Audio Banter - View Single Post - Audio Precision System One Dual Domani Measuirement Systems

**Terry Casey[_2_]** · February 10th 12, 02:13 PM posted to uk.rec.audio,uk.tech.broadcast

In article , says...

The manufacturers of many of the modulators sold for communal TV system
use claim that the output is so clean that filter combiners are
unnecessary. But I use filters anyway. The fact is that I seem to get
better results.

I wonder if they have any active stages AFTER the filter, possibly
because they might be used in installations with less than perfect
matching?

We used to use some tunable modulators, although most of them were
fixed. The idea of the tuneable one was that you had a near instant fix
if one of the modulators developed a fault. The downside was that the
broadband noise from the unfiltered output degraded the headend by 1dB
per modulator ...

The number of tunable modulators was reduced to one - we used it as the
reference for all of our distortion tests which, of course, used a spare
channel, hence no (fixed) modulator ...

One advantage of using filters is that if some of the RF sources only
provide low level signals it doesn't hurt, noise-wise, to amplify before
combining.

Obviously you will add noise to the amplified source but not to the rest
of the system.

--

Terry