[time-nuts] Oncore, Trimble Antennae
Lux, James P
james.p.lux at jpl.nasa.gov
Wed Oct 22 13:43:31 UTC 2008
On 10/21/08 9:31 PM, "Chuck Harris" <cfharris at erols.com> wrote:
> Tom Van Baak wrote:
>>> Both the Trimble and Motorola modules use active antennae with 5V power
>>> - what I don't know is whether they are the same polarity.
>>> all my trimbles and oncores have +5 on center, ground on shield...
>> I'd be interested to know if any antennas are in fact the other
>> way around. Never even considered that.
> It would have been fairly trivial for them to put a bridge rectifier
> before the amplifier's power stuff, allowing for either polarity.
But not so trivial to provide the DC blocks in the ground side of the coax.
The LNA is almost certainly some MMIC with RF ground==Vss
And, don't forget that these are cost sensitive devices. 4 diodes and their
installation and board real estate costs money, as would the extra couple
capacitors for the DC blocks, etc.
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