Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Analog Communication - frequencies for AM vs FM

Status
Not open for further replies.

rajasekharnbkrist

Junior Member level 2
Joined
Nov 10, 2013
Messages
21
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
182
Why we are using KHz to A.M and MHz to F.M. If we reverse the frequencies what happens i.e. for A.M MHz and for F.M KHz.
 

BradtheRad

Super Moderator
Staff member
Joined
Apr 1, 2011
Messages
14,226
Helped
2,814
Reputation
5,636
Reaction score
2,754
Trophy points
1,393
Location
Minneapolis, Minnesota, USA
Activity points
106,129
I think commercial AM radio developed in the .5-1.6 MHz spectrum because the equipment was easy to construct for that spectrum. Also it was found that frequencies up to 10 or 15 MHz are able to 'skip' high in Earth's atmosphere, to be picked up thousands of miles away. This was a major advantage in the early days of radio.

Commercial FM broadcasts have good sound fidelity. The carrier needs to modulate the audio spectrum (15 kHz), therefore the carrier frequency needs to be many times faster than 15 kHz. I don't know how they determined what minimum frequency would be satisfactory, whether it should be 1M Hz, or 10M, or 100M.
 

Audioguru

Advanced Member level 5
Joined
Jan 19, 2008
Messages
9,291
Helped
2,143
Reputation
4,280
Reaction score
1,968
Trophy points
1,393
Location
Toronto area of Canada
Activity points
58,484
I agree that when AM radio was invented then it was difficult to make circuits work at frequencies higher than 2MHz (2000kHz) so 540kHz to 1600kHz frequencies were used.
The very high frequency used by FM stations avoids interference from other radio services and static from car ignition and other interference. Also its antenna length is fairly short.

My model airplanes are controlled with digital signals at 2.4GHz. I think 40 of them can be active at the same time and automatically avoid interference between them.
 

c_mitra

Advanced Member level 5
Joined
Nov 13, 2012
Messages
3,787
Helped
928
Reputation
1,858
Reaction score
917
Trophy points
1,393
Activity points
29,830
The AM band runs from 300 kHz to 27MHz. The range is not continuous but is divided into several band. There is a LF band (rarely used) and a medium frequency and a number of shortwave bands. For AM (SW) radio, bands were usually designated by wavelengths, e.g., 13M band, 47M band etc.

The same spectrum was shared by defense, police, airplanes etc. In addition, considerations like atmospheric reflections were also considered.
 

Audioguru

Advanced Member level 5
Joined
Jan 19, 2008
Messages
9,291
Helped
2,143
Reputation
4,280
Reaction score
1,968
Trophy points
1,393
Location
Toronto area of Canada
Activity points
58,484
Aircraft and their control towers use AM so that another party can "break in" and say Mayday, my airplane is on fire! They operate on frequencies (108MHz to 136MHz) above the FM broadcast band. FM has a spec called "capture ratio" where it takes a strong signal to break in at the same frequency as an existing signal.
 
  • Like
Reactions: j33pn

    j33pn

    Points: 2
    Helpful Answer Positive Rating
Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top