Thursday, December 31, 2015

The N6QW Simple-Ceiver

I spent most of the holidays visiting relatives. and had quite a bit of time to work on something I had been thinking about doing for a while.  I have been following the development of the Simple-Ceiver that Pete N6QW has been posting on his blog.   N6QW.blogspot.com .  
Pete spends a lot of time going through the design of a DC receiver that is later converted to a single conversion heterodyne  receiver for 40 meters. He goes through the design using LTSpice to simulate each stage before he builds them.  This powerful tool allowed him to optimize the circuit design before melting any solder.
I have a bunch of 12 mHz. crystals left over from the IF amplifier for the Specan, so I could use the same frequency scheme that Pete used.  I plan on using a  version of the SI5351 VFO  I had  built for the "Canned Frog" transceiver.  Different from Pete's circuit I will use another clock output from the SI5351 for the BFO.

 Link to schematic at  https://www.dropbox.com/s/dersy23jgj6h37c/Simple-ceiver-schematic.pdf?dl=0
 


After drawing the schematic and getting it checked by Pete,  I did a single sided board layout using mostly surface mount components.  I did not have surface mount versions of the ICs for the AF amplifier so I did the layout with extended solder pads for the leaded components. Although I plan on using the SI5351 for the BFO, I decided to add the BFO oscillator to the board.   
Etched the board now to start building and testing the receiver, first the audio amplifier stages.


Friday, December 4, 2015

A PONG Game for Christmas

It is getting close to Christmas, and I need to come up with another present for my son.  He always says that when he was a little kid he had wanted a game system, instead he got a real computer.  He had been a programmer for a while so I guess it wasn't a complete waste.  I think it is time to finally get him a computer game.  Looking around I found a couple versions of the original computer 'PONG"  game for the Arduino. 
I chose  the project from http://michaelteeuw.nl/ 
that looked like it would be easy to port over to the hardware I have on hand.  And of course it would fit in an Altoids tin.
I had an OLED  like the display in my "Canned Frog", but it was two color instead of monochrome.  I had a small TFT display left over from the DL Watt meter project, so decided to use that.

Looking a the schematic, it was very easy to take the board layout from that project and modify it for use for the PONG project.  I was able to remove the Dummy Load and detector components from the board, and move the Arduino Pro Mini and display up towards one end of the board to give room for the two pots I needed for the game controls.  Only other thing was to bring out a pin to connect a small speaker.

After etching the board and installing the components, I started on porting the software to work with the TFT display.  The main advantage of the software I chose, was that it had used the Adafruit graphics library.  I had a compatible library for the TFT display I was using, so it was only took an hour or so to make the necessary changes to use this display.

Main changes was in the resolution of the display, and handling the different colors available to this display.  The OLED display has a clear() function that was used during the draw routine that was not available in the TFT library.  I tried to  replace this with a fillScreen(color) function. Unfortunately this was much too slow and there was a lot of jiter.  Instead of filling the whole screen, I used the fillRectangle(color) function to only clear areas that needed to be redrawn.  This was much faster, and greatly reduced the amount of jitter.  Just a couple of other changes of game play and the porting was finished.
The part of the project that took the longest was cutting and aligning the holes in the Altoids tin.

Friday, November 6, 2015

S9 signal generator Updated 12/1/15

While waiting for some parts for the Spectrum Analyzer, I was looking around for a quick project.

There was a post on the QRP-tech yahoo group about the NorCal S9 Signal generator
http://norcalqrp.org/files/NorCal_S9_Assy_V1.pdf

 








This is very close to the circuit for the Elecraft  XG2 Receiver Test Oscillator

http://www.elecraft.com/manual/E740084%20XG2%20Manual%20Rev%20F.pdf


This looked like something that might be useful for testing the Spectrum Analyzer after I get it finished.  I decided to build a similar unit, using parts from both design.  Looking at the NorCal circuit, I saw that they used  20 and 14 db pads instead of the single 34 db pad used in the Elecraft model.  I went with the NorCal circuit and added switching around both pads to have options of 50, 10, 5, and 1 uv. outputs. 


I want to put the signal generator in an Altoids tin, so I used the same template as my AD8307 power meter as the basis for the board layout.  I have found that I get more consistent etching of the ground pour if I do it as a hatch instead of solid.  I plan on using  2 row .1" header strips with jumpers instead of switches, so I placed extended solder pads on the board.  This way I can just bend the bottom part of the header pins out to the side and solder directly to the top of the board.

Now to etch the board after I get back from a hamfest tomorrow.

 11/8/15


Well it was a little damp and chilly at the Hamfest, so I didn't stick around as long as I usually would.  This gave me plenty of time to etch the circuit board.  For SMD boards I have been using the blue press-n-peel transfer paper to eliminate etch through, and I get a cleaner pad for the SMD components.  I also let the boards sit in some "Liquid Tin" solution for about a minute to give a nice tin coating to the traces.  This seems to solder a little better than the bare copper.


I built the oscillator portion of the board to test how much output I was getting.  From the Elecraft document it looks like the oscillator should put out about -50 dBm before the attenuators.  Hooked mine to my home-brew AD8307 power meter and got a reading of -48dBm.  Checked the voltage to the oscillator and had about 1.6 volts, I might try adding another diode in series to drop the voltage  and see what that does to the output. 
Now on to the attenuators,  I am missing a one of the values for the 20 db pad but will try with the  closest value I have for now.  Will replace with correct value when the assortment of low value SMD resistors I have comes in. 

Since it is raining out I decided to finish the board and add the attenuator  components.  With the attenuator pads out I measured -68.2 dBm on my power meter.  I added another diode in series with the existing diode, this dropped the voltage to the oscillator to 1.07 volts.  Measuring the output with the additional diode I measured a value of -72.8 dBm.  This is more than close enough to the desired -73dBm output level of the Norcal S9 generator.



Only have two crystals in the circuit for now (3.561 and 7.030) will add others as needed.  Listening to the output on a receiver. The 50uv gives about a S7 reading, readings for other levels are below S1 but I can hear definite changes in the signal as I change attenuator settings.
Unfortunately I do not have any calibrated test equipment to verify the values I found.  But I believe the accuracy should be enough for testing the home-brew equipment I am working on. 



Link to dropbox for Eagle files and toner transfer image.

https://www.dropbox.com/sh/p4qqfqab0z5g80k/AACJtjIMUgUTV1FqEuiN-Byta?dl=0


I finished drilling some holes in an Altoids tin and and mounted the circuit board.  I also printed a simple instruction card showing the jumper settings for the different signal frequencies and attenuator settings.  I sized this to fit inside the top cover of the Altoids tin.






Saturday, October 31, 2015

SPECAN 2nd IF filter UPDATED 11/4/15

Got back to work on the spectrum analyzer, with the 2nd IF filter board.     Revised 11/4/15

 This is two filters that are relay switched.  The narrow filter about 1Khz uses 9 crystals and has two in line amplifiers between each set of 3.  The wide filter should have about a 400Khz bandwidth and is comprised of 5 LC networks.



I did a board layout using mostly SMD components. During the layout of the narrow (1KHz.) filter, I found it would be easier to use leaded 2n3904s instead of the smd components.  Just too lazy to redo everything I had already finished to use the smd part.

 



I had ordered a batch of 30 12MHz. crystals, and using my SNA  to match them, I got 9 that were within about 100 Hz. of each other. 
After building this half of the board I decided to test and see what kind of a frequency response I had.




 Using the SNA jr. to check the bandwidth,I found the signal at just a few KHz. below 12MHz.  Narrowing the sweep range I found a nice peak and a bandwidth  of about the 1KHz. required.  From everything I have read, for a Spectrum Analyzer filter you want more of a peaked response than that for a SSB filter.  So this response looks like it will work.  After I finish the board I will check the responses with the Chinese SNA  that has  options for measuring bandwidth.  But, the SNA jr. is so easy to use on the bench it is what I usually go to when building.



Next to do the wide bandwidth filter.  I have not decided If I want to wind some toroids, or use some molded RF chokes.  If I use the chokes I had had added places for paralleling a couple of smd capacitors to tune to the correct frequency.  With the toroids I can try  to adjust spacing of the turns to help tune the filter elements.


I wound some toroids and tried to tune the segments by adjusting the coil spacing on the toroids.  This turned out to be a large pain, and I could not get them adjusted to the bandpass I wanted.
I had some 1.8uH molded RF chokes and some small 60pF trimmer capacitors that would fit on the board.  I  had placed pads for additional capacitors if needed, but found that I could tune the segments without adding any additional capacitors.

After finishing this filter I added the relay switching circuitry.  The relays I had were through hole, but I bent the leads and trimmed the length so I could solder directly to the elongated pads I had on the circuit board.

After completing I checked the bandpass filters.  The narrow crystal filter was about 1.1 kHz at 6dB. and the wide band filter was 456 kHz. at 6dB.

Just need to solder some .020" circuit board material as a shield around the assembly and on to the mixer stage.



Monday, October 26, 2015

Power meter and reference finished.

I finished up the AD8307 power meter and -10dBm reference. 

For the reference I soldered some .020 in double sided circuit board material around the outside edges to protect the components.  Since this will not be used very often I decided to not put in a switch, I just glued the assembly to a 9V battery holder.
I have a new circuit board layout with room for mounting holes that I will build for use as an internal reference in the Spectrum Analyzer I am working on.

After a little cutting and a lot of sanding and touch up work I painted and printed some decals for the Altoids tin I used to house the Power meter.

According to the readings on my oscilloscope the reference should be within 1 dBm of the desired -10 dBm.  After setting the calibration values in the Arduino sketch for the power meter, the readings are consistently within .5dBm.  Checking linearity with several in-line attenuators all readings were within 1dBm.

Without access to other calibrated standards, this is about as accurate as I can come up with, and should be accurate enough for checking most things an amateur would build. 
Now to get back to the spectrum analyzer build.








Sunday, October 18, 2015

20 Mhz. power Reference & Calibrating the Ad8307 power meter

I had the AD8307 power meter working, and compared it against the Chinese SNA in watt meter mode.  The SNA has a built in step attenuator, using that I found the linearity to be very good.  Only thing I was not sure of was the accuracy of the calibration on the SNA.
Looking around the web I found several articles on using a CMOS crystal oscillator can and adjusting for a certain DC output level.  I really wanted something that I could just build and not have to worry about adjusting.  I  would also like to use one as an internal reference for the spectrum analyzer I am building.

 I found a circuit from W1GHZ that looked like it would do nicely. 

http://www.w1ghz.org/small_proj/small_proj.htm 

His circuit uses a crystal oscillator and then takes its output and feeds a pair of back to back diodes.  This should give a very accurate and stable output signal.  This is fed through a low pass filter to remove harmonics of the square wave to a attenuator to set the final output level at -10 dBm.
 


Looking around I found a 20 Mhz. oscillator that I had form another project.  I used ELSIE to design a 5 pole low pass filter using component values I had on hand.  A small circuit board was built using mostly surface mount components except for the two molded RF chokes in the low pass filter.  I made room on the board so I could parallel resistors and capacitors to make the values needed.  Checking the output level on my scope I fund the output to be around 208 mv. p-p  Close enough the the 200 mv. value for -10 dBm.

The method I used to compute dBm. from the ADC reading on the Arduino does not have a calibration routine.  The correct value has to be determined by trial and error, and entered into the sketch.

While I was trying to find the correct value I noticed something interesting.  When I had the AD8307 meter powered by a battery the reading was very constant. 




 But, when I powered it from the PC when I was uploading the sketch with a different cal value the reading jumped around quite a bit, and was much higher.  Indicating that a lot of noise was coupled from the PC to the power meter.  Having the battery connected at the same time greatly reduced the noise but did not eliminate it completely.  
This indicates that any test instrument powered from the PC might be the cause of noise found during testing.  Powering from battery if possible would probably be the better choice.

It only took me 3 tries at setting the calibration value to get the AD8307 meter to read within 0.1 dBm. of the -10 dBm reference signal.  Now I still need to cut up another Altoids tin to put the meter in.









 

Friday, October 16, 2015

An AD8307 power meter

When I started on the SPECAN spectrum analyzer, I purchased several AD8307 log detectors.
I found several slightly different designs for power meters, but most are basically the same with different output circuitry.  I decided to stay with the circuit used by Farhan in his Sweeperino and Specan.  Only change I made was to use 33uf molded RF chokes instead of resistors to feed the +5v and bring the  output from the detector to the outside of the shielded compartment.
After deciding on that I took a look at the Arduino software used to read the log detector and convert to dB.  There are several different methods used, some very simple and others that require rather complicated calibration schemes.  

The best way  to test these would be to build a simple power meter.  I had the layout for the power meter part of the SPECAM and the Arduino and display that I had done for the Dummy Load Wattmeter.   Removing the dummy load portion of that board I was able to import the AD8307 power meter circuitry with only a little change  in the original layout.  For the Arduino Nano and Pro-Mini projects I use low profile IC sockets.  Since I want to move to more surface mount designs.  I changed the board layout to have solder pads for the Arduino and display sockets instead of using through hole. 

I etched up a double sided board, with the bottom being solid except for an isoleted block under the AD8307 circuitry.  I had a little problem and the board was over etched, with a lot of pin holes in the ground plane area on both sides.  I flowed a layer of solder over the board to cover some of them.  After populating the board, I cut a .25" wide strip of .020" circuit board material to use as a shield around the log detector circuitry.


I was able to use much of the software from the DL Wattmeter.
I tried several of the chunks of code for the AD8307 interface, and finally went back to Farhan's basic code.  It is one of the simplest and gives results that will be more than adequate for most amateur use.  It does not have a calibration routine, so a cal value has to  be put into the source code.  After only a couple tries comparing the readings with that of the wattmeter function in the Chinese SNA I found a cal value that gave readings within 1 dB of the SNA.

I wrote the software to include the numerical value from the log detector and also have a analog bar display.   I find that a bar display is often easier to use when aligning equipment.  I also added a little code to give another bar showing the peak value measured.  By implementing a counter in the main loop I was able to have the peak reset to the current level after 10 seconds from the last highest peak reading.      Next to put it in another Altoids tin. 

Looking around for a way to check the calibration, I found a simple RF power reference circuit on the web site of W1GHZ.  I had room on the same board as the power meter, so added that layout.  Will update after I finish building and test it. 

Added link to dropbox folder containing the Arduino Sketch, Eagle cad file ,toner transfer image, and parts layout for boards.  

https://www.dropbox.com/sh/ooubfjxdvjao8by/AABe6N-vTZjaMSgUAG0jeGSca?dl=0



Thursday, October 1, 2015

SNA jr Re-build Updated 11/9/2015

There is a upcoming 'Makers Fair' in Atlanta, and several of the local Ham Radio clubs are going to have a display there.  They will demo some equipment and modes of operation. There will also be  several hand's on activities for the attendees. 
I decided to rebuild the SNA Jr. as part of the exhibit. I redesigned the circuit board, making it a little larger to make it easier to build.  Being larger it will no longer fit in the Altoids tin, but I found a metal Crayola Crayon box that was the right size.
 
I also found a nice small 12 V battery pack with charger on e-bay, they are available in several amp hour ratings.  It is just the right size to fit under the circuit board.  It has a built in On/Off switch and  a separate cable with the charging connector, which makes it very easy to build into projects that are battery powered.

Since this will be a show and tell event, I needed to make it "pretty".  Cutting the required holes in the lid of the tin, caused the metal to deform around the cuts. To make it smooth and sturdier, I glued a piece of .020" circuit board material on top of the lid, and filled in around the edges with some auto body filler. After a paint job, I applied some laser printed decals for labels. I also printed a fake bezel to put around the LCD display.

Along with the new circuit board, I also made a new RLB board that will connect directly to the SNA instead of having to use cables.


Here is a picture of the finished unit with the attached RLB.
It shows a normalized scan of my 80-40 meter  dual band dipole antenna.  Using a RL-SWR table lookup, the  SWR values are the same as when I scan the antenna with my FoxDelta Antenna Analyzer.


I have placed all files  necessary for building
including Eagle files and toner transfer image 
 in the following dropbox 
https://www.dropbox.com/sh/kw7c14euqqi28pn/AABc384tePRDZBoqo6s4YDCRa?dl=0
 






Monday, September 7, 2015

My SPECAN 2nd IF Amplifier

I did a circuit board layout for the 2nd IF amplifier and quickly etched a board.  Everything is surface mount on the top of the board with the bottom of the board kept solid for shielding.  Since I plan on shielding all the RF circuitry, I added solder pad areas to the top of the board to make it easier to solder, and also help with the alignment of the shield pieces.  My favorite material for making shields is .020" double sided circuit board.  It is easy to cut with a scissors or paper cutter, nice and stiff and easier to solder than copper flashing.  Everything except  the power connections and some filter capacitors are inside the shielded box.  The circuit is the same as Farhan's except I added  some  added capacitors to the DC power line both inside and outside the shielded box.  I also used a variable capacitor to the output filter, but added pads for additional capacitors if they are needed.

 Since my eyeballs and fingers do not seem to work as well as they used to do, I stuck with 1206 size components but tried sot23 size transistors for the first time.  Unfortunately I only had the correct value for several resistors in 805 size, so I had to use them.  Since they were connecting to ground on one end I did not have to change the layout.  Actually after I got the hang of using paste solder and a hot air gun, it is probably easier and faster than soldering through hole components.  After it was done I hooked it up to the Chinese SNA to adjust the output filter.  The 60 pf capacitor I used tuned down to 12Mhz. so I did not need to add any capacitance.
12 Mhz 2nd IF amplifier response

After everything was adjusted, I soldered the shield sides on the module.  I will add the top when I get ready to put everything in a box.  Now I am in the process of laying out the relay switched band-pass filters, that is turning out to be more than a little interesting project.  Will keep you informed.
 





Friday, September 4, 2015

"Canned Frog" finished

I had a bit of a delay in getting the Canned Frog finished when my feline helper decided that the little plastic bags of parts for this and some other projects would make great Kitty Toys.  For several days I kept finding electronics parts spread throughout several rooms, and am still looking for several parts.  After finishing the transceiver board it was time to mount the VFO board and see about putting it in the can.

I soldered a couple small strips of .020" double sided circuit board to the new Arduino VFO board and then to sides of the transceiver board.  Also attached the input filter to the side of the transceiver board.  All in all it made a nice package that fit perfectly into the Armour Treat can. 

One of the biggest problems I have had in the past was how to label the panels. The best luck I have had was with press on lettering, but that limits what you can do and is a pain to get straight.  I thought I would see if the same toner transfer method I used for the boards would work for lettering panels.  I  cut and drilled a front panel from some more .020" circuit board material.  I cut out most of the bottom of the can so I could also make a rear panel from the same material.  Gave them a coat of Gray primer and let dry.

Using  MS-Paint I did up a set of panels and printed them in reverse on the same Hamermill Glossy Color Laser paper  I use for making circuit boards.  A half a dozen passes through the laminator, and a quick soak and the panels came out better than I had hoped.  The lettering looks like it is melted right into the paint.   A couple of heavy coats of Grey Hammer Tone paint on the can and then put it all together

One of the Kitty Toy parts I couldn't find was the final transistor for the transceiver, so I stuck in the closest I had on hand.  Power output was a little low, but I will not worry about that.  The receiver works well except that the audio is fine for phones, but not enough for an un-amplified speaker.

The project accomplished what I wanted.  A small dual output VFO with display that will be the basis for another transceiver some time in the future.


Saturday, August 29, 2015

My version of Farhan's SPECAN

A couple of months ago I started to think about building a simple Spectrum Analyzer.  I thought using a simple Direct Conversion receiver might work for what most hams would need.  Looking around the Web I found a discussion with Ashar Farhan about this approach from a couple of years ago.  I e-mailed him to ask how it had turned out and mentioned some of my ideas of doing simple software image rejection.  He responded and listed some of the problems he had encountered, and gave me  information on the SA he ended up building based on theW7ZOI/K7TAU articles from QST.  Later he gave me a link to the blog entry he was working on discussing the project build, but asked me not to mention until he had finalized it. Earlier this week he finished the article and posed the link.
   http://hfsignals.blogspot.in/p/specan-reboot-of-w7zoi.html

 This is an updated version of the W7ZOI/K7TAU S.A. replacing the vco with a si570 and the control and Scope interface replaced with an Arduino and a serial interface to a PC.  There is a corresponding piece of software on the PC that send control information to the S.A and receives and displays the acquired data.


I decided to build a stand alone S.A. based on this design.  I had been playing with different TFT displays for use in expanding the SNA Jr.  The one I liked most was a 3.2" 320x480 display, it is a nice large display that is designed for use with an Arduino Mega.

Using the Mega, it has a 16 bit parallel interface which is much faster than SPI that the others I had tried used.  I modified the design I had for a interface board to give the needed control and data lines needed for the S.A., also included some others for possible use in other projects.

 

Spectrum Analyzer Arduino Interface board
Did a quick board layout in Eagle and etched up a board so I could test the display.  I found that the display only needs the pins on the end connector and a connection to the RESET line on the Arduino.
This made layout easier than I thought it would be. and the board a little smaller. I did up a quick sketch to test the board with the appropriate drivers, and was pleased with the result.  Display is nice and large, and has more than adequate resolution for what I want to do. Since the driver graphic primitives are different and more limited than the ones I had used in the SNA jr. it is taking a while to port the software over to the new hardware.

  Since I already have the SNA jr and the Chinese SNA I can get to working on some of the S.A. boards.  The first board, was one I had already started on for expanding the SNA jr.  This was a detector board based on the ad8307, and is nearly the same as the W7ZOI board used in the PHSNA. Only change is that I had a bunch of 7805 regulators on hand and used that instead of a 78L05 , and used a buffer amplifier on the interface board. Later added a shield made from thin double sided PCB material around the detector part of  the board.


Now to lay out  and build some of the other S.A. boards.





Tuesday, July 28, 2015

"Canned Frog" part three UPDATED

Now that I had the VFO and controller completed, it was time to start putting the transceiver circuit board together.  This is a very nice double sided board with plated through holes, and good silkscreen on the top for parts placement. I started with the receiver portion, and checked that I had good audio to the headphone jack.

Since I am making this cover the whole 7Mhz band, I had to replace the single crystal input filter with a double tuned band pass filter. I wired this up on a small piece of perf-board, and tack soldered SMA connectors so I could easily connect to the SNA Jr.


    I could have used the Chinese SNA for this, but I decided to go with the SNA Jr.  I like to use the SNA Jr. for quick alignments because it is small and self contained.   Do not have to connect to my computer and run the software on there,
I set the frequency range from 5.5 to 8.5 Mhz.to put 7 Mhz on the center graticule., and set the SWEEP mode to FAST.  This mode is a reoccurring display instead of a one shot like the other SWEEP modes.  Took just a few minutes to adjust both tuned circuits, and the coupling capacitor.  Much faster than other methods I have tried in the past.


Now to put it in the circuit, connect up the VFO signal and see what I get.  After I connected everything I found that the receive level seemed to be a little low, and there was a constant tone on the signal.  I quickly rewired the input filter as a single tuned circuit, and that brought up the signal level.  Tuning across the band, I decided it would be adequate selectivity for normal operation so will leave it as is.  Looking at the values for the input filter, low-pass filter on the transceiver, and low-pass I put on the VFO board it would be no problem converting this to 10 Mhz. operation.  Just different tuning of the input filter and changing frequency settings in the Arduino code.  I had included a couple of extra Arduino pins when I did the circuit board, so could even add a relay and with a little code change make it a 2 band rig.

The other problem I found was the constant tone. Since I was using a separate transmit and receiver oscillator, I found that I was picking up the transmit signal all the time.  A little change to the code to toggle  the transmit  oscillator off  when receiving took care of that.  With the selectabel tuning step size it is easy to cover the whole band, and switch to the smaller step size for smooth fine tuning.  There are virtually no PLL lockup clicks when tuning in the smaller step size. The only time I heard any was when I made large frequency changes, then a quck click or two when the software switched to a different PLL divider setting. The RIT function works well, and since there is no limit to how far you can tune off the transmit frequency, it acts like true split mode.

Sunday, July 26, 2015

" Canned Frog" part two

I have been working on the circuit board layout for the "Frog Sounds" transceiver, in a "SPAM" can.
Everything fits on a board that just slides inside the can, and will be soldered to the transceiver circuit board. Using the small OLED display along with the Adafruit SI5351 board made this much easier, as they both use I2C for control.  This simplifies the hardware design and makes circuit board layout much simpler.  I was able to find Arduino code for a very simple CW keyer, and added the few required pins and provisions for a keying transistor to the hardware.
The transceiver uses a SA612 in a Direct Conversion receiver, and takes the 612 oscillator output to drive the transmitter.  Since the SI5351 puts out a square wave, I added low-pass filters to the output of the two clock signals I am using. Using Elsie I modeled the filters, and played around with values  so I could use components I had on hand.  Also added provision for attenuators to bring the signals down to the 200-300 mv. that the SA612 wants, also just used values I had on hand .















Everything fit on the board quite easily, except I had to stack the SI5351 board over the Arduino Nano board.  Using a cut down low-profile 40 pin socket, and trimming the pins on the Nano I was just able to get the clearance I needed.   If I wanted to solder the Nano directly to the board, this would not be a problem.
I put right angled pins on the back of the board to allow for easy connections to the transceiver board.



I was able to use  the software I had previously written for a simple VFO, with very little changes.  Since this is a CW transceiver, I limited the tuning rate to either 50 Hz. or 1 Khz.   I am generating  separate Receiver and Transmit VFO signals, so the RIT function is really  SPLIT frequency.  It just starts at the Transmit frequency when switched on.

 The OLED display is actually a monochrome display, with two different colored areas. I decided to use the larger blue area for frequency display, and the smaller yellow area for a status line.

When RIT is turned off there is only a single frequency displayed,  In RIT mode there are two frequencies, the top is the transmit frequency and the bottom is the receive frequency.  When in RIT the tuning rate is limited to 50 Hz. In either case the receive frequency is always shifted down the side-tone frequency.
Control is very simple, a short push on the encoder button toggles RIT on or off.  A long push (1 second) toggles the step size between 50 Hz. and I Khz.  After step size change RIT is turned off.


The only other function is changing the Keyer speed, this is done by pushing in the encoder button and turning the encoder.  If you need a TUNE  for an antenna tuner , setting the Keyer speed to 0 sets the Dit time to 5 seconds and the Dash time to 15 seconds.  This adds a couple of steps when 'tuning up', but simplifies the code a lot.

I also measure the supply voltage about every two minutes, and display this on the status line.  Other status line items are the Keyer speed and the step increment .


Now onto building a front end band-pass filter and making a few mods to the transceiver board. Then stuffing it all in the can.



                                                 

 

Tuesday, July 7, 2015

"Frog Sounds" meets si5351 meets SPAM can

I have been following Pete's (N6QW) LBS version 2 transceiver progress, and decided to put my BITX project on hold until he gets his finished.   I might just change over to some of his design instead of what I had been thinking of doing

A while ago I had purchased a small 40 Meter transceiver kit from e-bay.  This is a crystal controlled direct conversion transceiver.


Frog Sounds Radio QRP Kit Telegraph CW Transceiver Receiver Radio Station V3


I was able to listen to the streaming of some of the speakers at FDIM and one of the things mentioned was converting this transceiver from crystal control to a VFO, thought I might as well give it a try myself.
I had done a VFO using an Adafruit SI5351 break out board, and decided this would work well for this project. Looking at the schematic of the board, it uses a SA612 as a crystal oscillator, and has a simple circuit to shift the frequency when going form transmit to receive.  I will use two of the clock outputs of the si5351 instead of shifting the frequency in software when changing from R to T.  This will also make it easier to implement RIT or Split operation. 
Looking around for some Arduino CW keyer code.  I think I might be able to use some of the add on code developed for the TenTec Rebel.
I bread boarded a quick Arduino, SI5351, OLED display to see how it would work.  Most of the code from my earlier VFO ported over to use the new display with very little effort.

 


Looking at the size of the board, it looks like the ideal project to stick in a" SPAM" can.  Actually a " ARMOUR TREAT" can, it is much sturdier steel than the aluminum "SPAM" can. Just started laying out a circuit board for the VFO front panel, and working on adding to the software.



Will keep you informed.