It is true that analogue shortwave reception in cars is affected by electrical interference, even in strong signal conditions. One reason is that car antennas are mostly tuned for vertical polarisation and SW is horizontally polarised. This makes AM Shortwave reception often quite noisy and subject to annoying level variations.

And this is why a digital DRM broadcast in the shortwave band can bring a great advantage as it can provide reliable reception quality till 8-10dB SNR. It also supports various robustness mode (B,C,D) and advanced audio coding. DRM can give shortwave a new lease of life as it provides higher level of defense against the “electrical noise” in cars.