Triax 023269 Datasheet download pdf (Page 245)

245

Number of Correction to the

channel loads catalog value in dB

2 0

3 – 2

4 – 3

5 – 4

6 – 5

7 – 5.5

8 – 6

10 – 7

3. Planning and installation instructions

Technical appendix

3.1. Permissible output level for house

connection

ampliﬁers, multiple band

ampliﬁers, and postampliﬁers

It is always recommended to carry out these calculations on a

Windows PC using:

•

Triax-Hirschmann Turboplaner III

*) (Order No. 499 999-003)

• AND by CDS Germany (www.cdsgmbh.de)

• CACAO by PTE-software (www.ptesoftware.dk)

The following explanations can be an additional help for

solving problems and for understanding the underlying

relationships.

The permissible output level is dependent on:

• The required signal-to-noise ratio CTB, CSO

• The number of TV channels to be transmitted

• The frequency distribution of the channels

The signals of the FM radio band can be treated as a single

TV channel, if their levels are 6-8 dB below the level of the TV

channels. The 1st selection criterion is the number of TV

channels to be transmitted.

3.1.1 Maximum number of TV channels: 10

(MATV systems)

• Determine the permissible output level from the technical

data: for IMD2 (60dB 2nd order intermodulation products

acc. to EN 50083-5), for IMR3 (60dB 3rd order

intermodulation products acc. to EN 50083-5)

• Reduce the IMR3 value according to the number of

channels

*) This software is only available in deutsch

Table1:

Level reduction as a

function of the number

of channels loaded

The smaller of the two output levels (with respect to IMD2,

IMR3) is the permissible output level (dB(µV)) for a

signal-to-interference ratio of IMD=60 dB.

3.1.2 More than 10 TV channels

(broadband cable, MATV, CATV)

In order to obtain optimal gain from ampliﬁers with many chan-

nels loaded, it is necessary to use the permissible output levels

speciﬁcally deﬁned for each such case (for a CSO and CTB

ratio of 60 dB) and a channel raster as close as possible to a

deﬁned one.

3.1.3 Approximate calculation for the

permissible output level:

a) Permissible output level dependent on required CSO

and CTB values that are different from catalogue values:

CSO

Question: “How high is the permissible output level for a CSO

value D a dB above the catalogue value (CSO = 60 dB)?”

= output level in dB(µV) for CSO = 60 dB (catalogue value)

= output level in dB(µV) for CSO = (60 + D a) dB

= n

- D a

i. e. on an increase in the CSO requirement by D a dB, the

permissible output level is reduced by D a dB.

CTB

Question: “How high is the permissible output level for a

CTB value D a dB above the catalogue value (CTB = 60 dB)?”

= output level in dB(µV) for CTB = 60 dB (catalogue value)

= output level in dB(µV) for CTB = (60 + D) dB

= n

- D a/2

i. e. on an increase in the CTB requirement by d a dB, the

permissible output level is reduced by D a/2 dB.

Example ﬁgures for HEF 845 with the

CENELEC spacing

= output level in dB(µV) for CSO = 60 dB = 110 dB(µV)

= output level in dB(µV) for CSO = 69 dB = 101 dB(µV)

= output level in dB(µV) for CTB =

60 dB = 110 dB(µV)

= output level in dB(µV) for CTB =

72 db = 104 dB(µV)

In total for CSO = 69 dB and CTB = 72 dB a permissible

output level of 101 dB(µV) is to be observed.

b) Permissible output level for channel loads deviating

from catalogue speciﬁcations

The individual Triax operating instructions list the maximum

permissible output level for a signal-to-interference ratio of

60 dB for three different channel spacings:

- up to 450 MHz: 36 TV + 24 FM channels,

- up to 606 MHz: 29 TV channels (“CENELEC raster“)

- up to 862 MHz: 42 TV channels (“CENELEC raster“)

Refer to “Channel spacing” table

These conditions are very critical with respect to the develop-

ment of non-linear distortion (CTB, CSO). For small deviations

of the actual channel spacing from the standard ones, it is not

necessary to reduce the output level shown in the operating

instructions. For larger deviations, the following rules of thumb

can help to obtain a rough approximation for the adjustment:

1. Select the catalog values corresponding to the highest

channel frequency.

2. For a channel pattern with twice the number of channels

speciﬁed in the catalog, reduce the output level by

about 3 dB.

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Triax 023269 Datasheet Page 245

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