Thursday, May 25, 2017

FDIM 2017

Again this year I was able to schedule a trip to visit my daughter with a stop over in Dayton for FDIM.  I had a wonderful time, and got to meet many people that I have met on the air or through e-mail and on many of the e-mail groups I subscribe to.  The highlight was getting to meet and speak with Ashar Farhan.  His BITX and other projects have been an inspiration to me and countless other home brewers all over the world.  Because of the speed with which hotel rooms filled up at the Holiday Inn where the FDIM event was held, I ended up staying a few miles away.  I was not able to spend any time on Wednesday to get to meet anyone there.  

Thursday was pretty much filled up with  speakers presentations, but afterwards there was ample opportunity to meet and talk with many other people who are active home brewers. A bunch of  us had a chance to sit down and talk with Farhan as he showed and explained the circuitry in some of his projects he had brought with him.  Among them was his 'Sweeperino' , 'Specan', and the uBITX design he is working on finalizing. 

I have been having some problems with a knee for a little while now. And after the long drive up Wednesday, and sitting around most of Thursday it let me know that walking around the Hamvention would not be appreciated.  So I spent most of the day Friday at the hotel and took my wife out for dinner before I went over to 'Club Night'  and the home brew contest.  I had a short time to talk to some of the Club members at different tables and several of the others in the home brew contest.  I spent the next couple of hours doing demos and explaining the AD8307 power meter probe I had entered.  I had been hoping to get either the Spectrum Analyzer or SNA Jr. V3 finished in time, but had to go with one of my earlier project.  After the contest was over I had a better chance to talk to the other in the contest and look at their entries.  

I also met Dave  VE3OOI , and several other members of the Peel Amateur Radio Club in Brampton Ontario at their club table.  I had exchanged several e-mails with them after I posted building my version of the Norcal S9 Signal Source.    Dave showed me the version they had kitted based on my project for their home brew group. 

It is extremely gratifying to know that others think your work is of enough interest that they will go and build something based on what you had done. 
 He later sent me a a copy of the manual they had produced for the kit. They went into a whole lot more detail in their manual than I had ever considered for the kits I had put together for my club. I guess I will have to put more effort into my documentation next time. 
He also sent a picture of some of the 30 club members that attended their 'build a thon' earlier this year.  It looks like they have a very active group of home brewers.

My knee told me that it still did not want to do much walking around, so Saturday was much like the day before. That evening we went to the QRP ARCI banquet and had a wonderful time.  We listened to the presentation by Ashar Farhan about his history in Amateur Radio and the steps that led up to the BITX design. After that there was the awarding of the door prizes and the drawings for the KX2s and other main prizes.  Last the awards to the winners of the home brew contest.  I am pleased to say that I took the award in the Test Equipment, Construction Aid category with my power meter.

All in all it was a very nice few days.  Even though I did not get to go and wander around the 'Hamvention', I did manage to purchase a VNA kit from the Austin QRP group during club night.  That and my own projects should keep me busy for a while.  We will spend about another week up with our daughter then the long drive back home.  Then I guess I should get back to some of my other projects.

Sunday, May 7, 2017

Quick SNA Jr V3 update

With  FDIM only a couple weeks a way, I am hurrying up with the build and programming of the SNA Jr. version 3.   This uses a mixer and simple crystal filter to eliminate many of the problems with  with harmonics when using a square wave signal generator.  I have a bunch of 4.9152 Mhz. crystals that I had purchased for another project.  I use the SNA Jr version 2 and simple test fixture to match several in frequency, and having a similar response curve.
I put them in the new board and directly wired the output of the signal generator circuit directly to the crystal filter circuitry.  Then using some of the new software I am writing for the version 3 system, I checked the response curve of the filter.  I found it to have a 3db response of around 100 Hz. and an over all response of about 1.2 KHz.  Since I am running out of program space in the NANO, I also used the software to find the center frequency of the filter.  I will program this directly into the software instead of writing a calibration routine.  For not It looks like this should work OK. 

Using this signal for testing purposes, I added a pop up menu with additional functionality.  One option allows me to normalize the waveform after it is acquired, instead of having a separate normalized sweep like the version 2 software.  Another thing I added was a marker to display difference in frequency and amplitude between the marker and cursor.  This picture shows the response of the filter and the new software features.
I had added pads on the circuit board for several attenuators, but found that I am gong to be a little short on gain even with out them. I also found that with the single sided board I could not get the low level noise floor that I had with other power meter circuits I had built.  I am going to quickly make a couple changes to the board and etch up a double sided version.  Hopefully I can shield the AD8307 and get another 10 dB dynamic range in the power meter part of the circuit itself.