Electronic – How would you combine DC power, bi-directional serial data, and an RF signal on a single 50-Ohm coax feedline

Trying to think what 433 is used for off the top of my head :) Is that the weak signals band?

At any rate, most 2-way radios are made to match up to a 50ohm antenna and the matching is left up to you. You can get an antenna that is already tuned, or you can do impedence matching through a number of techniques (see the referenced article below).

With a good match, you reduce standing waves. Standing waves build up when the radio sends out a nicely modulated signal but the antenna isn't resonating at that frequency and causes standing waves, which feed right back into the radio and can blow out the final stage.

The higher the output power, the more this becomes important. At very low power, say <1watt, the worst you have to worry about is the antenna not resonating and your signal not going anywhere. At higher powers, say 50+ watts, you can damage your transmitter in less than 1 second. Modern radios have built-in SWR detectors that will cut the power if it detects a problem. Those aren't always guaranteed to work though.

This page lays out a few key things verey nicely

That's actually a subtle "gotcha" in asynchronous serial communications — if there are never any gaps in the data that are at least as long as a character time, it's possible for the receiver to get out of sync with respect to the byte boundaries, and there's no way to recover. Any '1' followed by a '0' could be construed as being a stop bit/start bit pair.

One possible fix would be to send a byte of all-zeros (or all-ones) every now and then. If the receiver is out of sync, this will force it to resynchronize on the next start bit.