If you try to read an analog (slowly varying voltage (*)) with a digital input you risk false triggering. You can either use a low-pass-filter and schmitt-trigger (ie hysteresis) to clean up the input signal, or use analogRead () and do that the equivalent in software (but this limits your bandwidth to 5kHz or so)
(*) slowly varying means less than a few million volts per second or so! The problem is that noise on the signal will take it above and below the
switching threshold of the input gate as the voltage "gradually" passes the threshold. The 328 has a little hysteresis on input pins to reduce this problem, but it sounds like the RFI near the transmitter is exceeding this. You would do well to filter out RF frequencies with an RC filter anyway, this might be enough to fix your problem.