Currently on Netflix is a movie series called "The Three Body Problem". It is Sci-Fi at its best and scary as hell. I have only watched a couple of episodes but can share that I have had at least one nightmare.
While a Sci Fi movie, it is a foretelling of the future. Yes, they laughed at DaVinci's helicopter design!
So that you don't have nightmares and are down to earth as you contemplate building a SSB transceiver, I want to introduce the Four Body Problem.
Friend N2CQR shared that his close friend and colleague VU2ESE, Farhan had identified four building blocks to any project. [AFMO]
- Amplifiers
- Filters
- Mixers
- Oscillators
Thus, The Four Body Problem is to identify and flesh out the sub-elements of AFMO.
Quite honestly, I had never thought about these broad classifications of what I call modules. But more aptly AFMO can be thought of as the LEGO building blocks of our hobby.
Once again, we see the sheer brilliance of VU2ESE! With his AFMO concept, Farhan, has given us a way to formulate an ordered approach to fabricating a homebrew SSB Transceiver. The LEGO analogy is very apt as in effect we snap together various circuit pieces to form a much larger circuit structure.
Our job now is to create a catalog of circuits within the AFMO scheme and then we have fill for the block diagram which is the initial step in creating a new design.
Amplifiers
For amplifiers we have two broad categories such as Audio and RF. Within these are subsets such as Microphone, Audio Pre-Amp and Audio Output. For the RF side we have Small Signal RF and RF Power Amplifiers.
Filters
Filters are represented by elements such as Band Pass, IF Crystal Band Pass Filters (or Digital Filters), Low Pass (or High Pass) Filters and lastly Power Rail filters.
Mixers
Mixers essentially take two frequencies and create a series of frequency combinations. A Receiver or Transmit typically converts one frequency into the sum or difference of a supplied frequency. In a single conversion stage, we have an incoming signal "mixed down" to an IF frequency. A Balanced Modulator impresses an Audio signal on to a Carrier frequency. A Product Detector reverses that process to create an Audio Output.
Oscillators
We have two major sub-sets to the Oscillator category to include Analog and Digital Generation. On the Analog side we have Beat Frequency Oscillators that can be either Crystal Derived of using an LC Network. For the Variable Frequency Oscillator, we have the LC or Varactor Tuned and using certain Crystal properties a Variable Crystal Oscillator or VXO. For the Digital generation of frequencies, the Si-570 or Si5351 driven by an Arduino or Raspberry Pi can do the BFO VFO task. In passing the Digital generation is a simple handshake with SDR homebrew transceivers.
A critical step is to learn the use of LT Spice where each of the aforementioned modules are documented and tweaked to perfection. If they work in the Spice simulation and assuming a circuit is built per the design--it should work. The value of LT Spice is the experimentation and evaluation capability without even turning on the soldering iron.
Now the trap. Often you simply pull a proven module and install it in a rig. Likely most of the rig is done this way. So, the end result is just another warmed over Bitx with a different front panel.
Thus, another part of The Four Body Problem is to constantly add to the AFMO catalog. One of my new adds will be the use of the 2N2905 (PNP version of the 2N2219A) as a Driver transistor. A bag arrived yesterday.
73's
Pete N6QW