Topband: Turning a 160 Inv-L into a 160/80 Inv-L

[Eric Rosenberg]

I use a 160 inverted L, approx 65ftx65ft, with 21 radials.  It's a
vertical wire supported by a tee branch, not a tower.

I'd like to make this antenna useable on 80m too, and have read ON4UN's
latest on this subject.  From what John says in chapter 9, section 7, I
need to install "an 80-meter trap to isolate the horizontal part of the
160-meter inverted-L antenna when operating on 80 meters."

My questions: 
- what is the makeup of this trap (I need "Heathkit-like" instructions,
as I am no designer!
- where do I put this trap?

John's reference (ch 9, section 6.4) didn't clarify matters for me. 

73 and thanks in advance! 

Eric W3DQ
Washington, DC