The External Modulator contains jumpers, which allow EXTERNAL INPUTS for Emergency messaging and transmitter status monitoring.
There are a total of four (4) EXTERNAL INPUTS. Three (3) require a Normally Closed contact, when opened the appropriate Emergency Message will be generated. The fourth input is usually connected to the Antenna Safety Unit and informs the operator of the Transmission System status.
There are an additional 3 Emergency switches on the front panel of the External modulator. These switches are IN SERIES with the corresponding external emergency switches.
The table below indicates the role of each jumper SET.

Jumper Role

JEM1 Remove to enable External Emergency Switch 1
J40 Install this jumper to enable Emergency Message 1 from Front Panel

Особо заставляют задуматься "external inputs" - это сигналы, входы, каналы входящего сигнала?

"switches are in series with" - последовательно соединены (?)
"jumper set" - почему "set", если в каждой строке по одной перемычке?

Буду очень благодарна за помощь.

The Twisted Pair is terminated with a 25 pin Female D connector on the External Modulator end and into the terminal strip on the Marshalling Box in the Headend.

The D connector may also have other inputs. These inputs are for the ASU status and any Emergency switches. Polarity is not important for these additional inputs.