Scope Dual-Input Coupler ???

I've successfully run my Asteroids Deluxe on my Tek 2235 scope (wow), but
I'd like to connect up the blanking (Z input) to the scope as well.

The docs indicate that I need a "dual-input coupler" -- I don't have one,
can't find anything about it on the Tek site, and web/group searches return
zilch.

Anyone care to elucidate what a dual-input coupler is and where I can
acquire one.

Much appreciated.

---
Bret Pehrson
http://www.vaps.org/members/nv/bret@classicade.com.html
mailto:bret@classicade.com
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