Aaack - Where's the break between AM and FM?

[Pro-95]

Ok, I thought for sure I knew where the break was for AM and FM. But apparently I am wrong so where is it?

 

[crayon]

This is kind of a hard question to answer because of the vaugeness of your query ..

AM or FM only describes how intelligence is superimposed, or modulated on a signal. There are certian bands of frequecies that you will generally find one type of modulation versus another.

But there is not any hard rule that draws a line between the two.

HTH's

 

[Pro-95]

This is kind of a hard question to answer because of the vaugeness of your query ..

AM or FM only describes how intelligence is superimposed, or modulated on a signal. There are certian bands of frequecies that you will generally find one type of modulation versus another.

But there is not any hard rule that draws a line between the two.

HTH's

Yea that helps because now I know I'm not crazy. I just figured below 130 (air bands) was AM and above was FM but I was reading places where it can be varied, like what you said. So other than switching between AM/FM is there any way to determine which a signal is? Sorry not trying to be vague.

 

[N_Jay]

Ok, I thought for sure I knew where the break was for AM and FM. But apparently I am wrong so where is it?

Michael - Proving that a little knowledge is still dangerous on a daily basis.

You are looking for something that is not there.

AM was invented and put to use earlier than FM,

AND

Lower frequencies were used earlier than higher frequencies,

SO

It could look like there is a "Line" or "Break" between the technologies.

I guess for practical purposes (although I would not hazzard a guess what those purposes are) you could say the "Break" was in the 1950's and 1960's, at between 30 MHz and 150 MHz, with exceptions to both rules.

 

[N_Jay]

This is kind of a hard question to answer because of the vaugeness of your query ..

AM or FM only describes how intelligence is superimposed, or modulated on a signal. There are certian bands of frequecies that you will generally find one type of modulation versus another.

But there is not any hard rule that draws a line between the two.

HTH's

Yea that helps because now I know I'm not crazy. I just figured below 130 (air bands) was AM and above was FM but I was reading places where it can be varied, like what you said. So other than switching between AM/FM is there any way to determine which a signal is? Sorry not trying to be vague.

If you know the service then you can assume the modulation with high confidence.

AM Broadcast, wideband AM
FM Broadcast, Wideband FM
SW Broadcast, Narrowband AM, or SSB
HF Amature, SSB or CW
Land Mobile Radio, FM (or digital)
Air Bands, Civilian and Milliatry, AM (moving to digital)
VHF/UHF Amature, FM (or digital)
TV (analog), FM Audio, AM Video
CB (27 MHz) AM or SSB
GMRS/FRS/MURS, FM

 

[fireant]

NJAY, in your post you make reference to military and civilian airbands (going digital) is it both going that route or just the military? and if when they do a digital scanner will recieve these frequencies correct?

fireant

 

[N_Jay]

NJAY, in your post you make reference to military and civilian airbands (going digital) is it both going that route or just the military? and if when they do a digital scanner will recieve these frequencies correct?

fireant

I have not folowed this issue closely. I believe teh FAA has out an RFI or RFP for a design of a fully digital system.

The military might get there first because they don't have to deal with all the commercial and private aircraft ownwers.

As for a scanner, that would be up to the scanner manuacturers.
The civil aviation side should be an open standard, sio there "shoul" not be much in the way of it happening.

I would guess it will not conform to any existing system, so todays scanners will not work.

GOOGLE "nexcom aviation"

 

[crayon]

Traditional frequency-splitting method used to increase communications channels will not meet future ATC requirements for voice and data communications.

 

[crayon]

Quote from www.faa.gov website:

The objective of the NEXCOM Program is to develop and begin the implementation of a new NAS air-ground (A/G) communications system by 2009. This will be accomplished under the management of the Air/Ground Communications Product Team (AND-360).

This system will replace and improve the existing obsolete NAS A/G radio infrastructure by introducing new systems using advanced digital technology to provide better VHF frequency utilization, system reliability, performance, and added capabilities.

The RPDE Program (and subsequent Full Scale Development Program (FSDP)) will culminate in the production of Ground Network Interface systems and Radio Interface Units that will be operated in conjunction with the Multimode Digital Radios (MDRs) to form the national NEXCOM Air-Ground Communications Network within the NAS.

 

[fireant]

So it is probably safe to say it will still be a few years before this takes place? It seems that scanning is slowly becoming more and more difficult hopefully they will never take this hobby away from us but who knows they might. Thanks for the quick reply keep us posted

fireant

 

[PanJurekMrJerry]

There is NO break between A.M. and F.M.. You can have A.M. or F.M. on ANY frequency but it seems that shortwave favours A.M. just like the "A.M." broadcast band.

 

[k8tmk]

The lowest frequency band that I am aware of FM being used is the 10-meter amateur radio band (28 to 29.7 MHz). This band can use both AM and FM, as well as many other modes of transmission. You can find the FM mode being used at the higher-frequency end of this band.

 

[waynesewell]

As far as amateur radio is concerned, that's the lowest band where FM can be used.

I just took the general test this week, so the following is fresh in my mind:

Question G8B05: Why isn't frequency modulated (FM) phone used below 29.5 Mhz?

Answer: The bandwidth would exceed FCC limits

Perhaps similar restrictions are placed on other services as well.

 

[Thornhill20]

Well, in theory, you *CAN* use FM at 3MHz, just the same as you *CAN* use AM at 3GHz - just - would you want to, and why?

-Mike

 

[waynesewell]

Let me qualify "can be used" as "can be used legally on a frequency allocated to the amateur radio service". FM can't be used by hams below the above cutoff frequency without breaking the rules. Again, I don't know what restrictions are on other services, if any.

 

[N_Jay]

And I got grief for trying to clarify an issue a few a few days ago.

These posts are much worse. )

 

[Voyager]

FM can't be used by hams below the above cutoff frequency without breaking the rules. Again, I don't know what restrictions are on other services, if any.

YES IT CAN. As long as you keep the bandwidth within the legal limits. (a modulation index of 1, I think)

Joe M.

 

[waynesewell]

Really? Perhaps they ought to reword the question then. They are certainly implying we can't. They should have said "The bandwidth would exceed FCC limits, unless something is done to reduce it". Or some such.

It doesn't do much good to learn this stuff if we get misinformation.

 

[N_Jay]

Watch This;

But the Hams Use FSK, which is FM, even in the HF bands.

(I call this a "granade post". Sort of the oposite of trolling)

(Toss - 5, 4, 3, 2, 1 . . . . )

And a who lot of microwave is QAM, which is AM .

(Toss - 5, 4, 3, 2, 1 . . . . )