8/7/2019 Low Frequency Subsystem for Dual Channel Attenaution Measurements

1/3

LOW FREQUENCY SUBSYSTEM TO ESTABLISH DUAL CHANNELSUBSTITUTION TECHNIQUE FOR THE RF ATTENUATION

MEASUREMENT TRACEABLE TO 10 KHZ ATTENUATION STANDARD

Shefali Goel*, Kamlesh Patel**, P.S. Negi

*Aim & Act Department, Banasthali Vidyapith, RajasthanElectrical & Electronics Standards, National Physical Laboratory, Delhi

**kpatel@nplindia.org

AbstractTo establish in-house traceable measurements in attenuation parameter, we havedeveloped and analyzed a Low frequency subsystem at 10kHz for feasible study to beemployed in the establishment of the Inductive voltage divider (IVD) based Dualchannel substitution technique. In the present paper, the study and measurements ofthe low frequency subsystem for Dual channel substitution technique have been

reported. This paper discussed the design of an amplifier, band pass filter, phase shifterand phase meter at 10 kHz on simulator and the same have been developed. Thesimulated and experimental results have been compared. The results will help todevelop and use the LF subsystem as an integrated unit and will establish a 30 MHzcalibration facility based on the standard IVD through the use of integrated unit.

I. IntroductionThe present paper emphasized on the development of Low frequency subsystem andthe related measurements for the feasible study of Inductive voltage divider (IVD) baseddual-channel substitution technique [1]. In the present metrology, the waveguide belowcut-off (WBCO) attenuator at 30 MHz and the IVD at 10 kHz and 1 kHz are being used

worldwide as primary standard of attenuation [2]. National Physical Laboratory, India(NPLI) is presently having attenuation measurement facilities up to 60 dB with

uncertainty of0.02dB/10dB in the frequency range 30 MHz to 18 GHz [3]. Presently,the NPLIs primary standard of attenuation is a 30 MHz WBCO attenuator of 60 dB

range with 0.005dB/10dB uncertainty. The attenuation standard of higher attenuationrange and better uncertainty in the measurement system would increase the attenuationmeasurement range with improved uncertainty.

II. Design and measurementsTo fulfill the proposed objectives, an amplifier of gain 70 dB, a BPF of BW 2 kHz, a

phase shifter from 0 to 180 and a phase meter of three digits have been designed at

10 kHz on simulator (circuit maker student version) and developed on breadboards[4,5,6,7]. The measurements were performed to study various parts of LF subsystem

using signal generator, digital multimeter, 15 MHz CRO and 15V power supply.However due to time constraint, the XOR gate response have been analyzed and theoutputs at IC 7490 decade counter, IC 7475 D-latch, IC 7447 Decoder have beenobserved on CRO. The developed low frequency subsystem to be employed in Dualchannel substitution technique is shown in Fig.1.

8/7/2019 Low Frequency Subsystem for Dual Channel Attenaution Measurements

2/3

III. Results and discussionThe simulated and experimental results of various parts of LF subsystem werecompared in Figs 2 3.

The amplifiers gain 40 dB, BPFs BW

1.8 kHz and phase shifter range 0 to

180 were measured at 10 kHz. The

responses of amplifier, and BPFand phase shifter were found well tofulfill the requirement. Thus this exercisewill help us to move one step towards toestablishment of the IVD based dualchannel substitution technique and alsoone can develop and analyze the LFsubsystem at any desired frequency.

Phase shifterAmplifier

1 & 2

Fig.1 Low Frequency Subsystem

Band passfilter 1 & 2

PhaseMeter

6 7 8 9 10 11 12

1

2

3

4

5

6

7

8

O

utputvoltage(volts)

Frequency(kHz)

Simulated

Modmeas

-10k 0 10k 20k 30k 40k 50k 60k 70k 80k

-20

0

20

40

60

80

100

120

140

160

180

200

Phasediff

eencebetweentheI/P&O/P

Resistance(ohms)

Measured

Simulated

(i) Fig.2 Simulated and Experimental response of (i) Band pass filter and (ii) Phase shifter

-20 0 20 40 60 80 100 120 140 160 180 200

0

10

20

30

40

50

60

70

ONtime(us)

Phase difference beteen the I/Ps

Simulated

Measured

Fig.3 Simulated and Experimental response of Output at XOR-gate

8/7/2019 Low Frequency Subsystem for Dual Channel Attenaution Measurements

3/3

References:[1] A. Widarta, T. Kawakami, and K. Suzuki, Dual channel IF substitution measurementsystem for Microwave attenuation standard, IEICE Trans. Electron, vol. E86-C, NO.8,Aug 2003.

[2] R Thompson and J Howes, The UK National Standards of RF and MicrowaveAttenuation- A Review, BEMC 2005.

[3] Ram Swarup, Precision microwave attenuation measurements and standards,Electrical and Electronic Measurements, Eds. V.N. Ojha and B.S. Mathur, Pub.Metrology Society of India, 1995, pp. 155-166.

[4] Ramakant A. Gayakwad, Opamps & linear integrated circuits, second edition,chapters 1-10, 1998.

[5] David A. Bell, Operational Amplifiers and Linear ICs, second edition, chapter 1,3 and

11, 2001

[6] Nwankwo D.I.D., The Development and Design of a Digital Phase Meter, M.Eng.Disertation, Nnamdi Azikiwe University, Awka, 2002

[7] V K Chandra, K Patel and V.S. Samuel Rajkumar, Design and performance offrequency counter based and microprocessor based digital Lux meter using LDRsensor, M.Sc. Project report 2/1999,1999.