None of the components I have for my SDR setup (including the wire I'm going to use for shortwave reception), are rated for outdoors except the feed wires and discone antenna that will also be used in this setup. I do have a 9:1 balun that I plan on using with the wire, but you lost me at adding a termination resistor. Are you saying that the wire should complete the loop and be connected straight to the balun at both ends, with a resistor on one of those ends? What about ground? From most of the posts and videos I've come across, having a ground source seems to be very important to help lower the noise floor and increase signal strength. Does the loop negate the need for ground? If so, any kind of resistor can be used, or you talking about some specific value/type of resistor? My pool of resistors is just a bunch of 1/2 watt carbon, and whatever I pull off old scrap components (mainly SMD).
The idea is to pick a spool of insulated wire (single conductor) and connect it as for the attached image, both the loading resistor and the 9:1 will be hosted inside two small weatherproof boxes, the antenna will be suspended, using some non conductive support (PVC pipes, fiberglass rods, broomsticks...), at 1ft (or more) above the garage roof, a run of RG6 coaxial cable will run from the 9:1 (inside the box) down to inside the garage where you'll have your SDR; the termination resistor placed at the opposite point of the 9:1 allows to obtain a decent match to the 9:1 (and then to coax) over a very wide bandwidth, the resulting antenna will be almost omnidirectional with a slight better reception in the direction of the feedpoint (the 9:1), being a loop it is a "self contained" antenna so doesn't need a ground connection, but willing to add grounding, you may do so at the SDR end of the coax
As for the 9:1 you may either use a commercial one, like
the one from NooElec or you may build it yourself, as explained
here (scroll down to see the BalUn infos and pics), in either case it must be a transformer offering galvanic isolation (as in the two examples) so that the loop antenna and the coax feedline will be insulated (at DC); optionally you may add a choke on the coax, it may be as simple as 10 or more snap-on ferrites placed on the coax tightly grouped together and covered with duct tape
Note: i modeled the antenna as a 40ft loop and calculated the resistor value for such a length, if the antenna will have a different size you'll need to adjust the resistor value