As with all of my hobbies, they are limited by money and time to pursue them. IF I were certain I would get a good enough signal, to be more accurate and stable than my current setup(OCXO disciplined by a CDMA signal), then I would go for a GPSDO recommendation. The GPS 18 from Garmin is ~130 list, since ti comes with some software for a laptop. How much would the GPDSO unit be, plus a display of the time or inputs into a laptop with time and other related information?
Message: 3 Date: Wed, 23 Jan 2008 10:17:33 -0800 From: Hal Murray <[EMAIL PROTECTED]> Subject: Re: [time-nuts] indoor GPS test. To: Discussion of precise time and frequency measurement <time-nuts@febo.com> Message-ID: <[EMAIL PROTECTED]> Content-Type: text/plain; charset=us-ascii > I have had no success getting anyone to loan me their GPS units. Does > anyone have suggestions as to what inexpensive unit to purchase, which > will give a good indication of whether a GPSDO unit will receive and > process the signals? Which end of the "nut" scale are you on? If you have to do the test, you might as well get the gear you will eventually use. There are two types of GPS receivers. One primarily tells you where you are and how fast you are moving. It also tells you the time. The other is primarily for getting the time. You tell it where it is (or ask it to figure it out, aka survey) and it uses that to do a better job of telling the time. There is a huge market for commercial GPS position receivers. They usually come with mapping software which jacks up the price. Most of them don't have PPS outputs. Many of them use USB. GPS chip sets have been getting better over the years. The Garmin GPS-18-LVC is popular with people running ntpd. You can get them for under $100. It takes some soldering. They need 5V. You can get that from USB. Note the LVC. The other GPS 18 models don't have the PPS signal. For ntpd, the PPS signal is usually wired up to a modem control signal and the kernel records the time when an interrupt happens. (There are a couple of good web pages on how to wire them up. I'll fish them out if you have any troubles finding them.) I have one. It just barely mostly works inside my house if I'm careful about where I place it. (which makes it good at tickling error cases) I have trees and neighbors but no serious RF shielding so my antenna position is probably "medium" on the wide scale of possibilities - better than many apartments but worse than most outside installations. The GPS 18 has been on the market for several years so its chip-set is not as sensitive as some newer ones. I just wired up a MR 350P from Global Sat. http://www.usglobalsat.com/p-58-mr-350p-bulkhead.aspx It uses the SiRF III chipset which is much more sensitive than the GPS 18 LVC. Unfortunately, the PPS output is only 1 microsecond wide which probably isn't enough to get into a PC. (But I haven't tried that yet.) This also requires some soldering. I cut off the connector. (Their RS-232 adapter cable drops the PPS signal.) So, depending on what you want to do, I'd suggest either the GPS-18-LVC or the MR 350P. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.