The best information I have so far on RFI and the Prius so far is from John VE3XKD, and it's daunting. I am still working on mounting my radio and thus don't yet have experience to report with my 2007 Prius. - Bruce
In working on my Prius, with significant help and encouragement from Alan, I developed techniques for identifying the location of noise sources. In the case of the Prius the DC-DC converter (the so-called Synergy Drive) radiates a 'huge' amount of broadband noise from abt 2MHz up to abt 15 Mhz.
After grounding and shielding the DC-DC converter and adding ferrites to each cable entering and exiting the box (not an easy job!), I was still left with S9 and greater noise. It seemed that HF mobile operation would be impossible! Clearly I needed techniques to locate, then reduce sources of noise.
It became apparrent that electrical fields generated by the DC-DC converter and other digital boxes are so large that they induce a large amount of HF signal voltage into the various vehicle wiring harnesses.
The harnesses travel from inside the engine compartment through the firewall, are distributed along the vehicle ending up in the rear of the vehicle. These harnesses are not shielded, bypassed or grounded and hence act like antennas and radiate noise.
Some of the major sources I identified, included four digital boxes, the exhaust and the ignition system. Another ham, using similar techniques, identified that the regenerative breaking system generates noise while the breaks are applied!
I used two techniques to locate noise. Firstly I used a small resonant whip antenna and attached it via a length of coax to a manpack radio (IC 703). The radio was tuned to a ham band, turned on and left outside the vehicle (there's a reason why). Using the antenna as a wand, I walk around the vehicle waving the wand over the vehicle surface listening for peaks in noise (hot spots).
On the Prius this identified the front windshield wipers as major radiators of noise. By simply grounding the wipers, noise was reduced(on all bands) by several S units. I also identified the front lights and the rear lights as noise sources (at least S6 noise). I also identified that the vehicle roof, at the back, was the least noisy location to mount an HF antenna!
Next, the wand is waved over the inside of the vehicle. I was surprised at the results! When I did this in the rear hatch (after opening the hatch)I found S9 plus 15 noise.
I then switched to my second technique. I disconnected the 'wand' and connected a length of coax terminated in a small 2 inch loop. I used the loop as a probe and identified specific noise sources inside the hatch (after removing the carpet and plastic molding. That's how I found that the Prius NiMh battery box is poorly shielded in one spot, found a digital control box that was radiating noise, and determined that the wiring harness was radiating noise.
After the loop identified major hot spots. I then used 3M 1181 copper foil shielding tape to shield, and then bond to ground, the offending hot spots. The tape is wrapped around the offending digital box or wiring harness. Seams are tack soldered and the assembly is grounded to the vehicle chassis.
In each case, after shielding/bonding/grounding I re-measured the noise using the loop and wand technique and found considerable reductions in received noise and 'hot spots' disappeared making for improved reception.
As a bonus, I realized that there were 'good' and 'bad' spots to mount my screwdriver antenna. In the case of the Prius it seems that the radio mounting location inside the Prius may also be of concern.
By the repeating the above processes throughout the vehicle eventually I could Operate 20 and 80 meters with noise levels below S3 and S5 respectively. 40 is still a problem with noise levels at S7.
I am not finished yet - it is a work in progress however the results are encouraging.
73 - John VE3XKD