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This is only true at higher frequencies where the shield path is a more attractive path than the ground plane beneath it, as explained by Henry Ott in his seminal 1976 book, Noise Reduction Techniques in Electronic Systems, 2 and demonstrated practically annually at EMC Symposia. For the purpose of this demonstration, the idea is that if the connectors don’t leak at all there should be no common-mode current, that is, the center conductor and shield current are equal and opposite, and net flux picked by the current probe is nil. For this investigation, transfer impedance nominal value is not of great interest it is the change when swapping out a threaded (N) for a bayonet (BNC) connector, or the effect of wiggling a connector, that is of primary interest.įigure 7b: Identical to Figure 7a, except one of the cable terminations changed to BNCįigures 7a and 7b require some explanation. Voltage and current may be compared to assess transfer impedance. Both current and the induced potential between coaxial center conductor and ground are displayed on a spectrum analyzer (Figures 3 and 5). A bulk cable injection (BCI) clamp induces an RF potential on the cable shield, and a current probe monitors the resultant current at the connector of interest. LMR-195 50 Ω coaxial cable with an N connector at one end and SMA at the other has its termination bonded to a ground plane at each end. This is achievable with a cable using a threaded connector such as SMA, and then adapting to other threaded and bayonet connectors, as was done in this investigation.įigures 2a, 2b, 2c, and 2d show the measurement. The optimal way to achieve that is to use the same exact cable, and change connectors. Therefore, if evaluating the transfer impedance contribution of one connector versus another, it is critical that the shield component of transfer impedance be constant.
Bnc connector series#
These two components of total transfer impedance are in series with each other and add linearly. Transfer impedance measurements on cables evaluate the performance of the cable shield as well as that of the connectors. 1 Coaxial Cable Used as Part of the Radiated Measurement System: Transfer Impedance Measurements And as a fringe benefit, we find that BNC connectors can make serviceable connector savers for smaller diameter cables terminated in fragile SMA connectors. The balance of this Tech Tip presents data substantiating the preceding statements. So, perhaps counter-intuitively, BNC connectors leak less from the outside in than from the inside out. And it turns out that certainly in the rod and biconical antenna ranges a BNC connector is suitable for this application and doesn’t leak much more than a threaded connector as long as it isn’t defective. And if the induced external cable current gets inside the coaxial transmission line, it will corrupt the radiated measurement. The issue there is transfer impedance because the potential problem with a leaky connector is that the same field that impinges on the antenna will also impinge on the coaxial connection to the receiver.
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But that isn’t the actual problem when the BNC connector is on an antenna. See A/V ports, coaxial cable and plugs and sockets.īNCs differ from many connectors because of their snap-lock architecture, which keeps the plug firmly in its socket.Figure 1: Measurement of connector leakageĪ measurement like that shown in Figure 1 will indeed verify The Rule. There are numerous definitions of the BNC acronym, including Bayonet Neill-Concelman (after its inventors), Barrel Nut Connector, Bayonet Nipple Connector, Bayonet Navy Connector, Baby N Connector, British Naval Connector and British National Connector.
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After the plug is inserted, it is turned, causing pins in the socket to be pinched into a locking groove on the plug.įor a more secure connection, TNC is a threaded version of BNC that uses screw threads instead of a locking pin and slot. Using a mount somewhat similar to the way a bayonet (knife) is mounted onto the end of a rifle, BNCs are used to connect a variety of different coaxial cable types. BNC connector( Bayonet Nut Coupling) A commonly used plug and socket for audio, video and networking applications that provides a tight connection. McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.