The DUTs.This page describes insertion loss on DUTs presented here. Using the HP8712C network analyzer to measure impedances and losses on 1296 MHz. The impedance data from that page is used to split the measured insertion losses into mismatch loss and dissipative losses below.The Tx port.The Tx port from which the signal generator sends its signal is the attenuators plus cables combination used as the Rx port in the HP8712C network analyzer measurements. That means that the impedance of the Tx port with or without DUT can be taken from the impedance measurements.The Rx port.Figure 1 shows the arrangement for insertion loss measurements. The important parts are the circulators. They guarantee that the LNA, an AD6IW amplifier always looks into the same impedance so it will always provide the same gain. | |||||||||||||||||||||||||||||||||||
Figure 1. Insertion loss measurement. Here DUT8 is inserted. | |||||||||||||||||||||||||||||||
The 40 dB power attenuator near the upper left corner of figure 1 is connected to a HP8657B which is set to 1296.11 MHz. The cable routed to the blue 3 dB attenuator, the attenuator and the adapter were used as the rx port for network analyzer measurements so the impedance seen by the DUT is precisely known in relation to the calibration kit load. The other side of the DUT, DUT8 in figure 1, is connected to an adapter followed by a 90 degree bend with N connectors. The bend is inserted because it happens to bring the impedance near 50 ohms. The two circulators guarantee that the impedance does not change, a 3 dB attenuator is inserted in front of the AD6IW LNA to ensure stability. A second LNA with a PSA04-5043 gives some more gain. The amplified signal is routed to the mixer port of a SBL-1 mixer which is fed by 384.07 MHz, +15 dBm from a HP8657A on the LO port for third overtone mixing. There is a 6 dB attenuator on the mixer to guarantee the impedance. The difference frequency 1296.11-3*384.07=143.9 MHz is obtained on the RF port and routed to a GaAs FET LNA followed by a high level amplifier and a filter for 144 MHz. From that a high level mixer converts the signal to 11 MHz where it is received by a SDR-IP. The loss measurement is performed by repeatedly insert and remove a DUT. It is essential that none of the RG223 cables that carry 1296 MHz is moved during the process. Moving these cables easily causes several tenths of a dB in the signal level. That is due to the impedance changes on bending the cables. The The circulators must thus not be moved during a measurement sequence so all the necessary movement will be on the black cable that is gently bentto allow the Tx port to be moved axially without any impedance change. The black cable is 1 meter of Flexiform 401 with an extra screen on it. The input impedance on the Rx port, the SMA female on the circulator is reasonably near the impedance shown in figure 2. The uncertainty comes from measurement through a SMA male to SMA male adapter with unknown characteristics. I do not have a female calibration kit that matches the male one. The electrical length of the adapter is compensated for, but only approximatively. | |||||||||||||||||||||||||||||
Figure 2. The impedance of the Rx port. There is an unknown error due to the adapter used for the measurement. | |||||||||||||||||||||||||
Results with a simple setup.Before arranging the setup of figure 1 experiments were performed with a RTLSDR USB dongle. Figure 3 shows the signal stability after a long enough warm-up period. It looks like AM noise modulation on the LO causes random fluctuations on the signal level just as phase noise causes random fluctuations on the frequency.The USB dongle does not allow very accurate level measurements. | |||||||||||||||||||||||
Figure 3. The stability of a RTLSDR dongle with the E4000 tuner. | |||||||||||||||||||
A measurement of the insertion loss of DUT1 with the RTLSDR dongle gives IL=0.030 dB with error limit of +/- 0.0042 dB. Measurements with the setup of figure 1.The signal stability is better with this more conventional setup. See figure 3. The stability with the same equipment on 144 MHz is far better which indicates that the much worse sideband noise of the HP generators is the limiting factor on 1296 MHz. | |||||||||||||||||
Figure 4. The stability of the setup shown in figure 1. | |||||||||||||
Table 1 gives the impedances measured previousle and the insertion losses measured with the setup in figure 1 with links to the raw data. | |||||||||||
Device Zre Zim Loss Stddev Equ (Ohm) (Ohm) (dB) (dB) none 52.02 0.21 0.0000 0 1 DUT1 50.34 0.69 0.0320 0.0008 2 DUT3 49.09 -2.56 0.0195 0.0008 3 DUT4 50.45 0.16 0.0503 0.0012 4 DUT7 51.84 -2.46 0.0600 0.0035 5 DUT13 54.04 2.24 0.0614 0.0004 6 DUT43 52.97 3.10 0.0836 0.0040 7 DUT73 55.71 0.68 0.0853 0.0008 8 DUT37 46.71 -2.12 0.0806 0.0012 9 DUT34 49.16 -0.95 0.0730 0.0011 10 DUT31 49.67 -1.00 0.0513 0.0017 11 DUT8 71.81 0.51 0.1652 0.0010 12 DUT83 75.04 5.42 0.2364 0.0019 13 DUT81 74.35 0.20 0.2284 0.0009 14 DUT813 69.27 -2.47 0.1969 0.0015 15 DUT318 55.75 14.82 0.1972 0.0008 16 DUT381 44.59 -18.52 0.2484 0.0014 17 DUT831 74.80 2.61 0.2560 0.0018 18 DUT183 34.89 3.87 0.2513 0.0006 19 DUT138 59.53 19.49 0.2665 0.0011 20 DUT6 53.04 1.89 0.1102 0.0012 - DUT18 36.77 4.60 0.1886 0.0015 21 DUT38 45.70 -17.41 0.1847 0.0021 22 DUT48 36.75 0.00 0.2002 0.0014 23 DUT84 73.83 1.24 0.2445 0.0035 24 DUT14 51.73 -0.41 0.0844 0.0016 25 DUT41 51.89 -0.11 0.0840 0.0011 26 DUT5 51.43 -0.19 0.0673 0.0013 - | |||||||||
Table 1. Impedances from the HP8712C network analyzer and insertion losses from the setup in figure 1. | |||||||
Evaluation of unknowns.The impedances in table 1 all contain the unknown calibration error from the calibration kit.The insertion loss should be the sum of the mismatch loss and the sum of the dissipative losses for the DUT. Disregarding DUT5 and DUT6 which are not measured together with other DUTs we have this set of unknowns: x(1)=The dissipative loss of DUT1 x(2)=The dissipative loss of DUT3 x(3)=The dissipative loss of DUT4 x(4)=The dissipative loss of DUT7 x(5)=The dissipative loss of DUT8 x(6)=The calibration error real part x(7)=The calibration error imaginary part x(8)=The Tx port impedance error real part x(9)=The Tx port impedance error imaginary part There are 26 equations that connect these 9 unknown variables. For each line in table 1, the loss should be the sum of the dissipative losses plus the insertion loss. The insertion loss can be computed from this formula: IL = 4 * Rt * Rr / [ (Rt + Rr)2 + (Xt + Xr)2 ] Rt is the real part of the Tx port impedance. Xt is the imaginary part of the Tx port impedance. Rr is the real part of the Rx port impedance. Xr is the imaginary part of the Rx port impedance. From the equation it is obvious that we can not determine Xt and Xr separately, only their sum. Also Rt and Rr are strongly coupled. This means that we have 26 equations and 7 independent variables. The RMS deviation produced by a least squares fit will give a good insight in the measurement errors. A simple Fortran program with a Makefile for Linux can be downloaded here: losscalc100.tbz (5536 bytes) Running it with table 1 as input produces the listing displayed in table 2. | |||||
DUT100 ( 50.340 0.690) il= 0.0320 Dissipat.= 0.0323 err= 0.0001 DUT300 ( 49.090 -2.560) il= 0.0195 Dissipat.= 0.0209 err= 0.0014 DUT400 ( 50.450 0.160) il= 0.0503 Dissipat.= 0.0534 err= 0.0022 DUT700 ( 51.840 -2.460) il= 0.0600 Dissipat.= 0.0564 err=-0.0039 DUT130 ( 54.040 2.240) il= 0.0614 Dissipat.= 0.0532 err=-0.0003 DUT430 ( 52.970 3.100) il= 0.0836 Dissipat.= 0.0743 err=-0.0011 DUT730 ( 55.710 0.680) il= 0.0853 Dissipat.= 0.0773 err= 0.0020 DUT370 ( 46.710 -2.120) il= 0.0806 Dissipat.= 0.0773 err= 0.0020 DUT340 ( 49.160 -0.950) il= 0.0730 Dissipat.= 0.0743 err= 0.0004 DUT310 ( 49.670 -1.000) il= 0.0513 Dissipat.= 0.0532 err= 0.0005 DUT800 ( 71.810 0.510) il= 0.1652 Dissipat.= 0.0358 err= 0.0032 DUT830 ( 75.040 5.420) il= 0.2364 Dissipat.= 0.0567 err=-0.0008 DUT810 ( 74.350 0.200) il= 0.2284 Dissipat.= 0.0681 err=-0.0005 DUT813 ( 69.270 -2.470) il= 0.1969 Dissipat.= 0.0890 err=-0.0015 DUT318 ( 55.750 14.820) il= 0.1972 Dissipat.= 0.0890 err=-0.0023 DUT381 ( 44.590 -18.520) il= 0.2484 Dissipat.= 0.0890 err=-0.0027 DUT831 ( 74.800 2.610) il= 0.2560 Dissipat.= 0.0890 err= 0.0013 DUT183 ( 34.890 3.870) il= 0.2513 Dissipat.= 0.0890 err=-0.0017 DUT138 ( 59.530 19.490) il= 0.2665 Dissipat.= 0.0890 err= 0.0002 DUT600 ( 53.040 1.890) il= 0.1102 Dissipat.= 0.1055 err=-0.0000 DUT180 ( 36.770 4.600) il= 0.1886 Dissipat.= 0.0681 err= 0.0053 DUT380 ( 45.700 -17.410) il= 0.1847 Dissipat.= 0.0567 err= 0.0027 DUT480 ( 36.750 0.000) il= 0.2002 Dissipat.= 0.0892 err=-0.0030 DUT840 ( 73.830 1.240) il= 0.2445 Dissipat.= 0.0892 err=-0.0001 DUT140 ( 51.730 -0.410) il= 0.0844 Dissipat.= 0.0857 err= 0.0005 DUT410 ( 51.890 -0.110) il= 0.0840 Dissipat.= 0.0857 err= 0.0013 DUT500 ( 51.430 -0.190) il= 0.0673 Dissipat.= 0.0683 err= 0.0000 RMS error= 0.00199 alfa= 0.000000 step= 0.000008 1 DUT1 Dissipative loss=0.0323 2 DUT3 Dissipative loss=0.0209 3 DUT4 Dissipative loss=0.0534 4 DUT7 Dissipative loss=0.0564 5 DUT8 Dissipative loss=0.0358 6 DUT6 Dissipative loss=0.1055 7 DUT5 Dissipative loss=0.0683 8 Source impedance real part= 52.090 9 Load impedance real part= 50.576 10 Sum of complex parts= 1.177 | |||
Table 2. Results from the evaluation of dissipative losses from insertion losses measured with the setup of figure 1. | |
The RMS error in the evaluation of the equations is 0.002 dB. That is 10 times better than the result obtained with the insertion loss measured with the HP8712C network analyzer. The size of the RMS error is as expected, the RMS value of the 26 estimated standard deviations in table 1 is 0.0017. With proper crystal oscillators the accuracy would probably have been another order of magnitude better. What error limits to set for the individual DUTs is beyond my skils. In total 8 unknowns are determined from 26 equations..... |