This document discusses radio wave propagation and the ionosphere. It describes how Maxwell laid the foundation for understanding electromagnetic theory and radio waves over 150 years ago. Experiments in the late 19th century by Hertz, Lodge, Bose and Marconi demonstrated radio waves. The document then covers the different atmospheric layers including the troposphere, stratosphere, mesosphere, thermosphere and exosphere. It focuses on the ionosphere, explaining the different layers of the ionosphere and how they are affected by solar activity and sunspots. Maximum usable frequency is also discussed in relation to radio propagation through the ionosphere.

1. Radio Wave Propagation
Ved Prakash Sandlas
Director General
Amity Institute of Space Science & Technology, Noida
Principal Adviser, Cogent EMR Solutions Ltd, New Delhi (2006-2008)
Distinguished Scientist and Chief Controller R & D, DRDO (1996-2005)
Director, Defence Electronics Applications Lab (DEAL), Dehradun (1986-1996)
Group Director, Electronics, VSSC, Thiruvanathapuram (1984-1986)
Project/Mission Director, SLV-3, ISRO (1980-1984)
AISST, Noida, Feb 1, 2010

2. About 150 years ago, Maxwell enunciated the
electromagnetic theory and laid the mathematical
foundation of radio wave propagation. However, the
credit for the generation and demonstration of radio
waves was shared by Hertz, Lodge, Bose and
Marconi through simple laboratory experiments
conducted about a century ago. The legendary work
of Sir JC Bose, reported in May 1895 at Calcutta
(Asiatic Society of Bengal) and read before the
British Association on Sep 21, 1896, is a milestone
in itself; his experiments at 50 G Hz were designed
to show that ‘electronic-waves’ possessed all the
characteristic optical properties of light waves.
When rest of the world was concerned with much
lower frequencies, Bose generated, the then, highest
imaginable frequency.

3. Direct and Ground Reflected Waves.

4. Radio Horizon for Direct Waves.

5. Sky-wave Propagation

6. Radio Spectrum
Symb
ol
Frequency
range
Wavelength,
λ
Comments
ELF < 300 Hz > 1000 km Earth-ionosphere waveguide
propagationULF 300 Hz – 3 kHz 1000 – 100
km
VLF 3 kHz – 30 kHz 100 – 10 km
LF 30 – 300 kHz 10 – 1 km Ground wave propagation
MF 300 kHz – 3
MHz
1 km – 100 m
HF 3 – 30 MHz 100 – 10 m Ionospheric sky-wave propagation
VHF 30 – 300 MHz 10 – 1 m Space waves, scattering by objects
similarly sized to, or bigger than, a
free-space wavelength, increasingly
affected by tropospheric phenomena
UHF 300 MHz – 3
GHz
1 m – 100
mm
SHF 3 – 30 GHz 100 – 10 mm
EHF 30 – 300 GHz 10 – 1 mm
8 1
; 3 10 msc f cλ −
= × = ×

7. Atmospheric Layers
• Troposphere: Earth’s surface to about 10 (8-11-16) Km
• Stratosphere: Extends from the Troposphere upwards
to about 51 Km
• Mesosphere: Extends to about 85 Km
• Thermosphere: Extends to about 600 Km
• Exosphere: Extends to about 10,000 Km
• Beyond this: Free Space
• Ionosphere: Extends from the Stratosphere
(50 Km) upwards to about 500 km

8. Ionosphere

9. Layers of the Ionosphere.

10. Ionosphere
• The layers that form the ionosphere vary
greatly in altitude, density, and thickness
with the varying degrees of solar activity.
• The upper portion of the F layer is most
affected by sunspots or solar disturbances
• There is a greater concentration of solar
radiation during peak sunspot activity.
• The greater radiation activity the more dense
the F layer and the higher the F layer
becomes and the greater the skip distance

11. Solar Cycle
• Every 11 years the sun undergoes a
period of activity called the "solar
maximum", followed by a period of
quiet called the "solar minimum".
During the solar maximum there are
many sunspots, solar flares, and
coronal mass ejections, all of which
can affect communications and
weather here on Earth.

12. Relationship of Frequency to Refraction in the Ionosphere

13. Ionosphere
• Three layers
– D: low frequencies can be refracted but
the high frequencies tend to pass on
through
– E: signals as high as 20MHz can be
refracted while higher ones pass through
– F: during the day light hours there are two
layers:
• F1 and F2

14. Ionosphere
• F: during the night hours the ionization layer
is relatively constant and the higher
frequencies can be refracted
• During the night hours, the D and E layers
virtually disappear and signals that would be
refracted at lower levels now are refracted at
higher levels.
• This results in greater skip distances and
better reception at greater distances than in
the daytime hours.

15. Maximum Usable Frequency
(MUF)

16. PROPAGATION, HOPS SKIPS
ZONES

18. Free-space propagation
• Transmitted power
• EIPR (equivalent isotropically radiated power)
• Power density at receiver
• Received power
• Friis power transmission formula
txP
txtx PG
2
txtx
rx
4 R
PG
π
=S

π
λ
π 4
;
4
2
rx
rxrx
2
txtx
rx GAA
R
PG
P ee =⋅=
2
rxtx
tx
rx
4 





=
R
GG
P
P
π
λ
Tx Rx
R

19. Free-space propagation (cont.)
• Taking logarithms gives
where is the free-space path loss, measured in
decibels
• Maths reminder






−+=−
λ
π R
GGPP
4
log20log10log10log10log10 10rx10tx10tx10rx10
( ) cbcb aaa logloglog +=⋅( ) ,loglog bcb a
c
a ⋅=
( ) ( ) ( ) ( ) ( )dBdBidBidBWdBW 0rxtxtxrx LGGPP −+=−
0L
( )dB
4
log20 100 





=
λ
π R
L
( ) kmdfL 10MHz100 log20log204.32dB ++=
( ) ,
log
log
log
a
b
b
c
c
a =

20. Basic calculations
• Example: Two vertical dipoles, each with gain 2dBi,
separated in free space by 100m, the transmitting one
radiating a power of 10mW at 2.4GHz
• This corresponds to 0.4nW (or an electric field strength
of 0.12mVm-1)
• The important quantity though is the signal to noise ratio
at the receiver. In most instances antenna noise is
dominated by electronic equipment thermal noise, given
by where is Boltzman’s
constant, B is the receiver bandwidth and T is the room
temperature in Kelvin
( ) 0.801.0log202400log204.32dB 10100 =++=L
( ) ( ) ( ) ( ) 0.940.802log102log1010log10dBW 1010
2
10rx −=−++= −
P
TBkN B= 123
JK1038.1 −−
⋅=Bk