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.