Keying Interface & RF?

[Eric & Bonnie Hall]

Hello Fellow TR Users:

    First of all I have to admit that I am mostly an appliance 
operator...

    My problem concerns the homemade keying interface that I put 
together: It works great on 80, 15, & 10m, BUT when I try to use it on 
either 40 or 20m it seems to get some kind of RF (?) interference. I 
put the little board in a metal box, used shielded cable...

    Has anyone had this problem or have any other tests that I could 
try? I was so proud of myself that I actually built the little gismo!

    Thanks for any input,
        Eric WD9GGY
        thehalls@ix.netcom.com 

(sometimes it's better to be geograhically challenged, then mentally 
challenged...)