The HDL-0108-IF2C (originally an accessory for the 102GXN, also usable as a multiplexer for the DLITE-0100A1) assembly/build has been modified in the 2021C build variant to minimize input losses for particular use-cases.
R44: This input resistor is used on the Tx input in series and damps or controls ringy (cable effects, etc.) input pulses among the things. The stock value is 10 Ohms. In the 2021C it has been changed to 1 Ohm. This still provides some current limiting and protection for typical use cases, but allows larger excitation (still safe) on the transducers tuned with a parallel inductor. If your use-case changes, you may want to change this value. Use a scope to check your pulse shape and voltages for any experimental transducers. For transducers without the inductor, the pulse signal generally “good”, so this change matters less.
R12, R45-R51: These are channel input protection (and other function) resistors. The stock value is 3k. The 2021C variation uses 1k or 1.5k here to minimize input losses and adequate protection remains for typical uses cases for the IF2C-MUX.
The preamp section has also been modified to maximize the response of the IF2C-MUX for typical use-cases.
Tests indicate that the changes, particularly for applications like “cross-channel” acquisition, show clear signal gain improvements over the stock build, originally configured for a wider range of use-cases that may not be relevant to standard field use conditions.
For details on allowable voltages, pulse settings and transducer test configurations, please be in touch.