JED - December 2013 - 50

EW 101

Digital Radio Frequency Memories

DRFMs - Part 3
By Dave Adamy

ANALYSIS OF THREAT SIGNALS
One of the important advantages that
DRFMs (and their associated processors)
provide to EW operations is the ability to
very quickly analyze intercepted threat
signals. One issue is the threat radar frequency. Measurement and replication of
transmission frequency is important because of the issue of frequency diversity
in modern threat radars.

FREQUENCY DIVERSITY

The Journal of Electronic Defense | December 2013

50

Hopping Range

Randomly
Chosen
Pulse
Transmission
Frequencies

One of the electronic protection (EP)
Frequency
measures that a radar can use is frequency diversity. A radar can have an
operator-selectable frequency, or with
Figure 1: A radar with pulse to pulse frequency hopping pseudo-randomly selects one of several
more complexity can change frequency
frequencies on which to transmit each pulse.
periodically. In both of these cases, the
DRFM can analyze the first pulse it sees and coherently transreturn signals. Every pulse is broadcast, but as shown in Figmit subsequent pulses at the same frequency. This requires
ure 2, the jammed frequencies are not chosen.
a DRFM system throughput latency short enough to receive,
analyze, set jamming parameters and rebroadcast during the
NON-COHERENT JAMMING APPROACHES
inter-pulse period (from many microseconds to a millisecond
Pulse-to-pulse frequency hopping gives a non-coherent
or so. This is well within the state of the art of wideband and
jammer two options to jam all of the pulses: either divide the
narrowband DRFMs.
jamming power among the observed frequencies, as in Figure
3, or spread jamming across the whole hopping range, as in

PULSE-TO-PULSE FREQUENCY
HOPPING
A more challenging situation is a
radar, which has pulse-to-pulse frequency hopping as shown in Figure 1.
This radar will have an array of transmit
frequencies that are pseudo-randomly
selected. The total frequency range can
be up to about 10 percent of the nominal
transmit frequency. This is to avoid the
loss of antenna and transmitter efficiency that occurs when operating over
wider frequency ranges.
The frequency hopping radar not
only choses a random frequency in its
hopping range for each pulse, but can
have a "least jammed" feature in which
the radar skips frequencies at which
jamming causes reduced quality of skin

Noise
Jamming
Frequency
Range
Pulse
Frequencies

Frequency
Figure 2: A least jammed frequency capability allows a frequency hopping radar to skip
frequencies at which jamming is present.



JED - December 2013

Table of Contents for the Digital Edition of JED - December 2013

The View From Here
Conferences Calendar
Courses Calendar
From the President
The Monitor
World Report
Seeing the Light: Laser Warning Systems Facing Increasingly Lethal Threats
2014 EW/SIGINT Resource Guide
EW 101
AOC News
Index of Advertisers
JED Quick Look
JED - December 2013 - cover1
JED - December 2013 - cover2
JED - December 2013 - 3
JED - December 2013 - 4
JED - December 2013 - 5
JED - December 2013 - The View From Here
JED - December 2013 - 7
JED - December 2013 - Conferences Calendar
JED - December 2013 - 9
JED - December 2013 - Courses Calendar
JED - December 2013 - 11
JED - December 2013 - From the President
JED - December 2013 - 13
JED - December 2013 - 14
JED - December 2013 - The Monitor
JED - December 2013 - 16
JED - December 2013 - 17
JED - December 2013 - 18
JED - December 2013 - 19
JED - December 2013 - 20
JED - December 2013 - 21
JED - December 2013 - 22
JED - December 2013 - 23
JED - December 2013 - World Report
JED - December 2013 - 25
JED - December 2013 - Seeing the Light: Laser Warning Systems Facing Increasingly Lethal Threats
JED - December 2013 - 27
JED - December 2013 - 28
JED - December 2013 - 29
JED - December 2013 - 30
JED - December 2013 - 31
JED - December 2013 - 32
JED - December 2013 - 2014 EW/SIGINT Resource Guide
JED - December 2013 - 34
JED - December 2013 - 35
JED - December 2013 - 36
JED - December 2013 - 37
JED - December 2013 - 38
JED - December 2013 - 39
JED - December 2013 - 40
JED - December 2013 - 41
JED - December 2013 - 42
JED - December 2013 - 43
JED - December 2013 - 44
JED - December 2013 - 45
JED - December 2013 - 46
JED - December 2013 - 47
JED - December 2013 - 48
JED - December 2013 - 49
JED - December 2013 - EW 101
JED - December 2013 - 51
JED - December 2013 - 52
JED - December 2013 - 53
JED - December 2013 - AOC News
JED - December 2013 - 55
JED - December 2013 - 56
JED - December 2013 - Index of Advertisers
JED - December 2013 - JED Quick Look
JED - December 2013 - cover3
JED - December 2013 - cover4
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