DE956701C - Arrangement for tapping coaxial cables - Google Patents

Description

The invention relates to an arrangement for the selective tapping of coaxial cables.

An arrangement has been proposed in which the coaxial cable is separated and to avoid it of interfering reflections with one consisting of two capacitances and one inductance Four-pole equal wave resistance is bridged, with the tap line at one Center tap of the inductance is connected. With such an arrangement it was previously possible at disconnected tap line the crosstalk, for which the ratio switch capacitance to Tap line capacity is decisive, in practice it should not be brought below 3%.

The invention aims at crosstalk by simple switching measures without any special effort to a smaller value.

According to the invention, an arrangement for the optional tapping of coaxial cables is proposed, in which the separated coaxial cable with one of two capacitances and one inductance existing quadrupole of the same wave resistance is bridged and the tap line Via the particularly low-capacitance contact spring sets of two relays with the middle handle of the Inductance of the quadrupole is connected, the ■. Earth capacitance of the tap line by a additional. Capacitor is increased so that in

switched off state the cross-talk ratio from the tap line to the coaxial cable is less than ι: 30.

According to a further development of the inventive concept, when the tap line is switched off, a capacitor of the size of the earth capacitance of this line is connected between the center tap of the inductance and earth in order to avoid detuning the quadrupole.
The invention is described in more detail below with reference to the figure representing an embodiment.

The separated coaxial cable K, which has a characteristic impedance Z = 75 Ω and is intended for a bandwidth of 6 MHz, is equipped with a four-pole 1, consisting of capacitances C ₁ of 180 pF (with connection points 1 and 2) and C ₂ of 40 pF and an inductance L ₁ of 1.85 μ ~ Ά, bridged. The inductance L ₁ is provided with a tap 2 which is connected to the tap line 6 via the line 15, via the switching springs 8 and 14 of two relays (not shown), via the mating contacts 9 and 10. The switch capacitance, which is brought about by the two relays, as by the line 15 and by the tapping line 6, is indicated by the capacitor C ₄ shown in dashed lines. This switch capacitance should be as low as possible, so that C _{4 is} small. The earth capacitance of the tap line 6 is indicated by the capacitor C ₆ shown in dashed lines and is increased by the additional capacitor C ₅ . This additional condenser Cg of about 150 pF reduces the value of the fraction CJ (C ₅ +; C ₆ ), which is decisive for the crosstalk ratio, so that this is somewhat less than 1:50 when the tap line is switched off.

It is useful to form the tap line 6 from a shielded cable. Through this as a result of the cable capacitance, the earth capacitance of the tapping line forming a busbar is increased to such an extent that only a few or possibly no further capacities at all need to be connected to the busbar reduce the crosstalk ratio to a small value. Especially with large television control consoles, in which a tap line can be optionally connected to many different coaxial cables which, for example, to the various television cameras, individual recording studios, to film transmission systems, to transmission lines, lines and the like result in such great cable lengths with appropriate cable routing and thus such a large earth capacitance of the tap line that the ratio switch capacitance is sufficiently small for tap line capacitance.

According to a further development of the inventive concept, when the tapping line is switched off, the switching spring 8 is connected to ground _{via the mating contact 7 and a capacitor C 3 , C 3 being} the size of the ground capacitance (C ₅ + ¹ C ₆ ) of the tapping line. Switching on the capacitor C ₃ is intended to prevent detuning of the four-pole connection when the tap line is switched off. The changeover spring 14 is grounded directly via the contact 12 when the tap line is switched off. This measure reduces the crosstalk ratio even further.

The above statements apply to the switching elements denoted by dashed symbols analogous. The invention is not restricted to the exemplary embodiment shown here, but rather can be applied accordingly within the framework of professional ability.

Claims (4)

Patent claims. 1. Arrangement to choose from tapping coaxial cables, in which the coaxial cable interrupted and to avoid annoying reflections with one of two capacitors and an inductance existing four-pole equal wave resistance bridged and the tapping line is connected to a center tap of the inductance, characterized in that that by switching on additional capacities the earth capacitance of the tap line is artificially enlarged in such a way that the over-speaking ratio in the switched-off state from the tap line to the coaxial cable less than 1:30, preferably is less than 1:50. 2. Arrangement according to claim i ,. characterized, that two sets of contact springs are arranged in series in such a way that when the tapping line is switched off, the switching spring (8) of the first set of springs connects the center tap of the inductance of the quadrupole via a capacitor to earth and the switching spring (14) of the second set of springs is connected directly to earth. 3. Arrangement according to claim 2, characterized in that the size of the capacitor (C ₃ ) lying between the center handle and earth when the tap line (6) is switched off is the size of the earth capacitance of the tap line in order to avoid detuning of the quadrupole. 4. Arrangement according to claim 1, characterized in "ο indicates that the tap line (6) is formed from a shielded cable. 1 sheet of drawings θ «09577/345 7.56 (609 773 1.57)