Weak FM radio reception in 2010 Prius?

Alas, I'm afraid that fitting a longer antenna doesn't fix the problem, in fact it makes it slightly worse.

I fitted a long (greater than 2ft) whip to the Prius antenna base, but the results just reinforced my view that the problem is a mix of poor radio front end design plus a high EM background from the car.

Jeremy

 

Should have read this theard before you went and did the fitting. I was going to do the same too but after I read this theard I realized there is no point because the longer antenna only boosting the noise.

 

I have dealt with RF systems for years, and from reading these posts & others, the problem appears to be between the antenna and the radio. There's evidence here of a bad ground at the antenna base or perhaps a damaged coax cable or a bad connector on the coax cable. Between the antenna and the coax cable, there should be a balun, which makes the connection between the antenna and the coax cable more efficient, and this might be damaged. The balun might be built into the antenna housing. Unfortunately, there's no alternative to removing the headliner and other interior parts to check the antenna connection and coax cable. Replacing the antenna might help.

BTW, I have good FM reception in my Prius, as good as in my Acura with a 2 1/2 ft mast antenna.

 

Definitely no cable damage on mine, plus the antenna pre-amp seems to be working OK (the Prius uses an active antenna set-up).

I'm not sure why you'd want a balun (BALanced to UNbalanced converter) on a system that uses an unbalanced antenna (essentially a loaded monopole on a ground plane) feeding an unbalanced transmission line (the coaxial cable). Anyway, the impedance conversion is done at the antenna base by the pre-amp, so the feed in to the cable should be a good match if the amp is working (mine appears to be).

The issue isn't just one of poor signal strength, I think just about everyone who's heard it will confirm this. The primary problem seems to be the radio producing artefacts when in FM mode. These manifest as typical multipath interference, indicating that the receiver front end just isn't good at remaining phase locked to the strongest signal in some circumstances.

The EMI stuff is speculation, based on some intelligent guess work as to likely causes within the receiver front end. Certainly I've seen similar effects produced by interference products confusing the ability of a receiver to lock to the tuned signal effectively in the past, which is why I remain fairly sure that EMI is a contributory factor. There's no doubt that the radio itself is also pretty poor, although those blessed with a good FM signal in their area may never really notice it.

In my case, I know that the signal strength locally isn't great, although the radio in every previous car I've owned has performed OK. The Prius FM radio is clearly unable to operate in these marginal signal conditions as well as a "normal" car radio, in fact in my case the radio is unusable on my commute to work, as the signal is buried beneath interference for much of the journey.

Jeremy

 

I concure to almost everything you've said. We have tested all new Prius HUs and they are all the same. Same radio problem. My bro works for Toyota dealer and get access to new Prius everyday and he knew of this problem and has been trying to see if there are just one prius that doesn't have this problem. They all do.

Now. As for poor radio. I am not sure if it is poor radio or just something in the HU thats causing it. Because like I said I've upgraded to the DAB and that also have problem. I think it is unlikely that they have produced poor radio and DAB unit at the same time.

 

Apparently, the problem is not fixed by substituting aftermarket radios. What signal-chain components remain after you swap out a radio? (and a properly tuned antenna, as I and others have reported doing?)

 

After installing my new Pioneer HU, my FM reception only got a tad better. I was a little disappointed. But after the post about the power antenna needing to be hooked up, I just went back into the dash and presto, what a difference. Not only did the signal clear up but the volume improved greatly. Now my favorite station comes in great even behind a 3500' mountain and inside my garage. Here is a [ame="http://s449.photobucket.com/albums/qq215/spideyatwork/car/?action=view&current=sound.flv"]video file[/ame] but the quality is not that great but you get the idea. Thanks all for pointing out the antenna amp needed to be powered!
I guess one question would be: is the OEM units powering the antenna properly?

 

I hooked up my antenna (amp) to the antenna/amplifier "trigger" output on my HU. Now the manual says this "trigger" has a 300mA rating. What do you think the antenna amp would draw? Anyone think I might be hurting the HU by hooking things up this way?
Thanks,

 

Well, I tore the dash apart again and measured it for myself. 36-37mA. No problem.

 

I've been trying to pin down the primary cause of the FM radio problem and think that I've tracked it to EMI from the cars systems. I wasn't able to get anything meaningful from doing a crude sweep around the car with an RF spectrum analyser, other than to confirm that the car does emit a fair bit of fairly broadband electrical noise. This didn't really help much in trying to determine whether the radio or the car is the principal cause of the FM problem though.

This evening I drove out to an electrically fairly quite spot in the countryside, one where the FM signal is known to be OK from reception quality in other cars, although still perhaps 30 miles or so from the nearest transmitter. I parked the car and with it "ready" but not in forward or reverse and without the ICE running there was a fair bit of background noise on the radio.

I then turned the car off and restarted it in "accessory" mode (press Start without putting your foot on the brake). The result was a near-perfect FM signal with no hiss or background noise at all. I repeated this several times, and when the car is in "Ready" mode, irrespective of whether the ICE is running, it emits, or induces, enough electrical noise into the radio to seriously affect reception.

The radio may be partially to blame, but it seems clear that the car is very nasty in terms of RF emissions. I've searched around for some sign of EMC certification but so far I can't find anything. My guess is that the Prius may not actually have any formal EMC approval, other than the very crude test requirements aimed at controlling ignition noise from ICE powered vehicles.

If this is the case, then it lends credence to the rant by Steve Wosniak regarding EMI induced runaway and system failures and needs investigation by Toyota. The FM radio interference problem may just be the tip of a rather nasty iceberg, waiting to catch us out with further unexplained EMI related problems.

If I get the chance, I'll try and put the car into the EMC chamber and do a broad band sweep. My guess is that I'll find that it's a pretty hostile EMI environment anywhere within a metre or two of the main systems and their wiring.

Right now, my only wish is that there was a way for consumers here in the UK to get this resolved by Toyota. I've taken advice and it seems that as the car is primarily for transport, the poor performance of things like the radio isn't a valid reason for getting things resolved via the law (the car still works OK as a transport device).

Jeremy

 

This is very intersting stuff. Why would the EMC be so different in this car than in the previous model (where there doesn't seem to be the same level of radio interference)?

 

To be honest I'm not sure. I had a 2005 Gen II Prius for three years, and although the FM radio reception wasn't great it was much, much better than the reception in the new car.

I'm guessing that Toyota haven't paid enough attention to screening on the new Prius. It's noticeably different in layout under the bonnet (hood in US-speak), plus they've separated out the radio and audio system from the rest of the car s systems (on the NHW20 the radio seemed to be tightly integrated into the MFD).

It may be that Toyota have also done some "value engineering" (read "cost cutting") on the radio components, which has resulted in the radio being more susceptible to interference.

The neat thing is that the test I did is easy enough for anyone else to replicate, perhaps to show a dealer that there really is an FM radio problem on this car. Whether or not Toyota face up to the problem and fix it is debatable, my guess is that any fix is likely to be way too expensive for Toyota to initiate without some serious pressure from the marketplace.

I know of one lost sale as a direct result of the radio problem, a colleague who ordered a Prius a few weeks after me. He had a ride in mine when I got it, was appalled at the rubbish radio reception and immediately cancelled his order. My guess is that others will do the same unless Toyota fix the problem.

Jeremy

 

Jeremy,

Not to doubt your data, far from it. However, there's this issue about noise floor and signal to noise ratio.

OK. Take a random boom box radio, running on batteries, place it in a field with a 40 foot antenna. You're going to pick up radio stations 100 miles away. (At least in part because of that 40' antenna!)

There's noise. There's always noise. At 100 MHz in the U.S. FM band, unless you're running around with liquid-nitrogen cooled RF preamplifiers, the noise flloor is from the transistors in the radio itself; thermal noise, shot noise, etc. But, with that 40' antenna, the signal's a lot bigger than the noise, so, with a big SNR, the boom box is going to have a good time.

Make the antenna 12 inches long, doing what's necessary to make an impedance match. There's a lot less wire out there; the signal level drops, the noise doesn't really change; and now stations 40 miles away or less can be heard.

Make the antenna 3 inches long. So, then, now you need to have a station within two miles to be heard. In each of these cases the SNR is being reduced.

Cut the antenna off. Lousy signal to noise ratio. One will still get something because, well, radio signals will leak in. But one will only hear, typically, extremely near by stations. (Kind of like people who pick up AM radio stations with their teeth. The teeth make a lousy antenna, but, if they're standing withing 100 m of a 1 MW radio station, it's amazing how they can hear the local rock bands!)

Now, put the boom box in the Prius. OK, the Prius is an RF noise emitter; anything that has digital logic and modern microprocessors is going to emit noise, that being life. There are standards for how much noise random electronics can emit; if you're in the EU, that's the EN5022 standards. One sec while I check that number.. Yep, that's it.

One of the ideas behind EN5022 is that the level of radiated emissions is controlled so that people's use of commercial radio and TV will not be impacted. The EU (and lots of other places) take a very dim view of manufactures who violate those standards and the fines, well, they're tremendous. And it's not that complicated to check, if one is a regulator: Stuff the car into any of hundreds of testing facilities with RF anechoic chambers and a turntable, switch on the turntable and the car, and hit the button for the automatic test. An hour or so later and one has results. (Yes, I've watched this happen, although admittedly not on a car.) If one does not pass EN5022, then one does not get the CE mark, and it then becomes very difficult to sell into the EU.

The U.S. has similar standards with the Federal Communications Commission. My brain wants to say part 97 of the rules, but it's been a little bit since the last time I was in a chamber.

So, low level emissions, yes. Noticeably interfering with very weak signals - yep, that too. Interfering with healthy signals? Now, that would be unusual.

So, there's possibilities.

1. The signal is weak because there's something wrong with the antenna, the connector at the bottom of the antenna, the coaxial cable (don't laugh, I've seen examples. And a cable that's pinched to the point of breaking is not unheard of.), bad connector at the other end of the coax (could be inside, I've seen real examples of badly built connectors, complete with cold solder joints or worse), or any problems in the connector assembly getting into the radio.
2. Bad ground somewhere. Especially around the antenna. If the shield at the antenna end isn't properly grounded but is floating, the signals can be badly attenuated.
3. Conducted emissions. OK, this car passed EN5022 in order to get into the UK. And if there are high RF currents floating around, well, wires are a good way to transfer energy from point A to B. However, in getting from A to B, given that (I guess) most wires in a car aren't shielded particularly, any wire carrying RF would tend to radiate same, too, and violate EN5022.

I'm a ham radio operator, ex-Navy aviation electronics technician, and an electronics engineer. There are tons of ways to test what you've got to find out what's going on. One could stick a 6" wire on a spectrum analyzer and see the local RF energy of a radio station. Then, if one stuck the radio end of the coax into the spectrum analyzer and see if the signal was severely attenuated. One could attach a 'scope probe to the spectrum analyzer and verify that the signal was getting into the radio internals (after taking the cover off the radio, natch.) There are things called time-domain reflectometers that, when attached to the radio end of the coax, will show every impedance bump along the length of the cable, not to mention the quality of the connection at the far end and what the impedance would be out there. And this is what occurs to me off the top of my head.

Twenty years ago before radios became throw-away items your random TV/Radio repair place stood an even chance of having a spectrum analyzer in the shop; they would certainly have had equipment to measure the sensitivity of a radio and verify its operation to manufacturers' specifications. Nowadays I get the impression is that these people are lucky to own a voltmeter and "repair" probably means throwing the old one into the trash and installing new.

What you need to find is an old geezer, retired, who shows up at his TV/Radio repair shop on the edge of town twice a week in order to get out of his wife's hair. He's probably got all his old gear; it works; and he putters about fixing the odd radio that his (mainly elderly) clientele shows up with. He'd have you sorted in a half hour.

In the meantime: Figure out how to get that antenna off and start checking coaxial cable. You want to ring it out with an ohmmeter for starters and check for shorts from the center to the shield.

Sorry to rain on your parade, but I don't think it's an RF noisy Prius.

Although I might guess at one other possibility. This is the UK and, if the understand the posts correctly, you're all using a newer radio system that involves spread spectrum techniques and digital encoding.

The trick with digital encoding is that, unlike carrier-based FM, the fidelity of the received signal is not exactly a requirement. One is not looking at whether the signal is received with a pretty pulse shape or whatever; rather, one is looking to see if a particular signal is a one or a zero. Or, if one is using a bunch of symbols, whether the received signal is one particular symbol or another. The general idea is that one has a constellation of signals and one attempts to make the signals orthogonal in some sense from each other, so a given amount of noise affects all the signals equally.

Say that one successfully pulls this trick off. If done correctly, this would mean that the overall signal level could be reduced in amplitude because, well, one isn't worried about fidelity all that much, just whether a received symbol is one particular symbol or another.

This would work well, say, in a house with few if any natural EMI emitters. But, if one has a car like a Prius (or any other type of modern car, I would hazard), it's possible that the reduced signal level would run afoul of the emissions of meet-the-EN5022-standards Prius.

If true, this is not exactly a failing of the Prius, but, rather, of the standards committees. EN5022 was created primarily to protect private radio and TV receivers in the home. It may be that cars were not part of the equation.

KBeck.

 

Help me out here. It's been 50 years. What kind of noise does an FM discriminator respond to, and how does the noise manifest itself in the audio? Are we hearing the dithering of clock signals?

 

KBeck,

I've already been around the car with a state-of-the-art RF analyser, in a relatively EMI free environment. The plan was to put the car in the EM chamber and do a full set of hemispherical emission measurements from DC to a few hundred MHz, but the inability to ensure that the car behaves consistently during the test makes this of limited value (I don't have the means to force the ICE to stay on, for example).

Your assumption about the radio isn't correct, this is a plain vanilla FM radio operating on the same VHF band with the same modulation and stereo encoding as you have in the US. The DAB issue that one poster has on here is related specifically to two known interference sources on the Prius, one of which may well be the result of using aftermarket LEDs in place of the standard incandescent lamps.

I agree that the EMC standards applicable to cars weren't written with a car like the Prius in mind. My guess is that this is at the heart of the problem - the car systems design team have met the EMC requirements, yet the radio is still affected by stuff that the standard wasn't designed to control.

BTW, just in case I seem to be an amateur without RF knowledge, I used to be the Head of Type Approval for all UK maritime radio, navigation and radar systems. It's my signature on the EMC approval and Type Approval certificates for a lot of the radio stuff driving around the Worlds oceans.............

Jeremy

 

Waiting on our Gen III w/o nav IV... next week.

What % of gen3 have this prob? I've read all pages, understood most ex the real Radio heads replies but appreciate their expertise.
:music:
We will pay attention to this issue during the inspection prior to accepting the veh! Worth while to reject it just for it? :fencing:

What other checks of a new veh should we do?

tia

 

If you can get past the drag, and the geek/ugly factor, you can go this route:



I'll have to post a pic of the one I had on my ford exploader back in 2003. It's call a screwdriver antenna. Now THAT'll get you some coverage

 

I'm pretty sure the issue will be magically fixed on the 2011 model.

 

Jeremy, my sincerest apologies for talking under your head (as compared to over).

But the whole business bothers me. I've got a 2010 Prius III with a JBL Satellite/FM/AM radio in it. I don't seem to have any problems picking up stations on the road, at least no worse than the last couple of cars I've owned.

On the other hand there's you and a bunch of other bitter owners whose radios have severe interference present and bad reception.

OK, let's try it from the top:

• Bad Design Hypothesis: All the radios of this type sold in Priuses in the UK are like this. Sounds odd to me: Are they all that bad?
• Broken Hypothesis #1: Bad antenna to radio connection. This might also include a bad antenna amplifier. Low signal amplitude at the radio interior means any old noise generator makes things sound bad. Would be true on both sides of the pond, and there are US owners complaining, too, I think. I suppose this might also involve bad radio internals, at least in the front end, but I'd guess that would attenuate both noise and signal.
• Broken Hypothesis #2: It really is EMI, but it would mean that your car and mine have a significant difference in emissions. That implies something is wrong somewhere - bad ground, bad transistor somewhere, EMI filter capacitors missing, blown, or not soldered down correctly, etc. Bad construction at the factory, somebody forgetting to clean off the paint before bolting down a ground somewhere? If true, a failing Prius and a non-failing Prius would show real differences with any kind of reasonable analyzer. And the very devil to find and fix. Maybe, with the right kind of UHF sniffer, this could be localized to a particular spot. Hmm.. One thing the Prius has that other cars don't have is serious DC-DC switching around the motors. Off the top of my head that'd be an obvious EMI generator. Somebody forget to screw down a shield on the high voltage cables?
• Broken Hypothesis #3: Large conducted emissions into the 12V of the radio? This goes along with the idea of non-proper grounding/shielding somewhere. If it's big enough.. Well, I used to own a (I think) 100 MHz current probe. That would show this kind of thing. Long gone with all the lab moves.. But if there was something, then a 200 MHz+ 'scope connected between car ground and 12V should show some pretty interesting hash on the 12V power near the radio. Hmm.. Putting a 1 MHz ferrite on the power/audio signals just before the radio might have interesting results. If it makes a major change in the received signal, that would be a sign of something.

For the first and second problems a spectrum analyzer should show either a ton of EMI at the antenna connector just before the radio or a vastly reduced FM radio signal. For the last one a 'scope should suffice, I think.

Comments?

KBeck.

 

There's certainly a fair bit of RF being emitted by the car, well up into the couple of hundred MHz range, I confirmed this with a simple (and admittedly crude) spectrum analyser sweep around the car. Whether this is enough to cause the radio reception problems I'm not sure, but it's probably a contributory factor. My crude radio reception test with the car in "ready" mode or in "accessory" mode tends to confirm this - the higher radio noise level when the car's systems are active show that it is contributing to the problem somehow.

I think that local FM signal strength plays a big part in the problem, too. Where I live the signal strength isn't that great, although it was perfectly adequate for giving noise-free FM radio reception on every other car I've owned in the past ten years. The Prius is so bad in my area as to make FM radio unusable on my daily commute, so for me it seems like a big problem that is specific to the Prius.

There may also be a great deal of variability in the standard car radio susceptibility to EMI and, perhaps, in the RF spectrum emitted from, or induced by, the cars' systems. One thing that I got used to when dealing with EMC problems was the big differences we'd see between two seemingly identical bits of equipment. Often something as subtle as a slight change in the gap around a component case could significantly change the potential for EMI. It maybe that the Prius has similar variability.

I don't know whether or not the interference (if it is the cause) is more likely to be conducted or radiated. I'd take a guess, based on the comparison between the relatively noise free AM reception and the grossly affected FM that it's radiated noise, at frequencies well above the AM band. This fits with what we'd expect from all the high frequency stuff in the car, plus the limited EMC requirements that the car has to pass, which are weighted against lower frequency impulsive emissions.

Some have reported that a head unit change has improved reception, which tends to indicate that the radio itself may be at least partially to blame for the problem. My guess, based on everything we seem to have gleaned so far, is that it's a combination of interference from the car plus a radio design that's more susceptible to interference than it should be when trying to receive a signal with a lower than average strength.

My plan is to wait for a while and see if one of two things happen. Firstly, Toyota might respond with a fix (if they ever acknowledge that there's a problem). Secondly, as more people fit after market head units I may be able to get an idea as to which, if any, offer improved FM reception. I don't want to spend a lot of money just to find out that it doesn't fix the problem, neither do I want to spend money fixing what I believe to be a Toyota problem.

Jeermy