FT8 - How to locate "TUNABLES" in Control Assistant

FT8 instruments don't have "Zero" and "Span" calibration adjustments, therefore the adjustment is done in the control software called "GAP". This article is going to describe how to locate the adjustment addresses called "TUNABLES", so that you can calibrate the control signal.

The FT8 Electrical Schematic Drawings and GAP Logic, have all the inputs and output channels in the order you find them on the RACK - CARD - CHANNEL,

starting with Rack 1, Card 1, Channel 1, and continues to the last Channel, in the last Card, in the last Rack.

There isn't an index of instruments, as you normally find on schematic drawings, to indicate the drawing page number where the instrument is located. Therefore you need to start with the "Input / Output List". This is a drawing (list of all the inputs and outputs that enter the control system) which can be found in the "Project Documents". The following information is what to expect in the I/O List. This is a "Mobile Pac"? (yours may be different).?

I am going to use Pressure Transmitter PT628 as an example in this article. You can see it is located in Rack 1, Card 6, Channel 4.