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Fast Signal and Noise Measurement Technique

IP.com Disclosure Number: IPCOM000044771D
Original Publication Date: 1984-Aug-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Liu, CH: AUTHOR

Abstract

The signal-to-noise ratio (SNR) measurement technique requires only one signal frequency (l MHz) to be written on a track and the overall SNR is thereafter derived from the read-back harmonics. For example, the true signal strength at 3 MHz would be three times the measured third harmonic. The figure shows the measurement setup. The measuring sequences are as follows: Step l: The front-end electronics (or pre-amp) noise floor (see figure). A) With the disk not spinning, connect the head to the pre-amp. B) Using the HP 3585A Spectrum Analyzer, record the noise level (voltage density) at each discrete frequency sample (l MHz, 2MHz,---).

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Fast Signal and Noise Measurement Technique

The signal-to-noise ratio (SNR) measurement technique requires only one signal frequency (l MHz) to be written on a track and the overall SNR is thereafter derived from the read-back harmonics. For example, the true signal strength at 3 MHz would be three times the measured third harmonic. The figure shows the measurement setup. The measuring sequences are as follows:

Step l: The front-end electronics (or pre-amp) noise

floor (see figure).

A) With the disk not spinning, connect the head

to the pre-amp.

B) Using the HP 3585A Spectrum Analyzer, record

the noise level (voltage density) at each

discrete frequency sample (l MHz, 2MHz,---).

Step 2: Total Noise Floor (Media plus the

electronics noise)

A) Spinning the disk, DC-erase a track under

study. B) Repeat Step l-B.

Step 3: Signal and Harmonics Strength

A) Write a l MHz signal on the track.

B) Obtain the harmonic spectrum.

C) Record the signal strength at the fundamental

(l MHz) and all the odd harmonics.

The algorithm for calculating the SNR profile at all odd harmonics is: NOSRMS(I) = NOISE(I) * SQRT(BW)

SNR(I) = 20 LOG (

SIG (I)*I

)

(NOSRMS(I) ) where:

.IN 5 I = l, 3, 5 ......... the order of harmonics

SIG(I) = the measured signal strength at frequency

I

NOISE(I) = the measured total noise voltage density

at

frequency I

NOSRMS(I) = the RMS noise voltage at I

BW = the band width of the measuring equipment

SNR(I) = the SNR at frequency I

In the past, the definition of

sig...