Optimum elevation gain and zero radiation at 90 degrees can be achieved with

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2 Question John FM Antennas: One way to reduce downward RF signal near the tower is to use short -spaced element antennas. Is there another way it can be accomplished? 2

3 Optimum elevation gain and zero radiation at 90 degrees can be achieved with The nulls in an elevation pattern are defined by: A null at 90 degrees will eliminate downward radiation 1 k k 90 sin or 1 nd nd sin 1 k nd k d n k n Null angle Integer Element spacing Number of elements Wavelength d = n 1 n k d n For k=1,2,3.. k n, 2n, 3n n 2 n 1 n 1 n 2 d...,,,... n n n n Where n 1 n will be the most aperture efficient spacing 3

4 (n-1)/n is much more efficient than ½ wave spacing (n-1)/n approaches the efficiency of a full wave spaced array as n increases, but has no downward radiation 4

5 Or..Increase the height of the antenna s uw/cm 2 = 33.4 F2 ERP r 2 F = field strength ERP in Watts r = distance in meters Double the height and reduce the signal strength 4X (6 db) 5

6 Question What special considerations are there for Channel 14? Looking forward to it! Dan 6

7 Noise power from high power transmitter can degrade land mobile radio SNR in the MHz band Required additional attenuation for each land mobile channel 7

8 C h a n n e l 1 4 Step 1: Get a consultants Study: -catalogs nearby land mobile receivers - calculates required filter attenuation Courtesy DuTreil, Lundin & Rackley 8

9 Design filter to meet requirement typically 12 pole Note: solid state Tx shoulder values <<- 40 db can simplify filter design 9

10 Up to 20 kw reflective 12 pole 143 x 24 x 24 (363 cm x 61cm x 61cm) Up to 40 kw CIF 12 pole 143 x 48 x 36 (363 cm x 112 cm x 91 cm) 10

11 Up to 60 kw CIF 12 pole blowers - w/g hybrids 146 x 48 x 84 (371 cm x 122 cm x 213 cm) 11

12 Use 14 pole or add notches 12

13 Use of V-Pol may be limited if H/V discrimination built into land mobile rejection calculation Lower band edge roll-off (-2.92 MHz) forces either carrier reduction or frequency offset 13

14 Question The other guys claim end fed antennas are a better choice over center fed antennas. Why? John 14

15 The truth is Not a choice of preference Dictated by technical limitations and decisions Need both end fed and center fed in the product portfolio 15

16 Mechanically convenient to feed top mount antennas from the bottom RCA introduced the J type pylon in 1966 Triax technology Historically highlighted Minimal beam sway Stable frequency response 1966 RCA 16

17 Phase taper Phase taper Phase taper Frequency response End fed Progressive phase taper Linear illumination Center fed Opposite phase tapers at the feed point Symmetrical mirror image illuminations Feed Feed 17

18 How does this effect performance / coverage? Example 1 MW ERP 1000 HAAT FCC (50,90) Radio Horizon = 44.7 miles ATSC A/53 min field strength = 41 dbu In this example, 41 dbu is well beyond the radio horizon, this implies any small slope imposed on the incoming signal should not present a coverage penalty The choice should take into account the HAAT and minimum field strength requirements 18

19 Heading into repack Overall antenna height maintained Going down in frequency and keeping same aperture length equates to lower gain antennas Going down in frequency requires less gain for equivalent coverage Dipole factor Lower gain antennas have wider beam widths Wider beam widths are less sensitive to beam sway Beam sway concerns lessen P r = P t G t G r λ 2 4πR 2 ERP Reduction = f pre repack f post repack 2 The choice should take into account the gain of the antenna 19

20 Beyond repack ATSC 3.0 Higher PAPR s Center fed antennas split the input power before hitting the first slot Slot coupler to inner voltage safety factor of a center fed antenna can be improved by 40% over end fed designs (For the same geometry) Inner to coupler spacing Coupler shape Zo VSWR The choice should take into account the power / voltage requirements 20

21 In some cases, center fed antennas are not an option Higher order modes Coax typically operates in the principal TEM mode Cutoff frequency for higher order modes Mean diameter between the inner and outer conductor f c MHz = D + d π 2 Large outer and/or inner conductors have low higher order mode cutoff frequency 21

22 At frequencies below cutoff, higher order modes can be excited by a discontinuity, but attenuate rapidly with distance α (db/length) = λ c λ c λ Coupling a slot inherently generates a high order mode Slot loading and radiation characteristics are only defined when fed with a TEM mode The excited higher order mode MUST be either attenuated or canceled. Designs such as omni directional and peanut patterns employ symmetrical internal coupling Acts as a natural mode canceler Not restricted by outer and inner diameters 2 Inner size must be small to attenuate higher order modes. This excludes the use of a harness feed Large inner harness can be used to center feed since modes naturally cancel Top mount high power directional antennas are typically forced into an end fed design 22

23 Very close in coverage End fed antennas theoretically have no zero nulls 23

24 Center Fed Summary Benefit Comparison End Fed Stable frequency response Typically higher voltage safety factors Wider main beam Operates below higher order mode cutoff High power directional designs No zero nulls for better very close in coverage More aperture efficient (Not compared to an off center fed design) Dielectric Breakdown Over 1100 repack proposals (many with 3 to 8 revisions) 44% of top mount designs are end fed 24

25 Choice between a center fed and end fed slotted coaxial antenna is usually not a choice of preference Choice dictated by a technical roadmap Size Azimuth pattern Power Gain Frequency response Very close in coverage Mounting Bottom Line: There is no one size fits all. Both center fed and end fed designs need to be in a product portfolio in order to provide a full range of technical solutions 25

26 Question How easy is it to retune a six or eight pole filter to operate on ATSC 3.0. Is there a simple way to check if the filter will operate on ATSC 3.0 without further adjustments? Dan 26

27 Six Pole filters do not need retuning for ATSC 3.0 Older 8 pole filters may

28 Reflective filter measure input return loss CIF measure input to reject load isolation Ripple bandwidth has to be >5.84 MHz Ripple Bandwidth 28

29 Requires field engineer with network analyzer and test adaptors A one to two hour shutdown 29

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31 Field engineer with network analyzer, test adaptors and tools 2 to 4 hour shut down Patience 31

32 Question John What are the factors taken into consideration when implementing ATSC1.0 but planning for 3.0? What is the most under-recognized antenna design feature that stations and RF Engineers should be taking more advantage of? 32

33 What does it mean to be ATSC 3.0 Ready? Addition of VPOL Future Fill Higher PAPR Adequate VSF s Design criteria 33

34 Margin Improvement with Circular Polarization All measurements have confirmed that transmitting circular polarization to a linearly polarized receiver in motion in a heavy scatter environment provides 5 to 7 db of margin improvement (MI) over transmitting a linearly polarized signal to the same receiver. For mobile and nomadic services, the addition of VPOL is critical 34

35 PAPR ATSC3.0 > PAPR ATSC1.0 Most likely 2 db higher Designing for higher voltage handling All about geometry Eliminate edges Increase radiuses Increase gaps Adequate voltage safety factors Impurities, dust, salt, corrosion, temperature, altitude, humidity, tolerances, gap variation, thermal expansion.. Apply appropriate conditions Composite safety factors Finite probability that OFDM carriers will add in phase at their max amplitude Design criteria 35

36 Boosting the signal strength Provide even distribution of high signal strength Saturate in the vicinity of the main antenna by increasing the null fill Add SFN sited around coverage perimeter to boost the signal strength outside of the high null fill area 7 db avg. increase in null fill 36

37 Question John Do all of your antennas have FutureFill option? 37

38 All high power center fed designs Not required on end fed traveling wave antennas 38

39 Question Is there a recommended procedure to tune a single or dual 4 port fine matcher for a C or M model antenna? What is the most efficient way to find the sweet spot Dan 39

40 1 Only one or a set of adjacent probes should be used Shape of raw impedance remains unchanged but can be shifted in any direction

41 Channel 1 Raw Channel 2 Z at 2 nd Var 2 to 6 λ Depending on freq spread Second variable centers the impedance 41

42 Question Your competition claims independent horizontal and vertical polarization provides better coverage. Do you agree? John 42

43 VS. Interlaced Fed VPOL Parasitic Fed VPOL 43

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45 I n d ependent H/V vs. Parasitic F ed Dipole ½ w a v e s p a c i n g AR = tan 2 sin 1 sin 2tan 1 PR sin RH CP LH CP Parasitic fed dipole has constant axial ratio throughout coverage area 45

46 Parasitic Fed VPOL Interlaced Fed VPOL HPOL VPOL HPOL VPOL Parasitic dipole is fed directly from the slot, maintaining equivalence in the H and V radiation pattern Independent feed systems and coupling methods make elevation pattern congruency impossible 46

47 Question I don t really have a specific question, but would like to hear more about peak and average power safety margins in transmission line and antennas for ATSC 3.0. ATSC 3.0 Ready Designing Antennas for Higher OFDM PAPR N255 Today at 9:20 John 47

48 Question Dan Will 8-pole filters adversely affect ATSC 3.0? Do you have a chart listing various filter losses so that accurate pre-filter TPO can be calculated? 48

49 8 pole f i l t ers and AT SC pole filters have two purposes: Adjacent channel combining (CIF) Adjacent channel noise reduction (reflective) 49

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51 channel combining t h e f i x Elevate filter VSWR Decreased NB input to reject load isolation NB and BB VSWR still good 51

52 Filter Integrated Rejection 5.38 MHz bandwidth Integrated Rejection 5.84 MHz bandwidth ATSC Full Mask (6 pole) 12.8 db 10.9 db 8 pole tuned for ATSC db 29.1 db 8 pole tuned for ATSC db 21.2 db 52

53 Power Level Number of Sections Cooling Filter Model Integrated Loss 5.84 MHz bandwidth Tuning Channel Range 1kW-4kW 6 Free Convection HT6E6F-4k 0.4 db Ch kw- 8 kw 6 Free Convection HT6E10F-8K 0.25 db Ch kw-15kw 6 Free Convection HT6E12F-15K 0.15 db Ch kW-3kW 8 Free Convection HT8D6F-3k 0.55 db Ch kW-7kW 8 Free Convection HT8D8F-7K 0.3 db Ch kw-15kw 8 Free Convection HT8D12F-15K 0.18 db Ch 7-13 For CIF double power rating, add 0.05 db insertion loss 53

54 Power Level Cooling Filter Model Integrated Loss 5.84 MHz bandwidth Tuning Channel Range 1kW-3kW Free Convection UT6E7F-xx 0.6 db Ch kw- 6 kw Water UT6E7F-6K 0.6 db Ch kw-10kw Free Convection UT6D11F-10K 0.32 db Ch kW-20kW Water UT6D11F-20K 0.32 db Ch kW-30kW Free Convection UT6E16W-30K 0.20 db Ch kW-60kW Forced Air UT6E16W-60K 0.20 db Ch For CIF double power rating, add 0.05 db insertion loss 54

55 Power Level Cooling Filter Model Integrated Loss 5.84 MHz bandwidth Tuning Channel Range.5kW-2kW Free Convection UT8D7F-2K 0.9 db Ch kw- 4 kw Water UT8D7F-4K 0.9 db Ch kw-10kw Free Convection UT8D11F-10K 0.40 db Ch kW-20kW Water UT8D11F-20K 0.40 db Ch kW-20kW Free Convection UT8D16W-20K 0.30 db Ch kW-40kW Forced Air UT8D16W-40K 0.30 db Ch For CIF double power rating, add 0.05 db insertion loss 55

56 Question At what power level do dual mode waveguide filters become more cost effective than coaxial cavity filters? Dan 56

57 Tunable coaxial cavity filters are least expensive but only usable to 10 kw free convection / 20 kw water cooled Tunable w/g is next most expensive makes sense where reflective filter is acceptable (to 60 kw 6 pole / 40 kw 8 pole) Where powers are large enough to require CIF (>60 kw / 40 kw) then dual mode w/g is less expensive than tunable w/g 57

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