This page is a sub-page to
LOSSES IN RELAYS, CABLES, ADAPTORS AND CONNECTORS.
The DUTFour cables and combinations of them is the set of DUTs for which this page is an attempt to evaluate dissipative losses using a HP 8712 C network analyzer.DUT1 = 0.125 wl 75 ohm, "TV cable" DUT2 = 0.125 wl 50 ohm, RG223 DUT3 = 0.25 wl 50 ohm, RG223 DUT4 = 0.25 wl 50 ohm, RG223 See figure 1. | |||||||||||
Figure 1. The four cables. Three of them RG223, one a 75 ohm TV cable with foam dielectric and a foil screen surrounded by a very thin braided screen. Two layers of braided screen are applied outside the original screen to make the cable RF tight. | |||||||
The network analyzer is run at minimum bandwidth and 4 times averaging to provida a stable reading with 3 decimals on the dB scale. The instrument is calibrated to show zero when the short or open part from the calibration kit is inserted. Table 1 shows the level of the reflected signal, S11 with open as well as short inserted at the other end of the DUT as well as the losses that is computed as the average of short and open divided by two. (The signal passes the DUT twice. | |||||
device 143 MHz 144 MHz 145 MHz Open Short loss Open Short loss Open Short loss DUT1 -0.317 0.346 -0.007 -0.320 0.351 -0.008 -0.324 0.355 -0.008 DUT2 -0.137 -0.183 0.080 -0.129 -0.192 0.080 -0.121 -0.202 0.081 DUT3 -0.433 0.310 0.031 -0.438 0.312 0.032 -0.440 0.315 0.031 DUT4 -0.170 -0.141 0.078 -0.164 -0.150 0.078 -0.155 -0.158 0.078 DUT13 -0.203 0.111 0.023 -0.195 0.108 0.022 -0.186 0.103 0.021 DUT31 -0.368 -0.064 0.108 -0.366 -0.070 0.109 -0.365 -0.078 0.111 DUT123 0.079 -0.313 0.059 0.071 -0.291 0.055 0.063 -0.268 0.051 DUT132 0.070 -0.337 0.067 0.062 -0.315 0.063 0.053 -0.293 0.060 DUT312 -0.116 -0.512 0.157 -0.128 -0.505 0.158 -0.140 -0.494 0.159 DUT213 -0.169 -0.410 0.145 -0.187 -0.403 0.148 -0.208 -0.393 0.150 DUT231 0.060 -0.268 0.052 0.050 -0.255 0.051 0.037 -0.240 0.051 DUT42 -0.198 -0.275 0.118 -0.215 -0.260 0.119 -0.233 -0.244 0.119 DUT24 -0.204 -0.269 0.118 -0.223 -0.255 0.119 -0.241 -0.238 0.120 DUT34 0.213 -0.567 0.089 0.218 -0.572 0.089 0.221 -0.576 0.089 DUT43 0.216 -0.570 0.089 0.221 -0.574 0.088 0.222 -0.577 0.089 DUT32 0.216 -0.575 0.090 0.219 -0.580 0.090 0.222 -0.581 0.090 DUT23 0.215 -0.570 0.089 0.219 -0.573 0.089 0.222 -0.576 0.089 | |||
Table 1 Return loss in dB for Open and Short and the loss computed from them. | |
It is obvious that this method does not work well for DUTs that are not well matched to 50 ohms. |