It's been mentioned here before, but try a counterpoise wire connected to 
the ground terminal of your rig, or of your external tuner if you are using 
one.
The other end of the wire connects to nothing.

This is a cheap way of accomplishing what MFJ does with their artificial 
ground tuner.

Make it a quarter wave on 40 meters, and it should cover you on most of the 
other bands. If it doesn't then add a separate quarter wave wire for 
whichever bands you wish.

You can run it around the baseboard, or toss it out the window and run it 
along the ground parallel to your house.

Of course, don't let anybody get hold of it while you are transmitting.

When I lived in a second floor apartment, a counterpoise was often the 
difference between an antenna that would tune and radiate vs one that would 
not.

In the case of RF on the equipment, the counterpoise will, in many cases, 
carry the rf away from the equipment, greatly improving your operating 
conditions.


Mike Duke, K5XU
American Council of Blind Radio Amateurs