Tuning Of Digital Signal Transmission Devices For Field

tuning of transmission devices

Introduction

We need to do tuning of Digital Signal Transmission devices time to time for delivery of proper signal to our subscribers. If you knows how to tune devices in field then you will not get any problem from field.

There are various device which we generally use in CATV field in which main devices are Transmitters , Nodes , Power Supply and Amplifiers. All of these devices are active devices. Now we will understand how to tune these devices properly for the maintenance of  cable tv field.

Diagram For Tuning Of Digital Signal Transmission Devices

To understand basic fundamental for Tuning of Digital Signal Transmission devices we are having a example for that in diagram mentioned below. For detail view open it in New Tab,

Tuning Of Digital Signal Transmission Devices

QAM

As shown above in the figure QAM is giving RF output level of 110 dB. which directly goes into the 8 way splitter where 8 way splitter losses approximately 12 dB. So 8 way splitter provides 98 dB RF output level. This 98 dB goes into the 16 way splitter which losses approximately 18 dB. Output of 16 way splitter is 80 dB which goes directly into the transmitter.

Generally in digital headends we gets RF output level from the QAM as high as possible. So it can be 90 dB to 110 dB. After getting this high signal level from QAM we can reduce it according to our network requirement. We need to use splitter after it to diminish the RF signal level.

Transmitter

As shown above in the figure transmitter is having 80 dB RF input level from the 16 way splitter. The RF input signal level range for transmitter should be 75 dB to 80 dB practically for proper tuning of cable tv field.

Now transmitter is giving optical power output which goes into the optical power input port of NODE.

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Node

Node is having optical input from the transmitter and giving RF output. The RF output level from the NODE can be 75 dB – 80 dB that depends upon the weather. In the summer you can give 80 dB and in the winter you can give 75 dB. These are practical values.

If you are getting more than 80 dB output from the node then it means there are heavy losses in your coaxial cable. Now the output from the node goes into the amplifier via coaxial cable.

Power supplies are used to power up to amplifiers which are connected in series in field. We are using a 6 Amp power supply which can run around 10 amplifiers in field.

Amplifier

As we known amplifiers are used to amplify or boost the signal. So we need to give 60 dB input RF level and get 75 dB RF output level from amplifier for tuning cable tv field.

STB

As shown above in the figure we are giving 50 dB signal to stb. This is practical value for RF input for stbs.

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The input RF level for the STB can be in range between 40 dB to 60 dB. Also RF input level depends upon the make of stbs. Because different make use different tuners for the stbs and these tuners have different resistivity level for RF signal.

Conclusion

In this article we have discussed about Tuning Of Digital Signal Transmission Devices in the field. Above discussed parameters in the figure for tuning are the practical parameters. So we need to maintain these parameters time to time for proper signal delivery.

As we know signal when the signal passes threw splitters , transmitters , node and amplifiers then it gets small variation in signal level. So we have taken S 21 or 306 Mhz  reference frequency to measure these RF signal levels mentioned in Tuning Diagram Of Digital Signal Transmission Devices.

Also signal level depend upon the weather. In the summer we needs to do high signal level while in the winter we need to do low signal level. In the summer resistance in the cable increases due to heat that is why we need to maintain high signal level. On the other hand in winter resistance of cable decreases that is why we need to maintain low signal level.

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Comments

  1. KAMAL BERA says:

    THANKS FOR MORE UPDATE

    1. Kamlesh says:

      HM1521
      M4K81690.2A
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  2. Bhupendra says:

    please provide details about how to set gain and slop of node?thanks……..

  3. Shahid says:

    I have kept my digital signal ranging from 75 to 78 dB and
    analog I have kept on 85 (first 10 channels) to 84 dB (rest channels 82.5 to 84)
    But In the field my digital signal has not valuable throughout faceing problem.

    Is this good practice.
    If don’t put analog signals at the mentioned level my first 20 channels of analog become more snowing in picture
    Kindly guide m experts what should I do

    1. We have Headend INFO Whatsapp Group to discuss these kind of problems with experts.
      If you want to join then send your request to join at +91 8239222444
      Thanks

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