Looks like the file is UNICODE text and you’re using a BigFix version earlier than 9.5. In 9.5 IBM introduced native UNICODE file handling. Pre-9.5 the embedded double-byte characters are all represented in the output and not handled as a single character.
The first two bytes, “fffe” indicate the file encoding type. I haven’t tried this on a UNICODE file yet but I expect this should give what you expect by stripping out the unprintable characters:
q: (concatenation of characters whose ( it as hexadecimal as integer < 127 and it as hexadecimal as integer > 31) of it)of lines of file "c:\temp\port-test.txt"
That should strip off the %00 in the double-byte characters, as well as the %ff%fe header, and anything else outside the “normal ASCII” range of printable characters.
And props to @jgstew, whose Challenge #3 at Challenge #3: What does this relevance do? is my constant reference on this 
