver which should be easier for the first time builders.

I am going to try to follow along with their progress, and build each module as they are presented.  Probably make a few changes as they progress to reflect some things I already have on hand.  They have a Zoom meeting about every other week, to present info on the next stage in the project, keep up with build progress, and provide assistance as needed.

This is a fairly conventional DC Receiver. The interesting thing is that they plan on using a home made Diode Ring Double Mixer, instead of  a ADE-1, SBL-1. or an active mixer like the NE602.

Here is the block diagram of the receiver, with each block being built as a separate module. Many of these blocks are similar or the same as used in their SSSB project. so there should be plenty support for the first timers available if needed.  They plan on using an Arduino and SI5351 as the VFO, but one of the members has already built an analog PTO that could be used instead.

Their last Zoom meeting went over the block diagram. And, a gain distrabution diagram to define the gain or loss in each stage to get up to the required overall system gain.  

Then went into the first module to be built. This is a basic LM386 AF amplifier circuit taken directly from the LM386 datasheet.  Nearly the same as used in most  all simple receivers.  The only thing that is slightly different, is a variable resistor in series with the gain determining feed back capacitor. Since almost all of the overall gain is in the AF amplifier stage, this resistor allows you to set the final stage gain to prevent clipping on strong signals with the volume control all the way up.

Most of the modules will be built manhatten style using MePads, but any other type of construction would be fine.  Since this is all at audio frequencies, a ground plane is not necessary and it could easily be built using perf bard.  This would be similar to the final stage of the version in my previous post. 

https://kv4qb.blogspot.com/2021/06/simple-ssb-xcvr-mic-amp-build-d-mp.html

I used some simple  PCB layout  software to position all the parts for easy building either with the pads, or to route or etch a board instead. This allows me to make a smaller bard than just eye-balling the parts placement on  a bare bard.  One thing that I did different from the diagram is swap connections to the plus and minus pins (2,3) on the LM386   That just made layout a little simpler. Since the LM386 has a differential input it will not change operation.

The board turned out very nice.  Not as small as could be done by using proto board, or doing a through hole PCB.  But, was faster than either of those two metnods, and should be fairly easy for the first time builder.  When I get a little time, I will do some testing on the board and see what the actual stage gain is, and how much it can be varried with the resistor.

Should be another group meeting later this week to see how everyone is coming along.  Will keep you updated on the next stage in the project.

Arduino controller VFO/BFO Test Set

I have done several versions of  VFO/BFO circuits using differentmicrocntrolers.  Any of these would work for the Simple SSB transceiver.  Looking at these, you can see that they are also very similar to some of the test equipment I have previously built.  I know that some people who are interested in building this transceiver, have very little in the way of RF test equipment.  So why not build something that can be used to test the modules as they are being built, and then as the Controller,VFO/BFO to finish off the project.

Doing something similar to the test gadget from a couple years ago, I went with a basic Arduino Nano, the SI5351 module, and a TFT Display.  To this I added header pins to bring out pins for a Rotary encoder and other controlls. To an expansion header I brought out  DC power, analog, I2C , and the SI5351 clock lines.  Since some of the TFT Display modules require 3.3 volt logic levels instead of the 5 volt out of the Nano, I added 1K resistors in the control lines to provide current limit for the display if using a 3.3 v module.  

This also helped make the layout a little easier.  After a number of tries I was able to get the layout to fit on one of the 50 x 70 mm perfboard in the kit I purchased.  When building this module I found that it worked quite well to bring the wired up from the bottom of the board and run them across the top and back down to connect at the other end.   Doing this kept the board fairly neat.  The only insulated jumpers I had to install were to bring the 5V line across the expansion header. This layout would also work well for etching or routing a single sided circuit board.

After building the board, the only thing I had to do to one of the early Arduino sketches I had for a simple VFO/BFO was to change a couple pin definitions for the SPI lines going to the TFT display.  This made a fairly compact board that can be easily mounted, with a connecting cable going to the rotary encoder and several switches on the control panel.

Since I also want to be able to use this as a test_set during construction of the RF stages. I built up a small board with a rotary encoder and 3 push button switches that plugs on to the control header pins on the Arduino controller board. 

 Looking back at the Sweepering Jr., and different versions of the SNA Jr. projects, I decided to go with much of the original SNA Jr. design.  I built a simple add on module that can be used as a Sig.Gen., SNA, RF voltmeter.

I bring out two of the SI5351 clock outputs throughs DC locking capacitors, one of them has a 50 ohm load placed across the output.  This can be used as a two channel signal generator. There is limited level control, but you can build  very simple attenuators to take care of that issue.  Instead of using an AD8307 Log amplifier for RF measurements, it used a 1N60P shunt diode detector feeding a MCP6002 operatinal amplifier.  This two channel op-amp is very nice to work with in microcontroller circuits.  It only requires a single ended power supply, and works well at 5 volts.  It has rail to rail output, so you can use the whole 5 volt input range of the Arduino Nano.  They are readily available in 8 pin DIP and SMD versions, and are less than $1 through most suppliers. This circuit does not have the sensitivity or dynamic range of an AD8307.  But, for use as a RF voltmeter or in a SNA over the range of voltages expected in testing the transceiver it will be very adequate.  One of the detectors has a 50 ohm load on the input for power measurements or use as an input for the SNA function.  The other is configured as a remote RF probe with a x1/x10 voltage divider, for basic RF level checking.   

Just like other parts of the project,

the test set options will be built as simple modules. The test set modules will plug onto the 18 pin expansion header on the VFO/BFO board.  It is built on one of the 50x70 mm. boards in the kit I purchased.  You can use edge mount SMA  connectors for all, but I substituted 3 pin right angle heder pins for the RF probe connection, so I could use it for other possible functions. A 3 pin keeps the layout the same for either, and makes a more solid feeling connection. 

 Adding an adapter board for the TFT display and making a simple 3D printed sleve to hold everything, the modules plugged  together make afairly compact test set.  

Now to finish the software.  It will have parts from the SNA Jr., 2 channel signal generator, and Sweeperino Jr. projects, plus a couple more if I can fit them all in the Nano.

 I hope to have several other modules that such as an antenna nalyzer. SWR power meter. measurement receiver, and possibly a very simple Spectrum Analyzer for up to about 60 MHz.  These will be added as the transceiver project progresses.

Testing Audio Amplifiers

 After finishing the microphone amplifier and the AF amplifier modules, it is time to test them.  For the experienced builder with  scope and signal generator available it is no problem.  If you are new to building, and don't have these available, there is a very inexpensive option that may even work better.  

I spent more than 25 years working as a field service technician.  During this I spent more time than I want to think of dragging scopes, and other pieces of test euipment around.  During the last years before I retired, I found several useful pieces of software that allowed you to use PC sound cards as scopes and or signal generators.  Although they were not suitable for calibrating the equipment I worked on.  They were more than adequate for trouble shooting, and verifying   basic system operation

Although these worked better with actual sound cards, they also work quite well with the very inexpensive USB sound cards that are available simular to this one. 

 Other USB sound cards will give more options such as dual channel input, but are more expensive. 

Only prblem I have found with the USB card is that sometimes there are higher frequency signals found because of traffic on the USB bus.  This has normally been  higher than the 5 KHz. I think of as the upper limit for frequency response in comunication equipment.

They only requite a simple interface to provide usable results. I have tried several, from basically just  DC blocking capacitors,to ones with internal amplification.  

The one I use most of the time uses a simple X1, X10 voltage divider along with DC blcking capacitors on the output to the MIC input on the sound card.  If you use an internal sound card with a Line Input, you can build a two channel version of the interface. 

If you use Line Input you can  elminate the DC blocking capacitor going into the sound card. It is there to remove the DC voltage out of the MIC input used to power Electoret microphones and provides protection for the sound card.  I like having some protection for the sound card from DC voltages in the circuit being tested.  Espically if you use this to test Tube circuits, with their higher voltages.  To add this place a pair of back to back diodes 1N4148 orsimilar across the input to the sound card to ground.

For the  Signal generator output, I capacitivly couple the sound card stereo channels to a 1K pot.  This couples the L and R channels , and lets you ballance the output levels so you can use this to generate a two tone audio signal for testing transmitter out settings. The combined output then goes to a Pot. for level adjustment and a DC blocking capacitor to the output connector.

This is also built with perf board, and use right angle header pins as output connectors.  The header pins let me use JST jumpers to connect to modules being tested or to build simple fixtures for making testing easier.   Instead of a switch I use a 3 pin header and jumper to selecdt voltage level.  You could also replace the voltage divider with a 1 Meg. Pot. to make construction even easier.  I used some 3.5 mm. jacks for the signals going to the sound card.  You could elminate them and use a 3.5 mm stereo cable cut in half and wired directly to the circuit.

There are two different software packages under Windows 10 that I use.  One is Soundcard Oscilloscop    and the other is Visual Analyzer.

They have similar basic functions 

    2 channel scope with XY display

    FFT based frequency spectrum display

    2 Channel signal generator

Visual analyzer has additional functions among them a Voltmeter, Frequency Meter, with additional hardware a ZLRC meter.  

Both free for non commercial use, a commercial license or donation available.

I am only going to use Soundcard Oscilloscope for this post.  After doing the install you get the main screen.

Functions are selected from a set of tabs above the scope display.  First thing you need to do is select your input and output device,  and set the scope paramateurs.  Amplitude calibration can be done later. For ease of learning the interface select scope loopback for input and output device

First function  to check out is the  Oscilloscope function selected by clicking on the first tab.  To the right you have controls for setting the voltage range per channel and the timebase for the sweep.  There are also options for setting trigger type , slope, and threshold.  

Just below th display area there is a button to set the type of measurement you can make.  You can set cursors for both amplitude and time. For both there is a display value for the reference cursor and the difference between it and the second.

The next thing to look at is the

signal generator tab.  This allows you to select the type of signal generated, frequency and amplitude for each channel.  It also allows you to set up frequency sweeps that are very handy for checking frequency response of amplifiers. This can be brought out as a separate window to make it easier to use.

The last function I commonly use is the frequency display.  This uses a FFT to compute a spectrum display of the input signal in the frequency domain, instead of the time domain.  This is very useful for measuring the frequency response of a audio  amplifier or filter, when used with the signal generator.  You can place a cursor on a signal  to get the frequency of the signal. Along with the cursor you can use the zoom function and position to look at a signal in more detail. Unfortunatly there is no vertical cursor, so you have to turn on the grid and reference signal levels to a scale on the side. Some of the other useful options in this function is the ability to look at the levels in dB, and usea peak hold when sweeping to plot the frequency response of a amp or filter.

One common way to check frequency response, is to set the signal generator start frequency, turn on sweep and set the end frequency and sweep time.  I usually set the end frequency to about twice the highest frequency response I am trying to measure.  Then on the frequency display set peak hold and set to dB and auto scale.  Let it run a few passes and you have a good indication of the frequency response of the amp or filter. Do this with two different signal levels and you can find the gain or loss of the device being tested.

Another method to measure frequency response is to select White Noise as the signal being generated.  On the frequency display panel everything is set the same.  After a few passes the frequency response shold be clearly seen.  Make sure you use White Noise and not Pink Noise.  White Noise has a  constant amplitude over the whole audio frequency range, where with Pink Noise  the amplitude fall off as frequency increases.  For checking frequency response it can show a incorrect result at higher frequencies.

Now lets switch to the sound card input and output, and connect to the microphone amplifier.  After setting the signal to a 1KHz Sine wave and a level  just before the output started to distort.

 I switched to the frequency mode and set the signal generator to sweep from 20HZ. to 20KHz. With the display in dB and max hold, you can see the frequency response is flat from 100 Hz to over 10KHz. 

 The log display makes it look noisier at the higher frequencies. But, if you look at the response you see that the noise level is fairly constant across the whole range.

There is one alignment of the test fixture that should be made, that is to adjust the balance between the two channels.  This signal will be used later to do a two tone test for setting the microphone level.  A good Youtube video by W2AEW  Two-tone test of SSB transmitter output explains the test quite well.  The two frequencies should be non-harmonically related and adjust the balance for equal levels. I used 750 and 1250 Hz. and set the cursor at 1000Hz.  Then use the zoom control to spread the traces apart.  Then just adjust the balance pot for equal amplitude.  Make sure you have peak hold turned off while doing this.

Testing the audio amplifier module is the same as the mic. amplifier.   Only thing different is that you need a load between 4 to 32 ohms on the output. The first stage of the audio amp. is nearly identical to the mic. amp., it is followed with a LM386 AF amp IC.   The volume control should be a audio taper pot, but I only had linear taper in my parts box.  You can approximate an audio taper by adding a resistor between the wiper and ground terminals on the pot.  You need to use a larger value pot. to compensate for the final parallel resistance.  Normally the added resistor value is around 20% of the pot. value. I ended up using a 20K pot and a 3K9 resistor.

Setting things up the same as for the mic. amp., 1 KHz. sine wave set the input level and volume control to just below the point of distortion on the output signal. This is kind of tricky because of the gain of the LM386 is set quite high and you can get the output to distort very easily. I turned on the  sweep from 200 Hz. to 20 KHz. and let it run for a while with peak hold turned on. I got a linear response from 200 to just over 8 KHz. where it started to drop off a little. Overall the AF stage has quite a bit of gain, that can start to distort fairly quickly, but has a flat response over the frequency range of interest for communications equipment.  Gain on the LM386 can be reduced by decreasing the value of th capacitor between pins 1 and 8 of the IC, if desired. Thats it for testing audio amplifier stages.  AF filter response can be tested iin the same way. 

 Next I will work on the VFO-BFO oscillator, based on a SI5351 module and Arduino.  I have done several versions of these before, but will layout a simple version that can easily be built on the same style perf boards.  I plan on bringing pins out that will allow the module to be used for testing RF stages in the transceiver. Hopefully I can get this to work similar to the original SNA Jr. or Sweeperino from my earlier posts.  This should be very helpful for those  who do not have anything in the way of RF test equipment.

 

 

 

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Simple SSB Xcvr Mic Amp build & AF amp layout

 I had decided to build most of the transceiver using perf board.  I prefer the double sided plated through hole variety to the bare variety.  For me it just makes it easier to solder the part in place, and then route the leads as needed.  Also if you have to replace a part, you can usually just  clip it off on the top and solder in a replacement without changing the connections on the bottom. 

This type is available in various sizes. You can find small kits with several small sizes for around $10.  You can also get larger size boards and cut to the size desired.

After I received the kit, I changed the layout to fit one of the sizes in the kit.  The extra time spent making an exact layout template really saves time, and frustration in the long run.  I also did the layout in ME Pad  and Muppet format, and all are available at

https://www.dropbox.com/sh/v9rr5cqg9a788qe/AADuZN4t4wCLGh8orBzdFUwTa?dl=0

When I first started building some of my projects, I used many components I had salvaged from junked equipment, or surplus supliers.  Anyone remember 'PolyPacks' ?  Because of this I got into the habit of always measuring the value of the components as I used them. Time spent doing this also paid for itself many times over.  Now I use better quality parts, but still test them before use.  Getting harder to read the values on these small parts for some reason. 

For this I use one of the inexpensive component testers available through the usual suppliers. The one usually use is similar to this one, and has pads for use in testing SMC components.  They are available with or without cases for $10 - $20.  Most of them measure R,L,C, along with diodes, transistors and FETs.  For the seimconductors, they give pinout along with values such as gain and internal capacitance depending on type being tested. The first one I bought did not have a case so I found the design for a 3D printed one.

Following the template, it only took a little while to do the actual construction.  For audio and  digital boards I use either straight or right angle header pins for connectors.  This allows me to use JST style jumpers for wiring for DC and control signals.  You  can also add connectors to shielded cable if needed.  Or, you can easily solder wires directly to the pins if desired.  For much of my test gear, I have adapters made up so I can use JST jumpers for ease of testing modules.

Now that this module is finished, I did a layout template for the AF amplifier.  Since the premap half of the AF amp is nearly identical to the Mic amp, I could just move components over a little to make room for the LM-386 and associated components. 

It turned out like this. This was fairly crowded on this size board, so I did another template using a slightly larger board in the kit.  This one allows plenty of room for components.  Either version will work.  Just up to the builder to choose the one they prefer.

I also did a ME Pad template for those that like that construction method. but only for the smaller size board.  They are available at

https://www.dropbox.com/sh/ia55ghqyibs5iur/AAAlbEp8ARKuvKQ38VONz5zMa?dl=0

Next time I will have the AF Amp board finished, and will describe the simple test gear and software I use for checking audio frequency stages.