Manual - 8500A Series Peak Power Meter - Giga-tronics

More documents

Recommendations

Info

Theory of Operation 4.2.7 Calibrator PC Assembly (A12) Refer to Figure 4-9 and schematic diagram #17097 in Chapter 8. The RF Diode Detector Automatic Calibrator uses a computer-controlled calibration circuit to generate precise calibration data using a simple power meter (thermistor) as a reference. This permits diode detectors to be used for absolute power measurements with the same accuracy usually associated with thermistor power meters. Since the automatic calibration system is a new concept developed by Giga-tronics for calibrating diode detectors, the first portion of this discussion will be a general description of the overall theory involved in the system operation. The last part of the discussion will cover the operation of the specific components contained in the calibrator assembly. Figure 4-9. Detector Calibrator (A12) Block Diagram Manual No. 20790, Rev C, November 1998 4-27 Superceded by Revision D, March 2009
Series 8500A Peak Power Meters The system consists of an amplitude-controllable oscillator operating at a fixed frequency of 1 GHz. A portion of the RF output is coupled into a thermistor leveling circuit which is physically mounted inside the metal housing of the calibrator assembly. Referring to Figure 4-9, the thermistor is maintained at a fixed resistance by applying a dc bias current through it. This is achieved by using a self-balancing Wheatstone bridge with the thermistor inserted in one leg of the bridge. The amount of power required to maintain the thermistor at the fixed resistance, RT, is constant so that the RF power plus the dc power dissipated at the thermistor equals a constant. This constant can be determined by switching the RF power off and measuring the bridge voltage. The oscillator output power can then be set by measuring this ambient bridge voltage and calculating the dc voltage which would balance the bridge when the oscillator has the required power output. When this required bridge voltage is written to the DAC on the GPIB/Cal Control PC board, the feedback causes the oscillator to settle to the selected RF power. The above technique allows the calibrator output power to be precisely controlled over a dynamic range of approximately 15 dB. The dynamic range is increased by passing the oscillator power through a set of switched attenuators. The attenuators are designed to allow attenuation values of 0, 10, 20, 30, and 40 dB. The overall gain is adjusted so that the 20 dB stage will provide a precise 0 dBm reference with a specific power level out of the oscillator. Integrated control of the calibrator and detector permits errors in the other attenuator stages to be completely removed in the following manner. With a particular attenuator switched in, the processor sets the oscillator output power to precisely 9 mW and measures the detector voltage. The next level of attenuation is switched in, and a successive approximation algorithm finds the oscillator power (about 90 mW) which will give precisely the same detector voltage. By dividing the two powers, the relative attenuation of the two ranges is obtained. Since the 20 dB range is adjusted to give a 0 dBm absolute reference, the absolute effective attenuation of each range can be calculated. The automatic calibration system generates a table of detector voltages that are equivalent to a known level of input power. This is done by applying many different input powers to the detector, measuring the amplified detector output, and storing the result. The calibration procedure is completely automatic, and the entire process including the range switching, attenuator measurements, and detector calibration takes less than one minute. Since there is 15 dB of dynamic range in the thermistor leveled oscillator and 40 dB of attenuation available for insertion, the calibrator operates over a total 55 dBm dynamic range. Below -33 dBm, the diode detector itself is linear (square law), so the total dynamic range of the system will be 60 dB (-40 to +20 dBm). The frequency response of each individual RF detector is measured over its entire specified range at the factory, and the information is stored in a ROM that is an integral part of the detector. Then, during the measurement of an unknown signal, the frequency response information contained in the detector’s ROM and the amplitude table generated by the calibration system are combined so that if a voltage equal to, say, -10 dBm is generated by the calibrator, the instrument looks at that voltage, compares it to its table, and by interpolating between data points knows that specific voltage level equals -10 dBm. In this way, offset and gain errors in the detector amplifiers are removed and the system has the capability of measuring power over the full dynamic range of the detector with just as much accuracy as the power that is produced from the calibrator. Refer now to DWG# 17097. Q1, together with the Base and Emitter Resonators, is the 1 GHz controllable oscillator. A portion of the signal from Q1 is coupled to a thermistor leveling circuit through the Low Pass Filter to remove harmonics, and through the quarter wave choke to allow connection to one end of the thermistor, RT1. The other end of the thermistor is connected to RF ground through an RF bypass line labeled FL5. RT1 samples the RF signal at the output of the low pass filter, and that sample is sent to the control circuitry on the GPIB/Cal Control PC board. The control circuit has a feedback system involving some amplifiers and associated circuitry as described in the GPIB/Cal Control board 4-28 Manual No. 20790, Rev C, November 1998 Superceded by Revision D, March 2009
Page 1 and 2:
Manual Part Number: 20790 Revision
Page 3 and 4:
Errata Sheet for Series 8500A Peak
Page 5 and 6:
QUICK REFERENCE CARD Giga-tronics M
Page 7 and 8:
Series 8500A Peak Power Meters 2.8.
Page 9 and 10:
Series 8500A Peak Power Meters 6
Page 11 and 12:
Series 8500A Peak Power Meters E
Page 13 and 14:
Series 8500A Peak Power Meters List
Page 15 and 16:
Series 8500A Peak Power Meters x Ma
Page 17 and 18:
Series 8500A Peak Power Meters Symb
Page 19 and 20:
Series 8500A Peak Power Meters xiv
Page 21 and 22:
Series 8500A Peak Power Meters xvi
Page 23 and 24:
Page 25 and 26:
Series 8500A Peak Power Meters 1.2
Page 27 and 28:
Series 8500A Peak Power Meters Auxi
Page 29 and 30:
Page 31 and 32:
Series 8500A Peak Power Meters ☛
Page 33 and 34:
Page 35 and 36:
Series 8500A Peak Power Meters 4 De
Page 37 and 38:
Series 8500A Peak Power Meters 7 Cl
Page 39 and 40:
Page 41 and 42:
Series 8500A Peak Power Meters Inte
Page 43 and 44:
Page 45 and 46:
Page 47 and 48:
Series 8500A Peak Power Meters In t
Page 49 and 50:
Series 8500A Peak Power Meters Wait
Page 51 and 52:
Series 8500A Peak Power Meters time
Page 53 and 54:
Page 55 and 56:
Page 57 and 58:
Page 59 and 60:
Page 61 and 62:
Page 63 and 64:
Series 8500A Peak Power Meters 1. C
Page 65 and 66:
Series 8500A Peak Power Meters 3. V
Page 67 and 68:
Series 8500A Peak Power Meters Figu
Page 69 and 70:
Page 71 and 72:
Page 73 and 74:
Page 75 and 76:
Series 8500A Peak Power Meters ☛
Page 77 and 78:
Series 8500A Peak Power Meters 2-48
Page 79 and 80:
Page 81 and 82:
Page 83 and 84:
Series 8500A Peak Power Meters The
Page 85 and 86:
Series 8500A Peak Power Meters Plot
Page 87 and 88:
Series 8500A Peak Power Meters Temp
Page 89 and 90:
Page 91 and 92:
Page 93 and 94:
Series 8500A Peak Power Meters Outp
Page 95 and 96:
Series 8500A Peak Power Meters Dete
Page 97 and 98:
Series 8500A Peak Power Meters User
Page 99 and 100:
Series 8500A Peak Power Meters Rela
Page 101 and 102:
Page 103 and 104:
Series 8500A Peak Power Meters Auto
Page 105 and 106: Series 8500A Peak Power Meters Auto
Page 107 and 108: Series 8500A Peak Power Meters MRKA
Page 109 and 110: Series 8500A Peak Power Meters (n =
Page 111 and 112: Series 8500A Peak Power Meters 3.3.
Page 113 and 114: Series 8500A Peak Power Meters 3.4
Page 117 and 118: Series 8500A Peak Power Meters Over
Page 119 and 120: Series 8500A Peak Power Meters Deci
Page 123 and 124: Series 8500A Peak Power Meters Comm
Page 131 and 132: Series 8500A Peak Power Meters high
Page 135 and 136: Series 8500A Peak Power Meters inve
Page 139 and 140: Series 8500A Peak Power Meters Addr
Page 143 and 144: Series 8500A Peak Power Meters Figu
Page 145 and 146: Series 8500A Peak Power Meters Trig
Page 147 and 148: Series 8500A Peak Power Meters Ramp
Page 151 and 152: Series 8500A Peak Power Meters feed
Page 155: Series 8500A Peak Power Meters A8 T
Page 159 and 160: Series 8500A Peak Power Meters 4-30
Page 173 and 174: Series 8500A Peak Power Meters 7. P
Page 177 and 178: Series 8500A Peak Power Meters Tabl
Page 179 and 180: Series 8500A Peak Power Meters 4. P
Page 181 and 182: Peak Power Linearity Data Step Atte
Page 183 and 184: Series 8500A Peak Power Meters 5-24
Page 187 and 188: Series 8500A Peak Power Meters b. P
Page 189 and 190: Series 8500A Peak Power Meters Self
Page 191 and 192: Series 8500A Peak Power Meters 8502
Page 207 and 208:
Page 209 and 210:
Page 211 and 212:
Page 213 and 214:
Page 215 and 216:
Page 217 and 218:
Page 219 and 220:
Page 221 and 222:
Page 223 and 224:
Page 225 and 226:
Page 227 and 228:
Series 8500A Peak Power Meters CAGE
Page 229 and 230:
Page 231 and 232:
Page 233:
Series 8500A Peak Power Meters 8-2
Page 267 and 268:
Series 8500A Peak Power Meters Func
Page 269 and 270:
Series 8500A Peak Power Meters Chan
Page 271 and 272:
Series 8500A Peak Power Meters A-6
Page 273 and 274:
Series 8500A Peak Power Meters MENU
Page 275 and 276:
Series 8500A Peak Power Meters B.3
Page 277 and 278:
Series 8500A Peak Power Meters MODE
Page 279 and 280:
Series 8500A Peak Power Meters D.2
Page 281 and 282:
Series 8500A Peak Power Meters D.3
Page 283 and 284:
Series 8500A Peak Power Meters D.3.
Page 285 and 286:
Series 8500A Peak Power Meters D.5.
Page 287 and 288:
Series 8500A Peak Power Meters Figu
Page 289 and 290:
Series 8500A Peak Power Meters E.3
Page 291 and 292:
Series 8500A Peak Power Meters SRQ
Page 293 and 294:
Series 8500A Peak Power Meters Trou
Page 295 and 296:
Series 8500A Peak Power Meters Summ
Page 297:
Series 8500A Peak Power Meters Inde
show all

Manual - 8500A Series Peak Power Meter - Giga-tronics

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?