[time-nuts] ThunderBolt question

[Dana Whitlow]

RIght! (about Ligado).

Well, it sounds like you might be OK with your 4 way splitter and roughly 10
dB of added attenuation.  Somewhat of a point can be made in favor of using
attenuation to the extent you can, just so that strong local disturbances
(like
those famous Arizona lightning strikes) are less likely to do damage.  This
depends on whether or not you want the most accurate PVT information or
if you can get by with less.

Enjoy!

Dana


On Sat, Jun 6, 2020 at 1:34 PM Wes <wes at triconet.org> wrote:

> Dana,
>
> I have about 45 feet of RG6 into a two-way splitter, currently feeding two
> receivers, a BG7TBL GPSDO (U-blox) and a TAPR/Synergy GPS Timing Kit
> (M12+).  So
> each device has about 7 dB loss in front of it.  As a crude test if I add
> a
> stepped attenuator in the line to the TAPR receiver and look at the dBc
> report
> in LH, a 10 dB step is hardly noticed, but a 20 dB step makes a noticeable
> change.  I still see tracking at 30 dB but at 40, gone.
>
> So there is a lot of margin but I don't see any issues and the plan is to
> go to
> a four-way split and add a couple of devices.  I'm in a rural area outside
> of
> Tucson so hopefully Ligado won't be an issue. We'll have to see if their
> technical expertise is as good as the PR and lobby lawyers are.
>
> Wes
>
> On 6/6/2020 8:49 AM, Dana Whitlow wrote:
> > Wes, it sounds like you're in pretty good shape with one thing that
> > concerns me.
> > Unless your transmission line is long enough to have substantial loss,
> that
> > 40 dB
> > gain figure seems awfully high and you may find yourself overloading the
> > front
> > end of your receiver.
> >
> > Most modern receivers are sensitive enough to do just fine with no
> antenna
> > LNA
> > at all, in the absence of line loss.   I remember reading a note from
> > Garmin on this
> > topic years ago when they were recommending no more than about 15 dB net
> > gain
> > between the antenna and the receiver.
> >
> > With your receiver and 40 dB antenna, even if it seems to work well now,
> > beware of
> > Ligado!  If/when they go on the air near you, you may find yourself
> needing
> > an
> > attenuator.
> >
> > Dana
> >
> >
>
>
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