Trunking Radio Compatibility Issues New
- 1. Trunking Radio Compatibility Issues by John Raymond Steffes Manager, Voice Systems January 2004 Kennedy Space Center Florida, 32899
- 2. Trunking Radio Compatibility Issues 1 Introduction The need for equipment using radio communications ranges from megawatt power radars used to track objects the size of a golf ball at a distance of a hundred miles or more to milliwatt power wireless computerized equipment that provides copper path elimination enabling greater system efficiency. The effects of non-ionizing radio frequency (R.F.) waves that makes these devices possible are a concern to all, since the R.F. spectrum is a finite resource and certain levels of radiation intensity may cause unintentional interference to other equipment and affect human anatomy. This paper reflects those R.F. concerns regarding compatibility issues with respect to the new Motorola Trunking Radio system currently being implemented at Kennedy Space Center (KSC). This system also supports the central computer trunking radio operations for nearby government facilities and United States Air Force installations. The scope of this effort includes: The rationale and purpose for use of trunking radio Electric field and antenna gain discussion that acquaints the reader to technical aspects of radio wave propagation and the peculiarities of radio transmission measurement Consideration of standards and specifications and their comparisons that affect compatibility issues Power conservation features of the new trunking radio portable radios that substantially reduce radiated emission
- 3. Conclusions and recommendations regarding trunking radio compatibility issues. 2 Rationale for Trunking Radio In an effort to promote efficient and effective R.F. communications, the National Telecommunications and Information Administration (NTIA) has planned mandates requiring a more restricted R.F spectrum that will apply to KSC, Cape Canaveral Air Force Station (CCAFS), Patrick Air Force Base (PAFB), and the Malabar Test Site (Malabar) radio communication operations. In addition, the NTIA will require a reduction of communication transmission bandwidth also known as narrowbanding. The NTIA mandates will result in a substantial change in the radio communication methodology and operation currently in use at KSC, CCAFS, PAFB and Malabar. In terms of R.F. spectrum restrictions, the new spectrum band plan for government use will result in the redistribution of all discrete communica tion frequency use within the Very High Frequency (VHF) portion spectrum by the year 2005. Additional frequency budgeting will affect the currently used discrete Ultra High Frequency (UHF) operations by 2008. Implementation of this plan will allow re-distribution of those discrete frequencies currently used by KSC, CCAFS, PAFB, and Malabar. Narrowbanding restrictions are described in chapter 5, section 5.3.5.2 of the NTIA Manual of Regulations & Procedures for Federal Radio Frequency Management. The standards outlined in that section apply to narrowband systems at KSC and its environs designed to operate in the 138-150.8, 162-174 and 406.1-420 MHz bands. Mandated transmission bandwidth characteristics indicate that the levels of emission to
- 4. be 70 dB down from the carrier peak at 12.5 kHz from the carrier center frequency. It should be noted that a substantial portion of the current land/mobile radio VHF communication equipment used by KSC does not meet this 12.5 kHz requirement. Consequences of nonconformance with the provisions of this chapter will result in the responsibility for eliminating the harmful interference. These consequences normally shall rest with the agency operating in nonconformance. The problem presented by the NTIA mandate regarding KSC radio operation is how compliance will be achieved through implementation of the proposed band plan in a timely manner with respect to VHF and UHF frequency redistribution, and conformance with equipment specifications that will ensure 12.5 kHz maximum bandwidth 3 characteristics. A potential solution regarding the NTIA band plan and bandwidth limit restriction for KSC, CCAFS, PAFB, and Malabar has been procured, installed, and is in the process of final implementation. It is called trunking radio; however, there are technical, managerial, and operational related issues that require resolution prior to full trunking radio implementation. As planned, the proposed trunking radio system at KSC will be fully compliant to all planned NTIA mandates for the VHF portion of the radio spectrum by 2005 and the UHF portion by 2008; thus, the planned frequency redistribution can be achieved and nonconformance of standards will not be jeopardized near or long term. Electric Field and Antenna Gain Discussion The following discussion introduces the reader to some of the technical aspects of the trunking radio R.F. performance with respect to antenna gain, power output attributes,
- 5. and the use of field measurements regarding antenna gain characteristics. Please note that the power levels indicated in this discussion are absolute worst case or highest power examples; thus, may not reflect actual operational conditions. This section is based on actual field measurements taken in August 2003 as provided by the Boeing-KSC-N120- 53410-03 report as performed by Electromagnetic Laboratory (EML) personnel at KSC. Calculation of the equivalent isotropic radiated power (EIRP), in dBm, emanating from the transmitting antenna is shown below. The calculation, based on the point-to-point received signal strength measured at a 25’ over an undisclosed height above the ground at a distance and 416.82 MHz, is as follows: Distance (RM ) = 25’ .3048 m/ft = 7.62 meters. Received signal power (S R ) developed at the receiver input = 1.17 dBm. Free space path attenuation (N ) = 20 log10 {(4 M R ) M } where M = c f, or 300 416.82 = .72 m 4 N = 20 log10 {(4 62 . 7 ) 72. } = 42.47 dB Published receiver antenna gain over an isotropic source at 416.82 MHz (GdBi ) = 4.9 dB Measured receiver cable loss at 416.82 MHz (LC ) = 0.5 dB The EIRP or P T from the transmitting antenna source is calculated as: P T = S R + N - GdBi + LC
- 6. = 1.17 dBm + 42.47 dB - 4.9 dB + 0.5 dB 5 = 39.24 dBm Thus, EIRP emanating from the transmitting antenna over an isotropic source is calculated to be 39.24 dBm. The EIRP emanating from the transmitting antenna in watts (W) is given by: P T = {log 1 (38.89 dBm 10)} 10 3 10 = 8,413 milliwatts 10 3 = 8.413 W To determine the volts per meter (V/m) at a distance of 25’ from the emanating transmit antenna, two methods of calculation will be employed. The first method requires that the antenna factor of the receiving antenna is known. The antenna factor equation is given as: AF (dB) = (20 log10Frequency in MHz.) – published receiving antenna gain (GdBi ) – 29.8 dB = (20 log10 416.82) – 4.9 dB – 29.8 dB = 17.70 dB Now the E field intensity in microvolts per meter, or E (V/m), at 25’ may be expressed as:
- 7. ((S R + 107dBV + LC + AF) 20) ((1.17 dBm + 107dBV + .5 dB + 17.70 dB) 20) 6 E (V/m) = log 1 10 = log 1 10 = 2,082,092 V/m or 2.08 V/m The second method requires that the gain of the transmitting antenna is determined. The gain (GT ) of the transmitting antenna is calculated as P T P A where P A is the maximum output power in watts of the transmitter final amplifier (4 Watts) delivered to the transmitting antenna expressed as: GT = P T P A = 8.413 W 4 W = 2.10 The equation for the E field intensity at a distance is given as: E (V/m) = (30 P A GT ) 2 / 1 RM = (30 4 W 2.10) 1/ 2 7.62m = 2.08 V/m
- 8. The two E field intensity results agree. If we carry out this exercise for the remaining samples from the Boeing report using the tabulated EIRP data at 25’ distance converted to V/m, the transmitting antenna gains may be calculated using the following: 7 (GT ) 2 / 1 = (E V/m RM ) (30 P A ) 2 / 1 Sample 1 (GT ) 2 / 1 = (2.09 V/m 7.62m) (30 4 W) 2 / 1 = 1.45 GT = 2.11 Sample 2 (GT ) 2 / 1 = (1.83 V/m 7.62m) (30 4 W) 2 / 1 = 1.27 GT = 1.62 Sample 3 (GT ) 2 / 1 = (1.53 V/m 7.62m) (30 4 W) 2 / 1 = 1.06 GT = 1.13 Sample 4 (GT ) 1/ 2 = (1.97 V/m 7.62m) (30 4 W) 1/ 2 = 1.37
- 9. E Field vs PA @ 25' Figure 1 8 GT = 1.87 Calculating the statistical average of the antenna gains reveals that x = 1.68; however, the , or standard deviation, is .415. This high value of suggests that the true antenna gain is uncertain within the band of frequencies of 411.35 through 418.02 MHz, as the coefficient of variation as measured by x is almost 25%. In fact, for E field intensity projections, published antenna gains produced by the manufacturer are highly desirable, if not mandatory, for use with standardized commercial E field calculations. Thus, proper E field measurements can only be approximated by actual measurement as electromagnetic field perturbations resulting from ground irregularities and soil conditions, signal reflections, atmospheric conditions, and other phenomena cause signal distortion at a distant point of interest. Figure 1 indicates the V/m versus transmitter power output (P A ) as a function on antenna gain at a distance of 25’. It is assumed that the antenna gain of the trunking radio portable units is 2 1 , or, 0dB to 3 dB gain over an isotropic source. 3.5 3 2.5 2 1.5 1 0.5 0 Ant. Gain = 2 Ant. Gain = 1 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 Volts per meter Transmitted Power to Antenna (W)
- 10. Consideration of Standards and Specifications There are various KSC and other industry documents that specify and outline overall requirements regarding Electromagnetic Compatibility. SL-E-0002 – Specification Electromagnetic Interference Characteristics Books 1, 2, and 3 are examples of such documents used by the Space Shuttle Program and KSC. These books apply to specified and unspecified airborne and ground equipment; thus they become a conflicting source of standards information when juxtaposed with other existing KSC and other documents such as MSFC-SPEC-521B - Electromagnetic Compatibility Requirements on Payload Equipment and Subsystems, SSP 30237 - Space Station Electromagnetic Emission and Susceptibility Requirements, NASA-STD- 8719.12, Safety Standards for Explosives, Propellants, and Pyrotechnics, and MIL-STD-1576 - Electroexplosive Subsystem Safety Requirements and Test Methods for Space Systems. The SL-E-0002 books 1, 2, and 3 are divided as a function of equipment procurement date. Book 1 refers to affected equipment procured prior to February 11, 1993, while Book 2 is assigned to equipment procured between February 11, 1993 and prior to May 7, 2001, and Book 3 includes equipment procured since May 7, 2001. The specified radiated susceptibility limits for Book 1, revision E, released in July 2001, are derived from MIL-STD-461A, as released in 1968. That released document indicated a radiated susceptibility (RS03) specification of 1 V/m from 14 kHz to 10 GHz. There have been 4 major revisions of MIL-STD-461A since 1968 directly affecting specifications used in determining susceptibility limits by radio frequency emission; however, subsequent revisions of MIL-STD-461A have not impacted SL-E-0002 Books 1 and 2. In essence, SL-E-0002 Books 1 and 2 continue to use the 1 V/m RS03 standard while MIL-STD-461E currently uses 10 or 20 9
- 11. V/m RS03 standard depending upon ground or space operation. Industry professionals considered the 1 V/m susceptibility limit a severe requirement; thus, it was relaxed by following revisions of MIL-STD-461 starting in 1980, prior to STS-1. It is interesting to note that the 1 V/m standard with respect to the RS03 specification is used today in SL-E-0002 Books 1 & 2 as an upper boundary guideline for the Radiated Emissions (RE102) specification for the purposes of issuing many deviations and waivers with respect to the RE102 specification. Variances of + 40 dB over the RE102 limits are typical and have been granted using the RS03 as an upper 10 boundary limit. There is one indicated waiver with respect to the RS03 specification in the Space Shuttle Specification Electromagnetic Compatibility Requirements for Equipment, SL-E-0001 Book 1 regarding the super lightweight headsets that were found susceptible to R.F. interfere nce below 1 V/m at 200 MHz. Other than the super lightweight headset example, specific equipment susceptible to R.F. emissions above 1 V/m between 400 MHz and 420 MHz is not known. The specified limits for RS03 in SL-E-0002 Book 3, revision basic released July 2001, indicates an equipment susceptibility limit of 20 V/m between 30 MHz and 1 GHz. The point of this discussion is that there exist varying degrees of susceptibility tolerances depending on date of equipment procurement and the origin of the standard. The next section will explore the variance of susceptibility specifications and standards. A Relative Comparison of Specifications This section will give the reader some insight as to various susceptibility limits and specifications regarding R.F. emissions by other agencies and standards. These
- 12. susceptibility limits apply to the maximum allowable human exposure, sensitive equipment thresholds, and electroexplosive threshold levels. The first example is referenced from the FCC OET Bulletin 65, Evaluating Compliance with FCC Guidelines for Human Exposure to Radio Frequency Electromagnetic Fields. Using 412 MHz to calculate the maximum permissible exposure E field strength, a value is 71.72 V/m or 1.373 mW/cm2 as calculated from the table below from that bulletin. This frequency was selected since the trunking radio samples used in the previous section are fairly represented. Shown below is the table as it appears in the FCC OET Bulletin 65 document. LIMITS FOR MAXIMUM PERMISSIBLE EXPOSURE (MPE) Limits for Occupational/Controlled Exposure ________________________________________________________________________ Frequency Electric Field Magnetic Field Power Density Averaging Time Range Strength (E) Strength (H) (S) |E|2, |H|2 or S (MHz) (V/m) (A/m) (mW/cm2 ) (Minutes) ________________________________________________________________________ 0.3-3.0 614 1.63 (100)* 6 3.0-30 1842/f 4.89/f (900/f2)* 6 30-300 61.4 0.163 1.0 6 300-1500 -- -- f/300 6 1500-100,000 -- -- 5 6 ________________________________________________________________________ f = frequency in MHz *Plane-wave equivalent power density The second example is referenced from the SSP 30237- Space Station Electromagnetic Emission and Susceptibility Requirements, Revision C. As shown below, the susceptibility requirement for Space Station components with respect to the trunking radio frequency spectrum 11 is 60 V/m.
- 13. 60 V/m is 59 V/m above the 1 V/m requirement of SL-E-0002 Books 1 and 2 and 40 V/m above the 20 V/m requirement of SL-E-0002 Book 3. The third example refers to MSFC-SPEC-521B - Electromagnetic Compatibility Requirements on Payload Equipment and Subsystems. In Change Notice 1 of that specification, 12 the chapter and verse appears as below. 3.3.2.2.1 Electric Field (RS03) Payload equipment shall not be susceptible to an electric field strength of 2.0 volt per meter from 14 kHz to 10 GHz, in addition equipment mounted in the payload bay shall not be susceptible to the field strength levels specified in Figure 3-9 for the frequencies show in Table 4-1. The levels in Figure 3-9 may be reduced by 20 dB for equipment installed in the space lab module or any enclosure known to have equal or greater shielding capability. Equipment that protrudes above the payload bay or that is ejected from the payload bay may be subjected to higher KU-band and S-band fields. These will be defined depending on the orientation and whether there are approved operational restrictions on the transmitters for the specific project. Figure 3.9 and Table 4-1 from the MSFC-SPEC-521B specification refer to specific equipments and their operating frequencies. No equipment is identified operating at or around the trunking radio frequency spectrum in those figures or tables. It is interesting to note the 20 dB requirement reduction once the payload is installed into an enclosed space. A 20 dB reduction to 2 V/m is equivalent to 19.95 V/m. The fourth example references NASA-STD-8719.12, Safety Standards for Explosives, Propellants, and Pyrotechnics. Table IV, Recommended EED Safe
- 14. Separation Distances and Power Densities in that document indicates (by calculation) the exposed EED maximum radiation limit to be .68096 W/m2 or 15.9 V/m at 400MHz. The maximum radiation limits for the EED in storage or transport is calculated to be 6.81 W/m2 or 50.3 V/m at 400 MHz. Both examples are well above the 1 V/m standard and are considered conservative as compared to guidelines indicated in MIL-STD-1576, Electroexplosive Subsystem Safety Requirements and Test Methods for Space Systems. Motorola XTS 3000 Portable Trunking Radio Power Conservation Features The Motorola XTS 3000 series radios have a programmable power conservation feature that automatically adjusts the output power (P A ) level of the transmitter to less than full rated output (4 watts) when conditions permit. This feature extends battery life between charges since the nominal P A output can be significantly reduced as the transmission confidence margin dictates. To illustrate how this feature works, consider a trunking radio transmission from Launch Complex 39-A. The Motorola XTS 3000 series radios are required to communicate to one of two repeater towers for proper trunking sequence of operation. Assume the distance between Pad-A and one of the towers is conservatively 5 miles. We will incorporate the previously used Boeing report power data at 416.82 MHz and introduce trunking radio receiver characteristics at the 500’ Weather Tower for purposes of this discussion. Distance (RM ) = 5mi 5,280 ft/mi .3048 m/ft = 8,046.72 meters. Free space path attenuation (N ) = 20 log10 {(4 M R ) M } where M = c f, or 300 416.82 = .72 m 13
- 15. N = 20 log10 {(4 8,046.72).72 } 14 = 82.46 dB Now the signal applied to the receiver input terminals is expressed as: S R = P T - N + GdBi - LC Where S R = Signal received at the receiver input terminals in dBm P T = EIRP of the transmitting antenna N = Free Space Path Loss GdBi = Published numerical gain (dB) of the 500’ Weather Tower antenna over an isotropic source LC = Calculated cable loss from antenna to receiver at the 500’ Weather Tower S R = 39.24 dBm – 82.46 dB + 6 dB – 3 dB = - 40.22 dBm Expressed as Watts: = {log 1 (-40.22 dBm 10)} 10 3 10 = .00009506 milliwatts 10 3 = .00000009506 W or 9.5 8 10 W
- 16. For a 50 system the Voltage E, applied across the receiver input terminals is 15 expressed as: E = (S R 50) 2 / 1 = (9.5 8 10 50) 2 / 1 = .00218 V = 2.18 mV = 2,180 V Now the trunking radio receiver sensitivity at the 500’ Weather Tower is published to be .25 V for a maximum bit error rate of 5%. We will use this figure as a minimum threshold for receiving and processing useful voice and data for purposes of acceptable trunking operation. Taking the applied or detected voltage across the receiver input and comparing it to the minimum threshold receiver input sensitivity establishes a margin of confidence that the receiver will properly detect and decode the intended information. This margin of confidence may be expressed in dB and used in overall system path loss budgets. For our example we may express the margin in dB as: 20 log (2,180 V .25 V) or 78.81 dB. This is an extremely high margin of confidence. To put this in perspective, assume that the EIRP or P T of an XTS 3000 portable is 8.413 W or 39.25 dBm and the P A from the transmitter to the antenna is 4 watts as in the previous sample 1. If we reduced the input power P A to 2 watts or 3dB, the resulting EIRP would be 36.25 dBm or 4.206 W. That would leave a confidence margin of 78.81 dB – 3 dB or 75.81 dB. This remains
- 17. an extremely high margin. By reducing the P A another 50% the result would be 33.25 dBm or 2.103 W leaving a confidence margin of 75.81 dB – 3 dB or 72.81 dB. Please note that these margins apply to ideal conditions. In a real world, a transmission path/system loss budget based on probabilistic information theory would be required to reflect an environment in which reliable margins could be established. Using data from known good engineering practices the theoretical transmission path/system loss error budget may include up to a 15 to 20 dB loss from atmospheric and ground conditions, and 20 dB additional losses resulting from building structure attenuation. If we added (worst case) 40 dB as an error budget to the signal strength of our minimum required power, the result would be 1.1 milliwatt (mW) EIRP required output from the transmitting antenna to reach the 500’ Tower for 100% effective communications. At a distance of 25’ the resulting E field magnitude from the 1.1 mW EIRP would be .024 V/m. The point of emphasis of this discussion is the unlikely probability that the portable trunking radio units would ever be transmitting at full power, or near full power, since only a fraction of that full reserve is required for proper operation throughout the entire 16 Kennedy Space Center. Conclusions and Recommendations The Motorola Trunking Radio system is an efficient and reliable means of radio communications that will meet all NTIA mandated requirements both near and long term. Failure to meet these requirements will jeopardize both near and long term performance standards set by the NTIA.
- 18. True radio transmitting characteristics should be established using only published or certified antenna data. Field data has been shown to result in a sizeable data scatter of the portable radio antenna gain characteristics. The radiated susceptibility specification per SL-E-0002 Books 1 and 2 is severe. The current specification of 1 V/m indicated in SL-E-0002 Books 1 and 2 is based on a 1968 revision of a Department of Defense standard that has since been updated 4 times to reflect a 10 to 20 V/m susceptibility limit. Other susceptibility specifications and standards that apply to human exposure, sensitive electronic equipment, and electroexplosive devices indicate a limit that would permit the use of trunking radio portable units at the full power compliment to operate safely at a reasonable distance. Equipment that is potentially susceptible to trunking radio R.F. emission has not been 17 identified. It is highly improbable that the trunking radio portable units will transmit at full rated power since they are designed to allow for path loss energy budgeting enhancing battery conservation. Theoretically, the new trunking radios can communicate from the LC-39A to the 500’ Weather Tower using about 100 microwatts of power with a 0dB margin of confidence. The probability of exceeding 1 V/m at 25’ during operation of the new trunking radio portables is extremely low since power conserving programming feature is in effect. Based on no known evidence of susceptibility to equipment by the R.F. emissions of the new portable trunking radios within reasonable transmission distances, it is recommended that the Motorola Trunking Radio Program for use at KSC and its environs continue with full planned implementation.
- 19. References Cited The Boeing Company Kennedy Space Center. (2003). Test Report KSC UHF Trunking Transceiver 1 Volt/Meter versus Distance Measurement NAS 10-02007 NTIA Manual of Regulations & Procedures for Federal Radio Frequency Management (May 2003 Edition, September 2003 Revisions) Federal Communications Commission. (1997). Evaluating Compliance with FCC Guidelines for Human Exposure to Radio frequency Electromagnetic Fields. OET Bulletin 65, Edition 97-01 Department of the Air Force Military Standard. (1984). Electroexplosive Subsystem Safety Requirements and Test Methods for Space Systems. MIL-STD-1576 National Aeronautics and Space Administration. (2001). Specification Electromagnetic Interference Characteristics Book 1- Hardware Prior to February 11, 1993. SL-E-0002 Book 1, Revision F National Aeronautics and Space Administration. (2001). Specification Electromagnetic Interference Characteristics Book 2 - Hardware After February 11, 1993 and Prior to May 7, 2001. SL-E-0002 Book 2, Revision F National Aeronautics and Space Administration. (2001). Specification Electromagnetic Interference Characteristics Book 3 - New or Modified Equipment. SL-E-0002 Book 3 Volume 1 Department of Defense Military Standard. (1968). Electromagnetic Interference Characteristic Requirements for Equipment. MIL-STD-461A National Aeronautics and Space Administration. (1990). Electromagnetic Compatibility Requirements on Payload Equipment and Subsystems. MFSC-SPEC-521B National Aeronautics and Space Administration, et all. (1996). Space Station Electromagnetic Emission and Susceptibility Requirements. SSP 30237, Revision C NASA Technical Standard, Safety Standards for Explosives, Propellants, and Pyrotechnics. (2003). NASA-STD-8719.12 (Draft) 18