[GreenKeys] Filters and so on

[wa2hwj at att.net]

ZCZC

My first TU was the "Twin Cities TU" from the New RTTY Handbook. Since I was 15 at the time, I did things I didn't know I should do:  I used a speaker transformer secondary with a capacitor across it as my MARK filter (I don't need no stinkin SPACE filter...). I used a broken polar relay my father found in the waste basket next to the Weather Service Model 15 at his office. The TU worked fine. My Model 26 was literally worn out copying the commercial press stations. Then I got up the nerve to contact Byron, W2JTP, who lived in my town, and asked him to tune up some toriods. He tuned them for me using the exotic gear he had in the RTTY Handbook(!), and they still work. Of course, when I went to his house I expected to see rows of Model 28's...he had a Model 26 and a 14 strip printer and the humongous AN/FGC-1 terminal unit. 
Anyway, I tried building several active filter TU's from articles in 73 Magazine. I found that most articles in 73 never really worked, but at least Wayne had some filler for his magazine. One gadget did finally get going; it used a single monolithic active filter for each tone. It had a ringing problem at first, but once settled down, it worked well. And, don't forget that all of those Flesher units had active filters. They were the favorite of the "RTTY appliance operator". 
Bottom line...if it works, don't fix it.

73,
Jack WA2HWJ

NNNN