Response to 13606

FCC ID: H25DSS950TX

Cover Letter(s)

Download: PDF

FCCID_98459

May1, 2000

Mr. Joe Dichoso
Federal Communications Commission
Laboratory Division
7435 Oakland Mills Road
Columbia, MD 21046

Michael J. Murphy
75 Northeastern Blvd.
Nashua, NH 03062
(603) 668-8549 FAX (603) 880-6965

Attention: Mr. Dichoso

Re: Answers to questions from E-mail of 04/05/00
Correspondence Reference Number: 13606
FCC ID: H25DSS950TX
731 Confirmation Number EA96934
Equipment Class: DSS-Part 15 Spread Spectrum Transmitter
Applicant: DTC

DTC has collected additional data on H25DSS950TX in order to satisfy the two questions on the referenced E-mail.

1. The SAR report has been uploaded to the RF Exposure info folder.

2. The receiver BER measurements made by Digital Wireless Corp (DWC) indicate a S/N of 12 to 14 dB for a BER of .0001. The
referenced 9.6 dB was not a measurement. It was simply a comment on the theoretical S/N for a BER of .0001 for coherent BPSK.
Coherent BPSK is not employed.

The DWC receiver is inferior to theoretical coherent BPSK this in two ways:

First of all it employs DBPSK demodulation which has a theoretical S/N for a BER of .0001 of 10.6 dB; 1 dB worse than coherent
BPSK, as shown in the S/N curve graph I have submitted. This curve is from RF and Microwave Circuit Design for Wireless
Communications, Artech House, Lawrence E. Larson, Editor, 1996. Also see Digital Communications by Bernard Sklar, Prentice
Hall, 1988.

Second of all, the receiver is not capable of achieving this theoretical number (10.6 dB), because of practical design considerations.
DWC quotes 12 to 14dB for this receiver in the Data EXHIBIT.
Using the worst case number and the equation: Gp =S/N + Lsys + (J/S); Gp = 12 + 2 + (-2.9) = 11.1 dB, which is compliant.

Best Regards,

Michael J. Murphy
Electronics Engineer
DTC Communications, Inc.
mmurphy@dtccom.com

Document Created: 2000-05-01 16:57:44
Document Modified: 2000-05-01 16:57:44

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