Weak FM radio reception in 2010 Prius?

I went out and did a bit more investigating this morning and have found something odd that I can't readily explain. The test area was open countryside, several miles from any possible EM source, other than the car. My intention was to try systematically turning electrical items on and off, try opening and closing doors etc to see if changing the electrical load on the cars systems made any difference.

As far as I can tell, switching most items on or off makes little or no difference, the background noise remained pretty much constant. One thing that made a major difference was the windscreen wipers, but not in the way that I anticipated. I'd guessed that the wiper motor might generate some extra noise and make things slightly worse. In fact, what happens is that as the wiper blades get about a 1/4 of the way up the windscreen the background noise starts to markedly reduce. By the time the blades are close to the end of their upward stroke the background noise has completely gone.

Despite years of witnessing odd EMI effects, I have to say that this one really has me puzzled. All I can come up with is that somehow the wiper blades are acting to screen, or perhaps absorb, emissions coming from under the bonnet (hood in US-speak) and so reduce the hash of electrical noise that's getting to the aerial.

The next step is to look at adding some temporary shielding over the most likely source of electrical noise, the inverter. It's noticeable that Toyota seem to have removed the big metal case that was over this on the NHW20 model, which has me wondering if this might be the root cause of the radio problem. It may be that just adding a decent earthing strap to the bonnet might be enough to reduce emissions, I'll report back following the next set of experiments.

Jeremy

 

Wow Jeremy we rely on you now. I am living in this radio nightmare and seems like you are our only hope. I am the one with the LED lighting and HIDS which interfer with the Radio like crazy (I know other cars don't have this problem).

Please lep to resolve this for us.

I must say I didn't notice inteferce when the wipers are turns on. Like I said when you operate the side mirros it also causes interference or noice.

My last resort is change my head light to the Light package £950 pounds and I am thinking about it because I can't stand it that I can't listen to the radio at night when the light is turned on.

This metal casing you are talking about will that solve the problem?

 

I also changed my Unit to a totally new one, and it made absolutely no difference whats so ever. The others think they have better reception I believe it is in their minds. Because of the DAB plus LED it enahcnes the problem. The moment the new unit is fitted turn the LED on and Bang no radio. So no change.

Even without LED I have inteferece when passing every tree with the new Unit. So it did absloutely nothing.

 

Jeremy,

Now, that is a good one. I'm good for a bunch of whacko (all probably wrong) ideas, so let me try on a few.

I'm wondering about the radiative pattern around the car. Those antennas are around 1/4 wavelength long in the FM band. Their spacing is, well, "significant" around 100 MHz. Further, they're grounded at the base of the arm where they attach to the pivot points. Suppose that the car is some kind of radiator - particularly, inside the passenger compartment. Put those wipers up, and one would get standing waves. Standing waves at these frequencies might very well result in some kind of directivity, much like a Yagi antenna.

Were you standing in a particular spot when the EMI reduced? If you moved, did the amount of reduction move around, too? What about the orientation of the receiving antenna? Was it always vertical?

Let's go back to the "antenna" theory. If they're up, there's a near short at the base of the wiper and an open at the top, and it's about a 1/4 wavelength long. The wiper's effective electrical diameter will be wide, too, making them broadband. Put them up, and electrical energy in the area would be coupled to the base. A true 1/4 wavelength antenna has an impedance at the base of around 15-30 Ohms. Well, it's a real good bet that the real impedance of the bottom of the wiper to bonnet ground might be in that range - with losses all over in the iron. So, if this idea is real, the electrical energy in the car is being efficiently captured and dissipated right into the iron of the car!

If true, this would imply that the noise source is inside the passenger compartment. Further, it would have to be directional towards the front windshield, from inside the dash, I would guess. Hmm.. Isn't that where the car computers live?

100 MHz and such are precisely the kind of frequencies one would expect from a microprocessor. It's not rocket science that things like this should be shielded. Bonding wires? Somebody cheaping out with a plastic, non-metal impregnated case?

All right. I have to go back to writing a document on synchronization techniques. But, when I get a chance, I'm going to look up the EMI requirements from the FCC and EU in the 100 MHz range and report back.

KBeck.

 

Maybe you should start a separate DAB topic. Also, spell checking (hint - look at the words that have red squiggly lines under them - then fix them).

For a base radio, I have found both a random Chinese brand (worked MUCH better), and Pioneer (Works better) to be superior to the stock. I think the opinions expressed by many are a bit more fact based - and not "in their minds". Please read the thread(s).

DAB seems to be a different topic that has a small amount of comments - so you are unlikely to find any kind of consensus here...

I suggest dabbling near a brook - fishing for something unseen and possibly unheard...

 

Firstly there are no red lines that I see here. So can't fix the spelling but thanks for correcting me. Feel like I am back in English class again.

Second if you have read other posts within this tread you will understand why I bought up the DAB radio. It is connected to the stock radio that came with my HU.

Its just the DAB radio shows a much clearer problem when listeinng to the problem.

 

I tried moving the car around, so that it was oriented at about three different angles, roughly equally around a circle, and repeated the "wiper test", with the same result. I also tried a portable FM radio inside the car, sat on the centre console, and repeated the test with this. Oddly, the portable radio wasn't affected at all, either by orientation or by switching the wipers on.

Overall, the portable radio inside the car seemed to work pretty well, certainly a bit better than the JBL head unit, which seems to indicate that the head unit isn't up to much (something I already suspected anyway, based on the reports of other units performing somewhat better).

So, rather than radiated noise being the problem, I'm wondering if it may be mainly conducted noise, getting in via the wiring? I can't explain the "wiper effect" at all, though, although I've seen some pretty bizarre EMI phenomena over the years.

If I still had access to the right test gear I'd start sniffing some of the wiring to see what's sitting on it. My guess is that there may be either some conducted noise getting in to the head unit, or perhaps some locally radiated noise getting in via wiring routed close to the head unit/aerial cable/aerial preamp. The latter sounds more likely, but I think that, rather than spend more time playing around trying to second guess things it might now be time to try additional low impedance grounding straps, perhaps some enhanced screening and the judicious application of some snap-on ferrite rings around some of the head unit cables.

Jeremy

 

The portable FM radio tests suggest that if the problem is interference, it's conducted, rather than radiated. Could it be as simple as bad power-line filtering?

 

Currently I'm coming to the conclusion that it may well be. It might also be something as simple as re-routing some wiring, or adding some low impedance grounds to key areas.

What seems clear is that, inside the cabin of the car, the radiated RF environment isn't bad enough to cause excessive interference in the FM band, so it seems unlikely to be wholly a radiated interference problem.

That leaves:

1. A conducted interference problem, getting into the head unit or aerial amp via the wiring.

2. Locally radiated interference from wiring close to the head unit or aerial amp.

3. Poor head unit or aerial amp design

4. A mix of any of the above.

Jeremy

 

OK , my newness is showing on this one. I have a GEN III w/nav. I do not see a radio antenna anywhere on this vehicle. I see one for the satellite (XM/Sirus), but none for the AM/FM radio.

I assumed (oh,oh) that it was in the windshield like most other new vehicles....

 

????? did you check the roof surface????
We dont have Sirius in Europe, but as I saw some pictures of US Package III all had roof antenna. I'm pretty sure Prius doesn't offer windshield antenna integrated.

 

I see it in the picture under your user name.

I can only assume that you see the antenna on the roof sticking up and are confused by the fact that it is so short. Or someone unscrewed and stole yours. The "shortness" is not the issue here, that is well tested and documented.

The radio antenna is the one you see on the roof in your picture.

For the topic in this thread, somewhere between that antenna and the speakers Toyota did a poor job with FM radio. Unusable to me and many others in the thread.

I am in the process of putting in an aftermarket add-on radio to the Nav. system but haven't found time to make much progress. Mostly I fixed my problem with an Ipod touch linked via Bluetooth for music and podcasts.

 

Personal feeling is poor head unit or wiring loom problem. Just using intuition. Although I don't think that the DAB is of poor quality but since it is connected to the Head Unit then I feel it is the head unit that is to blame.

 

What exactly IS a head unit?

 

Generally speaking it's a term now used to describe the dash mounted radio/CD/DVD/Nav system in a car.

Strictly speaking, the term used to apply to dash mounted car audio systems that didn't contain power amplifiers, just the receiver, CD deck or whatever. It was a way of differentiating between the control part of the audio system and the high power amplifier part, which was often mounted remotely.

Nowadays the term head unit is used to describe any dash mounted car audio system, irrespective of whether it has an internal power amp or not.

The Prius has a choice of three head units, the base model that has just a radio and CD, with built in power amplifiers, the JBL model that has an external power amplifier mounted under a front seat and the top spec nav model that has a big screen, GPS, rear view camera etc and a power amplifier mounted under a front seat.

 

As the owner of a new Gen3 Prius V w/Navi, all I can say is the FM radio is junk. Funny, as my last car an Audi A4 had virtually worthless AM reception. I will be making a very strong complaint to the dealership at my first service. I commute to Los Angeles daily, and cannot believe how bad the FM reception is in this car. It's completely unacceptable.
Toyota owes it's customers a fix or replacement.

 

Anyone who is having this problem make sure you remove all LED globes if you have fitted them after market.

Whilst there have been a couple of mentions of this briefly, let me reconfirm my testing today with LEDs. I have never noticed my radio reception to be much of a problem, but last night I installed LED's from "www superbrightleds". I installed Parkers, Map lights, Overhead light, door lights, rear licence plate lights.

This morning on the way to work I noticed that my radio reception was rubbish, drove in to my usual office underground car park and no radio reception at all.

Came up to the office, read this thread and went back downstairs and re-tested.

Turned car on....no reception. Because the car park is a little dark the parking light LEDs turned on automatically. Turned parking lights off completely and reception comes back perfectly. On/Off/on/off...direct correlation with parking LED's and/or licence plate LED's as these would have all gone on at the same time.

With Headlamps off then tested with Map Light. Turning map lights on and off, even one at a time had an impact on the radio signal. Not as pronounced as the Parking LEDs but still enough to be annoying.

Conclusion.....LED's stuff your radio signal confirmed. Ripping them out when I get home tonight and going back to bulbs......maybe this explains why Toyota didn't put LED's in originally.

For completeness......I have an Australian Model Prius (I-Tech) with Solar Roof and Navigation Head Unit. This equates to a Prius IV for those in the US.

 

GAM. these LEDs have (usually) an integrated constant current circuit inside, which probably produce the noise close to the FM band. Is AM band affected as well?

 

I agree, the switched mode current regulators in the LEDs, or, perhaps, the PWm lighting circuit drivers in the Prius, cause LEDs to emit a fair bit of noise. I'm pretty sure this came up earlier in the thread, as the most probable cause of some of the DAB problems that hsiaolc is having.

Jeremy

 

Lots of Cons on this thread - thought I would throw in a Pro. I've had a Gen 3 IV for a month and have not noticed any reception problems with the stock antenna. I just replaced it with a sharkfin from the PC shop and reception continues to be excellent. I was considering going to LED's and now have canned that idea.