[time-nuts] WTB: GPSDO
thomas at petig.eu
Thu Mar 23 04:44:15 EDT 2017
On Wed, Mar 22, 2017 at 05:20:31PM -0500, Chris Caudle wrote:
> On Wed, March 22, 2017 3:52 pm, Nick Sayer via time-nuts wrote:
> > My thunderbolt *insists* on being on the DC Pass port. If you put it on a
> > DC Block port (yes, something *else* is on the DC pass port and supplying
> > DC for the antenna and splitter at the time - other connected devices work
> > just fine) it's deaf.
> You need a DC load so that the GPS receiver thinks there is an active
> antenna attached. I think that is just a quirk of the Thunderbolts, that
> rather than just flagging an alarm and continuing to run, it gives up and
> won't even try to run.
They try to check if an active antenna is connected by measuring the DC
load. You can (not tested by me) simulate this with a Bias T and a
resistor to ground on the DC port. I think there are more receiver that
might require this. Many dedicated GPS splitters have such a DC load
'simulation' with around 200 Ohm to ground to keep the receiver happy.
> Chris Caudle
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