improving fm combiner/filter efficiency and size using non...

Improv ing FM Combiner /F i l te rE f f i c iency and S ize

Us ing Non-Conven t iona l Coup l ingC o r y E d w a r d sS a l e s M a n a g e r

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Today’s Presentat ion

• Manifold / CIF Comparison

• Combining Requirements Each Technique

• Introduce Cross Coupling  for Efficiency

• Introduce New Source / Load Coupling

• Small Space (Less Poles)

• More Efficiency

• New 2 Channel Design

• Manifold Channel Limited?

Company Confidential

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Eff iciency, Manifold or Direct ional

Manifold• More efficient• All channels same VSWR• All channels same loss• Mainline offers higher voltage safety margin• Compact, light and simple• Easy to assemble• Easy to test• Easily maintainable• Lower cost (by 60%)• Simple module design and installation• Expandable

Directional• Less efficient• VSWR degrades with distance • Loss degrades with distance• Hybrids limit voltage safety margin• Large, heavy and complex• Difficult to assemble• Difficult to test• Difficult to maintain• Higher cost• Part intense module design• Expandable

Company Confidential

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Combining Requirement

Combiner abc’sCombiner abc’s

Junction Combiner Channel isolation for reduced IM products 40 dB

Directional Combiner Enough rejection for low loss combining 27 – 30 dB

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Combining Requirements1.6 MHz Spacing Example

Junction Combiner• Isolation entirely dependent on filter• ∴ 40 dB min filter rejection• 4‐pole required for 1.6 MHz spacing

Directional Combiner• Hybrids provide directionality, or 

isolation, ~ 30 dB• ∴ 27‐30 dB min filter rejection• 3‐pole required for 1.6 MHz spacing

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Chebyshev

Number of PolesChebyshev

Min. CH Spacing, MHz

Directional  Junction 2 8.4 9.03 1.6 2.44 .8 1.2

Combining Requirement Summary

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Current FM BroadcastFi l ter Topologies

Chebyshev

Lump element inductively coupled filter

• Sequentially coupled from input to output• Chebshev g number from lowpass prototype/closed form equations• Normalized coupling coefficients, Mi,j determined• Coupling bandwidth given by dF1,2 = BWr * M1,2 

1 2 3

,1

Coupling routing diagram

S 1 2 3 L

dF1,2 dF2,3

1 2 31 0 M1,2 02 M1,2 0 M2,33 0 M2,3 0

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• More recently, X‐coupled filters have been used to provide greater rejection

• Filters designed using insertion loss theory

= ∙∙∙ ∙∙∙

• Tri‐Section, normalized coupling coefficients extracted from polynomials

1 2 31 0 M1,2 M1,32 M1,2 0 M2,33 M1,3 M2,3 0Places zero above passband

S L

2

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increasedincreasedreducedreduced

Tri‐Section

Current FM BroadcastFi l ter Topologies X-Coupled

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Source multi‐resonator coupling provides 2 transmission zeros

New Source/LoadMult i -Resonator Coupling

Key benefits

• Tighter channel spacing for given filter order

• Efficiency gain

• Size reduction

• Easy implementation

S 1 2 3 LS 0 1.36 0 ‐.052 01 1.36 0 1.47 0 02 0 1.47 0 1.41 03 ‐.052 0 1.41 0 1.39L 0 0 0 1.39 0

S L

2

31

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ExampleWhere this Technique was used

• Miami

• Small space for combiner

• TX has very little head room

• A frequency might be added Later

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• 99.1 MHz, high power • No Tx headroom• 3‐pole filters to minimize loss• 101.5 MHz may come in later• NEED < .1dB loss• Space constraints

Manifold

New S o u r c e / L o a d M u l t i - R e s o n a t o r C o u p l i n gS o l u t i o n f o r a n E f f i c i e n c y P r o b l e m

99.1MHz

105.1MHz

97.3MHz

93.1MHz

99.1MHz

97.3MHz

101.5MHz

n = 3VSWR =  1.05BWr = 550kHzLa = .128 dB

105.1MHz

93.1MHz

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• 24” Cavity• 3‐pole red• 4‐pole blue

New S o u r c e / L o a d M u l t i - R e s o n a t o r C o u p l i n gL o s s v s B a n d w i d t h

Loss vs BWr

Need ≈ 1 MHz BWr

Chebyshev

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New S o u r c e / L o a d M u l t i - R e s o n a t o r C o u p l i n gS o l u t i o n t o E f f i c i e n c y P r o b l e m

n = 3VSWR =  1.12BWr = 1150kHzLa = .06 dB

S 1 3

2

L

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Multi‐channel site in Miami

• Source multiple coupling used on a 3‐pole filter to provide transmission zeros and allow wider bandwidth to increase efficiency

• Filter loss:< .16 dB w/o X‐coupling< .06 dB with X‐coupling 

Efficiency improvement with wider bandwidth

New S o u r c e / L o a d M u l t i - R e s o n a t o r C o u p l i n gS o l u t i o n t o E f f i c i e n c y P r o b l e m

S 1 3

2

L

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Efficiency improvement with wider bandwidth

New S o u r c e / L o a d M u l t i - R e s o n a t o r C o u p l i n gS o l u t i o n t o E f f i c i e n c y P r o b l e m

Multi‐channel site in Miami

• Source multiple coupled MODULE loss:  .08dB

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New Design for 2 Sta t ion Combin ing

• Auburn

• Small space for combiner

• Very Tight timeline

• Limited resources on site

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Manifold Combiner

2‐Channel Manifold

• Filters placed ≈ n λ/2 from junctions

• Tees spaced ≈ n λ/2 

• Short ≈ n λ/4 from Tee

• Short can be replaced w filter to eliminate a Tee

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Load Mult iple Coupling Combiner

LPFM Common Case Combiner

• Simplified design• Elimination of Tees and delay lines• One filter “box”

• Band tunable• Tee/delay line design not easily tuned• Spacing set by rejection levels

• Lower cost• Reduced part count• Same design for all channels• Less labor: manufacture, assemble, test

• Easy Install• Smaller size• Space limited sites

Company Confidential

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LPFM Common Case Combiner, Test Results

Product highlights

• 3‐pole design

• 96.1 MHz and 98.5 MHz

• Loss < .45 dB

• VSWR  < 1.08:1

• Isolation >  40dB

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Manifold Limitat ions

• Project

• Small space for combiner

• 19 channels

• Very close spacing of channels

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Manifold Combiner, How Many CH’s?

19 CH FM combiner, 800 kHz spacing

10 channels, 1.6 MHz spaced (odd channels)

9 channels, 1.6 MHz spaced (even channels)

Feeding RHCP and LHCP antenna

IBOC compatible

4‐Pole Filter Size and Loss

24” 14” 9” 5.5”Power* 23kW 15kW 5kW 1.3kWLoss .25dB .35dB .45dB .68dB

*Convection cooled

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Manifold CombinerLumped Element Model

10 channels, 1.6 MHz spaced

IBOC compatible

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Manifold Combiner Lumped Element Model , Optimized Results

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Manifold Combiner, w/o “drip loops”

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Actual Data after Optimizat ion, Return Loss

‐30 dB

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Actual Data after Optimizat ion, VSWR

1.06:1

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Actual Data after Optimizat ion, Transmission, WXRK, 92.3 MHz

92.3MHz .72dB

Filter Loss ≈ .68dB

Combiner Loss

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Actual Data after Optimizat ion, Transmission, WNYC, 93.9 MHz

92.3 MHz .72dB93.9 MHz .79dB

Filter Loss ≈ .68dB

Combiner Loss

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Actual Data after Optimizat ion, Transmission, WXNY, 96.3 MHz

92.3 MHz .72dB93.9 MHz .79dB96.3 MHz .72dB

Filter Loss ≈ .68dB

Combiner Loss

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Actual Data after Optimizat ion, Transmission, WSKQ, 97.9 MHz

92.3 MHz .72dB93.9 MHz .79dB96.3 MHz .72dB97.9 MHz .76dB

Filter Loss ≈ .68dB

Combiner Loss

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Actual Data after Optimizat ion, Transmission, WBAI, 99.5 MHz

92.3 MHz .72dB93.9 MHz .79dB96.3 MHz .72dB97.9 MHz .76dB99.5 MHz .75dB

Filter Loss ≈ .68dB

Combiner Loss

Filter Loss ≈ .68dB

Combiner Loss

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Actual Data after Optimizat ion, Transmission, WCBS, 101.1 MHz

92.3 MHz .72dB93.9 MHz .79dB96.3 MHz .72dB97.9 MHz .76dB99.5 MHz .75dB101.1 MHz .80dB

Filter Loss ≈ .68dB

Combiner Loss

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Actual Data after Optimizat ion, Transmission, WNEW, 102.7 MHz

92.3 MHz .72dB93.9 MHz .79dB96.3 MHz .72dB97.9 MHz .76dB99.5 MHz .75dB101.1 MHz .80dB102.7 MHz .83dB

Filter Loss ≈ .68dB

Combiner Loss

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Actual Data after Optimizat ion, Transmission, WAXQ, 104.3 MHz

92.3 MHz .72dB93.9 MHz .79dB96.3 MHz .72dB97.9 MHz .76dB99.5 MHz .75dB101.1 MHz .80dB102.7 MHz .83dB104.3 MHz .75dB

Filter Loss ≈ .68dB

Combiner Loss

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Actual Data after Optimizat ion, Transmission, WQXR, 105.9 MHz

92.3 MHz .72dB93.9 MHz .79dB96.3 MHz .72dB97.9 MHz .76dB99.5 MHz .75dB101.1 MHz .80dB102.7 MHz .83dB104.3 MHz .75dB105.9 MHz .77dB

Filter Loss ≈ .68dB

Combiner Loss

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Actual Data after Optimizat ion, Transmission, WBLS, 107.5 MHz

92.3 MHz .72dB93.9 MHz .79dB96.3 MHz .72dB97.9 MHz .76dB99.5 MHz .75dB101.1 MHz .80dB102.7 MHz .83dB104.3 MHz .75dB105.9 MHz .77dB107.5 MHz .70dB

Filter Loss ≈ .68dB

Combiner Loss

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Actual Data after Optimizat ion, Transmission, X-coupled

X‐Coupledf0 +/‐ .8 MHz

Manifold Isol. 35 dBAntenna Isol.* 25 dBTx turn‐around loss 20 dBFilter rejection 35 dBIM Suppression 115 dB

* Antenna isolation typically > 30dB

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Actual Data after Optimizat ion, Isolat ion, X-coupled

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10 Channel FM ManifoldDesign/Performance

Actual Duration Times:

• Lumped element design in ANSYS – 2 days

• Mechanical design – 1 day

• Manufacturing – 10 days

• Individual filter tuning – 0.5 days

• 10 channel manifold assembly/test – 0.5 day

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Manifold Combiner Benefi ts

Specification Manifold CIF (# of modules from output)

VSWR < 1.06:1 < 1.1;1 (1st , takes a beating for others )< 1.16:1  ( 10th, pays dearly for position)

Loss, f0 < .35 dB < .35 dB (1st and keeping quite about it)< .95 dB (10th no beer money left)

• Better impedance for transmitters at ALL channels• Higher efficiency for ALL broadcasters• Lower initial cost• Lower operating cost• Design/component simplicity• Reduced size

Company Confidential

41Company Confidential