
36
Z
s
E
= 20 V (e.m.f.)
V
(p.d.)
Z
1
I
Figure 3.1 Impedance matching
3.3 Base band lines
These are the lines which generally operate at comparatively low fre-
quencies carrying information at base band, e.g. speech, music, video
or data. Generally provided by the telecommunications or telephone
companies, usually on a rental basis, they are no longer likely to be
hard wired, solid copper lines, although these may still be obtain-
able for lengths below about 10 km within one exchange area. Longer
lines will probably be multiplexed, and comprised of radio and optical
circuits over part of their length.
Baseband line impedance may vary between 450 and 750