Re: Do cars with plastic bodies, like the Saturn, give bad radio reception?

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>>Do cars with plastic bodies, like the Saturn, give bad radio reception? > What would prompt that question? What properties of Plastic, or the >behavior of radio waves????

Actually, it's that car radios have always given me better reception than house radios have. Is it the antenna, the ground plane? What?

If you are thinking of "ground planes" for the antenna, provisions for >that are easily designed into plastic vehicles, just like on airplanes >- but ground planes are most important for transmitting. Yes, a ground >plane WILL improve reception, but automotive radio antenna are seldom >anywhere CLOSE to "optimized" so the lack of a ground plane would make >an almost inperceptible difference to reception.
Reply to
micky
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Typically better reception in the car, yes, but that all depends on the antenna set up. You can have a very good antenna at home, but one with a fault in a car. I've owned both. I'd like to build an AM loop in my attic to get better AM reception at some point.

I am very into AM radio, especially long-distance AM stations at night. I've owned cars where they seem to put no thought into the AM radio band, and it shows (sounds). Dad had a Chevy Trailblazer (2006?) where you could always hear the transmission or something interfering with the AM reception.

Reply to
Michael Trew

micky wrote: ===========

** Car radios rely on a tuned, vertical whip antenna that has a modest ground plane - the car body. This tends to work better than a small, ferrite loopstik - partly because the car antenna is normally *outdoors*.

Also, it is common for car radios to have a tuned RF stage prior to the frequency converter and IF. So three tuned circuits instead of the usual two.

FYI they normally used inductance tuning.

.... Phil

Reply to
Phil Allison

Wow.

The '72 Buick and then the '84 Chrysler and 88 Chrysler would get perfectly here in Baltimore WRC, 980AM, in Washington, DC, a station no indoor radio, even the fancy receiver, would get at all. (I've only lost interest in that station because it changed format.)

And for decades, one car radio after another, (maybe the Buick,) Chryler and Toyota, would get WAMU, 88.5FM, (American University in DC), perfectly, when only one inside radio would get it. Even now a much different Toyota radio gets WAMU usually perfectly, when the one inside radio no longer does as well. (For a while I was reporting to the WAMU engineer when reception was good or bad, and he got it good, but months later, it got weak again sometimes. (And like I say, that's the one radio that gets it at all.)

At one point a friend gave me a nice wood "box" designed to hold a car radio, an antenna, and a DC adapter, just for the sake of using a car radio indoors, but at the same time he told me that it didnt' work for him (which is why he was giving it to me). So it seems like the difference is the metal body on cars, all but a few cars.

The urls people have posted here (before electronics.repair was added) make clear that the ground plane in the car makes a difference, and that cars without one need a special antenna cable, but a) they're mostly pushed for CB radios, b) it's not at all clear that the special antenna is as good c) when shopping for an antenna, any with ground plane provision probably make note of it, but those without do not, afaik, warn people what is missing.

Reply to
micky

One other thing about the radio in the house is that some homes have so much metal in them , especially the aluminum siding and foil reflecting insulation that the radio signals have a hard time getting in to the house.

Reply to
Ralph Mowery

For AM radios in cars, the ground plane effect is almost nill. There is some capacitance coupling from the frame to the gound, but that plays very little in the AM band. The FM antennas are often built in the windshelds and the metal of the car does not com into play there either to ammount to anything.

To be much of a ground plane at the AM band you would need a plate of around 100 feet, 200 feet would be better. Just look at how tall the AM transmitter antennas are. Those antennas have about 120 wires as long as the antenna is tall burried in the ground.

Reply to
Ralph Mowery

This is the big difference in spectra that I looked at:

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Shorter wavelengths penetrate better.

Reply to
Frank

I have T1-11 siding, not alumininum As to foil clad insulation, I don't think so. I've been in the walls a little bit when I put a floodlight in the outside bedroom wall. House built in '79, not cheap but not the most expensive either. Plus there is a 6-foot wide window facing DC from the bedroom, where many of the radios have been, with aluminum window frames but the frames are not very big.

Reply to
micky

Only one car had the antenna in the windshield. A long time ago, I can't remember which.

So what can I do to get reception inside as good as what I get in the car? Especially FM. In the past year, reception for WAMU, 88.5 and C-Span, 90.1, seems to have gone downhill.

Reply to
micky

I beg to differ. Nobody seems to have mentioned the bane of all MF (medium frequency) reception, RF noise. A metal ground plane (car body) does a tolerable job of isolating the AM antenna from the noise generating ignition, black boxes, and gizmos. With a plastic body, the antenna will pickup more noise from the engine.

The typical car antenna is sometimes located as far away from the noisy engine as possible and connected to the AM receiver with RG-62/u

93 ohm low-capacitance coaxial cable. There is an adjustable capacitor between the antenna and the receiver input capacitance to resonate the antenna system. The coax cable capacitance and the receiver input capacitance act as a voltage divider. The more coax cable capacitance to ground, the less signal and noise arrive at the receiver. Choose your coax cable type and length carefully.

You can have a really sensitive AM receiver, and still not be able to hear much. The threshold of sensitivity is atmospheric and man-made noise. Note the graph. At 1MHz, the RF noise (mostly from thunderstorms) is huge. RF noise from neon signs, motors, sparking of any kind, etc just makes it worse. If you simply build a bigger antenna, or add an RF amplifier, you increase both the desired signal and the noise proportionally. If a receiver and antenna produce some SNR (signal to noise ratio), and I add more antenna gain, or more RF amplification, the resultant SNR will be the same. In other words, a bigger antenna or a "signal booster" don't buy you anything. The trick is to somehow improve the SNR, which is not easy. See various articles on the PA0RDT mini-whip antenna for clues:

Car AM radios tend to have the minimum sensitivity and RF front end gain needed to function in a strong signal environment. They're not made for digging signals out of the noise. That's NOT because AM car radios are made to be inexpensive. It's because the receiver is sitting next to a very noisy car engine. Were it designed to be as sensitive as an LF or HF receiver, all you would hear is engine noise. Try it. Build yourself a BCB (broadcast band) RF amplifier and attach it to your car radio antenna input. In most cases, you'll hear your engine, pump motors, and atmospherics quite well, but the distant AM stations will still be buried under the noise.

I don't have any suggestions to improve your mobile AM reception. Well, maybe the obvious suggestion to do what you can to eliminate, move, shield, or isolate sources of RF noise. If weak AM signals magically appear when you turn off the engine, the source of the noise is obvious. The problem is that you might do a wonderful job of noise reduction on your car, such as buy a diesel, but that does nothing if you're stuck in traffic and surrounded by other noisy vehicles. Notice that the ultimate noise generator, the all electric car, usually does not come with an AM radio. For example, Tesla will sell you an optional overpriced infotainment package that includes AM:

Vendors used to sell rubber grounding straps, that discharge any static buildup on the car body. That should get rid of some noise. However, I believe carbon doped car tires have largely eliminated the need for those straps.

So, to answer your question, yes a plastic body gives lousy AM reception if your engine belches lots of RF noise and your receiver is reasonably sensitive. If your receiver is stone deaf, it doesn't matter.

Good luck.

--
Jeff Liebermann                 jeffl@cruzio.com 
PO Box 272      http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

For in the house put up an outside antenna and feed it with coax cable.

Reply to
Ralph Mowery

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I built a variation of this theme and it worked well. At the time I was living about 20 miles from the Mexican border and the highly directional nature of loop antennas let me null out the Mexican power houses.

This is a simpler version that doesn't require building a frame:

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That one is more technical. I didn't look through all the links but onr method was to use ribbon cable. When you solder the ends you offset the conductors and solder them to the one next to it so you're forming one long conductor.

Reply to
rbowman

And for the best outcome, build in a swamp.

Reply to
rbowman

Mpffff....

Car radios are optimized for cars. Cars are tiny, noisy, poorly laid out de vices operating in a noisy environment where the primary expectation is goo d reception. So, the radio designers ignore such niceties as S/N ratios, se paration, bandwidth, and so forth for capture. As such, a car radio will r eceive reliably under conditions that would have a home tuner in full-mute. And were you to take that car tuner and connect it to your home system - a ssuming the system is reasonably good - you would be horrified at the resul ts.

Horses for courses.

Peter Wieck Melrose Park, PA

Reply to
Peter W.

rbowman wrote

But that?s for the transmitter, it isn't the best way to do an AM receiver.

Reply to
Rod Speed

That's odd. If you go to the NASA space museums, you see that the early 1970's satellites have all of this gold and copper looking foil around the satellite's lower regions. I thought that helped with transceiver communications.

Reply to
bruce bowser

Heat.

Peter Wieck Melrose Park, PA

Reply to
Peter W.

rbowman wrote: ==============

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** LOL

I have been using a 5 turn frame antenna *just* like that since the late 70s !!

My * tube AM tuner* has a transformer balanced input for use with a loop. Like the Carver TX-11b, it also has 15kHz audio bandwidth and low THD at 95% mod plus a switchable, sharp notch at 9kHz.

But the maker ( here in Sydney) did not suggest using a frame antenna in the handbook, nor had one been tried when I asked. His method was to run a fixed, single turn loop around a window.

The frame is better as you can orient it to maximise the signal or null an unwanted one.

... Phil

Reply to
Phil Allison

My 1986 Chevy C10 has a windshield antenna. Then again, it has many parts from a 1976 also (including the VIN and title). It's hard to say which year had that windshield; maybe both.

Reply to
Michael Trew

Thank you!! I think I'll try that first antenna with the frame. I can put it out of place in my attic, if I can make a run downstairs easily enough.

If I were to make the other antenna, do you think I could use my home's breaker box grounding rod for the antenna, or might there be electrical interference from the circuits and appliances in my home?

Reply to
Michael Trew

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