n1das said:
The best thing about any radio installation of any kind in a TDI is....(drum roll please)....ZERO IGNITION NOISE!!!
Great when trying to listen to very weak signals that would otherwise be covered up by spark ignition noise in a gasser.
I've also found the rest of the car to be overall very quiet, which makes for a clean RF environment for a mobile radio installation, whether CB or Ham, or GMRS.
UHF and 800 MHz bands are very clean inside the car. Radiated and Conducted RF noise from modules in the car is virtually too low to be measured up in the UHF part of the spectrum. I've done a lot of scanner listening in these bands and I've found the car to be overall very clean.
In the VHF range (~ 138-174 MHz), I've occasionally found some radiated RF emissions from the Monsoon head unit. One problem frequency is 155.250 MHz, a busy local PD frequency in Lebanon NH, one of the freqs I listen to when I'm up in that area. The head unit has a logic CPU clock harmonic sitting right on that freq and I have to turn the head unit OFF whenever I want to listen to Lebanon PD. The clock harmonic's signal strength is weak but just strong enough for my handheld scanner to hear it when it's about 2 feet away from the HU, just enough to make it a PITA.
There's also some broadband noise in the VHF range that "wanders" across the band and sometimes bothers several VHF frequencies in my scanner. I've found it wanders around based on temperature inside the car. The exact frequency shifts as whatever module(s) its coming from warms up. Not a big problem but a PITA sometimes. I've verified that it's not coming from the Monsoon HU and may be coming from the instrument cluster or another module in the car. It hasn't been enough of a PITA yet to make me sniff it out and look at ways to fix it.
IIRC, 27MHz was completely clean inside the car. I've only verified this with a handheld CB inside the car. I expect a *real* mobile installation to also be clean. I won't do a mobile CB installation because I so rarely use CB at all. I stick to Ham and GMRS which I hold FCC licenses for.
Regardless of what radio installation you do, you may encounter some alternator whine on your DC power connection to the car, so consider installing a noise filter on the power connections to your equipment. I've successfully used a car stereo noise filter, designed to filter out ignition noise and alternator whine. There won't be any spark ignition noise but there could still be some alternator whine to deal with.
In case anyone's wondering why I've looked at the EMI/EMC (Electromagnetic Interference / Compatibility) performance of my car this closely is because....I'm an EMI/EMC engineer. I work these kinds of issues in my line of work. It also appeals to the ham radio operator and electronics hobbyist in me.
Gotta love ZERO SPARK IGNITION NOISE IN A TDI!
I'm curious how noisy a Toyota Prius hype-brid or any other gasser hybrid would be in terms of EMC performance!