THERE ARE SEVERAL INTERESTING THINGS ABOUT WRITING THE TROUBLESHOOTING COLUMN IN CA&E. First, there are problems that are pretty common to a lot of enthusiasts, and others that are pretty isolated and very strange. Going by the information you provide, I use my industry experience and knowledge to interpret what possible problems you're facing and try to offer direction and options to get you back on the road to enjoyment.
Second, this column is one of the few direct ways you can participate in this magazine and the one part that can't be written without your participation. I couldn't even make up questions to answer, since we reach a point in the industry where the only problems we encounter are on a level that would be helpful for other seasoned technicians to read in an industry publication, but a total waste of space in a consumer magazine. Industry mags have a lot of really good people contributing technical information already, so I find that I can learn more than I can offer since I evolved into the field of car audio education.
Everyone can use a source of education that pushes them further up the industry ladder. I enjoy being one of your sources and look forward to receiving your questions, and this latest batch was a real treat for me, since it included a couple of topics I haven't covered in the magazine. Keep the questions coming and thanks for the participation!
Q: I have one Alpine 600-watt monoblock amp pushing a single Rockford Fosgate 600-watt Power sub. I added a stiffening capacitor to my small system and got it completely set up and working. The other day it went completely out. I replaced the capacitor (at no charge), but even the new one won't work. I had it on a switch, so I thought the switch might have gone out (which is a major problem I've faced in the past) but the switch was still good. I replaced my 100-amp inline fuse but it still won't work. I charged the new capacitor and the only thing left to do is replace the wiring. I need someone to confirm my beliefs or give me a checklist before I replace 40' of 8-gauge wire.
Josh Hall
A: Capacitors are pretty straightforward devices. In this simple DC application, they're intended to store energy similar to the overall function of a battery, but at a much faster charge and release rate. They might fail over time as the electrolyte-soaked dielectric begins to dry out, but that can take a year or more. An electrolytic capacitor has a decently long lifespan, but not in a car's harsh environment. So I find it surprising that a new capacitor doesn't work, and as a result, I'd suspect a couple of possibilities.
First, you haven't mentioned the brand of capacitor, so it could be that you bought a cheap unit at a flea market with really questionable reliability. A new capacitor of any reasonable quality should have worked for at least several minutes. Don't bother to replace your wiring -- we can be reasonably sure that the wire itself is fine, although it might be undersized for your amplifier to draw through a 40' length.
Terminations are another matter, so you'll need to check the ground and positive connectors for a strong, secure connection. As a trick, I use the sense of touch to identify the possibility of a poor continuity: By pressing your fingertip firmly on a connection, you can uncover a "hot" connection. A resistive junction between connectors will produce a voltage drop that has no choice but to convert wasted energy into heat. Watch out, since some of these bad connections can get surprisingly hot. I've burned my fingers several times as I stumbled across one of these resistive "IR drops."
I also wonder about your wiring setup. A switch in line with a capacitor is a bad thing. First, it causes a resistance that won't pass the current without adding an RC (resistive-capacitive) time delay that crushes your goal of fast energy transfer through a capacitor. Second, you can't really confirm that your switch is good. In order to test the switch, you must have it connected in the circuit and attach a digital multimeter in voltage mode across the input and output of the switch. While the system is working, you should read zero volts across the switch, which I bet you won't. The reading will pulse up and down based on how much bass you're trying to deliver and at some point will be soaking up several critical volts of supply energy. You might even find from the fingertip test that the switch gets hot, revealing a loss of precious energy. Get rid of the switch.
The capacitor needs to be securely connected to the Alpine amplifier's power terminals, in parallel with the main power leads coming from the battery and ground. There must be no switches or fuses in series with the capacitor -- fuses are way too slow to add a safety measure or to do anything more than add more parasite resistance.
Your main 100-amp fuse needs to be in series with the main power lead, less than 18" from the battery's positive post. If you don't drive a bus, I suspect you can get away with much less than 40' of wire, keeping in mind that shorter is better. If you really need 40', I'd tend to go for 4-gauge wire to compensate for the losses. If your negative lead is running all the way back to the battery's negative post, you can save a ton of wire and reduce losses by connecting to a solid grounding point close to the amplifier's mounting location.
Q: Hello, I enjoy your mag! I have a TV tuner installed in my '95 Yukon. Is there a way or a product that can improve reception beyond the power diversity antenna? I have one on it now and I ordered another one to see if it works better. Are there any other tricks for better reception? Thanks a lot.
Chatmanlance
A: I am so glad we are only two years from eliminating analog television entirely. When the law passed by Congress comes into effect in February 2009, we'll officially be in the age of digital broadcast television. But that doesn't help you now.
One of the reasons we're shifting to broadcast HDTV is to help overcome some of the problems that prevent you from getting better reception. Let's start by examining how your system works, so you understand what you can do about it.
The originating broadcast signal comes from a transmitter that's putting out usually over 1 million watts (1 megawatt) of RF (radio frequency) power. The energy flows in line-of-sight form all over the terrain until it hits your receiving antenna. At this point, the energy that began in the megawatt range is now measured in microvolts. In contrast, the input of your amplifier is around 4 volts, which is millions of times less sensitive since the signal you're using is much more powerful in comparison.
Your receiver needs to pick a fragile TV signal out of a soup of RF interference from sources including other radio equipment, computers, machinery and even the sun's radiation. This requires a carefully tuned antenna that will electrically resonate with the TV broadcast frequency you're trying to receive while being dumb to the other junk. Ever notice that car radio antennas are always some multiple of around 31"? Same reason. The antenna needs to be very close to a fraction of a wavelength of the broadcast signal such as a 14 wavelength or 18 wavelength. It could be a full wavelength, but the length would be unacceptable on a vehicle.
A home TV antenna is a large device made of several "elements," which are then mathematically lined up to act like a telescope that needs to be pointed at the transmitting station or at least toward a city with several broadcast stations. These feed elements help to direct the signal toward the "drive element," which is the only part of the antenna that's electrically connected to your TV. If you live in the country, you might have two yagi (beam-style) antennas aimed in totally different directions to catch all the stations you want. The problem is that none of us wants a 6'-long beam antenna bolted to the roof of our car. Besides, that wouldn't work, since the moment you turn the corner, your antenna is now pointed in the wrong direction.
In automotive, we use omni-directional antennas that work regardless of the direction you are driving, compared to the higher-grade directional antennas used for fixed installation. The tradeoff is less range for more motion flexibility. We just have to put up with more static and dropouts. Some will add the "flying wing" antenna that you see on limousines to improve antenna effectiveness. Others will try adding a signal amplifier to boost reception, but both are only partial solutions. When you try to boost signal at the receiving end, you also boost noise. The net gain isn't very good.
Enter the diversity antenna system. Diversity is really two antennas with two independent receivers that use the philosophy that "just moving the antenna a bit might help." As you drive, a circuit called a comparator looks at both receivers, switching back and forth between the receivers to lock onto the one with the greatest signal strength at any point in time. By installing one antenna on the rear and another at the side or front, whichever way you turn there'll be a better signal on one of the antennas. Adding another diversity antenna won't help, since you don't have a comparator that will balance three antennas.
It's important to note that diversity isn't using two antennas to increase gain -- they don't add up. Instead, it's an "either/or" situation. Whichever antenna is receiving a better signal seizes the input until the other antenna can beat it. Installation of a diversity antenna system is about, well, diversity! You want them in two totally different RF profile positions, meaning if one is on the trunk lid, the other should be towards the front-left or front-right corner of the vehicle.
You would never want to mount the antennas close together, since this would defeat the whole diversity goal. Even different antennas, like a cell phone antenna mounted close to a radio antenna will cause interactions between the two. There's a technique for using dual antennas positioned closer together known as "co-phasing," which serves a different purpose. It explains why truck drivers have twin CB radio antennas on their mirrors. Co-phasing is not diversity, since the two antennas are simply paralleled together into one receiver.
When the signal from the two antennas hits the input of the receiver (the "front end") the phasing of the signals combines in a complex mathematical function. This causes the shape of the reception "field strength" pattern to change from round to oval, increasing range in the long ends of the oval while reducing reception on the narrow sides of the oval. Co-phasing allows you to point your car in the direction where you need the extended range, and the antenna interaction will give you maybe 30 percent better forward gain, while sacrificing about the same amount of sideways gain. In a sense, the antennas act a bit like a housetop television antenna, which is sometimes called a "beam antenna" for its very unidirectional nature.
My choice for broadcast TV in the mobile environment has been kicked up to the digital age with satellite. Yes, I know that any TV satellite antenna needs to be pointed exactly at the correct orbital position, but that is much easier to do than capturing analog broadcast signals lost in earthly terrain. I like the SpeedRay system and its smaller sibling, the T5 by RaySat. It's a slim platter that will sit discreetly on the roof of your Yukon and use its phased array antenna plates to constantly turn and focus on the satellite position as you drive. It's pricey, but if you like the fact that you can listen to Sirius or XM satellite radio anywhere, this is THE way to go since it works on any receiver. On my website, www.mobiledynamics.com/special.html, I have a video of a cutaway array that shows how it rotates and focuses. Come on into the hi-definition age if you're serious about video!