>need it to be shielded with the metallic mesh?
For 115 kilobaud and 30 feet maybe, but not for the baud rates an A500 can put out. I can't get better than 57 kbaud even with an A1200/68030 for Amiga Explorer; at 115 kbaud the serial port splashes data bytes onto the floor. Your A500 will probably have to run at 19.2 kbaud.
If you have trouble making one, null modem adapters are still fairly common items at computer stores, though not as common as they used to be before the popularity of USB.
