Return-Path: Received: from www08.netaddress.usa.net ([204.68.24.28]) by truman.olsusa.com (Post.Office MTA v3.1.2 release (PO203-101c) ID# 0-44819U2500L250S0) with SMTP id AAA3018 for ; Mon, 21 Sep 1998 19:19:42 -0400 Received: (qmail 18616 invoked by uid 60001); 21 Sep 1998 23:19:37 -0000 Message-ID: <19980921231937.18615.qmail@www08.netaddress.usa.net> Date: Mon, 21 Sep 1998 23:19:37 From: Dan Schaefer To: lancair.list@olsusa.com Subject: GPS frequencies, good tutorial X-Mailing-List: lancair.list@olsusa.com Mime-Version: 1.0 <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> << Lancair Builders' Mail List >> <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> >> I've been surfing the web for info regarding the GPS carrier frequencies for you guys wanting to design and build your own antennas. Though it sounds like a bit of a daunting task, the following may help. *********************** GPS Signals in detail Carriers The GPS satellites transmit signals on two carrier frequencies. The L1 carrier is 1575.42 MHz and carries both the status message and a pseudo-random code for timing. The L2 carrier is 1227.60 MHz and is used for the more precise military pseudo-random code. Pseudo-Random Codes There are two types of pseudo-random code (see tutorial for explanation of pseudo random codes in general). The first pseudo-random code is called the C/A (Coarse Acquisition) code. It modulates the L1 carrier. It repeats every 1023 bits and modulates at a 1MHz rate. Each satellite has a unique pseudo-random code. The C/A code is the basis for civilian GPS use. The second pseudo-random code is called the P (Precise) code. It repeats on a seven day cycle and modulates both the L1 and L2 carriers at a 10MHz rate. This code is intended for military users and can be encrypted. When it's encrypted it's called "Y" code. Since P code is more complicated than C/A it's more difficult for receivers to acquire. That's why many military receivers start by acquiring the C/A code first and then move on to P code. Navigation Message There is a low frequency signal added to the L1 codes that gives information about the satellite's orbits, their clock corrections and other system status. ********************** I copied this from a Trimble site which has a very well written tutorial on GPS, with pictures and animation for us "reading comprehension challenged" at "http://www.trimble.com/gps/" It's full of general info about the system and how it works and they have made it digestible. I'm sure there's other company's sites out there too, this is just the first one I hit via Yahoo. Good luck with your antenna design. Dan Schaefer ____________________________________________________________________ Get free e-mail and a permanent address at http://www.netaddress.com/?N=1