direction finding - itu
TRANSCRIPT
Slide 1Outline • Definition of Direction Finding.
• Tasks of radio Direction Finding.
• Direction Finding Techniques.
• DF Antennas.
• Direction finding refers to the use of specialized instruments, antennas,
and methodologies to determine the physical location of a source of RF
energy or “targets”
• DF purposes:
• location of an unauthorized transmitter.
• location of an interfering transmitter which cannot be identified by other
means.
• determination of the site of a source of harmful interference of reception.
• identification of transmitters, both known and unknown.
Direction Finding Techniques
• amplitude sensitive.
• phase sensitive.
Requirements on DF system
• High sensitivity
• Immunity to multipath propagation
• Immunity to polarization errors
Requirements on DF system
• Stable response in case of non-coherent co-channel interferers
• DF of short-duration signals
intercept (POI)
Error sources
• The DF accuracy is affected by a number of influences:
• Wave propagation (usually disturbed by obstacles)
• Signals radiated by the emitters are modulated, limited in time and their
carrier frequency is often unknown
• Received field is additionally superimposed by noise, co-channel
interferers
Components of a DF system
• Antenna • Design usually specific to a given DF methodology
• Receiver(s) and processing unit • One or more receive channels with analog-to-digital conversion • Integrated or separate digital signal processing
• User interface • Software for display and control • Position fix and map display software
DF antenna Receiver(s) Processing unit Display and control
DF Antennas
• Beam/Yagi Antenna.
• Log-Period Antenna.
• Loop Antenna.
• Tune to null (sharper than gain)
• Front to back ratio > 50 db
• Can use front to help find weaker signals but with reduced bearing accuracy
Ron Milione - W2TAP 11
• 7.5 dBi typical gain in free space
• Good directivity: 14 dB typical front-to-back ratio
• Uniform pattern over up to 10:1 frequency range
• Radiating elements are fed by central transmission line
• Individual elements are repeated at intervals constant with logarithm of
frequency
Loop Antenna
• The loop antenna acts much the same as the secondary winding of a transformer.
• The voltage at the output is proportional to the amount of flux passing through it
and the number of turns.
• To obtain the most accurate bearings, the loop must be balanced electrostatically
with respect to ground.
• Otherwise, the loop will exhibit two modes of operation, One is the mode of a
true loop , The second mode is called the antenna effect.
Loop Antenna
• Very compact
Ferrite Rod Antennas (loopstick antennas)
• The true loop antenna responds to the magnetic field of the
radio wave, and not to the electrical field.
• The voltage delivered by the loop is proportional to the
amount of magnetic flux passing through the coil, and to the
number of turns in the coil.
Ferrite Rod Antennas (loopstick antennas)
• If an air-core loop is placed in a field, in essence it cuts the lines of flux without disturbing them (A), On the other hand, when a ferrite (magnetic) core is placed in the field, the nearby field lines are redirected into the loop (B).
• To get higher loop output is to increase the permeability of the medium by winding a coil of wire around a form made of high permeability material, such as ferrite rod, much greater flux is obtained in the coil without increasing the cross- sectional area.
Sense Antennas
• There is ambiguity as to which null indicates the true direction of the
target station.
• Modify a loop or loopstick antenna pattern to have a single null by
adding a second antenna element.
• It senses the phase of the signal wavefront for comparison with the
phase of the loop output signal.
Phased Arrays and Adcock
• The field radiated from a linear (straight) element, such as a dipole or
vertical monopole, is proportional to the sum of the elementary
currents flowing in each part of the antenna element.
• Many directional patterns are possible depending on the spacing and
phasing of the elements.
• The directional frequency range of this antenna is limited to one
band, because of the critical length of the phasing lines.
Adcock Antenna Adcock Antenna Pattern
LOOPS VERSUS PHASED ARRAYS • loops can be made smaller than suitable phased arrays for the same frequency of
operation.
• sharper nulls can be obtained with phased arrays.
• Loops are not as useful for skywave RDF work because of random polarization of
the received signal.
• Phased arrays are somewhat less sensitive to propagation effects, probably
because they are larger for the same frequency of operation and therefore offer
some space diversity.
• Doppler direction finder.
• Correlative Interferometry
Manual Direction Finding
Manual Direction Finding
• Evaluating the receive voltage is the simplest way of direction finding.
• Manual direction finding involves the use of a receiver and hand-held directional
antenna : usually some type of yagi / log-periodic.
• The antenna is moved / rotated until the point of maximum signal strength is
determined.
• Rotation can also be performed using an antenna mounted on a rotor or swivel.
Manual Direction Finding
• High sensitivity due to the directivity
• Simple and Low-cost, no need for dedicated DF receiver or complex
antennas
• Same antenna can be used for direction finding and monitoring
• Effectiveness depends strongly on the skill level of the operator.
• Typically four to eight antennas are arranged in a circular array and
are RF combined in a way that simulates rotation.
• As we move closer to a signal, the received frequency will shift
upwards (or vice-versa). This shift can be detected and used to
determine if we are moving in the right direction.
Doppler DF Concept
Doppler DF Concept
Doppler Direction Finder • Low cost compared to other DF systems .
• Cannot handle multiple signals.
• Antenna sensitivity : Low.
• Normally works best on VHF/UHF frequencies (< 1 GHz).
• Doesn’t work well for horizontally polarized signals (Doppler antennas
usually vertically polarized)
Watson-Watt DF Principle
• This DF method is based on two directional antennas pairs and one omni-
directional antenna
• The response of the two pairs are proportional to sine and cosine of the arrival
signal.
• Watson-Watt DF consists of three phase-matched receivers and displays angle of
arrival in terms of sine and cosine functions utilizing third omni-directional
channel to solve ambiguity.
• Benefits: • minimum signal duration is sufficient. • simple implementation. • Little space required (small aperture antenna array).
• Drawback: • Small aperture system (D/λ<0.2) leading to errors in case of multipath
propagation. • large DF errors in case of skywaves with steep elevation angles
Watson-Watt principle
Watson-Watt principle
• Improved error tolerances for skywave reception
• Implementation of wider apertures to avoid errors in case of multipath
reception
Angle of Arrival • AOA simply measures the angle(s) at which a signal arrives at an antenna array :
not the phase or time differences of the signal at different elements.
• To determine if a signal is “arriving” at an antenna, we make a determination of
the power of the incoming signal at one or more antennas, so AOA is sometimes
also called “power of arrival” (POA).
• AOA antennas are typically circular array of (somewhat) directional antennas.
• Resolution / bearing accuracy is increased with an increasing number of antenna
faces.
Interferometer
Interferometer Based DF
• This concept is based on phase measurement between a subset of possible pairs
of antennas with minimum of two coherent receiver channels
• Phase measurement for a specific pair can be used for arrival angle
determination, based on knowledge of relative antenna distance
• When more then one pair is used elevation calculation is possible
• Antenna sensitivity: low
• Azimuth accuracy: σ = 1.5°–3°
Time Difference of Arrival (TDOA) • Three or more receivers at different locations receive
a signal from the target.
• Usually the paths between the transmitter and the
receivers are of different length, so there are
differences in the time of arrival at the different
receiver locations.
hyperbolae which cross at the location of the
transmitter of interest.
Time Difference of Arrival (TDOA) • Once we have computed the time difference, Δt, between the times the signal was received at
two stations, we can then compute / plot a hyperbola representing this distance between them.
• The intersection of multiple hyperbolae yields the estimated target location.
Time Difference of Arrival (TDOA) • Requires small aperture antenna array
• Requires single-channel receiver
Correlative Interferometry Technique
• Minimizes effect of signal modulation and fading
• Measures amplitude and phase
Correlative Interferometry
• Antenna Sensitivity: high
• Data Collection Time: fast; depends on number of receiver channels
Locating the Transmitter source
1. Monitoring (Frequency – B.W - Modulation)
2. DF (Fixed Stations)
3. Detection of location (2 fixed stations – one fixed and one mobile – SSL)
4. Homing using Mobile.
Single Site Location
• When a propagation path of no more than one reflection at the
ionosphere can be assumed, position of an HF emitter can be
determined by a single observing site using vertical triangulation,
provided that the height of the ionosphere at the point where the
radio wave is reflected, can be determined.
Single Site Location
• Elevation angle of arrival is measured by HFDF system
• Electron density profile of the ionosphere is measured by ionospheric sounder
• The path of the electromagnetic wave through the ionosphere can be reconstructed
using a ray tracing algorithm
• The distance to target transmitter can be calculated based on Martyn's Theorem
(with correction terms)
SSL Distance Calculation
Direction Finding Measurement
Direction Finding Measurement
Direction Finding Measurement DF Scan Summary Report Task No: 38097 Storage Interval: 15 secs Operator ID: TCI-WS-2 Noise Riding Threshold: 15 dB Schedule Time: 10/4/2016 11:49:00 AM Fixed Duration: 30 secs Completion Time: 10/4/2016 11:49:30 AM DF Resolution: 1 deg Site Location: N 30 1' 21" Azimuth Range: 0 --- 360 E 31 12' 32.1" All Single Band
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation Summary 1 794.000000 0 -- -- -- -- 2 794.012500 0 -- -- -- -- 3 794.025000 0 -- -- -- -- 4 794.037500 0 -- -- -- -- 5 794.050000 0 -- -- -- -- 6 794.062500 0 -- -- -- -- 7 794.075000 0 -- -- -- -- 8 794.087500 0 -- -- -- -- 9 794.100000 0 -- -- -- -- 10 794.112500 0 -- -- -- -- 11 794.125000 0 -- -- -- -- 12 794.137500 0 -- -- -- -- 13 794.150000 0 -- -- -- -- 14 794.162500 0 -- -- -- -- 15 794.175000 0 -- -- -- -- 16 794.187500 0 -- -- -- -- 17 794.200000 0 -- -- -- -- 18 794.212500 0 -- -- -- -- 19 794.225000 0 -- -- -- -- 20 794.237500 0 -- -- -- -- 21 794.250000 0 -- -- -- -- 22 794.262500 0 -- -- -- -- 23 794.275000 0 -- -- -- -- 24 794.287500 0 -- -- -- -- 25 794.300000 0 -- -- -- -- 26 794.312500 0 -- -- -- -- 27 794.325000 0 -- -- -- -- 28 794.337500 0 -- -- -- --
10/18/2020 9:33:19 AM Page 1 of 22
DF Scan Summary Report
Operator ID: TCI-WS-2 Noise Riding Threshold: 15 dB
Schedule Time: 10/4/2016 11:49:00 AM Fixed Duration: 30 secs
Completion Time: 10/4/2016 11:49:30 AM DF Resolution: 1 deg
Site Location: N 30 1' 21" Azimuth Range: 0 --- 360
E 31 12' 32.1"
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
46 794.562500 0 -- -- -- --
47 794.575000 0 -- -- -- --
50 794.612500 0 -- -- -- --
51 794.625000 0 -- -- -- --
53 794.650000 0 -- -- -- --
54 794.662500 0 -- -- -- --
57 794.700000 0 -- -- -- --
61 794.750000 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
71 794.875000 0 -- -- -- --
72 794.887500 0 -- -- -- --
75 794.925000 0 -- -- -- --
79 794.975000 0 -- -- -- --
82 795.012500 0 -- -- -- --
83 795.025000 0 -- -- -- --
86 795.062500 0 -- -- -- --
89 795.100000 0 -- -- -- --
90 795.112500 0 -- -- -- --
93 795.150000 0 -- -- -- --
97 795.200000 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
108 795.337500 0 -- -- -- --
111 795.375000 0 -- -- -- --
118 795.462500 0 -- -- -- --
119 795.475000 0 -- -- -- --
125 795.550000 0 -- -- -- --
126 795.562500 0 -- -- -- --
129 795.600000 0 -- -- -- --
133 795.650000 0 -- -- -- --
136 795.687500 0 -- -- -- --
140 795.737500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
147 795.825000 0 -- -- -- --
154 795.912500 0 -- -- -- --
155 795.925000 0 -- -- -- --
158 795.962500 0 -- -- -- --
161 796.000000 0 -- -- -- --
162 796.012500 0 -- -- -- --
165 796.050000 0 -- -- -- --
166 796.062500 0 -- -- -- --
167 796.075000 0 -- -- -- --
168 796.087500 0 -- -- -- --
169 796.100000 0 -- -- -- --
172 796.137500 0 -- -- -- --
173 796.150000 0 -- -- -- --
176 796.187500 0 -- -- -- --
179 796.225000 0 -- -- -- --
180 796.237500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
183 796.275000 0 -- -- -- --
184 796.287500 0 -- -- -- --
186 796.312500 0 -- -- -- --
187 796.325000 0 -- -- -- --
190 796.362500 0 -- -- -- --
191 796.375000 0 -- -- -- --
194 796.412500 0 -- -- -- --
197 796.450000 0 -- -- -- --
198 796.462500 0 -- -- -- --
201 796.500000 0 -- -- -- --
204 796.537500 0 -- -- -- --
205 796.550000 0 -- -- -- --
208 796.587500 0 -- -- -- --
209 796.600000 0 -- -- -- --
212 796.637500 0 -- -- -- --
215 796.675000 0 -- -- -- --
216 796.687500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
222 796.762500 0 -- -- -- --
223 796.775000 0 -- -- -- --
226 796.812500 0 -- -- -- --
227 796.825000 0 -- -- -- --
230 796.862500 0 -- -- -- --
233 796.900000 0 -- -- -- --
234 796.912500 0 -- -- -- --
237 796.950000 0 -- -- -- --
241 797.000000 0 -- -- -- --
251 797.125000 0 -- -- -- --
252 797.137500 0 -- -- -- --
255 797.175000 0 -- -- -- --
256 797.187500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
259 797.225000 0 -- -- -- --
262 797.262500 0 -- -- -- --
269 797.350000 0 -- -- -- --
270 797.362500 0 -- -- -- --
273 797.400000 0 -- -- -- --
277 797.450000 0 -- -- -- --
284 797.537500 0 -- -- -- --
288 797.587500 0 -- -- -- --
291 797.625000 0 -- -- -- --
292 797.637500 0 -- -- -- --
294 797.662500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
298 797.712500 0 -- -- -- --
306 797.812500 0 -- -- -- --
313 797.900000 0 -- -- -- --
316 797.937500 0 -- -- -- --
320 797.987500 0 -- -- -- --
327 798.075000 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
334 798.162500 0 -- -- -- --
342 798.262500 0 -- -- -- --
356 798.437500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
374 798.662500 0 -- -- -- --
378 798.712500 0 -- -- -- --
381 798.750000 0 -- -- -- --
388 798.837500 0 -- -- -- --
389 798.850000 0 -- -- -- --
392 798.887500 0 -- -- -- --
393 798.900000 0 -- -- -- --
395 798.925000 0 -- -- -- --
396 798.937500 0 -- -- -- --
399 798.975000 0 -- -- -- --
400 798.987500 0 -- -- -- --
401 799.000000 0 -- -- -- --
407 799.075000 0 -- -- -- --
408 799.087500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
415 799.175000 0 -- -- -- --
418 799.212500 0 -- -- -- --
419 799.225000 0 -- -- -- --
422 799.262500 0 -- -- -- --
426 799.312500 0 -- -- -- --
429 799.350000 0 -- -- -- --
430 799.362500 0 -- -- -- --
432 799.387500 0 -- -- -- --
433 799.400000 0 -- -- -- --
436 799.437500 0 -- -- -- --
437 799.450000 0 -- -- -- --
440 799.487500 0 -- -- -- --
443 799.525000 0 -- -- -- --
444 799.537500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
454 799.662500 0 -- -- -- --
455 799.675000 0 -- -- -- --
458 799.712500 0 -- -- -- --
465 799.800000 0 -- -- -- --
469 799.850000 0 -- -- -- --
472 799.887500 0 -- -- -- --
473 799.900000 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
494 800.162500 0 -- -- -- --
508 800.337500 0 -- -- -- --
516 800.437500 0 -- -- -- --
519 800.475000 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
526 800.562500 0 -- -- -- --
527 800.575000 0 -- -- -- --
530 800.612500 0 -- -- -- --
533 800.650000 0 -- -- -- --
534 800.662500 0 -- -- -- --
537 800.700000 0 -- -- -- --
541 800.750000 0 -- -- -- --
544 800.787500 0 -- -- -- --
545 800.800000 0 -- -- -- --
548 800.837500 0 -- -- -- --
551 800.875000 0 -- -- -- --
552 800.887500 0 -- -- -- --
555 800.925000 0 -- -- -- --
559 800.975000 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
562 801.012500 0 -- -- -- --
563 801.025000 0 -- -- -- --
566 801.062500 0 -- -- -- --
569 801.100000 0 -- -- -- --
570 801.112500 0 -- -- -- --
573 801.150000 0 -- -- -- --
577 801.200000 0 -- -- -- --
580 801.237500 0 -- -- -- --
581 801.250000 0 -- -- -- --
583 801.275000 0 -- -- -- --
584 801.287500 0 -- -- -- --
585 801.300000 0 -- -- -- --
587 801.325000 0 -- -- -- --
588 801.337500 0 -- -- -- --
591 801.375000 0 -- -- -- --
595 801.425000 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
602 801.512500 0 -- -- -- --
616 801.687500 0 -- -- -- --
617 801.700000 0 -- -- -- --
624 801.787500 0 -- -- -- --
634 801.912500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
638 801.962500 0 -- -- -- --
645 802.050000 0 -- -- -- --
660 802.237500 0 -- -- -- --
670 802.362500 0 -- -- -- --
674 802.412500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
677 802.450000 0 -- -- -- --
678 802.462500 0 -- -- -- --
681 802.500000 0 -- -- -- --
688 802.587500 0 -- -- -- --
695 802.675000 0 -- -- -- --
696 802.687500 0 -- -- -- --
699 802.725000 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
714 802.912500 0 -- -- -- --
717 802.950000 0 -- -- -- --
724 803.037500 0 -- -- -- --
732 803.137500 0 -- -- -- --
739 803.225000 0 -- -- -- --
746 803.312500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
753 803.400000 0 -- -- -- --
760 803.487500 0 -- -- -- --
761 803.500000 0 -- -- -- --
762 803.512500 0 -- -- -- --
763 803.525000 0 -- -- -- --
764 803.537500 0 -- -- -- --
765 803.550000 0 -- -- -- --
766 803.562500 0 -- -- -- --
767 803.575000 0 -- -- -- --
768 803.587500 0 -- -- -- --
769 803.600000 0 -- -- -- --
770 803.612500 0 -- -- -- --
771 803.625000 0 -- -- -- --
772 803.637500 0 -- -- -- --
773 803.650000 0 -- -- -- --
774 803.662500 0 -- -- -- --
775 803.675000 0 -- -- -- --
776 803.687500 0 -- -- -- --
777 803.700000 0 -- -- -- --
778 803.712500 0 -- -- -- --
779 803.725000 0 -- -- -- --
780 803.737500 0 -- -- -- --
781 803.750000 0 -- -- -- --
782 803.762500 0 -- -- -- --
783 803.775000 0 -- -- -- --
784 803.787500 0 -- -- -- --
785 803.800000 0 -- -- -- --
786 803.812500 0 -- -- -- --
787 803.825000 0 -- -- -- --
788 803.837500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
Direction Finding
Direction Finding Techniques
DF Antennas
Slide Number 20
Correlative Interferometry Technique
• Tasks of radio Direction Finding.
• Direction Finding Techniques.
• DF Antennas.
• Direction finding refers to the use of specialized instruments, antennas,
and methodologies to determine the physical location of a source of RF
energy or “targets”
• DF purposes:
• location of an unauthorized transmitter.
• location of an interfering transmitter which cannot be identified by other
means.
• determination of the site of a source of harmful interference of reception.
• identification of transmitters, both known and unknown.
Direction Finding Techniques
• amplitude sensitive.
• phase sensitive.
Requirements on DF system
• High sensitivity
• Immunity to multipath propagation
• Immunity to polarization errors
Requirements on DF system
• Stable response in case of non-coherent co-channel interferers
• DF of short-duration signals
intercept (POI)
Error sources
• The DF accuracy is affected by a number of influences:
• Wave propagation (usually disturbed by obstacles)
• Signals radiated by the emitters are modulated, limited in time and their
carrier frequency is often unknown
• Received field is additionally superimposed by noise, co-channel
interferers
Components of a DF system
• Antenna • Design usually specific to a given DF methodology
• Receiver(s) and processing unit • One or more receive channels with analog-to-digital conversion • Integrated or separate digital signal processing
• User interface • Software for display and control • Position fix and map display software
DF antenna Receiver(s) Processing unit Display and control
DF Antennas
• Beam/Yagi Antenna.
• Log-Period Antenna.
• Loop Antenna.
• Tune to null (sharper than gain)
• Front to back ratio > 50 db
• Can use front to help find weaker signals but with reduced bearing accuracy
Ron Milione - W2TAP 11
• 7.5 dBi typical gain in free space
• Good directivity: 14 dB typical front-to-back ratio
• Uniform pattern over up to 10:1 frequency range
• Radiating elements are fed by central transmission line
• Individual elements are repeated at intervals constant with logarithm of
frequency
Loop Antenna
• The loop antenna acts much the same as the secondary winding of a transformer.
• The voltage at the output is proportional to the amount of flux passing through it
and the number of turns.
• To obtain the most accurate bearings, the loop must be balanced electrostatically
with respect to ground.
• Otherwise, the loop will exhibit two modes of operation, One is the mode of a
true loop , The second mode is called the antenna effect.
Loop Antenna
• Very compact
Ferrite Rod Antennas (loopstick antennas)
• The true loop antenna responds to the magnetic field of the
radio wave, and not to the electrical field.
• The voltage delivered by the loop is proportional to the
amount of magnetic flux passing through the coil, and to the
number of turns in the coil.
Ferrite Rod Antennas (loopstick antennas)
• If an air-core loop is placed in a field, in essence it cuts the lines of flux without disturbing them (A), On the other hand, when a ferrite (magnetic) core is placed in the field, the nearby field lines are redirected into the loop (B).
• To get higher loop output is to increase the permeability of the medium by winding a coil of wire around a form made of high permeability material, such as ferrite rod, much greater flux is obtained in the coil without increasing the cross- sectional area.
Sense Antennas
• There is ambiguity as to which null indicates the true direction of the
target station.
• Modify a loop or loopstick antenna pattern to have a single null by
adding a second antenna element.
• It senses the phase of the signal wavefront for comparison with the
phase of the loop output signal.
Phased Arrays and Adcock
• The field radiated from a linear (straight) element, such as a dipole or
vertical monopole, is proportional to the sum of the elementary
currents flowing in each part of the antenna element.
• Many directional patterns are possible depending on the spacing and
phasing of the elements.
• The directional frequency range of this antenna is limited to one
band, because of the critical length of the phasing lines.
Adcock Antenna Adcock Antenna Pattern
LOOPS VERSUS PHASED ARRAYS • loops can be made smaller than suitable phased arrays for the same frequency of
operation.
• sharper nulls can be obtained with phased arrays.
• Loops are not as useful for skywave RDF work because of random polarization of
the received signal.
• Phased arrays are somewhat less sensitive to propagation effects, probably
because they are larger for the same frequency of operation and therefore offer
some space diversity.
• Doppler direction finder.
• Correlative Interferometry
Manual Direction Finding
Manual Direction Finding
• Evaluating the receive voltage is the simplest way of direction finding.
• Manual direction finding involves the use of a receiver and hand-held directional
antenna : usually some type of yagi / log-periodic.
• The antenna is moved / rotated until the point of maximum signal strength is
determined.
• Rotation can also be performed using an antenna mounted on a rotor or swivel.
Manual Direction Finding
• High sensitivity due to the directivity
• Simple and Low-cost, no need for dedicated DF receiver or complex
antennas
• Same antenna can be used for direction finding and monitoring
• Effectiveness depends strongly on the skill level of the operator.
• Typically four to eight antennas are arranged in a circular array and
are RF combined in a way that simulates rotation.
• As we move closer to a signal, the received frequency will shift
upwards (or vice-versa). This shift can be detected and used to
determine if we are moving in the right direction.
Doppler DF Concept
Doppler DF Concept
Doppler Direction Finder • Low cost compared to other DF systems .
• Cannot handle multiple signals.
• Antenna sensitivity : Low.
• Normally works best on VHF/UHF frequencies (< 1 GHz).
• Doesn’t work well for horizontally polarized signals (Doppler antennas
usually vertically polarized)
Watson-Watt DF Principle
• This DF method is based on two directional antennas pairs and one omni-
directional antenna
• The response of the two pairs are proportional to sine and cosine of the arrival
signal.
• Watson-Watt DF consists of three phase-matched receivers and displays angle of
arrival in terms of sine and cosine functions utilizing third omni-directional
channel to solve ambiguity.
• Benefits: • minimum signal duration is sufficient. • simple implementation. • Little space required (small aperture antenna array).
• Drawback: • Small aperture system (D/λ<0.2) leading to errors in case of multipath
propagation. • large DF errors in case of skywaves with steep elevation angles
Watson-Watt principle
Watson-Watt principle
• Improved error tolerances for skywave reception
• Implementation of wider apertures to avoid errors in case of multipath
reception
Angle of Arrival • AOA simply measures the angle(s) at which a signal arrives at an antenna array :
not the phase or time differences of the signal at different elements.
• To determine if a signal is “arriving” at an antenna, we make a determination of
the power of the incoming signal at one or more antennas, so AOA is sometimes
also called “power of arrival” (POA).
• AOA antennas are typically circular array of (somewhat) directional antennas.
• Resolution / bearing accuracy is increased with an increasing number of antenna
faces.
Interferometer
Interferometer Based DF
• This concept is based on phase measurement between a subset of possible pairs
of antennas with minimum of two coherent receiver channels
• Phase measurement for a specific pair can be used for arrival angle
determination, based on knowledge of relative antenna distance
• When more then one pair is used elevation calculation is possible
• Antenna sensitivity: low
• Azimuth accuracy: σ = 1.5°–3°
Time Difference of Arrival (TDOA) • Three or more receivers at different locations receive
a signal from the target.
• Usually the paths between the transmitter and the
receivers are of different length, so there are
differences in the time of arrival at the different
receiver locations.
hyperbolae which cross at the location of the
transmitter of interest.
Time Difference of Arrival (TDOA) • Once we have computed the time difference, Δt, between the times the signal was received at
two stations, we can then compute / plot a hyperbola representing this distance between them.
• The intersection of multiple hyperbolae yields the estimated target location.
Time Difference of Arrival (TDOA) • Requires small aperture antenna array
• Requires single-channel receiver
Correlative Interferometry Technique
• Minimizes effect of signal modulation and fading
• Measures amplitude and phase
Correlative Interferometry
• Antenna Sensitivity: high
• Data Collection Time: fast; depends on number of receiver channels
Locating the Transmitter source
1. Monitoring (Frequency – B.W - Modulation)
2. DF (Fixed Stations)
3. Detection of location (2 fixed stations – one fixed and one mobile – SSL)
4. Homing using Mobile.
Single Site Location
• When a propagation path of no more than one reflection at the
ionosphere can be assumed, position of an HF emitter can be
determined by a single observing site using vertical triangulation,
provided that the height of the ionosphere at the point where the
radio wave is reflected, can be determined.
Single Site Location
• Elevation angle of arrival is measured by HFDF system
• Electron density profile of the ionosphere is measured by ionospheric sounder
• The path of the electromagnetic wave through the ionosphere can be reconstructed
using a ray tracing algorithm
• The distance to target transmitter can be calculated based on Martyn's Theorem
(with correction terms)
SSL Distance Calculation
Direction Finding Measurement
Direction Finding Measurement
Direction Finding Measurement DF Scan Summary Report Task No: 38097 Storage Interval: 15 secs Operator ID: TCI-WS-2 Noise Riding Threshold: 15 dB Schedule Time: 10/4/2016 11:49:00 AM Fixed Duration: 30 secs Completion Time: 10/4/2016 11:49:30 AM DF Resolution: 1 deg Site Location: N 30 1' 21" Azimuth Range: 0 --- 360 E 31 12' 32.1" All Single Band
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation Summary 1 794.000000 0 -- -- -- -- 2 794.012500 0 -- -- -- -- 3 794.025000 0 -- -- -- -- 4 794.037500 0 -- -- -- -- 5 794.050000 0 -- -- -- -- 6 794.062500 0 -- -- -- -- 7 794.075000 0 -- -- -- -- 8 794.087500 0 -- -- -- -- 9 794.100000 0 -- -- -- -- 10 794.112500 0 -- -- -- -- 11 794.125000 0 -- -- -- -- 12 794.137500 0 -- -- -- -- 13 794.150000 0 -- -- -- -- 14 794.162500 0 -- -- -- -- 15 794.175000 0 -- -- -- -- 16 794.187500 0 -- -- -- -- 17 794.200000 0 -- -- -- -- 18 794.212500 0 -- -- -- -- 19 794.225000 0 -- -- -- -- 20 794.237500 0 -- -- -- -- 21 794.250000 0 -- -- -- -- 22 794.262500 0 -- -- -- -- 23 794.275000 0 -- -- -- -- 24 794.287500 0 -- -- -- -- 25 794.300000 0 -- -- -- -- 26 794.312500 0 -- -- -- -- 27 794.325000 0 -- -- -- -- 28 794.337500 0 -- -- -- --
10/18/2020 9:33:19 AM Page 1 of 22
DF Scan Summary Report
Operator ID: TCI-WS-2 Noise Riding Threshold: 15 dB
Schedule Time: 10/4/2016 11:49:00 AM Fixed Duration: 30 secs
Completion Time: 10/4/2016 11:49:30 AM DF Resolution: 1 deg
Site Location: N 30 1' 21" Azimuth Range: 0 --- 360
E 31 12' 32.1"
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
46 794.562500 0 -- -- -- --
47 794.575000 0 -- -- -- --
50 794.612500 0 -- -- -- --
51 794.625000 0 -- -- -- --
53 794.650000 0 -- -- -- --
54 794.662500 0 -- -- -- --
57 794.700000 0 -- -- -- --
61 794.750000 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
71 794.875000 0 -- -- -- --
72 794.887500 0 -- -- -- --
75 794.925000 0 -- -- -- --
79 794.975000 0 -- -- -- --
82 795.012500 0 -- -- -- --
83 795.025000 0 -- -- -- --
86 795.062500 0 -- -- -- --
89 795.100000 0 -- -- -- --
90 795.112500 0 -- -- -- --
93 795.150000 0 -- -- -- --
97 795.200000 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
108 795.337500 0 -- -- -- --
111 795.375000 0 -- -- -- --
118 795.462500 0 -- -- -- --
119 795.475000 0 -- -- -- --
125 795.550000 0 -- -- -- --
126 795.562500 0 -- -- -- --
129 795.600000 0 -- -- -- --
133 795.650000 0 -- -- -- --
136 795.687500 0 -- -- -- --
140 795.737500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
147 795.825000 0 -- -- -- --
154 795.912500 0 -- -- -- --
155 795.925000 0 -- -- -- --
158 795.962500 0 -- -- -- --
161 796.000000 0 -- -- -- --
162 796.012500 0 -- -- -- --
165 796.050000 0 -- -- -- --
166 796.062500 0 -- -- -- --
167 796.075000 0 -- -- -- --
168 796.087500 0 -- -- -- --
169 796.100000 0 -- -- -- --
172 796.137500 0 -- -- -- --
173 796.150000 0 -- -- -- --
176 796.187500 0 -- -- -- --
179 796.225000 0 -- -- -- --
180 796.237500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
183 796.275000 0 -- -- -- --
184 796.287500 0 -- -- -- --
186 796.312500 0 -- -- -- --
187 796.325000 0 -- -- -- --
190 796.362500 0 -- -- -- --
191 796.375000 0 -- -- -- --
194 796.412500 0 -- -- -- --
197 796.450000 0 -- -- -- --
198 796.462500 0 -- -- -- --
201 796.500000 0 -- -- -- --
204 796.537500 0 -- -- -- --
205 796.550000 0 -- -- -- --
208 796.587500 0 -- -- -- --
209 796.600000 0 -- -- -- --
212 796.637500 0 -- -- -- --
215 796.675000 0 -- -- -- --
216 796.687500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
222 796.762500 0 -- -- -- --
223 796.775000 0 -- -- -- --
226 796.812500 0 -- -- -- --
227 796.825000 0 -- -- -- --
230 796.862500 0 -- -- -- --
233 796.900000 0 -- -- -- --
234 796.912500 0 -- -- -- --
237 796.950000 0 -- -- -- --
241 797.000000 0 -- -- -- --
251 797.125000 0 -- -- -- --
252 797.137500 0 -- -- -- --
255 797.175000 0 -- -- -- --
256 797.187500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
259 797.225000 0 -- -- -- --
262 797.262500 0 -- -- -- --
269 797.350000 0 -- -- -- --
270 797.362500 0 -- -- -- --
273 797.400000 0 -- -- -- --
277 797.450000 0 -- -- -- --
284 797.537500 0 -- -- -- --
288 797.587500 0 -- -- -- --
291 797.625000 0 -- -- -- --
292 797.637500 0 -- -- -- --
294 797.662500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
298 797.712500 0 -- -- -- --
306 797.812500 0 -- -- -- --
313 797.900000 0 -- -- -- --
316 797.937500 0 -- -- -- --
320 797.987500 0 -- -- -- --
327 798.075000 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
334 798.162500 0 -- -- -- --
342 798.262500 0 -- -- -- --
356 798.437500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
374 798.662500 0 -- -- -- --
378 798.712500 0 -- -- -- --
381 798.750000 0 -- -- -- --
388 798.837500 0 -- -- -- --
389 798.850000 0 -- -- -- --
392 798.887500 0 -- -- -- --
393 798.900000 0 -- -- -- --
395 798.925000 0 -- -- -- --
396 798.937500 0 -- -- -- --
399 798.975000 0 -- -- -- --
400 798.987500 0 -- -- -- --
401 799.000000 0 -- -- -- --
407 799.075000 0 -- -- -- --
408 799.087500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
415 799.175000 0 -- -- -- --
418 799.212500 0 -- -- -- --
419 799.225000 0 -- -- -- --
422 799.262500 0 -- -- -- --
426 799.312500 0 -- -- -- --
429 799.350000 0 -- -- -- --
430 799.362500 0 -- -- -- --
432 799.387500 0 -- -- -- --
433 799.400000 0 -- -- -- --
436 799.437500 0 -- -- -- --
437 799.450000 0 -- -- -- --
440 799.487500 0 -- -- -- --
443 799.525000 0 -- -- -- --
444 799.537500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
454 799.662500 0 -- -- -- --
455 799.675000 0 -- -- -- --
458 799.712500 0 -- -- -- --
465 799.800000 0 -- -- -- --
469 799.850000 0 -- -- -- --
472 799.887500 0 -- -- -- --
473 799.900000 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
494 800.162500 0 -- -- -- --
508 800.337500 0 -- -- -- --
516 800.437500 0 -- -- -- --
519 800.475000 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
526 800.562500 0 -- -- -- --
527 800.575000 0 -- -- -- --
530 800.612500 0 -- -- -- --
533 800.650000 0 -- -- -- --
534 800.662500 0 -- -- -- --
537 800.700000 0 -- -- -- --
541 800.750000 0 -- -- -- --
544 800.787500 0 -- -- -- --
545 800.800000 0 -- -- -- --
548 800.837500 0 -- -- -- --
551 800.875000 0 -- -- -- --
552 800.887500 0 -- -- -- --
555 800.925000 0 -- -- -- --
559 800.975000 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
562 801.012500 0 -- -- -- --
563 801.025000 0 -- -- -- --
566 801.062500 0 -- -- -- --
569 801.100000 0 -- -- -- --
570 801.112500 0 -- -- -- --
573 801.150000 0 -- -- -- --
577 801.200000 0 -- -- -- --
580 801.237500 0 -- -- -- --
581 801.250000 0 -- -- -- --
583 801.275000 0 -- -- -- --
584 801.287500 0 -- -- -- --
585 801.300000 0 -- -- -- --
587 801.325000 0 -- -- -- --
588 801.337500 0 -- -- -- --
591 801.375000 0 -- -- -- --
595 801.425000 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
602 801.512500 0 -- -- -- --
616 801.687500 0 -- -- -- --
617 801.700000 0 -- -- -- --
624 801.787500 0 -- -- -- --
634 801.912500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
638 801.962500 0 -- -- -- --
645 802.050000 0 -- -- -- --
660 802.237500 0 -- -- -- --
670 802.362500 0 -- -- -- --
674 802.412500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
677 802.450000 0 -- -- -- --
678 802.462500 0 -- -- -- --
681 802.500000 0 -- -- -- --
688 802.587500 0 -- -- -- --
695 802.675000 0 -- -- -- --
696 802.687500 0 -- -- -- --
699 802.725000 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
714 802.912500 0 -- -- -- --
717 802.950000 0 -- -- -- --
724 803.037500 0 -- -- -- --
732 803.137500 0 -- -- -- --
739 803.225000 0 -- -- -- --
746 803.312500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
753 803.400000 0 -- -- -- --
760 803.487500 0 -- -- -- --
761 803.500000 0 -- -- -- --
762 803.512500 0 -- -- -- --
763 803.525000 0 -- -- -- --
764 803.537500 0 -- -- -- --
765 803.550000 0 -- -- -- --
766 803.562500 0 -- -- -- --
767 803.575000 0 -- -- -- --
768 803.587500 0 -- -- -- --
769 803.600000 0 -- -- -- --
770 803.612500 0 -- -- -- --
771 803.625000 0 -- -- -- --
772 803.637500 0 -- -- -- --
773 803.650000 0 -- -- -- --
774 803.662500 0 -- -- -- --
775 803.675000 0 -- -- -- --
776 803.687500 0 -- -- -- --
777 803.700000 0 -- -- -- --
778 803.712500 0 -- -- -- --
779 803.725000 0 -- -- -- --
780 803.737500 0 -- -- -- --
781 803.750000 0 -- -- -- --
782 803.762500 0 -- -- -- --
783 803.775000 0 -- -- -- --
784 803.787500 0 -- -- -- --
785 803.800000 0 -- -- -- --
786 803.812500 0 -- -- -- --
787 803.825000 0 -- -- -- --
788 803.837500 0 -- -- -- --
Chan Frequency Total Num. Cuts Used Azimuth Field Str. Standard
Num (MHz) Of Cuts in (Degrees) (dBuV/m) Deviation
Summary
Direction Finding
Direction Finding Techniques
DF Antennas
Slide Number 20
Correlative Interferometry Technique