I totally agree with using a loop antenna, though you may need to experiment with 'back shielding' [since you want to 'knock down' signals, coming from the undesired direction]. Too bad you couldn't latch on to some of the radio compass units, I maintained while in the USAF.

But, BEFORE screwing around with antenna connections [etc] get out your trusty AC voltmeter, and with the radio connected to power, VERIFY, to a known good ground reference, that none of the antenna connections/other exposed metal parts are 'live'. Older radios, particularly Shortwave units, had what is known in the repair trade, as a 'HOT CHASSIS'; where-in they lacked a power isolation transformer, & usually had non-polarized power cord plugs [both blades the same dimensions. Depending upon plug insertion, into the receptacle, it can put the full voltage of the power source, onto any metal, attached to chassis. Flip the plug over, and the chassis is no longer 'HOT].

Best to replace the plug with at least a newer version, with one wider blade. Or the latest '2 wire w/GND' style. Look at your receptacles, and note there is a longer slot (this is the a/c 'neutral' line {WHITE wire connection}, the short slot is the 'HOT' line {BLACK wire connection}, and if the receptacle is newer, it has the '3rd' wire round GROUND {GREEN wire connection}. If you don't know how to verify, find someone who does, like a member of your local Amateur Radio Club, Electrician, etc.
There is an inexpensive device to plug into the latest receptacles, and verify some connections; but may not always confirm that the GROUND/ Neutral are, in fact, seperated clear to the Utility Panel. Not verifying, can result in DEATH.

A neumonic, to help remember proper connections: 'BLACK on brass to save your ass', referring to the brass colored terminal. The WHITE goes to the silver screw terminal, and Green goes to {duh} the Green terminal.
NOTE: if your mounted receptacles are orientated with the Ground terminal UPWARDS, then 'WHITE on the RIGHT' applies.