[time-nuts] Oncore, Trimble Antennae

[Chuck Harris]

Lux, James P wrote:
> 
> 
> 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

Not any worse than providing the DC block on the center of the coax.

> 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.

There is certain to be one diode on the hot lead anyway... engineers get nervous
when they leave out stuff like that.. so adding a bridge would eliminate that
diode.  A quick check of Mouser gives me a cost difference (qty 1000) of one dime
for the added bridge and capacitor... 12 cents if there was no diode in the original
circuit.  Circuit boards on devices like hockey puck antennas tend to be sparsely
populated, so I don't think it would make any difference there.

It would be worth the cost if the antenna was meant to be a universal device,
but probably not if it was intended to be used on only one receiver.

-Chuck Harris