Wright's Aerials

Rogues Gallery

As you can see, the installer has punched a hole in the junction box cap and poked a second cable through it. Left like this the box would soon be full of rainwater. The water would enter the air-space in the cable and would probably drip into the VCR or TV set at the other end.

Television aerials are designed to be connected to 75Ω coaxial cable. This is no place to discuss impedance matching: it's enough to say that the aerial terminals should not be connected to cable of any other impedance, or-horror of horrors-directly to two cables as shown here. In this example the aerial is a cheap 'contract' type, so it probably doesn't impedance-match the cable properly in any case, but even so connecting two cables like this will result in inefficient signal transfer and will probably alter the directional properties of the aerial. In general, severe impedance mismatch can cause standing waves to form on the feeder, resulting in weak signal on one or more channels or multiplexes, degraded teletext on analogue channels, and an effect called 'ringing', which looks like close-spaced ghosting.

The lower photographs show other examples of this particular type of botchery, including a remarkable 'three cables into one aerial' example.

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