Apartment antennas are a crapshoot. You won't know what works until you try one... or two, or a dozen. Eventually you'll tire of the high RFI level and look for something quieter. I shoot for keeping the usual suburban RFI down to S1. No point in an antenna that transmits local RFI at S9 because any weaker broadcasts will be buried in the noise anyway.
For a few years I used homebrewed passive fugly loops made from TV coax. I just experimented with the diameter and number of wraps until I got good results in the vicinity of the 40m band. The most successful variation was two wraps around a closet door. It wasn't directional for HF signals, but was directional for MW and for nulling out local RFI. Just swinging the closet door was enough to minimize the main source of RFI, a parking lot light. I finally took down that antenna a few months ago, intending to rebuild it with a tuning capacitor. A project for this fall or winter.
A better looking version of the same principle is the
KR1ST loop. I know of several folks who've built these and reported good results for shortwave listening.
Meanwhile I'm using
this doodad strung along the ceiling diagonally. Works fine indoors for now because the adjacent apartments are vacant. When those apartments were occupied, especially upstairs, I picked up too much RFI. To minimize noise from my own computer and other devices I coil up the coax feedline and snap on ferrite chokes. Works about as well as the homebrewed passive loop.
For outdoor use, mostly for holidays and special occasions when there's likely to be a lot of activity, I occasionally string up some magnet wire as a sloper. It'll get torn down by the maintenance crew eventually, so cheaper is better. I'll just string up around 30' of magnet wire out the window, fed directly to the Hi-Z input on the Palstar. I don't have a proper ground but another length of magnet wire, via the ground input, and strung along the ground or baseboard helps a bit as a counterpoise. If left alone by the maintenance crew these magnet wire antennas will last several weeks, sometimes months, before tension and the breeze fatigue the metal enough to break. I keep a close eye on these because they can foul the outdoor A/C units.
To sling the wire up a tree I use small white HDPE pill bottles filled with coffee grounds, and some heavy duty fishing line. I just sling the bottle as high as possible over the nearest tree, which is only the height of a utility pole. If I miss, no big deal - the bottle is soft plastic and won't break anything, and the whole sling is non-conductive in case it hits the electric line (which hasn't happened yet - I'm pretty careful). I tie the magnet wire to the end of the fishing line and pull it up the tree. corq used a similar trick for her Squirreltennas, but I think she used a slingshot to get better height into the taller trees in her area. Our trees are pretty short, only 30-40', tops.