User Manual

requirements which are much more stringent in the internally diplexed case. This
is because the 30 dB (or thereabouts) of aural to colour subcarrier isolation
normally provided by the diplexer is not there, and it simply means that
internally diplexed system intermod numbers have to be much better.
At the output of U2, a match to 50 Ù is provided by C12 and the device lead
inductance, which together create a low pass matching network in boards where a
type CA2885 cable amplifier is used; conversely a type MHW6185 device
characteristics give it a wideband match to 50 Ù therefore no special output
matching is necessary, and C12 is not present.
U3 is a voltage regulator providing +24 V to the preamplifier stage(s).