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Problems with Grundig SD FREESAT Receiver
The fault was that it would not switch to vertical channels from the IRS GTU. The receiver was tried on a standard dish set up and all worked fine, the GDU was replaced and the same fault was still present. I could get the GTU to work correctly with my Promax and a Humax HD Freesat.
I think that the LNB line voltage from the Grundig SD FreeSat is the problem and may be a bit high causing the GTU to switch to Horz. I have checked the LNB line volts on a Grundig SD Receiver and found that the vertical is 14.94v , Horz. 20.29v this voltage would be ok on a standard dish / LNB with a cable run of 15-30m and would get some volt drop but on a cable of 1.5m there is no drop. Some years ago I seem to recall that there was a problem with Pace receivers not switching some LNB’s and a 2v dropper was fitted in line.
Signal levels:- We have found that the MDU work best with a optical signal level below -5dBm. If you are only using a Fibre LNB and a Optical cable less than 200mts you will need to put in at least a 10db optical attenuator on the optical cable input to the MDU.
Most Optical LND's produce a optical power of +5dbm this level is the same no matter the size of the dish. Satellite power can only be mesure via the Global Fibre Meter or on the output of a MDU after it has be converted back to the coax IF freq of the satellite.
On some MDU there is a 10db switch, although this helps with BER at the recever, it is still best to get the optical power to the MDU to below -5dbm.