Using the standard supplied antenna, should this receiver still be fairly
lively on medium and long wave, or is it very deaf down there and needs an
external antenna?

If the latter, is there a max length to avoid overloading the receiver?

Reason for question, just bought one, and can hardly hear anything below 90
MHz, but putting an indoor wire about 20 feet long on it causes it to
totally crossmod right across from 100kHz to 30MHz.