bell 870 radar detector tests

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RADAR DETECTOR TESTS - 2002

Developed under

Georgia Tech Research Institute Project Number A-6515Beltronics Agreement Dated 02-15-01

Prepared by

Ekkehart O. Rausch, Spiro G. Sarris, Eugene F. Greneker

Sensors and Electromagnetic Applications LaboratoryGeorgia Tech Research InstituteGeorgia Institute of Technology

7220 Richardson RoadSmyrna, Georgia, 30080

Prepared for:

Beltronics, Inc.

2422 Dunwin DriveMississauga, Ontario

Canada L5L 1J9

1 July 2002

GEORGIA INSTITUTE OF TECHNOLOGYA Unit of the University System of Georgia

Atlanta, Georgia 30332


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BELTRONICS CORPORATION PROPRIETARY INFORMATION

LIST OF TABLES

Table Page

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1 Power Level Linearity .................................................................................................................... 5

2 Calibrated Power Density at Each Frequency (2002 Data)...................................................... 6

3 Calibrated Power Density at Each Frequency (Phase 2 Data) ................................................ 6

4 Power Level Limits Output by the Synthesizer (2002 Data) ................................................... 7

5 Power Level Limits Output by the Synthesizer (Phase 2 Data).............................................. 7

6 Typical Output Files ..................................................................................................................... 12


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ACKNOWLEDGEMENTS

This project was funded by Beltronics Corporation. The project manager was Gene Greneker.

The task manager and test director was Ekkehart Rausch. Spiro Sarris generated the final testmatrices and graphs from the test data.


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RADAR DETECTOR TESTS - 2002

1. OBJECTIVE

Beltronics, Inc. contracted with the Georgia Tech Research Institute (GTRI) to test the sensitivityof a number of radar detectors purchased from various manufacturers. The primary objectivewas to measure the radar detector sensitivity in an anechoic chamber in order to eliminateexternal radiation fields that could initiate an unpredictable false alarm. The tests wereconducted at five frequencies (10.525, 24.15, 33.5, 34.7 and 35.9 GHz) and divided into threephases. Phase 1 was completed and published in a final report dated 27 April 2001 [1]. ThePhase 1 results represent the performance of the detectors that were on the market prior to1 April 2001. Fifteen additional detectors were purchased for Phase 2. These units represent thedetector technology that existed between 1 April 2001 and 1 September 2001. The results of thePhase 2 detectors are found in a report published on 9 September 2001 [2]. The current resultsare based on detectors that were on the market between 1 September 2001 and 1 June 2002.

These detectors were manufactured by Beltronics, Whistler, Cobra, Uniden and Snooper UK.

2. INTRODUCTION

Radar detector sensitivities obtained on the road vary with weather, soil and terrain conditions,and are subject to reflections from other obstacles. These tests may not be repeatable and areusually not consistent over a long period of time. The inside of an anechoic chamber is immuneto the external environment and electromagnetic fields. Therefore, anechoic measurements arerepeatable and consistent over time.

The Georgia Tech Research Institute has an indoor microwave-millimeter wave anechoic

chamber. This chamber was available for the detector tests. It measures 20 ft by 30 ft and has acombination of 12 inch and 24 inch absorber panels. The chamber is completely shielded with ametallic enclosure that has been tested to 100 dBm at 1 to 18 GHz and is useful into themillimeter wave region. A picture of the interior and exterior of the anechoic chamber with aview toward the door is shown in Figure 1. A layout of the chamber is given in Figure 2.

Figure 1. Photograph of the interior and exterior of the Georgia Tech anechoic chamber


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Door

REMOVABLE

HYBRID

ABSORBERS

TRANS

MITTERAREA

Door

RADAR

DETECTOR

AREA

20 FT

8" x 18"

Access

Panel

8" x 18"

Access

Panel

36 FT

8" x 18"Access

Panel

6 FT

8" x 18"Access

Panel

6 FT 22 FT

TRANSMISSION

DISTANCE

17 FT

Figure 2. Anechoic chamber floor plan

For measurements to be repeatable the power density of the radiated fields inside the chambermust be calibrated and the test procedure must be identical for each radar detector unit. Theprocedures that accomplished this goal are presented in the following sections. Section 3describes the calibration process. The test procedure is outlined in Section 4, and the results ofthe tests are discussed in Section 5.

3. CALIBRATION

Georgia Tech used three standard gain horns to calibrate the power density at the front of adetector. For Phase 2, Horn #1, with a gain of 22.47 dB, was selected for calibration at 10.525GHz. Horn #2 had a gain of 24.73 dB at 24.15 GHz. Horn #3 operated at the highest threefrequencies, 33.5, 34.7 and 35.9 GHz, with gain values of 23.4, 23.6 and 23.78 dB, respectively.For the 2002 calibration, Horn #1 and 2 were identical to those used in Phase 2. Only Horn #3,manufactured by MI-Technology - Model 12A-26, was different. The respective gains were24.51 dB at 33.5 GHz, 24.67 dB at 34.7 GHz and 24.81 dB at 35.9 GHz.

The procedure of the calibration method was to measure the received power with the respectivestandard gain horns at the frequencies of interest. The power was divided by the aperture of

the horn to obtain the power density. The effective horn aperture A was determined fromEquation 1 using the corresponding gain G of each horn at the selected frequency.

A = G ( 2 / 4 ) (1)

To simplify the calibration process, the transmitter horn was sufficiently broad to cover the 10 to40 GHz band. Therefore, the transmitter horn did not have to be changed at differentfrequencies. This single ridge, broad band, transmitter horn was obtained from Beltronics


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Corporation. The transmitter horn was mounted on a plastic platform, shown in Figures 3 and4, and connected to a Hewlett Packard synthesizer (HP 83640A), visible at the bottom ofFigure 4. Power radiated by the transmitter horn was captured on the other side of the chamberby a standard gain horn and routed to a spectrum analyzer (HP 8565E) by means of a cable.This calibration configuration is shown in Figure 5. The loss of the cable was not insignificantand, therefore, was taken into account in the final calibration equations. The power density atthe standard gain horns was derived with a power level of +5 dBm as indicated on thesynthesizer display. This power level was selected because it provided a high signal to noiseratio and, thus, accurate power readings. Higher power levels were avoided, because therelationship between the synthesizer output power and the display at levels > 5dBm was nolonger linear, which could have led to errors in the calibration data.

Figure 3. Close-up photograph of transmitter horn


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Figure 4. Plastic tower with the transmitter horn


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TRANSMITTER

HORN

SUPPORT

STRUCTURE

STANDARD

GAIN HORN

TRIPOD

SYNTHESIZER

27.25"

1.75"

55"

67.5"

16.5"

SPECTRUM

ANALYZER

CABLE

Figure 5. Calibration configuration

To ensure linearity over the full range of power levels used during the tests, GTRI measured thelinear correlation between power levels read from the spectrum analyzer and the synthesizerdisplay at levels down to 50 dBm. In this case, the power output by the synthesizer was inputdirectly into the spectrum analyzer. The display was set to +5 and 50 dBm. Differencesbetween these numbers and the power measured at the spectrum analyzer were due to cableand connector loss. The results of this experiment are shown in Table 1. The differencebetween the high and low power readings should ideally be 55 dB as indicated by thesynthesizer display. The actual differences are shown in the right hand column of Table 1.

TABLE 1. POWER LEVEL LINEARITY

FREQUENCY(GHz)

MEASUREDPOWER @ +5 dBm

(dBm)

MEASUREDPOWER @ -50

dBm(dBm)

DIFFERENCE(dBm)

35.9 0.3 0.1 -55 1.0 -55.3 1.1

24.15 1.6 0.05 -53.7 0.5 -55.3 0.5

10.525 1.7 0.05 -53.2 0.1 -54.9 0.1

Table 2 shows the measured power at the spectrum analyzer, as well as the gain, aperture, andpowerdensity obtained at each frequency using the respective standard gain horns with thesynthesizer output set to +5dBm. For comparison, Table 3 shows the calibration data collectedin Phase 2. The difference between the calibrated power densities (last column of Table 2 and 3)is 0.9 dB, 0.6 dB, 0.7 dB, 0.5dB, and 1.5 dB for 35.9 GHz, 34.7 GHz, 33.5 GHz, 24.15 GHz and10.525 GHz, respectively. Thus, the calibrated power density differences are under 1 dB for theK and Ka-band frequencies and 1.5 dB at X-band. The power densities usually vary by + 2 dB


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or less (which includes calibration differences) between different data sets collected at differenttimes of the year.

TABLE 2. CALIBRATED POWER DENSITY AT EACH FREQUENCY(2002 CALIBRATION DATA)

FREQ. POWER AT CABLE POWER POWER HORN HORN HORN POWER

SPECTRUM LOSS AT TEST AT TEST GAIN GAIN APERTURE DENSITY @

ANALYZER PEDESTAL PEDESTAL DETECTOR

(GHz) (dBm) (dB) (dBm) (mW) (dB) (cm2) (dBm/cm2)

35.9 -45.33 5.50 -39.83 1.040E-04 24.81 302.691 16.80 -52.08

34.7 -45.33 5.33 -40.00 1.000E-04 24.67 293.089 17.41 -52.41

33.5 -44.67 5.17 -39.50 1.122E-04 24.51 282.488 18.00 -52.05

24.15 -41.50 4.33 -37.17 1.919E-04 24.73 297.167 36.44 -52.79

10.525 -40.83 2.66 -38.17 1.524E-04 22.47 176.604 114.02 -58.74

TABLE 3. CALIBRATED POWER DENSITY AT EACH FREQUENCY(PHASE 2 CALIBRATION DATA)

FREQ. POWER AT CABLE POWER POWER HORN HORN HORN POWER

SPECTRUM LOSS AT TEST AT TEST GAIN GAIN APERTURE DENSITY

ANALYZER PEDESTAL PEDESTAL

(GHz) (dBm) (dB) (dBm) (mW) (dB) Linear Units (cm2) (dBm / cm2)

35.9 -45.00 5.00 -40.00 1.000E-04 23.78 238.78 13.27 -51.2

34.7 -45.20 4.70 -40.50 8.913E-05 23.60 229.09 13.63 -51.8

33.5 -44.90 5.00 -39.90 1.023E-04 23.41 219.28 13.99 -51.4

24.15 -41.30 3.60 -37.70 1.698E-04 24.73 297.17 36.49 -53.3

10.525 -39.30 2.70 -36.60 2.188E-04 22.47 176.60 114.18 -57.2

Tables 2 and 3 give the power densities at the detector test stand with the synthesizer displayset to a power level of +5 dBm. The power at the test stand was higher than the powermeasured at the spectrum analyzer, because the measured power level was attenuated by thecable between the spectrum analyzer and the standard gain horn. The cable attenuation wasmeasured again and found to be 2.7 dB at 10.525 GHz, 4.3 dB at 24.15 GHz, 5.2 dB at 33.5 GHz,5.3dB at 34.7 GHz and 5.5 dB at 35.9 GHz. These cable losses were added to the powermeasured at the spectrum analyzer to give the correct power level at the aperture of thestandard gain horn. That aperture was located at the front edge of the detector pedestal.During the tests the front of the detectors were placed at the same location.

The power density levels in Table 2 and 3 were derived with a synthesizer power level of +5dBm. The numbers required by the test software, however, are the synthesizer power levelsthat correspond to a power density of 120 dBm/cm2. These levels may be computed by takingthe difference between the power densities computed in Table 2 (2002 data) and the powerdensity of 120 dBm/cm2and subtracting that difference from + 5dBm as indicated in Equation2.


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PSYN-OUT-LL = +5 dBm - [(PDENS5- (- 120 dBm/cm2)] (Lower Limit) (2)

PSYN-OUT-LL is the lower limit power level at the output of the synthesizer. PDENS5 is thepower density at the detector with the synthesizer output power at + 5 dBm. The power levelscomputed with Equation 2 are shown in Table 4 for 2002 data. The equivalent levels derived inPhase 2 are given in Table 5 for comparison.

TABLE 4. POWER LEVEL LIMITS OUTPUT BY THE SYNTHESIZER

(2002 DATA)

FREQUENCY(GHz)

POWER DENSITYAT DETECTOR

@ +5 dBm(dBm/cm2 )

SYNTHESIZEROUTPUT POWER@ - 120 dBm/cm2

(dBm)

35.9 -52.1 -62.9

34.7 -52.4 -62.6

33.5 -52.1 -62.9

24.15 -52.8 -62.2

10.525 -58.8 -56.3

TABLE 5. POWER LEVEL LIMITS OUTPUT BY THE SYNTHESIZER

(PHASE 2 DATA)

FREQUENCY(GHz)

POWER DENSITYAT DETECTOR

@ +5 dBm(dBm/cm2 )

SYNTHESIZEROUTPUT POWER@ - 120 dBm/cm2

(dBm)

35.9 -51.2 -63.8

34.7 -51.8 -63.2

33.5 -51.3 -63.7

24.15 -53.3 -61.7

10.525 -57.2 -57.8

The original specifications were to test the detectors between 120 dBm/cm2 and 80 dBm/cm2.However, it was found that the alarm for some detectors is triggered at power densities greaterthan 80 dBm/cm2. Hence, the upper power density limits were set to the levels in column 2 ofTable 4, which were equivalent to the maximum synthesizer output power of + 5 dBm.

It is now possible to determine the sensitivity of any radar detector by setting the synthesizer tothe lower power level and increasing the power in steps of 1 dB until the upper power limit is


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obtained. At some point between the two limits, the detector will provide an audible alert. Thesynthesizer output power at the alert point was converted to the actual power density withEquations 3, 4, 5, 6 and 7. These calibration equations were obtained by computing thedifference between the recorded alarm power level and the power level at 120 dBm/cm2 andthen adding that difference tothe 120 dBm/cm2power density. The Power-level-Recorded isthe power output in dBm reported by the synthesizer to the LabView software when thedetector alarms. PDENS is the power density computed from measured data.

PDENS (35.9 GHz) = Power-level-Recorded + 62.9 dBm - 120 dBm / cm2 (3)





4. TEST PROCEDURE

The radar detector test configuration is shown in Figure 6. This configuration is nearly identicalto the calibration configuration, except that the spectrum analyzer and standard gain horn wereremoved. The detectors were placed onto a plastic platform, which was mounted to the top of atripod. The tripod height was adjusted so that the center of the detector in the verticaldimension was at the same height as the center of the transmitter horn. A microphone attachedto the rear of the detector platform transmitted the audio alert signal to a laptop computerexternal to the anechoic chamber. A photograph of the tripod, microphone and the detector is

shown in Figure 7. Masking tape was used to hold the detector in place during the test run.The paper clip shown in Figure 7 was removed.

Small changes in range between the detector and transmitter horn had a negligible effect on themeasured power. To prove this point, the received power at range R and R + 0.5 feet iscalculated below with Equation 8.

PR = (PTGTGR2) / [(42) R2L] (8)

In Equation 8 power is proportional to range squared. All other variables in that equation areconstant for this calculation. Hence, the ratio of the received powers with R equals to 17 feetand 17.5 feet is

PR/ PR + 0.5 = (17.5)2 / (17.0)2 = 1.06

In dB, the power ratio is

10 log (PR/ PR + 0.5) = 10 log 1.06 = 0.25 dB

Thus, this calculationshows that a range increase of 6 inches results in a 0.25 dB change in thereceived power. Most range variations were less than 0.5 inches and, thus, negligible.


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TRANSMITTER

HORN

SUPPORT

STRUCTURE

DETECTOR

TRIPOD

SYNTHESIZER

MICRO

PHONE

OUTPUT

27.25"

1.75"

55"

67.5"

16.5"

Figure 6. Test configuration

Figure 7. Tripod with detector and covered microphone

Prior to the tests, all radar detectors were stored overnight in the anechoic chamber to ensurethermal equilibrium with the chamber temperature. In addition, the test source was turned onand left on overnight. The tests were initiated the next morning in the following sequence:


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1. The detector was placed on the pedestal facing the source at the same height. Thechamber was closed and a new file was initiated on the laptop computer labeledwith the appropriate manufacturers initials and model number of the detector.

2. As soon as the file was created the software initiated a 5 minute count down.

3. After the 5 minute warm up period, the HP synthesizer source was set to the firstfrequency. The power level was increased from -120 dBm per square cm in 1 dBsteps with a 4 second period between the steps.

4. When the detector alert was initiated the power level (at the time of the alert) andfrequency were written into the file and the power level was reset to -120 dBm persquare cm. A 10-second delay was introduced before the power was increased againas in step 3 above, but at a different frequency.

5. After all 5 frequencies were tested the detector was turned off and turned on again.A new file was created for the second run with the same detector and steps 2, 3 and 4above were repeated.

6. Next, the test sequence 1 through 5 was repeated with a different detector. This

procedure reduced the test time for one detector to about 30 minutes.

The test station that automated the test procedure is shown in Figure 8. It consists of a RadioShack Model 32-1214 audio mixer, an analog to digital converter and a laptop. The microphoneoutput was routed to the audio mixer to amplify the signal voltage between 0 and 5 volts. Thissignal was digitized and sent to the laptop computer where it was processed by the LabViewsoftware written expressly for this test. The LabView computer software also controlled the HPsynthesizer by means of a HP-IB link. The software provided a Windows-type display on thelaptop computer, which facilitated easy control of the waiting periods and other parameters,primarily for debugging purposes. A view of the software control panel is shown in Figure 9.The waiting period between the 1 dB power steps was adjusted until the software was able tosense the audio alert, write the trigger power into a file, and plot the trigger power on thedisplay window. The plot served as an instant visual check of the trigger power points.


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Figure 8. Automated test station

Figure 9. Display window of the radar detector test software


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5. RESULTS

At least two files were created for each detector run. These files contained the test frequenciesand the corresponding trigger power points. An example of these files is shown in Table 4. TheB in the file name refers to Beltronics Corporation, 870 designates the radar detector modeland the 1 or 2 refers to the first or second test run for that model.

TABLE 6. TYPICAL OUTPUT FILES (PHASE 1)

FREQUENCY(GHz)

FILE B-870-1TRIGGER POWER (dBm)

FILE B-870-2TRIGGER POWER (dBm)

10.525000 -45.500000 -46.50000

24.150000 -45.500000 -46.50000

33.500000 -40.300000 -41.300000

34.700000 -38.400000 -37.400000

35.900000 -36.500000 -35.500000

The power points were entered into an excel file and converted to power density by means ofEquations 3 through 7. The power densities at each frequency from the two available files wereaveraged and the resultant average density displayed in matrix format. The left half of thematrices provide the manufacturers name, model number and serial number. The right halfcontains the measured detector sensitivities for two at least two runs plus the average of theruns.

To ensure reliability and credibility of the test results five detectors purchased under Phase 1were re-tested in Phase 2 as shown in Figure 10. The detectors included the Whistler DE1780,Whistler DE1785, and Beltronics 870, 950 and 980. Most of the Phase 2 data agreed within 2 dBor less with data that were collected during Phase 1. An exception to the reference data was theBel 870 at 35.9 GHz. This Phase 2 point varied from the Phase 1 data by 3.8 dB. The change insensitivity was assumed to be due to changes in the detector. Thus, the accuracy of themeasurements between test phases is estimated to be within 2 dB. The measurements for the2002 detectors are shown in Figures 11 and 12.

6. CONCLUSIONS AND RECOMMENDATIONS

The 2002 results show that the sensitivity of the Beltronics radar detectors is superior at the Kand Ka-bands to the other detectors. In one case (primarily at 35.9 GHz) the Beltronic detectorsare almost 100 times more sensitive than the other 2002 detectors. The Snooper detectors maybe an exception to this rule, because they were intended primarily for the European market.The sensitivities of these radar detectors may not be representative of their true capabilities,because the police radar frequencies in Europe are, in some respects, different from those in theUnited States. Thus, a retest of the Snooper detectors using the European frequencies isrecommended in the future.

bell 870 radar detector tests

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