Friday, April 28, 2017

A New Line of Transceivers ~ DifX

Transceiver Architecture 2.09


Dual Conversion Band Switching

In this posting I want to talk about some of the specifics of the band switching and how to cause the proper Band Pass Filter and Low Pass Filters to be put in line for the band in use.

The Arduino Mega 2560

The first realization I had with the dual conversion multi-band approach was that you needed a lot more pins. There will be those who immediately jump up and say but you can add a pin expander to the standard UNO, Nano and/or Pro-Mini and no need to move up to the larger footprint and more costly microcontroller. There is another requirement that is answered by the Mega 2560 and that is the 10X increase in program size. That perhaps is the bigger driver for the Mega 2560. Undoubtedly there will be more things you want to add to your homebrew rig and then pins is not the issue but programming space will be. The Mega 2560 has 54 digital pins and 16 Analog pins and thus you have many more options available to you. Now as I discovered there are differences from the  Uno, Nano and Pro-Mini so you will need to think about pin assignments and it is not a straight pin for pin compatibility. I will highlight those differences.

The Band Switching Scheme

My band switch scheme involves two band switches and has the capability for 17 band positions. One band switch has 12 positions and the second band switch has 6 position. So OK you have a blank look on your face. Hey guys Ten Tec did this with some of their transceivers, where you placed the main band switch on 10 Meters and the auxiliary band switch then selected four sub bands within the 10 Meter band.
For my Dual Conversion DifX when the main band switch is placed on 60 Meters  that merely connects to the auxiliary band switch where you can select the five channels on the 60M band including one channel that will be tunable as I did in my 60M DifX rig. Moving away from the 60M position in effect disconnects the second band switch.  The process of selecting the operating band with the band switch will automatically trigger a comparable Mega 2560 Pin that has 5 Volts on that Pin to control either relays or Pin Diodes in the Low Pass and Band Pass filters. One switch position changes frequency and selects the proper filters.

Mega 2560 Pin Assignments

The logic of the code is that the digital pins are read, as an example Pin 30, which is designated for 20 Meters when that pin is sensed LOW, then Pin 39 will go HIGH and that switches in the proper Band Pass Filter and Low Pass Filters. On 60 Meters Pin 49 is made HIGH for all of the 60 Meter Pins.
Pin A10 and A11 on the Mega 2560 are used for Encoder A and Encoder B. (Thanks Rob!)
Keep good notes as we are moving forward with the design.
Pete N6QW