Browse Prior Art Database

RECEIVE IF FILTER COMPENSATION

IP.com Disclosure Number: IPCOM000005685D
Original Publication Date: 1987-Oct-01
Included in the Prior Art Database: 2001-Oct-26
Document File: 1 page(s) / 65K

Publishing Venue

Motorola

Related People

Ron Chapman: AUTHOR [+2]

Abstract

The push for spectral efficiency in future land mobile systems calls for narrow channel spacings with tight frequency tolerances. One of the major concerns in designing such a system is in the make, temperature and aging tolerances of the IF filters.

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 53% of the total text.

Page 1 of 1

m

MO7OROLA Technical Developments Volume 7 October 1987

RECEIVE IF FILTER COMPENSATION

by Ron Chapman and Mark Marsan

   The push for spectral efficiency in future land mobile systems calls for narrow channel spacings with tight frequency tolerances. One of the major concerns in designing such a system is in the make, temperature and aging tolerances of the IF filters.

   Ceramic filters are commonly used in mobile and portable radios but unfortunately exhibit extremely poor tolerance specifications. Typical ceramic filters operating at 455 kHz have a center frequency which may shift up to 910 Hz due to temperature shifts, 910 Hz due to aging and 750 Hz due to manufacturing tolerances,

   This IF compensation technique is a calibration procedure that removes all IF center frequency shifts by measuring the IF center frequency offset and tuning the second local oscillator proportionately. This calibra- tion procedure is accomplished in three steps.

   The first step in the procedure is to calibrate the discriminator. This is accomplished by turning the se- cond LO off and turning on a455 kHz oscillator. The discriminator output voltage is then read by the A/D con- verter and stored in the microprocessor.

   The second step is to measure the offset of the IF filter. With the second LO and 455 kHz oscillator both off the noise at the discriminator output is averaged by either the microprocessor or a low pass filter. Since the average frequency of the noise in the IF approximates th...