JED - September 2017 - 46

E W101
as viewed from the target receiver, we can ignore atmospheric
and rain losses (they are very small).
The formula for the Fresnel zone distance is:

JAMMER
65.8 dBm
ERP

828 km

FZ = (hT x hR x F)/ 24,000
Where: FZ is the Fresnel zone distance in km
hT is the height of the transmit antenna in meters
hR is the height of the receive antenna in meters
F is the transmission frequency in MHz
For the desired signal link, the two antenna heights are 2
meters and the frequency is 400 MHz, so:
FZ = (2 x 2 x 400)/24,000 = 67 meters

5 km

Since FZ is less than the link distance, the propagation
mode is 2 Ray, so the propagation loss is:

40 dBm
ERP

2 meters

2 meters

R
TARGET
RECEIVER

T
DESIRED
SIGNAL
TRANSMITTER

Fig. 2: The jamming geometry and the ERPs of the desired signal and
jamming transmitters determine the J/S ratio.

The Journal of Electronic Defense | September 2017

46

Misalignment loss: ∆G = 12(θ/α)2
Where: ∆G is the loss in dB from antenna misalignment
θ is the antenna misalignment
α is the antenna 3 dB beam-width
∆G = 12(1/15.8)2 = .05 dB
(which we can ignore in our calculations)
The equation for the jamming-to-signal ratio in communications jamming is given in the December 2008 "EW101" column.
If the target receiver has a whip antenna, the equation is:
J/S = ERPJ - ERPS - LOSS J + LOSSS
Where:

J/S is the jamming to signal ration in dB
ERPJ is the effective radiated power of the jammer
ERPS is the effective radiated power of the desired
signal transmitter
LOSSJ is the loss from the jammer to the target
receiver
LOSSS is the loss from the desired signal transmitter
to the target receiver

Now we will determine the propagation modes and losses
from the desired signal transmitter and the jammer to the target receiver using the formulas presented in the July and August 2007 "EW101" columns.
We will assume that there is clear line of sight between all
of the members of the hostile network we are jamming. Because the frequency is UHF and the satellite is at a high angle,

LOSSS = 120 + 40 log(d) -20 log(hT) - 20 log(hR)
Where: d is the link distance in km
The desired link loss is thus:
120 + 40 log(5) - 20 log(2) - 20 log(2) = 120 + 28.0 - 6.0 - 6.0
= 136 dB
The jamming link propagation mode is line of sight (also
called "free space", which it literally is in this case). The loss
from antenna misalignment is extremely small, so the total
loss from the jammer to the target receiver is:
LOSS J = 32.4 + 20 log (d) + 20 log (F)
= 32.4 + 20 log(828) + 20 log(400)
= 32.4 + 58.4 + 52.0 = 142.8 dB
The ERP of the desired signal transmitter is 10 Watts (40
dBm). The ERP of the jammer is 100 Watts (50 dBm) increased
by the antenna gain (15.8 dBi) = 65.8 dBm

JAMMING-TO-SIGNAL RATIO
The jamming to signal ratio is:
J/S = ERPJ - ERPS - LOSSJ + LOSSS
= 65.8 - 40 - 142.8 + 136
= 19 dB
This is a very respectable job of jamming (10 dB would usually be enough). However, it must be noted that one satellite
can only jam that network for up to 19.3 minutes . . . so an
array of satellites would be required to perform continuous
jamming.
Note that if the satellite had been at the horizon from the
jammed network (i.e. 1,978 km away), the achieved J/S would
have been reduced to 10.5 dB (including the effect of 1 dB of
atmospheric loss).

WHAT'S NEXT
The author lied last month when he said this would be the
last column in the Space EW series. We will finish this series next month with a column on jamming of radars from low
earth orbit. For your comments, Dave Adamy can be reached at
www.lynxpub.com. a


http://www.lynxpub.com

JED - September 2017

Table of Contents for the Digital Edition of JED - September 2017

The View from Here
Conferences Calendar
Courses Calendar
From the President
The Monitor
Washington Report
World Report
Army Brigade Electronic Warfare Weapons Teams Learn New Lessons at NTC
Technology Survey: Counter-UAS Systems
EW 101
Index of Advertisers
JED Quick Look
JED - September 2017 - intro
JED - September 2017 - cover1
JED - September 2017 - cover2
JED - September 2017 - 3
JED - September 2017 - 4
JED - September 2017 - 5
JED - September 2017 - The View from Here
JED - September 2017 - 7
JED - September 2017 - Conferences Calendar
JED - September 2017 - 9
JED - September 2017 - Courses Calendar
JED - September 2017 - 11
JED - September 2017 - From the President
JED - September 2017 - 13
JED - September 2017 - 14
JED - September 2017 - The Monitor
JED - September 2017 - insert1
JED - September 2017 - insert2
JED - September 2017 - 16
JED - September 2017 - 17
JED - September 2017 - Washington Report
JED - September 2017 - 19
JED - September 2017 - World Report
JED - September 2017 - 21
JED - September 2017 - Army Brigade Electronic Warfare Weapons Teams Learn New Lessons at NTC
JED - September 2017 - 23
JED - September 2017 - 24
JED - September 2017 - 25
JED - September 2017 - 26
JED - September 2017 - 27
JED - September 2017 - 28
JED - September 2017 - 29
JED - September 2017 - 30
JED - September 2017 - 31
JED - September 2017 - 32
JED - September 2017 - 33
JED - September 2017 - 34
JED - September 2017 - 35
JED - September 2017 - 36
JED - September 2017 - Technology Survey: Counter-UAS Systems
JED - September 2017 - 38
JED - September 2017 - 39
JED - September 2017 - 40
JED - September 2017 - 41
JED - September 2017 - 42
JED - September 2017 - 43
JED - September 2017 - 44
JED - September 2017 - EW 101
JED - September 2017 - 46
JED - September 2017 - 47
JED - September 2017 - 48
JED - September 2017 - Index of Advertisers
JED - September 2017 - JED Quick Look
JED - September 2017 - cover3
JED - September 2017 - cover4
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