Sting,
You really cannot determine what kind of transducer you have just by 1823C Multifuction Display. It will tell you what frequency that's its using for the Sounder Module.
However, In most cases transducers usually have a label attached to its cable, located somewhere near the top of the transducer or where the cable plugs into the back of the module or display. This label contains information that is helpful in identifying the transducer and locating the correct service parts for it.
Most Airmar Transducers will use this label to show:
• The transducer’s model name
• It’s manufacturing date
• Any certain performance characteristics (i.e. the transducer's frequency)
• Airmar part number (PN)
• Or a Customer Part #
-Deep Blue