[time-nuts] WTB: GPS Antenna Splitter

Tim Shoppa tshoppa at gmail.com
Wed Oct 8 11:31:56 EDT 2014

e.g. HP58540A will raise the red alarm LED if DC antenna current is less
than 5mA [open] or bigger than 50mA [short]. I thought this was in common
with Z3801A but I don't see it mentioned in the Z3801A book.

Page 15 of M12+ users guide says: "The M12+ is capable of detecting the
presence of an antenna. The receiver utilizes an antenna sense circuit that
can detect under current (open condition), over current (shorted or
exceeding maximum receiver limits), or a valid antenna connection. " then
goes on to note that an external bias-T will make this detection
meaningless. It lists the current limits as 15mA [open] and 80mA [short].

Tim N3QE

On Wed, Oct 8, 2014 at 11:22 AM, Dave M <dgminala at mediacombb.net> wrote:

> Thanks, Tim,
> I have wondered about the available antenna current from GPSDO units, but
> haven't been able to find a spec on any of them, or at least, the GPS units
> that I have. I have an HP Z3801A and a Nortel GPSTM NTBW50AA. Have you (or
> anyone) any information on typical available antenna current, or alarm
> conditions for antenna overcurrent?  I know the Nortel unit spec says that
> it can survive a shorted antenna/cable without damage, but no info on
> alarms or current limits.  My guess is that the unit won't see any
> satellites and will just go into holdover.
> The Z3801A must have an active antenna connected (no passive antennas
> allowed), but no specs in the manual on antenna current limits.
> I guess I could substitute an active load (transistor or FET) for the
> antenna so I can vary the current drawn, and see what alarms pop up.
> Thanks for more info,
> Dave M
> Tim Shoppa wrote:
>> At the very low end, a F-cable splitter for like Cable TV will likely
>> (*) get the job done. Many of us are already using RG-6 type cable
>> for the GPS antenna run anyway.
>> (*) Some GPS units may get confused if they have active sensing on the
>> antenna preamp current and this goes out of tolerance.
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