Wednesday, December 14, 2016

Building the BITX 40 v 3 A SI5351 VFO update 1/22/17

Between getting ready for the Holidays and a couple things i need to do around the house, I have not been spending much time working on the BITX.  Except for the drift issues I still have not been able to get resolved, I am very happy with the performance so far.  The simple AGC seems to be working well, and makes listening much more comfortable.  I took a look at the output of the detector on the AGC board, and it looks like it will be usable for a signal strength meter.

With the drift problems, and desire to add a signal strength meter I decided to go ahead and build up a digital VFO. I have a 9850 module left from the SNA Jr.  and a couple  Adafruit SI5351 modules from earlier projects. I had ordered 2 of the BITX boards, and had planned on making the second one into a multi-band rig.  With this in mind I decided to go with the SI5351, because I could use a second clock in the multi-band version for side band selection.

Over a year ago I had built a 5351 based VFO for use with Frog Sounds 40 Meter CW transceiver.  I called it the Canned Frog, because I put it in a canned meat can.

I had used a separate clock for the receiver and transmitter LOs, so had about everything I needed in the board I had laid out for it.  This VFO used a Arduino Nano, and a small OLED display.  This will be fine for the single band version, but want a larger display when I get around the the multi-band version.  I used the basic layout I had, and brought out most of the Arduino pins for use with a different display, and other options I am thinking of adding.  When I did the original VFO. I found the regulator on the Nano got quite warm when running on 12 volts.  So, I added a 9 volt regulator to the board to keep the Nano cooler. 
I also changed most of the passive components on the board from leaded to SMD versions, that will be mounted on the back.  I have started to try to use SMD components where ever possible.  Drilling holes is the most tedious problem of making my circuit boards.  Only problem with home made PCBs and SMD components is watching out for solder bridges.  I have been playing around with UV curable solder mask, and have gotten the process down to something fairly easy with consistent results.  So after etching and tinning the board, I added a solder mask before drilling.   Everything looks very nice, now to build the board and modify the existing sketch to take care of a IF offset.

12/18/2016 board and software mostly finished

Finished getting most of the board populated except for the filter and attenuator circuits, and the basic software working.  Now I can try setting different levels and filter values on the board to see what values work best.    The software is basically what I had used for the 'Canned Frog', with the CW keyer and CW offsets, and RIT removed.  Since this used a direct conversion receiver, the signal output was on the transmit frequency. The BITX is a super-hetrodyne, and has a IF  frequency around 12M Hz. Therefore the VFO signal must run at a different frequency.   Because you are receiving the Lower Side Band  the exact frequency used is the BFO frequency. Basically the VFO frequency is the BFO frequency minus the operating frequency. 

 For the 7 Mhz. band this is around 4.7 Mhz. to 5 Mhz. The original software used the actual operating frequency for display and setting the si5351.  I measured the frequency of the BFO and used that value in computing the required VFO frequency. This value was used to set the si5351 clock 0 output.

After making the changes to the software, I ended up spending an hour or so trying to find out why the frequency was not changing when I turned the rotary encoder.  I finally looked at signals with a scope, I found I had a bad rotary encoder.  After changing that everything worked the way I expected it to.  

Update 1/2/17

I spent most of the holidays visiting relatives, and did not have much time to work on any of the projects I am working on.  I did bring my laptop along and had some timeto work on a BITX front panel that will work with the SI5351 VFO and Display.  The original front panel was designed to work with a small counter and had a grill opening for a small speaker.  After trying the BITX  receiver, I found that even with an AGC circuit added, the audio sounded much better with a larger external speaker.   This version has a built in bezel for the display, mounting posts for the circuit board. 
I also had to include a recess to provide room for the stacked Display and Adafruit SI5351 board.  To center the display, I had to move the microphone and volume control to the opposite side of the panel.  

 Update 1/22/17

I 3D printed the new design front panel and tested the VFO out when connected to the BITX board. I found some of the same kind of receiver noise I had at first with the frequency counter.  It looks like the BITX board  is very sensitive to any noise on the DC supply line.  I had a reverse polarity diode on the board, that I replaced with a 10MH. choke and added a 100 uF. capacitor across the input to the regulator on the board.  With this I could not hear any noise unless I turn the volume all the way up and disconnect the antenna. 

 The recess I put in the back of the front panel helps keep the display and si5351boards in position, along with reducing the overall depth in the case.

Just a little more work on the software to make sure the RIT is working correctly and possibly add a  S-Meter

Wednesday, November 30, 2016

Building the BITX 40 v 3, receiver portion 8/1/17 UPDATE

12/2/16   Added link to Eagle files for making AGC Board

8/1/17 I uploaded the eagle file to  For those who want the boards  they can be can be ordered directly  $11.70 including shipping for 3 boards.

A couple of things came up and I was delayed in building Farhan's SMD BITX 40.  With the availability and price point on the board, I decided I will stop work on the version I was designing and building.   I will instead spend my time on trying some modifications to enhance the board from Farhan.  
For those who are building with this board, there is a website devoted to different mods for it.

Since I haven't gotten around to build a si5351 VFO yet,  I installed a 10 turn tuning pot.  This made it much easier to tune, but I found there was quite a bit of drift during warm up.  Looking over the bitxhacks blog, one of the first mods I made was to change some of the resistor values in the bidirectional amplifiers.  Changing them from 100 to 220 ohms reduces current in those stages,  should reduce heating of that part of the circuit board.  I also coated the VFO coil with several coats of clear nail polish to prevent  coil winding movement.

Another change I made was to cut the short trace going from  switched 12 volt to the  U2 (VFO  9 volt regulator) input pin. Then I ran a wire from the input pin of U2 to un-switched 12 volts.  I also added a .1 uF capacitor from the regulator input pin to ground, and a 47uF and .1uF  from the output to ground.  This keeps the VFO circuit on at all times, and hopefully further reduces warm up drift. 
After all of this it is much better, but I still have some drift, up and down in frequency even after warm up.  Ordering some NPO capacitors to use in the VFO and will see if this helps.

With much of the drift problem solved, I next looked at the audio.  Since the BITX does not have AGC, having to adjust audio level when going from station to station can be aggravating.  Farhan posted a simple AGC circuit on the bitxhacks blog, and I decided to add it to mine.  

I took his hand drawn schematic, and input it
to Eagle and laid out a simple board that can be built as mostly SMD or Muppet style. 

After etching a couple boards, I built up one of each to give a try.  For the SMD version I also added a solder mask to make assembly easier.  Adding the AGC board to the BITX took care of leveling the audio, but the added circuitry reduced the audio level.  Replacing the 1 uF. capacitor from pins 1 - 8 of the LM386 with a 10uF. brought the gain back up to where it was.

Link to Eagle files and a .pdf with mirrored top layer image for making toner transfer boards.

Next to add the frequency counter.  With a little change to the gain on the counter pre-amp I had it reading correctly.  Using the setup function on the counter, I measured the BFO frequency, and set the counter mode to subtract the VFO for proper frequency display.  There was some noise introduced on the audio output.  A 220uF capacitor across the counter power supply leads, and a 10mH. choke in series with the positive  supply lead took care of that.

Except for a small amount of frequency drift the receiver portion of the BITX is working.  Now to wire up the microphone and test the  transmitter.  It is starting to look like a transceiver.

Saturday, November 19, 2016

Some nice words about the SNA Jr.

I have been following Paul M0XPD "Shack Nasties"  Blog for quite some time.  This year at FDIM, Paul gave one of the seminar presentations.  I was pleasantly surprised when he mentioned my early version of the SNA Jr. in his presentation.  Later, I had a chance to speak with him about some of our common interests and projects.  I also gave him one of the extra SNA Jr II boards I had had made.  
A week or so ago I received an e-mail from him with a picture of the SNA Jr. that  he had just finished building.  Today I saw that he had updated his blog with a very nice write up about the SNA Jr II.  I want to thank him for his kind words.
If you have not read his blog before, it is one you should follow.  I know I always find something interesting and informative in each post.

Friday, November 11, 2016

Light Weight 3D Printed CW Paddle

I am a member of the North Georgia QRP Club ( NOGA). Many of the members are involved in portable operations such a SOTA.  One of the common discussions involves small light weight CW paddles for field use.  After getting the 3D printer and becoming familiar with its CAD software, I decided to see if I could come up with a small, very light weight paddle.  

The design I came up with is a combination of several different designs I found while searching the Net.  I also decided to customize it with the NOGA name built into the frame.

I printed up a few and gave them out at a recent meeting. The response seemed to be quite favorable. The suggestion was made that this was something we could sell at a upcoming Hamfest.  

I printed up a couple of sets in different colors for the hamfest, and we sold several in each color.  Now we are deciding if we want to make them available, and what would be a good price point including shipping.  I would like to get an idea of the interest in this.  So, if you think you would like to purchase one of these please drop me a e-mail at

Monday, October 31, 2016

BITX 40 v 3

I have been gone for a while visiting family, and have not had a chance to work on the projects I have on the bench.  One of these is a SMD version of the BITX 40, that was only available in India.  Just before I left, I saw that a newer SMD version was available for sale world wide.  And, at only $45.00 including shipping I decided to order one.  A couple of days after I returned home, I received a little box from India.  Inside was a very nice assembled SMD BITX board, and a bag of components needed to build a working transceiver.  Since the local QRP club was going to have a table at a hamfest next week, I decided to quickly build this up for something to display.
I want to make a few minor changes to the kit, first I wanted to use a 10 turn pot instead of the one included in the kit.  Along with that I will add one of the re-packaged DL4YHF counters I designed a couple years ago. I also will use an external hand microphone with PTT instead of the electroet mic. that came with the kit. 

 Next was to come with a case to put it in.  This is exactly what I bought the 3D printer for.  I printed some 6" corner pieces I had designed right after I got the printer, and cut up some double sided circuit board material to use for the sides of the case. I have switched to using .032" PCB material for chassis panels. It is very easy to cut accurate size pieces with a simple paper cutter. The back panel is very simple just two mounting holes for the power and RF connector, and 4 screw holes for mounting the panel.

The front was a little more difficult.  I needed mounting holes for the tuning pot, volume control,a separate power switch, along with a hole for the display. I also decided to add a grill opening for a small speaker to mount behind the front panel.  I went with a panel .2" thick to give room to build in a bezel for the display, and allow enough depth to add a recess to hold the 7 segment display for the counter.
After a couple hours to lay out the design and a few more to do the printing I came up with a very nice looking case for the project. I cleaned up the printed parts, assembled the top and bottom of the case, and gave everything a coat of paint.

 Now to put everything together tomorrow, and see how it works.

Friday, October 7, 2016

Another SNA Jr. lives UPDATE 3/3/18

I have been exchanging  e-mail  with Caglar TA2UH , concerning compile problems with the SNA Jr. he is building.  Only problem seems to have been the version of  the 'rotary' library he had been using.  After sending him the correct one, he now has his Junior working. .  It still needs to be put in a box and some accessories built, but from the picture he sent me it looks like everything else should not be a problem.

I just copied the correct version of library to the SNA Jr version II dropbox folder to help eliminate this problem for builders.

Just got some pictures of  Caglar's finished SNA Jr with some accessories. Looks great, a lot of work with some hand tools to get it fit into a cast aluminum box.  

 And another of it in use testing a crystal filter

 ANOTHER ONE   10/14/2016

Just received an e-mail from Vincenzo IZ5GVP with some pictures of his version of the SNA Jr.  He also included an Arduino sketch with some of the additions he has made to the software.  I took a quick glance at it, and it looks very nice.  I will take a longer look  (with the help of Google Translate) and  see what I want to add to my version of the sketch.

When I did the latest version of software, I was in a hurry to get everything ready for FDIM.  I did not do much in the way of calibration, Vincenzo's sketch has some cal routines that I will defiantly have to look at.

And another one from John VK5COR, he made his own 2 layer board.  He said it worked but didn't look very nice. then he had a couple boards made.  Said they look a whole lot nicer.  He is now working on a box to put it in. 

It is very gratifying to receive e-mails with pictures of other peoples build of some of my projects.  Sometimes when you write a blog, you wonder if you are just wasting your time.  When you get pictures of other people building your projects, you know that what you have written is of interest to more than just yourself.  So please if you have built any of my projects please send a picture and I will put them in a Dropbox folder for all to see.

Update 3/4/17
Just found a Blog entry by Gerry with some pictures of his SNA Jr. build

Update 3/30/17
Just received a em-mail from John KG9DK   with a picture of his finished SNA Jr.  I have been exchanging e-mails with John for over a year now about the SNA and other topics. Nice to see he has his SNA finished, really like the work he put into the design of his front panel.

Update 3/3/18
I updated the link in the dropbox.   Also adding an additional link to ones that have been built.



Thursday, October 6, 2016

8307 power meter repackage

I was adjusting the gain on several broadband amplifier stages using a noise generator and my AD8307 power meter.  It worked well, but was a little inconvenient without a small test probe.  A couple months ago some one had brought a RF probe from QRP Guys for show and tell at our local QRP club meeting.  I liked the format, but I preferred the direct reading in dBm. that I have with my existing meter.  I guess it was time to see about doing a repackage.
It was very easy to move the components in the layout, and change from an Arduino Nano to a Pro-mini. Switching to the Pro Mini allowed me to stack the display directly over the Arduino.  This reduced the width of the board, and gave me a nice probe like form factor. I etched up a board and assembled the new format meter.  I had one small error in the board, but a simple jumper took care of that. After changing some pin assignments in the sketch, I had everything up and running. Now it was time to see about packaging it.  
I have been playing with the CAD software I use with the 3D printer.  I tried several ways to make a housing with a top and bottom piece, but couldn't get one to print that held together tightly. 
Probe Cross Section
I had made a set of corner pieces for a cabinet that had in a built in PCB holder that had worked well.  So I did a design that was basically a rectangular tube with built in slots to hold the PCB. display board and centering for the display itself. It also kept the 9 volt battery from moving around.  I printed a long tube with this cross section, and checked that everything would slide in easily.  It looked OK, but I wanted it to look more like a probe. With a little cutting and slicing of the design I had a nice looking probe housing with cutouts for the display and on/off switch. Simple pieces closed up the open end and provided a removable cover for the 9V battery compartment.

I kept the SMA connector for the input to the meter.  That allows me to use a cable to check output levels of modules with connectors, or install a probe tip for in-circuit measurements.  One thing I decided to add to the software was  to display the difference between the last peak and current reading.  This allows you to get the stage output level, then go back and take the stage input reading.  The displayed difference should be the stage gain/loss in dB.  I took some readings across several known value  in line attenuators,  and found it very easy to measure stage gain/loss.

Monday, August 8, 2016

More 3D printer play things

The main reason I wanted a 3D printer was to make parts for some of my other projects.  Now that I have a printer, it is time to see what I can come up with.  I have two versions of the cheap Chinese Frequency Counter boards that have been sitting around for a couple of years.  I had been planning on finding cases for them, but I had not done anything with them yet.  They would be the perfect projects to start with, nice and small, need several mounting posts, and holes in the front or rear for connectors.
I have been playing with several versions of design software, and am now trying the 15 day evaluation version of Cubify Invent.  It is less than $50 and I will probably settle on it after the eval. period.  It is much more like some of the 2D CAD programs I have used before.
First thing I did was layout a front panel with built in bezel for the display and mounting posts for the counter board.  I also added a recessed mounting holes for a BNC connector, and the screws that will hold everything together.
Next I designed the rear panel, it has a recess to reduce the thickness. The recess is high enough to allow a 9-V battery holder to be mounted in this recess. I also put in a through hole for a small rocker switch for system power.  It also has 4 recessed holes that will hold glued in 4-40 x 1/4" stand off.

The last thing I needed was to make a case deep enough to hold everything.  This is a simple shell the size of the panels, with 4 through holes for the 2" screws that hold everything  together. 

After it was put together, everything looked nice.  Some of my dimensions were a little off on the front panel, and I had to ream out the holes a little.  I could touch it up with a little body putty and repaint, but I will leave it as is for now.

The only problem I could see with this design was in laying out a new shell for everything I want to build.  Most of my cases are built from Copper Clad circuit board material soldered together. This works well, but it is a pain to get everything cut straight and fitted. 

 I would like to come up with a way to simplify the process.  I tried several versions of corner piece that would allow the case panels to just slide in slots in the corner piece.  This corner piece also has a through hole that you can use to glue in a threaded standoff for mounting the front and back panels.  These can be printed to the length required, or stacked if you need something larger than the print height of your printer. 

 I also designed a slightly different version of the corner bracket to include a slot for a circuit board to slide into.  This would eliminate the need for using stand offs to mount the circuit board.

I modified the design and printed  the front and back panels to fit the larger frequency counter board. Because of what I wanted to use this counter for I put the hole for the BNC on the back instead of the front.  There are also a couple of small holes in the front panel to allow you to get to two push button switches on the board.  I printed up a set of the corner brackets and cut some circuit board material for the top, bottom, and side panels. 

 I assembled it and am very happy with the way it looks. Here are some pictures before I finished wiring the battery holder. You can see the way the copper clad board panels fit into the corner brackets.  Another one shows the printed mounting posts for the circuit board.  I think using the printed corner brackets will make it much easier to build  cabinets for some of my future projects.  Since they can be stacked there is no limit to the size of enclosure that can be made.

Saturday, July 30, 2016

SMD BITX Audio amplifier

I quit playing with the new toy (3D Printer) long enough to populate and test the AF amplifier section of the SMD BITX.

As you can see even though it is built with mostly SMD components, the layout is much larger than it really needs to be. But since I plan on putting it in an old CD drive case there was no real reason to shrink it down any more.  I do have another project in the very early stages that shrinks a transceiver down a lot more.

After getting the AF stages built, it sounded good with a low level test signal injected, no hiss or background noise.  But, I decided to test it to see what the output response looks like.  I connected up my sound card based audio spectrum analyzer-signal generator, and started the Visual Analyzer program. I didn't bother calibrating the input level, so values are just relative for measuring stage gain. 

With everything connected but the signal generator turned off and the Volume pot all the way up I had a fairly flat baseline out to over 16Khz. that had a value of about -115 dB at around 1500 Hz. Not sure where the 1 Khz. spikes are coming from, probably from something in the computer. But after applying the pink noise signal I could not see them in the output at any volume setting.

After turning on the pink noise generator and averaging the signal, the amplitude at the same frequency increased to -83 dB, a 32 dB gain at  1.5Khz.  The maximum gain was around 500 Hz. with a gain of 39 dB.  The 6dB response is from about 200Hz. to 1.2 Khz.  The higher frequency response is more than I would like, but I will live with it for now.  If I start hearing a lot of hiss after I get more stages built, will see about changing the response.
Next to build and test the microphone amplifier.  Then I will have to get one of the early si5351 VFO test circuits I built a couple of years ago modified to work as a test VFO and BFO.

Now I NEED to get back and play with the new toy some more.

Friday, July 29, 2016

Playibng with a new toy- a 3d Printer

I have been interested in getting a 3D Printer for some time now, and a couple of months ago I bought a kit from a supplier on eBay.  There is a fairly active Facebook group dedicated to this printer, so I thought it would be the one to try.  After starting assembly, I found that it would be a little larger than I had room for on my work desk, and would have to be moved around when I wanted to use it.  So it kind of sits, mostly assembled while I am working on some other projects.  
I was browsing for something else on eBay and checked out the 3D printers, and found the Cube generation 3 printer for under $200 including shipping.   This is made by 3D Systems, one of the larger players in the 3D printing market.   I had looked at this printer before, and it had been selling at around $1000. 
3D Systems Cube gen 3 Printer  I checked their web site, and saw that this model had been discontinued, but they said they are still supplying the print cartridges.  

I looked at several other places such as Amazon, and found that they were also selling it for about $250. Sounds like a close out deal, so I decided to get one from one of the eBay sellers for $180 shipping included.  I was surprised when it was delivered in 3 days.
It came in what must be the original double boxing..  Unpacking and setup took less than a half hour.  I really like its small size, less than 14"x14"x10" and it fits on my desk with no problem.  This is a two color printer, and uses cartridges instead of spools of filament.  This helps keep the overall size down. 
 You can copy prints to the printer using either a supplied USB stick or with the built in WiFi,  I tried both and they work well.  I setup the WiFi connection using the small touch screen display on the printer, and then downloaded and installed the Cube -Print program on my PC, and ran through the activation.  I ran the calibration and auto bed leveling routines using the setup functions through the touch screen on the printer.  The test print turned out well, so I downloaded one of the free projects that 3D Systems has available.  That also printed well, so I decided to get a project from  Thingiverse. 

I downloaded a small spinner knob for a rotary encoder, and loaded it into the Cube-Print program and tried to print.  I got a message about needing to update the firmware on the printer.  I did a quick firmware down load from the 3D Systems website and transferred it to the printer on the USB sick.  Using the update routine in the printer 
Settings, it only took a few minutes to update the firmware.  I tried the print again, and it turned out very nice.  I downloaded and printed a couple other projects and was pleased with the results I got.  
Next I setup an account at OnShape , a free web based 3d Cad program.  After a little playing around I was able to design a simple bezel for the 1.4" display I used in several projects.  The print results are usable, but I will probably refine the design a little later.

 The picture shows the bezel and one of the other knobs just sitting on the top of the AD8307 Power meter.  My printer came with White and Green PLA filament cartridges, and just ordered Black ABS cartridge to try.

So far I am very pleased with the printer.  Mechanically it is very well built, under the plastic shell is a solid metal framework.  It uses linear slide bearings instead of the rods and slides used by most of the kits.  The built in alignment routines are very easy to use, and from what I can tell work quite well.  It does not have a heated bed, instead uses a water soluble glue that you have to apply to the bed before use.  I have only tried with PLA, but so far it seems to work well.  Will see how it works with ABS when the cartridge I ordered arrives.  The build area is 6"x6"x6" which should be large enough for anything I want to do.  
The cartridge system with the print nozzle and filament feed mechanism seem to work well.  This is more much expensive than using bulk filament if you do a lot of printing. I have seen a couple things on You Tube showing ways to use bulk filament, so will give them a try when I use up one of the original cartridges that came with the printer.  
So far I am very happy with the printer. This is about the cheapest and easiest way to give 3D printing a try that I have found. So if you want to try I don't know how long the supply of these printers will be available for the price they are going for now.  I will let you know how everything goes after a little more use.  But now I just started a print job that should take about 7 hours, so I might get back to some of the other projects I have going.

Tuesday, June 28, 2016

A Surface Mount version of the BITX-40

Because of the availability and price point of the BITX40 board now available through  I have decided to stop work on my version , and now work on modifications and upgrade to that board.

I have been happy with the results I have been getting with new version of the Spectrum Analyzer interface board.  Unfortunately now I am waiting on the new si5351 board I want to use.    Looking around for something to do I came across the BITX-40 board by Asher Farhan.  This is a single board version of his BITX design, and is being produced by a collective of local women in their homes to provide a livelihood. 
More information including schematic and a great circuit description is available  at
I had previously started a modular version of the BITX, but this looked like would make a nice small portable transcever.

This board is only available in India, so if I wanted one I would have to build one for myself.  I decided to layout a board using using SMD components.   Although I am using SMD components, I will keep the board size about the same as the original.  Since I will be using a home made  PCB without a solder mask I used 1206 size components and allowed plenty of space around each component.  Without a solder mask it is very easy to have problems with solder bridges with SMD components.  I also made it a double sided board, with the the DC power lines on the bottom of the board.  Unlike the original, I did not include the VFO and BFO circuitry.  I plan on using a si5351 much like the one I built for the Canned Frog. 

Because of the size of the board I could not use the free version of EAGLE that I have been using. There are several other free PCB design software packages around, but I had some experience using ExpressPCB.  There is not a large  component library as available for EAGLE, but it is fairly easy to add custom components to the ExpressPCB library.  The other issue with ExpressPCB is that it is designed to be used with the ExpressPCB board service, so there is no provision for generating  Gerber files if you want to use a different board service.  One of the other PCB software packages I had tried was Copper Connection.  It was fairly easy to use, but I preferred ExpressPCB.  One of the things Copper Connection can do is read ExpressPCB files and then generate Gerber files.  It also has a very easy way to print the bottom and mirrored top copper layer for use with toner transfer at one time.  So I will use ExpressPCB to layout the board, and export that to Copper Connection to print the toner transfer images.
After I finished the layout, I tried to make a board.  I have had very good luck using the Cold Toner Transfer method, But because of the board size, the clamping fixture use would not cover the whole board, and I ended up with areas on the board where the toner did not adhere to the copper.  
I tried using the Hot method with my laminator, but could not get the toner to stick to the copper at all.  As a last resort I processed a board with the Cold method solvent, and instead of using the clamping fixture I fed it through the laminator without waiting for it to heat up.  I ran it through a couple more times as it was warming up and when I checked the board and it was nearly perfect. I had to touch up a few pinholes in large copper pours, but all the traces were perfect.  I got the board etched and now to start building the board.

Saturday, June 18, 2016

Back to the Spectrum Analyzer project

Now that FDIM is over and finished with the SWR - Power Meter for the QRP club, it is time to get back to some of my other projects.  Top of the list is the Spectrum Analyzer.  Looking at the modules I had finished, and some of the things learned when I built the SNA Jr II, I decided to make some major changes in the overall design.  The first change will be to the interface board.  The new board will be similar to the SNA Jr. II,  I am going to include the AD8307 circuitry on this board, and have provisions for a si5351 or si570 on the same board.  For the first try, I will be using the si5351 board from QRP-labs.  This has a very close pin-out to the Ad9850 modules used in the SNA Jr.  I plan on using machined pin header stock to create a socket for the QRP-labs board.  If I later want to try a si570, I will build a small breakout board with the same pin-out.  Then it is just a matter of plugging each board in to see if there is any noticeable difference in the results I get.  The si5351 would have an advantage, in that I could program one of the other clock outputs to use as a tracking generator.
The other main change was in what I was going to use as a user interface device to control the operation.  On the SNA Jr and other projects I used a rotary encoder with a built in push-button.  This worked quite well, but the software got to be fairly complicated as more functionality was added to the software.  I thought about push-buttons, but they would take up a lot of panel space.  And from using several other devices with push-buttons I really didn't think that was what I wanted.  I had a couple of the small joy stick controller boards that I picked up for something else, and thought I would give them a try.  I wired one up on a breadboard, and tried several different methods until I came up with one I liked.  A ReadJoystick function reads the Horizontal and Vertical axis position, and if it is more than 20% from center updates a global variable for that axis to either + or - 1 depending on direction.  This joystick also has a push-button, so I detect  either a short or long push, and update another  variable with that value. To make processing these variables a little easier, I only allow one to be changed at a time. If any of these occurs a global flag is  set.  This global flag allows the flag to be reset in the program to speed up processing by bypassing further testing in that pass through the loop. 

I did a  quick board layout  and etched a board to test the functionality.   Since all the pins used by the display except reset are through the end connector on the Mega board, I have all the other pins available.  This makes the board a lot easier, because I can just use a tall stacking connector and not have to do anything on the interface board for the display except bring out a couple of pins for the reset line. I also included several places on the board for push buttons that I might use for more advanced features later on.  And also brought out a couple  sets of I/O pins for control of the RF boards.

I took some of the code from the SNA Jr. and modified it for use with the new board, display and Joystick.
It was quite a bit simpler, and worked very well.  I think the Joystick will work nicely in the Spectrum Analyzer.  I really like the larger, higher resolution displayWith it having a parallel interface instead of SPI the response is nearly as fast as the small display in the SNA Jr.  It has already got me thinking about a SNA Jr version III.

 With the power detector and clock generator on the same board, I can modify more of the code from the SNA Jr. and have a stand alone version of the Sweeperino for testing some of the RF filters in the Spectrum Analyzer.  Then after I finish the RF circuitry, I can just connect it to the interface board and change the software to make it a Spectrum Analyzer.