AM vs. FM Radio

[CFP387]

In your opinion, what are the pros and cons of AM versus FM radio?

AM Radio pros:

• Travels farther at night
• Most stations have higher wattage outputs
• Where the real music was first played and where it still sounds good.

AM Radio cons:

• Sometimes a weak signal around power lines
• Lightning makes the signal scratchy
• The signal can be off a few kilowatts during sunrise and sunset times.

FM Radio pros:

• It's in stereo
• The signal is strong no matter what time of day
• More variety of music on more stations

FM Radio cons:

• A lot of trash talk and untasteful music
• Not much (if any) news coverage
• Hardly ever a mention of the call sign or (real) dial location.

Obviously, I'm an AM radio fan. I enjoy listening to stations at night that a far away that really have a good signal. AM stations in North Carolina that push around 50,000 watts can be heard from Maine to Florida. Why does AM radio travel farther at night than daytime? Why does lightning effect the AM signal and not FM?

 

[n3ijw]

Simply put, the FM broadcast band which is in the VHF spectrum between 88-108MHz has much different propagation characteristics than the AM broadcast band which is in the medium wave spectrum between 530KHz-1.71MHz.

The long, long wavelengths in the AM bc band are well suited to long-distance groundwave and skywave propagation and can often be heard thousands of miles away, depending on everything from transmitter power to frequency to topography to time of day to the number of sunspots (both of which have an effect the reflectivity of the ionosphere at those frequencies).

In contrast, VHF frequencies tend to simply travel right through the ionosphere - but they can still be propagated long distances by a phenomenon known as tropospheric ducting, which occurs when there is a temperature inversion - a cool layer of air on the ground trapped under a warmer layer of air above. FM signals can travel hundreds of miles by bouncing along this refractive temperature boundary.

AM reception is more susceptible to electrical noise such as static and lightning as they are AM emissions by nature.

hopefully others can elaborate further, but this is a start

 

[N_Jay]

Three major differences:

1) Frequency
AM Broadcast band is MW 530 to 1710 kHz
FM Broadcast Band is VHF 88 to 108 MHz

Affects propagation and noise susceptibility

2) Modulation
AM is "AM",
and
FM is "FM"

Affects noise susceptibility and fidelity

3) Bandwidth
AM is 10 kHz per channel
FM is 200 kHz per channel

Affects fidelity and capacity (second channels, stereo, etc.)

Its like comparing apples and oranges.

Or more like apple sauce and orange jello! :lol: :lol:

As for the content of AM vs. FM, that is all about the economics.

One question. Just what is "real" music, and under what conditions do you think it sounds better on AM broadcast? :roll:

 

[Grog]

Then there is satilite radio, where you have "real" options Alas, no AM :lol:

 

[CFP387]

One question. Just what is "real" music, and under what conditions do you think it sounds better on AM broadcast?

"Real" music (a term coined by myself) is music from 1959-1979 that was originally on AM stations. You have to agree that the same song will sound differently from AM to FM. Especially on AM stations that haven't changed any broadcasting equipment in years, the music just seems to have more natural base (compression, maybe?) to it than FM does.

We have a local AM station that, until just recently, was still using glass tubes in their tramsitters. After the new owner had bought the station, he upgraded the transmitters and the station just doesn't sound as good as it used to.

 

[N_Jay]

"Real" music (a term coined by myself) is music from 1959-1979 that was originally on AM stations. You have to agree that the same song will sound differently from AM to FM. Especially on AM stations that haven't changed any broadcasting equipment in years, the music just seems to have more natural base (compression, maybe?) to it than FM does.

We have a local AM station that, until just recently, was still using glass tubes in their tramsitters. After the new owner had bought the station, he upgraded the transmitters and the station just doesn't sound as good as it used to.

Its not the transmitter that sets the stations sound, its the compressor/limiter.
The base you like is probably just a lack of highs and a overemphasized low/mid range.

Listen to those old 45s on a decent stereo, and they will sound better than AM or FM, (but much closer to FM)

 

[blinddog50]

Then there is satilite radio, where you have "real" options Alas, no AM :lol:

Satellite is the only way to go!
No more waiting for John Boy or Sheri to shut up long enough to play a song.
No static, no fade out.
It lacks the adventure and mystery of searching the dial, but just for pure listening pleasure while you're riding it can't be beat!

Ain't no AM or FM, just pure digital.

 

[CFP387]

Satellite is the only way to go!

I've only heard good things about satellite radio, but I guess I'm a little old-fashioned. I'll stay with AM radio and if in time they sink, I'll sink with them.

 

[Thayne]

Some AM stations are now simulcasting digital, but IMHO I don't think it will catch on. (You can't buy many receivers that will decode it)

 

[CFP387]

A few more questions:

Why do most AM stations not transmit in stereo, while most FM stations do not transmit in mono?

All things considered (in a perfect world) which frequencies in both AM and FM will most likely travel the farthest at any given time? Would it be frequencies at the far ends of the spectrums or dead in the middle?

How can FM stations in the same market have frequencies so close together while AM stations in the same market are placed farther apart?

 

[Thayne]

1. Because the FM band developed as a "High fidelity" medium, and stereo was a natural prgression of it; hence no demand for AM stereo.
2. As long as you stay in THIS world, AM or FM is(Theoretically) irrelevant to distance. Distance characteristics are determined primarily by wavelength (Frequency); but of course changes in antennas, receivers, ERP, (power) can overcome nature to a certain extent. Of course, if you are talking about outer space, it's out of this world, DUH
3. Actually the AM band only goes from about 530Khz to 1700Khz so the stations are actually closer together than the FM band (88-108Mhz)

Now I would like to know why I went to the trouble of writing this? :roll:

 

[CFP387]

Now I would like to know why I went to the trouble of writing this?

Because there's no other thread on this site dealing with AM or FM radio!

 

[N_Jay]

Why do most AM stations not transmit in stereo, while most FM stations do not transmit in mono?

Because FM has sufficient bandwidth for secondary channels. Only recently has the technology become available to provide AM stereo.

There are few AM stereo receivers.
There are few FM mono receivers.

All things considered (in a perfect world) which frequencies in both AM and FM will most likely travel the farthest at any given time?

AM will go further but not by as much as most people think. It has more to do with WHERE it goes. Higher frequencies travel more in a "line of Sign" manner, lower frequencies bend around the earth more.

How far it goes is also a factor of the amount of noise. There is more noise in the lower bands.

Would it be frequencies at the far ends of the spectrums or dead in the middle?

NO.
And what spectrum are you speaking of? Each band or the radio spectrum over all?

How can FM stations in the same market have frequencies so close together while AM stations in the same market are placed farther apart?

The FM channels are wider so the "next" channel is not as close as they are in AM.
FM modulation is more tolerant of noise, such as the noise from the adjacent channel than AM is.


I think it is time to put down the mouse and pick up a book!

 

[Randall]

A few more questions:

Why do most AM stations not transmit in stereo, while most FM stations do not transmit in mono?

All things considered (in a perfect world) which frequencies in both AM and FM will most likely travel the farthest at any given time? Would it be frequencies at the far ends of the spectrums or dead in the middle?

How can FM stations in the same market have frequencies so close together while AM stations in the same market are placed farther apart?

actually the mono signal is contained in the stereo signal of fm broadcast, and the reason stereo is seldom used in am is that am stations are more limited in bandwidth, and stereo requires more information to be transmitted which uses more bandwidth. i have an am stereo radio in my old truck (c quam) but find very few stations broadcasting in am stereo.

 

[Randall]

just a note.... the entire fm band in the united states goes from 88 to 108 mhz which is a span of 20 mhz while the am broadcast band goes from just over .5 mhz to just over 1.5 mhz, just a little over 1/20th the spectrum of the fm broadcast band.

(pointless ramble)

 

[CFP387]

I think it is time to put down the mouse and pick up a book!

You've got a good point!

AM will go further but not by as much as most people think. It has more to do with WHERE it goes. Higher frequencies travel more in a "line of Sign" manner, lower frequencies bend around the earth more.

I've heard that AM stations have to "adjust" their signal direction and sunset and sunrise because the sun's ray effect the signal strength. Is that because they "bend around the earth more"?

 

[N_Jay]

You've got a good point!



I've heard that AM stations have to "adjust" their signal direction and sunset and sunrise because the sun's ray effect the signal strength. Is that because they "bend around the earth more"?

Yep, mostly to protect others stations licensed on the frequency.

Station have different day and night power and patterns, some station are daytime only (I think these still exist) (Been out of the B-Cast world a few years)