The radio spectrum

A journey into frequency macro to micro

The whole terrestrial range: up to 50 GHz

SatTV
Ku-Band
Sat
C
WLAN
5GHz
0-3 GHz
see below
grey space:
used by non-public services
mostly military, also ships, airnav, amateur radio
above 10 GHz generally point-to-point connections
very directional
0
10000
20000
30000
40000
50000 MHz
Radio signals can be transmitted up to about 50 GHz. An hifi stereo signal could well fit into a 40 KHz slot. So it would be theoretically possible to transmit 1.250.000 signals simultanously in a city if there was no other use of the spectrum. The lack of frequency for radio stations is a myth. The range above 3 GHz is extremely empty. Only the marked areas have been allocated for general purpose: satellite TV around 4 and 11 GHz and the new 5 GHz Wifi band. Unfortunately freqencies above 3 GHz posess disadvantages for broadcasting. Trees and buildings will not let them pass. Consequently most communication is highly directional point-to-point from dish to dish with the ability to transmit high amounts of data at once.

The broadcast-suitable spectrum below 3 GHz

LTE
800
UMTS
2100
up/TDD
UMTS
2100
down
UMTS
2100
TDD
DCTP
cordless
phones
GSM
800
up
GSM
800
down
GSM
1800
up
GSM
1800
down
FM
radio
DAB
digital
radio
DAB
radio
L-Band
DVB-T
UHF
digital TV
Wlan
2.4G
LTE
2600
LW
MW
SW
0
500
1000
1500
2000
2500
3000 MHz
Still space for 75.000 radio signals. At least the amout of publically available frequencies has grown with the expansion of cell/mobile phones (blue). UMTS and LTE can transmit internet radio. But everyone has to request his own stream - not very efficient. Large part of the broadcast spectrum (red) is still reserved for TV. Digital radio DAB/DAB+ has overtaken the former TV band III. Still, coordination is extremely careful. You could well place 100 FM, 400 DAB and 200 TV stations in a large city via terrestric if some interference in the surrounding area would be taken in account.
So what is in between? Some ranges are reserved for rescue, police, air-traffic, ships, public transport, company communication, amateur radio, GPS but it does all not take that much. Large parts go to the military. As a matter of fact, considerable amounts of the spectrum remain widely unused.

LW/MW/SW Worldwide propagation below 30 MHz

LW
MW
75m
49m
41m
31m
25m
22m
19m
16m
13m
11m
0
5
10
15
20
25
30 MHz
On shortwave from 3 to 30 MHz signals can travel the world- a fundamental difference. Once there were many radio stations in the broadcast ranges. Hence audio was reduced in order to place as many signals as possible. Today the bands are abandoned. Only China, missionaries and a few other stations have stayed. Digital audio DRM offers improved sound quality. But DRM receivers have never reached the market in larger numbers. Only on the radio bands there is space for 200 AM or 400 DRM stations. Unfortunately propagation is always a little unpredictable and you must switch frequencies from time to time.

LW/MW (AM)

lw mw waterfall spectrum
Long Wave
Medium Wave
0
0.5
0.75
1
1.5
2
Long- and Medium Wave (known as AM) have a similar problem: Local reception during daytime and a radius of about 2000 km in the night. MW has 120 channels, each one occupied by about 50 stations worldwide. Now let's take a closer look at the single channels.

MW in focus

a closer look at 3 out of 120 channels

756, 765 and 774 KHz spectrum
0.756
0.765
0.774 MHz
These are 3 adjactent channels: 3 carriers surroundes by their audio in both side bands. What cannot be seen here: Usually there is more than one carrier per channel.

One MW carrier in high resolution

+/- 10 Hz where signal addition leads to constant fading

765 KHz in high resolution
0.764990 (-10 Hz)
0.765
0.765010 MHz (+10 Hz)
This is the frequency microcosmos: Several carriers, some of them with very specific characteristics. Many are stable over years with 0.1 Hz-accuracy. It's a challenge to identify them but you cannot hear the audio of the stations.


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