February 23, 2019

The end of the road for digital radio

I have been driving an EV for a month now. No more spark ignition to suppress. No pesky electronic Diesel injectors.
So smooth and quiet a ride - I call it the MagicCarpet.
Common to most EV and Hybrid vehicle systems is a number of high power electronic inverters to drive the 100kW or so electric motors and regenerate to the storage battery. Some manufacturers such as Tesla and BMW disable the  AM band reception because of this.


I thought it would be interesting to enable the AM radio and also run the DRM digital AM tests to see if COFDM can improve reception under high noise conditions.

First step is to scan the bands with a spectrum analyzer and record the noise floor with vehicle off and then driving.
0 thru 40 MHz is where the major trouble is, +40dB of noise. There is minimal disturbance 50MHz and up, so FM, DRM+ /  DAB bands should not be an issue.











Enabling the radio for AM band is the next step. Followed some posts on the net and all is working in that area.
The reception is very good while parked up. Nearest local is 50km away and clear, big surprise that it's networked AM station some 500km away also readable here during the day. As soon as driving is started they get wound up in lots of electro-noise, some of it quite musical. The local station is part useable when driving around, but not good enough to be acceptable for owners accustomed to and in primary coverage of FM or DAB+ services. I would descibe the quality as on par with the shortwave and DAB service, both have been discontinued in this region.

I will keep the AM band enabled, it works well enough in the primary coverage contour, where there are 15 stations vs. the  3 'local' FM services available.

Today the test antenna and DRM receiver with DReaM decoder as used previously was fitted up to the car and performance tested in similar conditions to the other tests done.
While the DRM did work stationary, it was rendered unuseable while driving, with silence intervals of 2 - 3 minutes and the occasional burst of stuttery audio lasting up to 10 sec. at a time.
A re-run with AM mode transmitted showed good reception throughout the area free of serious degradation from the electric drive noise.

Final Conclusion
The reception difficulty is caused by the vehicle systems. Current developed digital radio does not overcome this, neither should it be expected to.
In - car radios should continue to tune AM and shortwave bands as it may still be relevant for the area. DRM specification radios include a range of bands less affected by this type of EV interference.

The results are specific to the BMWi series vehicles and probably their -e suffix variants. There doesnt seem to be anywhere quiet for antenna location and the body is carbon fibre / plastic therefore shielding from the electrical system is difficult.
 I have also sampled the Toyota Prius system at similar field strength AM and the degradation when in electric drive mode is present but to a lesser degree, in the order of 10dB.

It is expected the issues will be similar for all EV systems and may extend into the higher bands with some models. Lets hope RF induction charging doesnt take hold!