Duffy, you are my hero (wow, that was a girly thing to say, but well, guilty as charged). This is exactly the kind of information I'm looking for and am capable of understanding at my level of non-expertise, as well as good questions for me to think about.
Love the idea of the SQUID as well, as a ring of superconducting material capable of detecting quantum interference would fit perfectly with my wheel-shaped alien space station. And "Space Bunny 2000" cracked me up -- though for the record, her name is Niki, which is much shorter to type!
So perhaps Niki's job could be to build or cobble together Parts 1, 2 and 4 to the necessary specifications (provided by her Clever Alien Programmer Friend)? And as for the antenna, perhaps she could hijack that Algonquin Radio Telescope I linked to before, since it's not that far away? (Note: There are some great pictures of the exterior and interior before its recent restoration on
this page.) A five-hour road trip for Niki and her friends would not be a bad thing at all in the context of the plot, so might it be possible to use the ART as the directional antenna if my characters sneaked through the bush at an appropriate time of day/night and set up their homemade rig close by? Or would using an existing telescope negate the need for any kind of homemade equipment?
As for the answers to those questions about frequency, sensitivity, location and duration, they can be whatever I need them to be, so any plausible values will do. Though duration, I would think, would be a very brief burst, since it's a simple "OFF" command. (Unless I am greatly underestimating the complexity of telling a device to turn itself off, which is entirely possible. See: Not An Expert, Me.)
Thanks again to all of you for giving me so many great ideas and food for thought.