Steve, I think Garey meant that the 2nd IF filters in the R-4C, like the filters in the TR-7, are all designed for 50-Ohm terminations. That makes them quite easy to test outside of the receiver or transceiver (or test the antenna to filter input or the filter output to speaker paths). The 8-kHz wide roofing filter and any of the Sherwood or Inrad substitute roofing filters are designed for the 1-kilohm terminations mentioned by Garey. Any substitute 2nd IF filters are 50-Ohm designs.
Bob K9JU
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