Alpha Build PARC SNA Update 3

Got a lot accomplished over the last few days on the SNA project.  All the parts are now installed including the LCD screen. In order to expedite the build I went on a “field trip” to Ottawa to pick up extenders for the LCD.   And then off to Toronto to pick up the LCD… Ok I did pick up the xyl at the airport so it was a multi-purpose trip.

The shield for the AD8307 circuit I managed to get done without any real fuss. I thought for sure it would be a little problematic to do, but in the end it went ok.  Sure it’s a little ugly and not as good as I would have liked, but it will do. 

The final smoke test was completed and software routines for testing the individual circuits were completed. Dave VE3OOI, had written routines to test the functionality of the 8307, 9850, encoder and buttons, memory chip, as well as the LCD.  What a terrific idea that was. Well done Dave.

The main SNA program was loaded and went smoothly.  I am having a problem with the calibration routine, but I’m sure Dave will set me straight before too long.  The only other issue at the moment is the display is not oriented correctly with the controls. I’ll have to lean on my hardware department to be on the same page as the software department. Can’t be making mistakes like this again. Not sure yet how I’m going to remount the controls, but I don’t think it’s going to be as clean as it is now.  Well, that’s what Alpha builds are for, work out the details.

Up next is putting the SNA through its paces. I need to think up some protocols that will include not only the real world and most likely scenarios, but some with extreme specifications as well so I can see how the SNA behaves.  You never know.  

Alpha Build PARC SNA Update

Finally after spending considerable amount of time tracking down and removing solder bridges and a couple of shorts in the traces, checking the board over several times to ensure no shorts remain, I had to admit it was time for the smoke test.  But first a beer to think about it.  Never have I've been so apprehensive to power up a board.

I'm pleased to say all went well with the smoke test. The 8v and 5v voltage regulators remained cool as was the 8307 and memory chip.  Now it was time to plug in the Mega and following that the AD9850 board.

Almost perfect. I have a bit of a loose connection on the ground for the 12v power supply but that's no big deal.

Current draw for the board alone was .03A.
Current draw for the board and Mega was .11A
Current draw for the board, Mega, and the AD9850 board came in at .21A.

Not sure what the draw should be but there's the baseline for the 2 other Alpha builds underway now.

9850 board in the upper right corner, 8307 behind the left bnc connector and the memory chip to the left of the 8307. The MAR6 amplifier is located just to the left of the right side bnc.  The blue wire passes just beside it.  The rather big looking blob of solder is due to the several ground pins coming through the board to ensure good ground for the MAR6.  Hidden under the blue and purple wire is the ground connections on the other side of the MAR.

Up next is to nibble away the pcb area containing the holes for the LCD.  They are not needed and are in the way for the pin extenders needed to raise the LCD to the proper height.  I'll be picking up the screen tomorrow and once that is working ok it will be time to load up the software and put this puppy through its paces.

So far I have about 9 hours into the build. Lesson for me here is hand soldering with such narrow clearances is not the best methodology to be putting a board together.  Good experience though.

Alpha Build PARC SNA

Started to build the PARC SNA.  The challenge I figured was going to be, and still likely will be, putting it through its paces and hopefully cover off on all the possibilities. But I'm sure our software designer, Dave VE3OOI, has thought of everything and it will be perfect.

However, as with most projects on my bench, there are challenges with each project.  No different with this project either.

This board was etched by a laser machine and it is a very nice looking board. The trace clearances are somewhat tight and the through holes are not plated.  The clearances did present some challenges with a few solder bridges that proved to difficult to remove in a couple of cases. After using a solder sucker and solder wick, the shorts had still remained.  Even under a well lit magnifying glass the short could not be seen. Scrapping with a dental tool in one case did not help but a rub with a small fine wire brush did work.

The other self inflected problem, one that I can never seem to avoid, was, well, stupidity. I knew the via's were not through plated and I was given some fine wire to use where necessary. Yet I still managed to forget this and went ahead and soldered in headers tight to the board when I needed to allow a space in order to apply solder. Gave the solder sucker a really good workout and I'll bet I used up more solder wick on this project than all the others I've done combined. HiHi.  But thanks to the quality of the board, it survived the abuse.

About 6 hours into the build so far and today I shall carry on with installing headers and connecting up the via's

BITX 40

Spent a pleasant afternoon yesterday working on the Bitx 40 with two other hams. Sort of a mini buildathon I suppose. Dave, VE3EAC, offered up his terrific shack/workshop for our get together. 

Dave not only has all the usual electronic test equipment you would ever need, but has all the tools needed to work on your cases as well. This makes things go so much smoother.  No need to mess around with inappropriate tools to accomplish what would be a simple task.  I need to re-think that end of my shack.  Another thing that came to light is the use of a 3d printer.  Dave printed up bezels for the lcd screens. Makes for a nice finished front panel that would not have been possible in my hands. 

I got no further than mounting the lcd, circuit board and the various controls and jacks. I did manage 2 connections as well but I decided that the layouts and mounting the hardware was time better spent first. Paul, VA3LX however, went with wire up the whole thing first and put it into a case later. It wasn’t too long before while filing out the square hole for my lcd, that we heard the hiss of 40 meters. Connecting up an antenna we were able to hear some strong ssb signals and we were pleased with the initial tests.  It was very encouraging to hear this. 

Since I’ve built transceivers before, kits and from scratch, I'm looking forward to putting most of my energies into other aspects of building transceivers with the Bitx. Software improvements and other hardware modifications. Possibly the move to 60 meters comes to mind but maybe a multiband would be a better proposition. Playing around with enhancements and not just getting the rig to work does have some appeal. Maybe not all the time but this time anyway.

Incomplete projects on the bench is growing again and I really need to start finishing some of them. The shack is in a little bit of disarray as I work on repairing my spectrum analyzer and SNA. The SA is so big that the other equipment that lived on top of it are now on the floor. The SNA is in pieces and the SA covers and various brackets spread out. In the middle of all that mess is the current project. It’s getting a little hard to move around.

AD8307 Response to Sin and Square Waves

During the engineering phase of a project, there most likely, or should be a time where a question will arise that will take you off in another direction. Latest examples of this are the characterizing of amplifier outputs at RF frequencies, AD8307 behavior with sin and square waves, and RF measurement techniques. All of which can involve a considerable amount of research time that adds to the project development phase. It's not necessarily a bad thing, and one of the things I like about the hobby.

Another thing that can happen is while doing this research, new projects come to mind as I contemplate new found knowledge.  The SNA project has brought in for consideration a VNA. Learning more about complex impedance's and how to measure them has now got me thinking about a project involving the AD8302 board I bought on spec a while ago.  Now that I have amplitude and phase I can do some interesting calculations.  Except now I have to learn how to do polar charts and of course the intricacies of the 8302. Again all fun.

I made some comparisons between two AD8307 chips.  One smd sourced from eBay and the other a dip package from Digikey.  The Digikey part was sourced about 5 years ago.  I ran the test using both Sin and Sq waves.

Interesting results. In that the the package type overall did not really differ and I'll come back to that. There is enough of a difference between the sin and sq wave that I think you would need to  consider the signal type when making measurements.  Especially at the lower frequencies.

The sq wave results are very linear and the sin wave not as good but still not bad at all.  Considering that the 8307 output is 25mv/db,  I'd say you definitely would need to be aware of what you are measuring when taking the readings.  Here are the numbers for the spread between the sin and sq waves:
 

71

62

51

40

29

17

5

   

   

A New Toy

I was able to obtain some great additions for the shack over the weekend. Helping someone clean up their spaces of no longer used equipment and find new homes for it was time well spent.

I was able to obtain a HP 3595B Spectrum Analyzer.  Great addition to the shack but unfortunately it will only go up to 40MHz.  However it will still be a useful piece of test equipment and fills a hole in that aspect that I didn't previously have.  I can at least see the 1st harmonic for most of the hf band and more than that for the lower frequencies. 

I still have plans to build a spectrum analyzer so it will be interesting to see some comparisons to the big expensive unit.

As well I picked up a bench meter, cable organizers, hand tools, and a resistor capacitor substitution box. I sure could have used that last week when doing my impedance characterization tests.

Almost finished but not really.

I think I can say that the lpf/mar6 circuit is finished. All’s left to do is documentation.  Making some more changes so the prototype has all the components that will be in the final product, had me add in an 8volt regulator.  Of course when I started this board it had not been decided as to what voltages would be available so I went ahead and fed the MAR-6 with 12v.

To accommodate the regulator, I had to think up some way of fitting it in.  No room on the board that was easy so I came up with the idea to insert the regulator in-between molex connectors. I soldered the pins onto the regulator and inserted the load side into the molex connector mounted on the pcb.  The input of the regulator in soldered directly to a connector and the original 12v feed plugs into that.  Worked out pretty nicely and I didn’t short anything out. Pictures below detailing this.

Interestingly the most important thing that came out of this session was making rf measurements.  This topic rears its head every one and a while and this time I took the opportunity to dig into it a little more.

Making measurements during this project became very frustrating. Noisy signals along with measurements that did not agree on repeated tests been the primary cause.  Hand/body placement or nudging the probe was enough to drastically alter the readings.

Of course it pretty much came down to the ground lead on the oscilloscope. Reading up on the subject and most importantly, viewing Alan’s, W2AEW, video on this was most informative.  Alan describes a spring or a wire wrapped around the ground contact on the probe as an effective way to minimize ground lead induced problems.  Going through the bag of items that came with my new scope revealed such a device. 

So as much as I hated the thought of more testing, I was curious to see the difference in making measurements with it.  Big difference. The signals were now much clearer with less noise, making those measurements easier.  Only problem now is figuring out a way to make a probe socket to mount on prototype boards to make the measurements easy.  So here we are again, a project driving the need for another project.

 73, Peter