[time-nuts] eBay GPS antenna.

Attila Kinali attila at kinali.ch
Tue Feb 6 15:46:15 EST 2018

On Tue, 6 Feb 2018 07:08:42 -0600
John Green <wpxs472 at gmail.com> wrote:

> Thanks for the responses. It looks similar to but not exactly like the two
> antennas referenced. They say the preamp is 3 to 5.5 volts, whereas the
> eBay antenna says its preamp is good from 3.3 to 18 volts, indicating I can
> run it off 12 volts.

I am pretty sure that this is either a mistake or a deliberate
deceit. Most LNA's I am aware of work between 3.3V and 5V. The
cheap ones are definitely all in that range. Some of those might
work for a short time with higher voltage, depending on the actual
semiconductor process used for production. But that means using
those chips outside their specs and putting a high straign on the
semiconductor, which will lead to an early death. It also cannot
be an LDO inside the antenna, as 3.3V is pretty much the lowest
voltage you can get an LNA for. There are some that work at 3.0V
still, but that would leave only 0.3V for the LDO, which requires
a more expensive LDO. I am pretty sure there are some LNAs that work
at 2.5V or even lower, but those would be definitely in the
way-too-expensive category.

So, my guess is, they tested the antenna whether it works with 12V,
seen that it does, and just "adjusted" the specs. But in reality,
the LNA still maxes out at 5V if you want a reliable device.

			Attila Kinali
<JaberWorky>	The bad part of Zurich is where the degenerates
                throw DARK chocolate at you.

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