Removing the hood blanket and AM radio reception.

[03DOHC]

I'd like to remove my hood blanket, but have heard that it could cause interference to my AM radio reception. Is there any truth to this? I listen to the traffic report every morning, not to mention I enjoy listening to my local AM radio station on the way to work. Any and all input from those who've removed it would be appreciated.

 

[NastyWS6]

I don't see how it would mess up the radio reception, but i guess anything is possible

 

[KNGOBRA]

Umm, isn't that what the antenna is for..... :shrug:

 

[03DOHC]

huh? The antenna is for radio reception. The hood blanket is grounded and could act as an RFI suppressant. A few people have posted that they experienced decreased AM reception after removing the hood blanket, possibly due to RFI emanating from the engine and it's components. Remember spark plug wires? I know we don't have any, but back in the day, some caused RFI to the radio. RFI is radio frequency interference.

 

[Friendchicken]

The blanket is for noise insulation. The strap by the passenger hinge is a grounding strap to drain off the static electricity generated by air over the composite hood and friction by the blanket material. I've never heard of a charge generated by the combo above large enough to set off a fuel leak or a battery leak, but I'd hate to be the first example.


Edit: By noise, it is meant RF noise and audible noises. Also edited foot from mouth

 

[03DOHC]

The purpose of the winding you see on the factory antenna is to keep it from whistling in the wind. It is not large enough, by itself or even combined with the 1/4 wave FM antenna, to be resonant at any AM broadcast frequency.

 

[03DOHC]

A resonant 1/4 wave antenna for the FM broadcast band is approx 2 1/2' in length, which is what comes on our cars. A resonant 1/4 wave antenna for the AM broadcast band is about 340' long. There isn't enough inductive loading in the tiny antenna on our cars to account for this difference. Just an FYI.

 

[Friendchicken]

Thanks 03DOHC, i didn't realize it was that long. my bad

1/4 for FM is 30"? I'm not going to measure it...

 

[Friendchicken]

sorry for kinda off topic. is there any interior antenna on the market? I'd love to get rid of it on the outside for all kinds of reasons.

(and no, I won't buy one of those windsheilds with it embedded )

 

[03DOHC]

Originally posted by 98kobra
Thanks 03DOHC, i didn't realize it was that long. my bad

1/4 for FM is 30"? I'm not going to measure it...

The basic formula for a resonant 1/4 wavelength antenna is 234/freq(mhz). Therefore, 234/90mhz=2.6', which is close to the length of the factory antenna. That's close enough to work for frequencies you receive in the FM band, but would be way too short for AM reception. There has to be some method of inductive loading to get the AM band. Exactly how they do it, I don't know.

If you've ever taken apart an AM radio you'll see a ferrite bar wrapped with copper wire. That would be an inductive loaded antenna. It's a method of achieveing resonance. The factory antenna is what is called a resonant antenna, which means it's length alone is sufficient for reception.

I've built quite a few antenna's in my time, so that's why I know something about them.

 

[Friendchicken]

I think this is what you are looking for...


The size of an optimum radio antenna is related to the frequency of the signal that the antenna is trying to transmit or receive. The reason for this relationship has to do with the speed of light, and the distance electrons can travel as a result. The speed of light is 186,000 miles per second (300,000 kilometers per second).

Let's say that you are trying to build a radio tower for radio station 680 AM. It is transmitting a sine wave with a frequency of 680,000 hertz. In one cycle of the sine wave, the transmitter is going to move electrons in the antenna in one direction, switch and pull them back, switch and push them out and switch and move them back again. In other words, the electrons will change direction four times during one cycle of the sine wave. If the transmitter is running at 680,000 hertz, that means that every cycle completes in (1/680,000) 0.00000147 seconds. One quarter of that is 0.0000003675 seconds. At the speed of light, electrons can travel 0.0684 miles (0.11 km) in 0.0000003675 seconds. That means the optimal antenna size for the transmitter at 680,000 hertz is about 361 feet (110 meters). So AM radio stations need very tall towers. For a cell phone working at 900,000,000 (900 MHz), on the other hand, the optimum antenna size is about 8.3 cm or 3 inches. This is why cell phones can have such short antennas.

Complements of www.howstuffworks.com

 

[03DOHC]

You got it.

I've talked to a guy in Texas from California before by bouncing my radio signals off the moon. It's called EME, which stands for Earth-Moon-Earth. That's my other hobby.:-D

 

[Silver 03 Cobra]

I took off my hood blanket last weekend. The underside of the hood does not look good cosmetically. The structural members do not look very good. I also found that the backside of the liner has a foil liner that I'm sure is to deflect heat. I would still be willing to leave the blanket off but it just doesn't look good. I am planning on painting my liner.

 

[dmreitz]

03DOHC... one of the purposes of the blanket is definitely to block RF interference coming from the engine, so that AM radio reception is better. I guess the only way to tell how bad the interference is on your particular station, is to try it.

On a side note... I also think I need a new hood blanket. I didn't do the hood blanket mod in time and it is totally water logged. This is why I'm considering just taking it off as well.

 

[03Sssnake]

Originally posted by 98kobra
sorry for kinda off topic. is there any interior antenna on the market? I'd love to get rid of it on the outside for all kinds of reasons.

(and no, I won't buy one of those windsheilds with it embedded )

You could do the antenna delete and get Xm radio, puts and antenna in/on the back window.

 

[03rocks]

Its not even baseball season yet. Why are you so concerned about AM radio?

 

[03DOHC]

Thanks Tetge.:beer:

 

[Cobra'03]

Originally posted by NastyWS6
I don't see how it would mess up the radio reception, but i guess anything is possible

I do - the Cobra hood is non-RF suppressive due to its composite construction. The factory liner has a foil backing and a ground connection to the body to suppress radio freq interference. I posted previously on that issue and the antenna length needed for optimum reception, which i estimated as 31" - close enough to )3DOHC's wouldn't you say?

 

[luvMy2003SVT]

Aren’t you worried about the heat cracking the paint on your hood?

 

[kens03cobra]

Originally posted by 03DOHC
You got it.

I've talked to a guy in Texas from California before by bouncing my radio signals off the moon. It's called EME, which stands for Earth-Moon-Earth. That's my other hobby.:-D

Dan, whats your call? Do you have an operational station at this time?