Amplifier Derating for Wideband IRS installations

Within the IRS industry, Wideband satellite IRS installations are becoming more commonplace and it’s easy to forget that when derating amplifiers, we are dealing with a lot more satellite transponders on our Wideband satellite paths and we need to apply appropriate derating.

We have been familiar with amplifier derating for Quattro LNB Satellite IRS installations for a long time but, there is a difference for Wideband systems.

Let’s use Astra at 28.2° east (Sky) as our example. On a Wideband LNB output you could have approximately 55 Vertical and 62 Horizontal transponders. We would need to include all transponders on that path (data services etc) not just Sky and FreeSat services.

Typically, Wideband distribution amplifiers have the maximum output relative to 2 channels stated as part of their specification.
The rule of thumb for derating is… “Where we have a doubling of transponders, we derate by 3dB incrementally plus another 3dB for the signal variation.”

Number of Transponders:                              2              4             8              16           32           64

Derating Figure (dB):                                      0              3              6              9              12           15

Back off dB (inc. 3dB Gain Variation):         3              6              9              12           15           18

We can see in the mini table above that, Wideband satellite installations do require to be backed off more than the more common Quattro installations and this value will typically fall between 15dB to 18dB (depending on the total number of transponders on that Wideband path).

For derating a cascade IRS installation, the number of amplifiers also needs to be taken into consideration:

Number of Amplifiers:                                   2              4              8              16

Derating figure (dB):                                       3              6              9              12

In applying the correct method of backing off for Wideband systems and considering the extra transponders per satellite path we can optimise the MER and Pre-BER. Whyte Launch amplifiers feature individual path gain and slope controls providing the ideal solution for either Wideband or Quattro launch applications.