RF input level calculation

When adding digital carriers to the transmitter you probably did not think too much about it.  The digital carriers are -10 dBc to -6 dBc relative to the peak power of the analog video carrier level.(Society of Telecommunications Engineers, 2007, p. 9)  Even with the digital carriers at – 6 dBc from analog the addition of power is minimal as long as the number of digital carriers is equal to or less than the number of analog carriers. For example if we had originally installed a transmitter that was specified for 112 carriers at +15 dBmV/carrier and we input 80 carriers the input drive level would have been set for 16.4 dBmV/carrier. We just added the 1.4 dB that we calculated as the power difference between 112 and 80 channels. When we added 32 digital carriers at -6 dB from the analog peak level the additional power added would have only been +.5 dB.

As the number of digital carriers increases above the number of analog carriers the  total power that is attributed to the digital carriers cannot be ignored. Digital carriers now account for the majority of carriers on systems and the formulas that use analog carriers to determine input level without taking the power of the digital carriers into account may not be accurate.

As cable television systems start to reduce the number of analog carriers and increase the number of digital carriers, the power added from these carriers requires more attention. A more accurate method of determining the channel input power is to calculate the total power for the analog and digital carriers individually and then add them together.

Reference

Society ofTelecommunications Engineers. (2007). ANSI/SCTE 22-1 2002R2007

Data-Over-Cable Service Interface Specification DOCSIS

1.0 Radio Frequency Interface (RFI) [Standard]. Exton, PA

This entry was posted in Welcome to Fiber For Learning. Bookmark the permalink.

One Response to RF input level calculation

1. dertyo.xyz says:

Figure 9 demonstrates the dynamic range of the receiver subsystem along with the corresponding amplitude induced additional phase error. As the input amplitude decreases past –20 dBm, the phase error calibration accuracy begins to degrade. The system user will need to determine the accept-able level of signal chain error to determine the minimum acceptable signal magnitude.