Four Days in May 2016

Well because of my schedule it was only Two Days in May, but it was still fun.  I really enjoyed the seminars on Thursday, and was pleased to hear Paul M0XPD mention the SNA Jr. during his presentation.  The WBB was great! You would not believe how much work must have gone into getting everything ready for that.  It was more work than I thought it would be just getting 8 kits of the SWR Power Meter ready for the last club meeting.
Enjoyed the vendor night, although with the limited space it was quite crowded.  I did manage to pick up a couple of things that looked interesting. Also had a chance to talk to several people I had exchanged e-mails with over the last year or so.
After a long day Friday of trying to see as much of the Hamvention as possible, I finally made it back to the hotel in time for club night and the homebrew contest.  The only problem with having an entry in the homebrew contest, was that I did not have a chance to walk around and look at the other entries and club presentations.  But it was still a fun experience.
I spent a lot of time talking about and demoing the SNA Jr.
After suggestions from several people, I am in the process of writing an article on it for QRP Quarterly.  Hope to get that written and submitted within the next two weeks or so.
That's  all for now.

SNA Jr. version II update

Well, after a lot of time working on the top half of the box for the SNA Jr. v.II, I have it finished.  It took quite a bit of time with some small files, but it looks very nice.  The extruded aluminum box is nice and solid, the push button on the rotary encoder has a nice solid feel.  Earlier versions using small tin containers flexed when the button was pushed, and it felt kind of mushy. 

Did some work on the software, and now have most of the basic functionality working with the AD8307 instead of the diode detectors.   With the diode detectors I had range of about 50db, with the AD8307 I have a range of about 10 to -75 dBm.






 5/13/2016
 Finished making changes to get all functions to use the AD8307 and added a simple Frequency Correction  factor to correct for the ~11dB drop in signal output I saw when sweeping form 1 to 40 MHz.  This large drop is probably because I did not include a buffer amplifier, and just take the output of the DDS module through a 100nF capacitor.  I have not had any problems using the instrument for what I want without an amplifier, so decided not to complicate the design.

I added a Watt Meter function for use with a 40 dB. Tap.  It gives the signal in dBm and auto scales to either  a watt or miliwatt reading .  I also keep a peak power reading for each time RF power is detected.  With no power applied the screen flashes NO POWER and resets peak reading after 2 seconds.
 

Watt Scale

milli Watt scale

I want to add some calibration routines if I have time.  Also trying to get some preliminary assembly instructions written for the pilot run of the SWR/power meter before the club meeting this Saturday

SNA Jr. Version II Part 1

I need to visit my daughter and help her with a couple remodeling projects around her house. I set the schedule so I can stop in Dayton for a couple of days at FDIM and decided to build an entry for the home-brew contest.  
With the success I had with the stand alone AD8307 power meter, I thought it was time to upgrade the SNA Jr. with a real power detector.  The SNA Jr. had started out with my version of the K6BEZ antenna analyzer and a need to check some filters I was working on for another project.  I replaced the SWR bridge circuit with a couple simple diode detectors and used the Arduino to compute  gain/loss in dB.  For such a simple project, I was really pleased with the results I was getting.  It was a vary small hand held instrument that I could use as a signal generator, SNA for testing filters.  With  the addition of a Return Loss Bridge I could check antenna SWR.  Then I added a simple pickup coil and a little software I also had some of the functionality of a Dip Meter.

It was very easy to edit the board layout for the original SNA Jr. to remove the diode detector and amplifier, and merge in the AD8307 circuitry from the power meter board.  The board house that I was using for the pilot run of club SWR meter project had a special going on.  Since I know of several people that would be interested in one of these boards I ordered 10 SNA Jr II boards.  It took about 2 1/2 weeks to get the boards, and am really pleased with the way they turned out.  The only issue I had was the spacing of the RF chokes I use to feed DC and signal into and out of the AD8307 circuit.  The ones I had are a little larger than the ones I had used in the stand alone power meter, and I had to bend the leads back on themselves to make them fit.  Other than that everything else works well.
In the original SNA Jr. I used a couple of 4.2 volt Li-ion batteries for power.  Only problem was that I had to remove the batteries to charge them.  In a rebuild of the SNA Jr. I used a 12V battery pack designed for use on security cameras.  This worked well, but I was not getting as long of operation on each charge as I had with the individual Li-ion batteries.

Looking around on eBay for something else I found some 2S Li-ion Lithium Battery 18650 Charger Protection Board Modules.
They are very small and take care of the charging and protection of 2 batteries in series,  there are also other versions available for different size battery packs.



 
I mounted a couple of battery holders , the charge controller board,  connectors and On/Off switch in the bottom half of the extruded aluminum box I bought for the project. The charge controller board is very small and after wiring it up I covered it with a piece of heat shrink and stuck it down beside one of the batteries. 


 I checked charging with a couple batteries and was very pleased with the way it operates.  I monitored charging current and voltage, it charged at about 1.6 amps with a wall wart power supply that put out 10.3 V. with no load.  While charging it put out around 8.6 V.,
and when charge was complete the current dropped to nearly 0 and voltage jumped up to the open circuit voltage. 

I built up one of the boards, and gave it a quick check to make sure everything was working.  Since I did not have the software modified to read the 8307, I checked the output of that circuit with a voltmeter.  




I got around the .25 V. I expected with no input and it jumped up to around .5V. when I touched the input with a screw-driver.  These are just about the same as I was getting with the circuit in the stand alone power meter.  Now that I know it is working I can build the shield box to cover the AD8307 circuitry

After adding the SMA connectors for RF output and input to the detector, I finished building a shield around the AD8307 circuitry using some .008" double sided circuit board.  That has become my favorite for building shields, easy to cut and solder, and stiffer than copper shim stock.  Here is a pictures of everything ready to be assembled, and one showing how tight everything fits in the box




Next to finish a little final fitting on the top half of the project box and mount everything, then on to the changes to the software.  Also thinking about adding a couple additional functions, such as directly computing VSWR instead of just Return Loss.  And add a wattmeter function, using a 40-dB tap to drop the power level down to that required by the AD8307.  Watch for updates, FDIM is less than two weeks away.




 

SWR Power meter update UPDATED 5/7/16

Because of a family emergency I had to make a two week trip to the winter wonderland I escaped from about 30 years ago.  I was not able to do much on the SWR Power meter I am working on that the local QRP would like to kit.  I was able to get back in time to get a board stuffed in an Altoids tin and take it to the monthly club meeting.  
The club member that has been testing my early prototypes seems to be happy with the results he was getting with the latest version that incorporated a diode compensated amplifier to improve linearity and low signal response.  The power readings he was getting were linear from less than .5 watt to over 50 watt, and were good up to 6 meters.
I will stay with this hardware and just have to do a little clean up on the software and couple things I want to add.  Just in the process of ordering parts for a pilot run of 10 units for some club members to assemble and test on their own.  If that works out the club will probably start selling the kit along with the kit they presently have.

Including a picture of a prototype board mounted in an Altoids tin this time.  For the Altoids tin I am using edge mount SMA connectors. They are nice and small and easy to install.  There are adapters from SMA to BNC and most other types of connectors available fairly inexpensively through the auction sites.

Will let everyone know how the pilot run turns out.  
For now I am spending most of my time working on something for the home-brew contest at FDIM.

Just a quick update on the pilot run of boards. The boards I got from China look really nice. Finally have all the parts in and built one to test.  Found that the display boards I received use a different driver chip.  I found the appropriate driver that was compatible with the Adafruit libraries I use, but runs at a slightly different resolution.  So I have been rewriting some of the display functions to reflect the changes.  Shouldn't take too long, and also doing some  clean up of the code at the same time.

 
 

Sweeperino Jr. Part 1

Now that I have the SWR meter nearly finished, I want to get back to working on the spectrum analyzer.  I will need to build and align several filters that are higher in frequency than either the SNAJr. or the Chinese SNA cover.  Lookng at some posts by Asher Farhan on his blog, he has a simple SNA that he called the  Sweeperino.


  http://hfsignals.blogspot.in/p/sweeperino.html  

This uses the same AD8307 power meter I had used before and a SI570 for the signal generator.  His version has a 2 line LCD display for frequency and measured power level , and uses a pot for tuning. There is a PC program for doing a display of the sweep, same program is also used for the SPECAN display.


Since I was only interested in displaying the sweep while aligning filters, I did not need the display or tuning pot.  I wanted to save the last si570 I have on hand for the spectrum analyzer, so I used a Adafruit si5351 breakout board I had left from another project.

   The power requirements for the si5351 board and ad8307 are very low, and could be powered directly from the 5 volt output on the Nano.  I used some 100uH. molded RF chokes with additional filter capacitors to feed power to the 5351 and 8307 .  I had used this before in the stand alone power meter, and with shielding was able to get a -74 dBm noise floor.
When I built the power meter I found it was fairly difficult to solder the SMD parts without a solder mask, very easy to have shorted traces.  After I finished etching a double sided board, I decided to try adding a solder mask. 
I found two methods of doing solder mask at home, the simplest appears to be using UV curable paint.   I watched a You-Tube video that makes it look like it should be fairly easy.

https://www.youtube.com/watch?v=Vj_cdBZO1Tk

Other than the paint, the only other thing needed was a UV light source, although you could probably just take it out into the sun to cure.  Looking around for UV light sources, I found a small unit that is designed for use with UV curable finger nail polish.  This was under $10.00 and can be powered from a USB port or USB power cell.  This unit has a push button that turns the light on for 30 seconds at a time, this will make timing the exposure very easy.


I printed up a stencil of where I wanted the mask to leave bare copper on a plastic overhead projector sheet.  Then got everything all ready to give it a try. I did a couple of quick tests on some scrap board to get the exposure time down. About 2.5 minutes seems to give good results.

Using a small plastic card as a squeegee and a piece of plastic cut from a zip lock bag, I spread a thin layer of the UV paint on the board and aligned the stencil with the etched pads.  I exposed the board to UV light for 2.5 minutes, and then removed the stencil and the piece of plastic.  Using a paper towel with some rubbing alcohol, I cleaned off the un-hardened paint.  After checking the mask, I exposed the completed board for another couple of minutes to make sure everything was hardened.










 
The board looked pretty good, with only a small area where the mask came off the ground plane area.  Not as pretty as a commercial board, but looks like it will do what I want it to do.  Looking at the area where the SMD components for the power meter circuitry will go, everything looked very nice.  I think this will make it much easier to solder in the SMD parts using my hot air gun.  I used the same process and masked the bottom layer of the board.

Next to build up the board, and get the Arduino software working with this configuration.

QRP SWR Meter UPDATED 3/14

The North Georgia QRP Club has been selling several small kits for the last few years.
One of them is a simple QRP SWR meter, but the small meters that were originally used are becoming hard to get and much more expensive then when the kit was first offered.
Several members of the group spoke to me about coming up with an updated replacement.


I had the Arduino and display circuit along with software I had used in the DL Power meter and the AD8307 power meter.  Using the board layout from these projects, I added a simple directional coupler and detectors built with a binocular core transformer.  With a slight change in parts placement it is possible to build in an Altoids tin.  Or with the display mounted vertically, it can be built in an aluminum project box.

I split the display area with a digital display of the VSWR value in the top half, and bar graphs with digital display of Forward and Reverse values in the bottom. I later added a warning message that would pop up if the VSWR is greater than 3 to 1.   This picture shows the layout I decided to go with. For initial testing I used a couple of variable resistors to input DC values into the Arduino , so values shown are percent of full scale.




After building the directional coupler and detector circuit I did some playing with the software to get a close approximation of the actual power readings.  Everything seems to be working well down to around 2.5 watts.  Below that SWR value starts to loose accuracy.  I am waiting on some different diodes to see if I can get everything working below that level.  If that does not work, I am thinking of changing the detector  to add a little DC bias to the detector diodes.

Here is a quick video of the meter as my auto tuner matches to my multi band antenna.
Will update when I get the new diodes, or have to change the detector circuit.

I gave the first prototype to a club member that has better test equipment than I for test.
After a few minor changes to the software most of everything looks good, except for power values below about 2 watts.  It looks like this is because of the non linearity of the diodes. used.  Tried different types of diodes, but non linearity remains.
I decided that I would add a diode compensated amplifier to rectify this. I was able to find enough room on the board for the op-amp and associated components.  Initial testing looks like the power readings remain accurate down to about 100mW.  Some more testing is requited, but looks like the design is finalized, now to write documentation and see about getting everything ready to do a sample run of the kit.

 

Cold toner transfer and chemical dangers

After linking my two posts on the Cold Toner Transfer method to 
https://groups.yahoo.com/neo/groups/Homebrew_PCBs
there has been much discussion about the danger of the chemicals involved.
Some of these mentioned the effects of day to day heavy exposure found in some industries.  The amount of chemicals used in this method is minute in comparison.  I still have about a third of the 4oz. bottle of mixture I made up after doing 3 single sided and and 3 double sided boards. 


But .it is always advisable to take precautions when working with any chemical.  Even the most common such as dihydrogen monoxide can be dangerous under the right condition.
Years ago I made a simple air filter that I use when etching boards and soldering. It is very small and can be easily setup next to where-ever I am working.

  I had a broken 12 v brushless fan from an old computer.  I cut out the bottom of a disposable food storage container and glued the fan to the bottom, making sure the fan would draw air in through the container.  I then glued a 9 v battery holder to the side of the fan and wired up a switch.

To the back of the fan I attached two of layers of zeolite air filter material, with a single ply of a two ply paper towel between them.  The filter is just held on by twisted wires through the normal mounting holes in the fan.


Very simple and very low cost.  Only thing I had to buy was the air filter material  about $2.00 ( replacement air filter from a kitty litter box).
I can move it around between the soldering station, etching tank and board prep.