NATIONAL RADIO ASTRONOMY OBSERVATORY Green Bank, West Virginia. Electronics Division Internal Report No. 142 AUTOMATIC NOISE FIGURE METER FRONT-END

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1 NATIONAL RADIO ASTRONOMY OBSERVATORY Green Bank, West Virginia Electronics Division Internal Report No. 142 AUTOMATIC NOISE FIGURE METER FRONT-END Richard L. Fleming MAY 1974 NUMBER OF COPIES: 150

2 AUTOMATIC NOISE FIGURE METER FRONT-END Richard L. Fleming TABLE OF CONTENTS Page 1.0 Introduction.... OOOOOOOOOOOOOOOOOO OOOOO Description of Unit Operation as Noise Figure Meter Front-End Operation as a Receiver Back-End LIST OF FIGURES. 1. Noise Figure Meter Frequency Converter Block Diagram Receiver Back-End Block Diagram Overload Detector Schematic MHz Filter and Detector Schematic Local Oscillator Frequency Control Schematic Photo of Unit Front Panel Photo of Unit Top Photo of Unit Sides...

3 AUTOMATIC NOISE FIGURE METER FRONT-END 1.0 Introduction This report describes the construction and operation of a wide frequency range front-end for use with the AIL-75 Precision Automatic Noise Figure Indicator (PANFI). The PANFI accepts a 30 MHz input frequency with a 5 MHz bandwidth and when used with the noise source supplied will indicate noise figures automatically in one of five ranges up to 33 db. To extend the usefulness of the PANFI, this front-end will enable noise figure measurements to be made in the frequency ranges of GHz and GHz. 2.0 Description of Unit The GHz range is covered by converting these frequencies to a 30 MHz IF to be used with the PANFI. By tuning the LO adjust control on the front panel, automatic measurements can be made through the passband of a unit under test. The LO adjust control is calibrated to read out the RE frequency where the spot (5 MHz BW) noise figure test is being made. Another feature incorporated in the unit is essentially a broad-band receiver back-end covering the range of MHz with a square law detector with better than 1% accuracy. The output of the detector is indicated on a 4 1/2 digit high accuracy DPM which also has an external DC input jack. A DC offset control is available on the front panel to back out the noise temperature of the input amplifier so the DPM can read directly in K, after calibration. The square-law detector incorporated in the unit consists of a carefully matched detector (HP 423A) and DC amplifier, all of which is housed in a temperature controlled oven. The deviation from square law is less than 1.0 percent with typical input/output levels of -23 dbm = 1.0 volt and -13 dbm = 10 volts.

4 -2- The first LO is a Yig oscillator which also has a heater built in. A 30- minute warm-up time should be allowed before using the unit due to the fact that temperature stabilization should occur in the two components just mentioned. 3.0 Operation as a Noise Figure Meter Front-End The lower half of the unit is designed to be used as a front-end (converter) for the AIL-75 PANFI. Inputs in the frequency ranges of 100 MHz to 850 MHz and GHz are converted to 30 MHz for use with the PANFI. The PANFI accepts a 30 MHz input with a 5 MHz bandwidth and a -60 to -10 dbm level. The front-end always produces a 30 MHz IF signal and the RF frequency that the unit is tuned to is indicated by the first LO dial. In the MHz band, the yellow band marker light and the yellow strip on the LO dial are associated. The 1-2 GHz band (green light) and green strip on the LO dial indicates the RF frequency on the high band. The "Peak with LO Adjust" meter is driven by a narrow' (1 MHz) filter and a detector centered at 30 MHz so that there is always indication that 30 MHz is appearing at the output. This is particularly important when doing spot (5 MHz BW) noise figure measurements at a particular RF frequency. To measure the noise figure of an amplifier, connect the amplifier output to the GHz input of the frequency converter section. Connect the proper noise diode that comes with the PANFI to the amplifier input. The noise diode is driven from the back of the PANFI (with the rack panel switch set on "Diode"). Select the proper frequency band and tune the "LO Adjust" for the frequency at which a noise figure measurement is desired. If the amplifier is narrowband., it is necessary to slightly tune the "LO Adjust" for a peak in the 30 MHz output meter. This will guarantee that you are centered in the passband of the amplifier. The "LO Adjust" dial is accurate to within 15 MHz (worst case) across the 1-2 GHz

5 3 band. Connect the 30 MHz output to the IF input of the PANFI. Enough 30 MHz output is present for the PANFI if the AGC light is on. An automatic or manual noise figure can now be made using the PANFI in the normal way. 4.0 Operation as a Receiver Back-End The top half of the unit consists of several amplifiers, variable attenuators, square law detector and a digital panel meter. The bandwidth is MHz with switchable and vernier gain controls. The following outputs/inputs are available on the back panel: amplifier/attenuator chain output, detector RF input, detector DC output and DC input to DPM gain and zero controls. These output/input ports are normally connected together but can be separated by changing the connections on the back panel. There is also a front panel EXTERNAL VIDEO (DC) input to the DPM for V DC input. Excellent square law detector measurements can be made using the amplifier/ detector/dpm chain. To be within the square law region the front panel controls should be set as follows: 0-10 db attenuator set to 5 db, 0-60 db attenuator set to 20 db, 23 db/43 db switch set to 43 db, DC gain adjust set to 500, level set to 515, offset/total power switch set to total power and adjust the DPM to volt using external padding. This would be equal to an input level of approximately -55 dbm. Adjust the input level ± 3 db and check the DPM for an appropriate change in voltage (2.0 V, 0.50 V). If this is within mv (due to the change not exactly 3.00 db), the unit is set for making good measurements.

6 - 2 GHz GHz -15V TO TS - 13 C OSC V LARK BF P I -2GHz GRN.28V 0 S2B r MA, -9V 100 FREQ. OFFSET --e A TEXCAN SW PDT COAX. SW. WITH 1 DC WAFER I INPUT.I-2GHz +I5V -120T0-60dBm AVANTEK AMT- 2004M GHz N.F.= dB 26dB GAIN + 5 dbm S1A-D LO. ADJ. (10T ) SIA LP F f=850 MHz LARK N RAO 4PDT RF PART OF TEXCAN SW. 21 S 2A-D = DC SW. PART OF DC WAFER ON SW. 21,GRN. S IB SAMPLER 5YEL. 1 OSM (-15dBm) (OVLD) +15V OVLD IISOLATOR NARDA db PAD 10dB RYK A SCIEN. 620L GHz LARK L PF cc = IGHz RDL SAMPLE 1-2 GHz 2 mw -I5V SCIEN. COM. SC-2012 N.F.= 5dB MHz 18 db GAIN + 3dBM OUT SAMPLE 1030 MHz 2 mw 3dB PAD 4dB PAD EMF SYST. TS-13C MHz (1030 MHz) OSM (-10dBm) NARDA (OVLD ) V TO S 2C OVLD I NRAO PWR I DIVIDER MERRIMAC PDM BPF 30/1 NR AO PEAK WITH LO. ADJ, DET OUTPUT 30MHz -10 TO -70 dbm METER SEN. FREQUENCY CONVERTER GHz TO 30MHz FIG. 1

7 MHz VAR. ATTN. -70 TO dB dbm TEXCAN MA-50 VDC 4.7p. H NRAO TEXCAN MA-51 3d8 PAD +I5VDC 0 F 3dB WB - 2 PAD NRAO 21 Cer's RL2 \ 01 I' + I5VDC RECEIVER -BACK END FIG. 2 4 H -= 3dB PAD 6.5K -15 4*-w, VDC TOT. ZERO SET PWR. 6. 5K 1 K +15 vdc /OFFSET 100K -= 100K NRAO K GAIN INT. 100K ci EXT. 100 pf 2K NEWPORT DP M EXT. DC INPUT RLI + RL2 WAVECOM R F SW. 0 1 C 2 0 I = 2 C SPDT, LATCHING NON - SELF DEENERGIZE RF 1 C 2 oa TELEDYNE V DC 14O.Q COILS 115 VAC -> ACOPIAN > +I5VDC D15-15O > GND -15 V DC

8 OVERLOAD N LAMP 5V 60 ma NEGATIVE > DETECTOR INPUT FROM OVERLOAD SAMPLER 110 5W -15 OVERLOAD DETECTOR FIG NA MMMO 3.3/4.H RF IN > FROM 30 MHz SAMPLER -60 TO -I0dBm 51 BPF 30MHz BW- I MHz 2-1IpF / 0.12mV TO I85mV DETECTOR A BD-7 10K 1M 10K K 2K 10K IOT METER DRIVER 10K METER SENSITIVITY 2M.05 10K "PEAK WITH LO ADJ. (F.P.) 500 P-A IN5297 ImA 68 IN mA 30MHz BPF DETECTOR METER DRIVER FIG. 4 +I5V W +I5V c ma 10V ialln4740a +15V IK LO ADJ. (F.P.) Is K IOT LIN. 20K IOT ZERO +I5V I S IS IK IN K G 2ND /..LF 3V 3.0 YIG OSC.(1-2 GHz) RYKA SCIEN. 620 L TOUT YIG OSCILLATOR FREQUENCY CONTROL FIG. 5

9 * 85 Hz -2GHz OFFSET Figure OVLD. Photo of Unit Front Panel 030 SAMPLE AUTOMAT.0 NOISE FIGURE METER FRONT ED DET. METER 200 PEAK WITH LO ADJ 30 MHz OUTPUT

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11 9 Figure 8 -- Photo of Unit Sides