Proposal Break Through

• Working Together and getting best minds in

same room creates a more optimal solution

• This presentation will go through the design

steps and actual measurements of the Peru

Master FM system

SUCCESS is Accomplished when

Both Groups Design Together

RF Engineers Combiner Based on

Combiner Specifications

Antenna Engineers Design Based on

Antenna Specifications

3

Desired Channels and Spacing

Frequency (MHz) Spacing (MHz)

88.3

93.1 4.8

93.7 0.6

97.3 3.6

100.1 2.8

106.3 6.2

107.1 0.8

107.7 0.6

0.6 MHz Spacing and Size of Room How to Handle?

4

FM Antenna and Combiner

Antenna designed to assure population coverage

Combiner designed to assure IM compliance

Designing together – antenna attributes can be used to

simplify combiner design

Reduced combiner cost and floorspace required

5

Lima Peru – Population and Antenna Azimuth Pattern

6

Resulting Terrain Limited Coverage Map

300 kW ERP

per station

8 stations

Plot courtesy

of Progira

7

Antenna Feed – Power Dividers

2/3 Power to Face A, 1/3 Power to Face B

Dual Feed per Radiator

• Two Faces

• Ten Elements High

8

Antenna – dual feed (HDCBR)

Ch 1,3,5… Ch 2,4,6…

On Air at

six master

antenna

sites

9

Cloverleaf Radiators – Minimize Cross Coupling

Symmetry in Design Yields High Isolation Between Inputs

10

Antenna Isolation Between Feedlines

11

Antenna System VSWR

12

Antenna System VSWR

13

Combiner Design – Types of Combiners

Constant Impedance Filter (CIF) combiner

IN ISO

-90

-18

0

IN ISO

-90

-18

0

IN ISO

-90

-18

0

IN ISO

-90

-18

0

IN ISO

-90

-18

0

IN ISO

-90

-18

0

input

fa

input

fb

input

fc

wideband

hybrids

bandpass

filters

narrowband

hybrids

reject

loads

ballast

load

combined output

fa + fb + fc

input

fa

input

fb

input

fc

0

manifold spine - consists of coaxial tee's and precision line lengths

combined output

fa + fb + fc

Manifold combiner

-30 dB Isolation removed from Hybrids – Moved it to Antenna

14

CIF vs Manifold Combiners

• Constant Impedance Filter (CIF)

+ More isolation with fewer filter

sections

+ Works well with tube amplifiers

+ Easy to add channels

+ Good for higher powers (30 kW +)

- Large

- Expensive

- VSWR increases for up stream

channels

- Loss increases for up stream

channels

• Manifold

+ Smaller

+ More Economical

+ Less Parts Means Higher Reliability

+ Same insertion loss all channels

+ Good match for all channels

- Filter limits power rating

- Requires more filter sections to

achieve same isolation

15

Combiner Design – IM Budget

inputfa

inputfb

combined outputfa + fb

IN ISO

-90

-18

0

IN ISO

-90

-18

0

TAL (-20 dB)

HYBRIDISOLATION (-30 dB)

FILTERREJECTION @ fb (-25 dB)

FILTERREJECTION @ 2fa-fb (-25 dB)

inputfa

inputfb

combined outputfa + fb

TAL (-20 dB)

FILTERREJECTION @ fb (-40 dB)

FILTERREJECTION @ 2fa-fb (-40dB)

-30 dB Isolation removed from Hybrids – Moved it to Antenna

16

Cross coupled filters

Increased rejection for fewer filter sections

Less Loss and Group Delay

17

Cross coupled filters

Chebychev four pole

25 dB at 800 kHz

Cross coupled four pole

25 dB at 600 kHz

18

Channel Spacing vs Required Filter Sections

Channel spacing in MHz

# of poles CIF manifold

2 cheb 4.4 10.2

3 cheb 1.6 2.6

3 with X 1.2 1.6

4 cheb 0.8 1.6

4 with X any 0.8

5 cheb any 0.8

Minimum channel spacing to get -80 dB min IM rejection:

19

IM Budget with Dual Feed High Isolation Antenna

MANIFOLD

(dB)

Filter rejection at fb -25

Antenna Isolation -25

TAL -20

Filter isolation at 2fa - fb -25

total -95

20

IM Calculation for Closely Spaced Pairs

93.1 into

93.7

106.3 into

107.1

107.7 into

107.7

106.3 into

107.7

100.1 into

97.3

Frequency Spacing 0.6 0.8 0.6 1.4 2.8

Antenna Isolation -38.7 -23.1 -22.2 0 -38

Incoming Rejection -33.5 -32 -35.2 -57 -40

TAL -23 -23 -23 -23 -23

Outgoing Rejection -26.5 -32 -32 -50 -39

total -121.75 -110.1 -112.4 -130 -140

IM frequency 94.3 107.9 108.3 104.9 102.9

21

Channel Assignment for Lima

Combiner Frequency

In

combiner

Spacing

Cross

Combiner

Spacing

Filter poles

1 93.1 MHz 4.8 MHz 4 w/ cross

1 97.3 MHz 4.2 MHz 3.6 MHz 3

1 106.3 MHz 9 MHz 6.2 MHz 3 w/ cross

1 107.7 MHz 1.4 MHz 0.6 MHz 4 w/ cross

2 88.3 MHz 3

2 93.7 MHz 5.4 MHz 0.6 MHz 4 w/ cross

2 100.1 MHz 6.4 MHz 2.8 MHz 3

2 107.1 MHz 7 MHz 0.8 MHz 4 w/ cross

22

23

24

Conclusions

• Manifold combiners are less expensive and smaller than

equivalent CIF combiners

• Consideration of solid state transmitter turn around loss and the

use of cross coupling makes the loss of a manifold comparable

to CIF combiners.

• Dual feed antenna with good isolation can reduce the number

of filter sections required in combiners, reducing loss

• Teamwork amongst Design Engineers will Optimize Best

Solution for Customers Desired Outcome – Do not Design in

Silos

Proposal Break Through

• Working Together and getting best minds in

same room creates a more optimal solution

• This presentation will go through the design

steps and actual measurements of the Peru

Master FM system

SUCCESS is Accomplished when

Both Groups Design Together

RF Engineers Combiner Based on

Combiner Specifications

Antenna Engineers Design Based on

Antenna Specifications

T H A N K S F O R Y O U R T IM E !

A N Y Q U E S T IO N S ?