Browse Prior Art Database

COMPLEMENTARY ANALOG DELAY MEASURING METHOD

IP.com Disclosure Number: IPCOM000006301D
Original Publication Date: 1991-Dec-01
Included in the Prior Art Database: 2001-Dec-21
Document File: 2 page(s) / 118K

Publishing Venue

Motorola

Related People

Steven J. Goldberg: AUTHOR [+2]

Abstract

For various systems it is necessary to measure the delay that signals will experience as they transverse var- ious communications paths. The path may involve tele- phone twisted pairs, radio frequency transmission and reception, splitters, nonanalog transmission medium (ex. digitized analog facilities), etcetera. The delay measure- ment is usually performed as a loop back type of opera- tion. Figure 1 is a typical example.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 50% of the total text.

Page 1 of 2

0 M

MOTOROLA INC. Technical Developments Volume 14 December 1991

COMPLEMENTARY ANALOG DELAY MEASURING METHOD

by Steven J. Goldberg and Pete Figueredo

  For various systems it is necessary to measure the delay that signals will experience as they transverse var- ious communications paths. The path may involve tele- phone twisted pairs, radio frequency transmission and reception, splitters, nonanalog transmission medium (ex. digitized analog facilities), etcetera. The delay measure- ment is usually performed as a loop back type of opera- tion. Figure 1 is a typical example.

  In order to perform this measurement the source sends a known sequence. At some point in the sequence a timer is started. It is stopped when the same point in the sequence is received.

  Digital communications over telephony type medium usually uses frequency shit? keying for data rates up to 2400 baud. Signals sent over these paths will however experience frequency dependent propagation times. Although bit states may be recoverable, accurate timing of the received bit stream delay may not be due the uncertainty of the exact switching points.

  Above 2400 baud phase shitliig of a single frequency is often used. This avoids the diierent delays due to using multiple frequencies, but it is even more difficult to derive a precise switching pdint due to the phase discontinuities.

  Amplitude modulation also has the advantage of being a single frequency. In telephony type systems it is not generally used for modems because the change from one amplitude to another is a discontinuity which gen- erates higher frequencies. The phone lines however act as low pass filters. The result is a ringing which decays with time. Figure 2 shows this with the extreme form of amplitude modulation known as on/off keying. (The curves shown are approximations to the actual wave- forms.) The problem then is to differentiate the true end of the signal from the decaying transient response. One approach is to use a curve known as the raised cosine when switching from on to off or off to on. By not pro- ducing a sharp discontinuity, the receive signal on prop- erly conditioned lines is very close in form to that

0 MOfOro,a 1°C. 19%

transmitted (Figure 3). The difference between the full amplitude cycle and the transition cycle can be deter- mined by simple comparisons ofthe amplitudes.

  A problem however exists on lines which have a large mismatch and/or are heavily capacitively and/or inductively loaded. Instead of a low level transient sig- nal occurring, a...