[Coco] On the subject of RF output

[Charles Hudson]

My CoCo 1 is being output to a 20" Toshiba LCD TV of a certain age, from 
the RF output on the CoCo through a cable and a coax converter plug into 
the TV's RF input.  The TV is plenty stable and sharp but the output 
from the CoCo is a mess of banding, video "noise" and herringbone.

Yesterday out of frustration I "tweaked" the two accessible coils in the 
RF section just to see if I could make things better. (Using anti-static 
plastic tools)  I did, sorta; the text was in sharper focus and the 
v-noise abated somewhat.  I was working without the RF shield on the CPU 
so probably things could have been better, but I wanted to ask:

What are the two coils controlling?  If I turned one of them too far I 
lost the color signal.  I also noticed I could produce noise.  So I 
guess one of the coils acts as a signal mixer for the final output?  
What's the other one for?  Where might I find documentation on this topic?

Thanks for your replies.

-CH-