So initially when i was thinking about building a receiver to mate up with the 10w CW transmitter project, I was thinking SimpleCeiver by Pete N6QW would be the go as a direct conversion receiver. I even did a bunch of work on laying out boards i was going to route up and populate. Now its all good and proper to copy someone else’s design, I mean that is why we publish build details and blogs and Pete’s project is awesome, but there is not a lot of design learning in monkey see monkey do. If you have not read all 20 something blog posts for the SimpleCeiver project, here is a link to the beginning. http://n6qw.blogspot.com.au/2015/09/moving-on-to-simple-ceiver-project.html
Rather than build a cut and paste copy of the SimpleCeiver, I am going to copy Pete’s design methodology of Simulate, Evaluate, Compare, Prototype and Modify, and roll my own design from the best designs i can find.
Simulate: Starting at the front end of the receiver, I will simulate each stage in turn using LT Spice.
Evaluate: Using the tools within LT Spice evaluate the performance of the circuit.
Compare: Using LT Spice, simulate a number of different circuit typologies for each stage selecting the best performing one.
Prototype: Build on perf board or Manhattan style on copper clad board a prototype and document its performance against the simulation.
Modify: Make modifications to the prototype if needed to improve its performance if the actualized circuit does not measure up to expectations.
Now we have the methodology sorted, lets set of some specifications for the design. There are number of limitations in the design based on things I already have in the parts box. This project is not about reinventing the wheel, it is about using what I have on hand and making the most of those things.
Design Limitation 1: The mixers will be Mini Circuits TUF-1 double balanced mixers. I have had these mixers in the parts box for a long time now doing nothing. This seems like the right project to pull them out for and put to good use.
Design Limitation 2: The LO and BFO functions will be fulfilled by a SI5351a driven by an Arduino Nano. Now there is a lot to be said by designing and building analog oscillators and for those that have the patience and the skill to make such things I really do take my hat off to you, its just not my thing. I am more inclined to use things that are easy to use and work well out the box. Also writing and modifying software is well within my skill set, and i find Arduino C as easy to use as others find making ceramic resonator VFO’s.
Design Limitation 3: 12Mhz IF I have a couple hundred of these crystals so i should be able to match up enough to make quite a few IF filters with these. At this point I am thinking 6th order, 600Hz wide Cohn Min Loss. But i might also get excited and categorize the motional parameters of the crystals and design another topology using Dishal.
Design Limitation 4: Use what I have in the parts box. I have a bunch of things I have collected over time that might have been used hear or there for learning, but never put to use in a project. I have some TDA1905 5w AF IC’s MC1350 IF Amps, NE5534 Op Amps as an example of parts I have in the box that really should get a run and used in a project. But, I could also go with popcorn variety circuits also and just use J310 or 2n3904’s
Above we have a block diagram of what I am envisioning at this moment. Nothing revolutionary, nothing extraordinary, just a very typical single conversion superhet design. So in the next part of this series of posts, we will start looking at band pass filter designs and simulations.