easaman,
Understood your explanation, but leads me to more questions:
The voltage regulator is supposed to maintain a certain voltage.
Now, when the starter is engaged, obviously the voltage will drop. The voltage regulator will try to maintain the desired voltage (eg. 28V) but of course will not be able to due to the high demand from the starter.
So let's say the voltage drops to about 10V, and fluctuates to maybe 14V, how is this harmful to the radio?
It is mentioned that transient voltage (as you mentioned voltage spikes) are the harmful one, but I find that there is no more than 28V, so how can the "spikes" be harmful?
Or am I getting this all wrong? Or are "spikes" you refer to not voltage of more than what the radio can handle (in this case 28V) but "spikes" as in rise & drop (non-consistent) of voltage, not OVERvoltage.