Dave et al, Be very careful trying to apply +12V to a GPS antenna. Connector type does not matter. About the only timing antennas I have seen that accept a 12V input voltage are the timing antennas from Micropulse (now Andrew). They are typically rated for 5-26V. This makes it easier to use them on long coax runs, but ONLY if the antenna bias is supplied through an external bias-T or splitter. I can just about guarantee you that you will blow up your receiver if you try to run 12V through it.
As far as failure modes go, by far the most common failure I see (at least on Motorola receivers) is due to a lightning near miss. There is a little 5.6V zener across the antenna input circuitry that typically shorts if it sees a large power surge. Occasionally the DC coupling inductor will get popped too. The rest of the receiver works fine, and will normally light back up again as soon as the zener is removed or replaced. When this happens it is quite possible for the antenna and splitter to survive. They usually have larger surge suppression components that will survive this type of event. If any of you out there have any old Motorola receivers that appear to run OK but don't pick up SV's, put an ohmmeter across the antenna connector on the receiver and see what reading you get. If it is down in the 0-20 ohm range you probably just have a dead sacrificial diode. Randy ________________________________________________________________________ ________________________________________________________________ -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of David Smith Sent: Sunday, December 17, 2006 3:26 PM To: time-nuts@febo.com Subject: Re: [time-nuts] Failure mode in GPS receivers Bruce, I've owned a Trak Systems 8821 for over a year, and had a problem with the antenna side. Yours may be different. My unit is designed to work with a powered antenna, and it feeds 12V up the coax to power it. Apparently this is the "standard" voltage for TNC antenna connections - the smaller MCX etc. are 5V standard. In my ignorance, I initially connected one of the regular "mouse" type antennas to it that requires 5V. The antenna worked OK for months, and I only discovered the error when I was fitting another more permanent antenna. Strangely, the "mouse" no longer works on 5V, but seems to get by on 12V. Because most powered antennas these days seem to be 5V, I modded the Trak with a 78L05 in the antenna power circuit to match. So, what you could have done is fried the port on your splitter with the 12V? Just a guess. Regards, David Smith. P.S. Have you got any software for yours? I've got a User Manual PDF for mine if that helps. _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts