User manual GARMIN GPS 25 LP TECHNICAL SPECIFICATION

[. . . ] GPS 25 LP SERIES GPS SENSOR BOARDS GPS25-LVC, GPS25-LVS, GPS25-HVS TECHNICAL SPECIFICATION _______________________________________________________________________ GARMIN· 1200 E. 151st St· Olathe, Kansas 66062· (913)397-8200· (913)397-8282 FAX ©2000 GARMIN Corporation 1200 East 151st Street, Olathe, KS 66062 All rights reserved. No part of this manual may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying and recording, for any purpose without the express written permission of GARMIN. Information in this document is subject to change without notice. [. . . ] Coaxial cable supplies +Vin-0. 4V @15 mA to antenna/preamp. 1. 57542 GHz signal returns to the sensor board. The recommended GARMIN remote antenna for the GPS 25LP series is the GA27. It has eight feet of RG-174A/U type cable with a MCX connector installed for attachment to the sensor board. An extension cable with up to -5dB additional attenuation at 1. 5 GHz may be used with the GA27 (either 50 Ohm or 75 Ohm impedance cable is permitted). A passive antenna may be used with the GPS 25LP series sensor boards, provided no more than -2dB or -3dB cable loss is inserted between the antenna and the sensor. Higher gain competitors' antennas may be used provided there is adequate cable attenuation to prevent overloading the sensitive GPS 25LP receiver. 15dB excessive antenna system gain (LNA Gain - Cable Loss) should be considered a maximum. Check to insure that the antenna in question will operate properly with the antenna bias voltage that is supplied by the GPS 25LP, when powered by the desired Vin voltage. The GPS 25LP will current limit for loads above 50mA to prevent damage, should the antenna cable become accidentally shorted. The following table may be used to estimate the typical attenuation of various cable types at 1. 5 GHz. For example, a 15 foot length of RG-188 may have 4. 5 dB attenuation. The attenuation of different styles of the same cable type may vary. Refer to the specifications of the actual cable that will be used. 14 Type RG-211A/228A RG-217/224/293/14 RG-8/215/216 RG-6 RG-59 RG-58 RG-188 RG-174 RG-178 Typical Attenuation dB/100' @ 1 GHz 4. 5 5. 8 9 11 11. 5 20 30 31 45 15 Section 4 Software Interface The GPS 25LP interface protocol design on TXD1/RXD1 is based on the National Marine Electronics Association's NMEA 0183 ASCII interface specification, which is fully defined in "NMEA 0183, Version 2. 0" (copies may be obtained from NMEA, P. O. Box 50040, Mobile, AL, 36605, U. S. A. ) and the Radio Technical Commission for Maritime Services' "RTCM Recommended Standards For Differential Navstar GPS Service, Version 2. 1, RTCM Special Committee No. 104" (copies may be obtained from RTCM, P. O. Box 19087, Washington, D. C. , 20036, U. S. A. ). The GPS 25LP interface protocol, in addition to transmitting navigation information as defined by NMEA 0183, transmits additional information using the convention of GARMIN proprietary sentences. Binary phase data information is output on TXD2, see Appendix D for details. The following sections describe the NMEA data format of each sentence transmitted and received by the GPS 25LP sensor board. The baud rate selection, one-pulse-persecond output interfaces and RTCM differential GPS input are also described. 4. 1 NMEA Received sentences The subsequent paragraphs define the sentences which can be received on RXD1 by the GPS 25LP sensor boards. Null fields in the configuration sentence indicate no change in the particular configuration parameter. All sentences received by the GPS 25LP must be terminated with <CR><LF>, but do not require the checksum *hh. [. . . ] The bottom section contains program messages. Upload and download status messages will appear here as well as any program error messages. Commands: D - Download Almanac: The GPS25 sensor will be sent a command to download almanac information. GPS25PM. EXE will create the file ALMANAC. DAT and locate it the current working directory. [. . . ]