[time-nuts] LightSquared vs old GPS gear: Antennas?

George Dubovsky n4ua.va at gmail.com
Sat Jun 11 11:29:30 UTC 2011

I have recently done some side-by-side testing of a new PCTel antenna vs an
older Trimble bullet antenna to see if there was any degradation of GPS
operation. The PCTel had 26 dB gain and a sharp bandpass filter incorporated
that was 60 dB down at the the lower edge of the GPS band (upper edge of
lightsquared), but the Trimble bandpass rolled off more gradually. Both
operated fine in GPS service, but the PCTel would be more likely to survive
LS QRM in timing apps. Unfortunately, the price is the same as just about
any new GPS basestation antenna, which places it at the upper end of the
budget for all but the dedicated hobbiest.


geo - n4ua

On Fri, Jun 10, 2011 at 9:15 PM, Hal Murray <hmurray at megapathdsl.net> wrote:

> Is it possible/interesting to design an antenna that has a low-angle cutoff
> at 20 or 30 degrees?  That probably won't eliminate many satellites that
> are
> useful for timing receivers.
> I'm interested in things like a Z3801A or a ThunderBolt.  I'm assuming it
> is
> not reasonable to replace the GPS unit.  Replacing the antenna might be
> reasonable, assuming it's cost is low enough.
> That only helps in a donut shape area around the LightSquared antennas.
> Farther away it's not necessary.  Too close and either the antenna would be
> too high or the power would burn through the antenna anyway.
> I live in flat ground.  I'm not sure where the nearest cell phone tower is.
> I don't know of any on the nearby hills to the west.  To the east, they are
> either low or far away.  (Maybe I just haven't noticed them yet.)
> Another option would be a setup to null out an signal at a specific compass
> angle.
> I realize this won't help the zillions of currently installed GPS
> navigation
> units.  They are mostly consumer gear with relatively short expected
> lifetimes so the FCC might do something like say "5 years from now..."
> which
> would be nasty for people like us using ancient gear.
> --
> These are my opinions, not necessarily my employer's.  I hate spam.
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