Hi Michael,
Take a look in the Files section and open the old Fox Tango Newsletters pdf. Do a search for "Filter". These page number entries came up under FT-101ZD: 7942, 8233 & 8213. There are others as well but these are the first three.?
You will find 7942 (Year 1979 page 42) in the pdf at page 477 (of 1292 pages). This looks like what you are looking for. If not just keep searching.
73
Roger VE7LB
