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EE audio help needed
I've been arguing with the Toyota dealer over the crappy radio reception in our new Highlander. This unit has the worst reception of any vehicle we've driven in the last 10 years and the dealer says it's normal. Many channels that we have had no trouble pulling in with Fords, Dodges, Jeeps and Subaru's in our driveway fade out within 10 miles of the house in the Highlander. Even the Toyota Tacoma loaner they gave me had no trouble pulling these stations in. Others on Edmunds.com have also complained about the crappy reception in the Highlander. Anyway, they faxed me the specs for the factory radio. Can anyone tell me if these tuner specs are good? The factory specs list an AM sensitivity of 34 dBu or less and FM sensitivity of 14 dBu or less. Then it has something called "Electronic Tuning Sensitivity Distant" for AM of 40 +/- 5 dBu and FM of 24 +/- 6 dBu.
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Those specs are not all that good. I don't know how they compare to other car radios, but I do know how they compare to my good amateur radio receivers and they are not even in the same neighborhood.
I had an Audiovox stereo in a car a few years ago that had terrible sensitivity. I bought a signal booster for it and it completely cured the problem. It just plugs into the antenna line and connects to 12VDC. It cost about $30. They are probably available at auto parts places and on ebay.
I don't know if they still do this, but it used to be quite common to have an unlabeled adjustment screw on the radio to "peak" up the antenna for AM reception. The antennas used for the AM band are quite a bit shorter than optimal, but you can't make them too big on a moving vehicle. So, this peaking adjustment tunes up the system to do the best it can. If this adjustment is not optimal, then it can make the receiver seem as dead as a fencepost.
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I had a radio in a Toyota 4Runner we had in the fleet a few years back with the same problem.
The people at the stereo shop I deal with said it was designed for poor reception. The problem in Asia is not pulling in distant stations, but rather filtering out the cross-channel interference, so they intentionally de-tune the radios to minimize the problem.
It wasn't a great radio anyways so I just changed it for an aftermarket stereo, better sound, better reception and a happy employee, all for $200 installed.
Best of luck.
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The small amount of research I've done indicates that lower sensitivity numbers are better, but the aftermarket units all seem to be rated in db F. How does that compare to db u? Many of the aftermarket numbers are less than 12 db F.
I'll look into an antenna booster and see if there's some sort of adjustment on the radio. Thanks for the tips!
We'd really like to keep the oem radio since it looks good and is easy to operate with big, well laid out controls. Plus it has cassette and CD built in. But if we have to go aftermarket we will.
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I have the same issue with my 99 F350 and 95 Grand Marquis, but not my 01 Crown Vic. AM is so bad in the two vehicles that I cant listen to it some days. FM isnt that bad in the truck, but is terrible in the 95 GM. I am in the same boat, I dont want to replace the radio in the truck because it looks good as it is, and a replacement would be only half the current height. The Grand Marquis though, there is no possible way to replace the radio without rewiring the entire audio system. The radio is actually in the trunk behind the seat, the head unit in the dash is just a tape player and controls. All the speaker wires run from the trunk.
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taheide brings up a good point, the newer NA vehicles all seem to either run what is called a one and a half or double DIN radio, the old regular size radio is called a single DIN size.
They sell both oversized radios, and also adapters, one of several of fleet's trucks have upgraded stereos installed in them, the adapter takes up the additional size by adding a little cubby hole beneath the radio to fill the dash opening. One of them has a double sized radio in it with a huge screen that includes a GPS navigation system.
My dealer tells my the move to non-standard sizes was an attempt by the manufacturers to capture more consumer money. By making non-standard openings in the dashboard, or remote radio installations, the consumer was more likely to spend the money for a FACTORY upgraded stereo than an aftermarket one.
Best of luck.
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dBu means Decibels above a microvolt. I have no idea what dBF means. Lower numbers are better if you are not comparing apples and oranges. I will do a little more digging. But that is for my own education.
34 dBu means that it takes about 25 microvolts of radio signal to generate an acceptable audio signal. This is normally accompanied by a resulting signal to noise ratio which defines how much signal you have compared to the noise or static in the background.
A very good radio receiver will be able to detect a signal on just a few microvolts of signal. In some modes I can get by with less than one microvolt, so 30 is not a particularly good number. AM and FM will generally take a few microvolts for a good audio signal.
I still think that the preamplifier/signal booster is the least complicated way to solve the problem. I have heard of some systems that will disable large sections of the car electrically if the radio is removed from the integrated electrical system. On my Hummer, the radio is connected to the On-Star, GPS, and who knows what else. The other interesting point about the Hummer is that the radio antenna is only about eight inches tall, but the radio is very sensitive.
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OK, I found the answer, but it is not an easy conversion. dBf means 1 dB relative to a femtowatt or 10e-15 watts.
To further complicate the issue you need twice as many dB difference for voltage measurements to be on equal par with dB related to power (watts).
On a low impedance transmission line I normally use dBm which is dB relative to a milliwatt. A milliwatt is a trillion femtowatts. A good receiver will be capable of sensitivity in the -110 dBm range. That is 10e-11 milliwatts or 10 femtowatts or 10 dBf. This is compatible with the sensitivities that I found on JVC, Pioneer, and other high quality receivers.
So 10dBf is equivalent to 0 dBu or 1.00 microvolt. At 34 dBu on AM, your receiver in the Toyota will take 25 uV to give you a good signal. That means that the Toyota receiver will have a dBf sensitivity of around 24 dBf which is quite low compared to the aftermarket radios. On FM the story is a bit better, but the radio will still be around 17 dBf in sensitivity. So, the comparison specifications back up your observations.
Most preamplifier/RF boosters will give you at least 10dB and probably closer to 15dB. That number subtracts directly from the 24 dBf sensitivity to put the radio right into the 10dBf range which is good compared to the aftermarket radios.
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The aftermarket AM/FM/CD that came with my Samurai will not pick up the 50,000 watt AM station that broadcasts from 30 miles away, but it gets any FM signal in the area.
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Here is something funny. When I was driving through west virginia, I was getting WLS AM much clearer than I can get it being only 50 miles from Chicago!
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