[time-nuts] ThunderBolt question

[Wes]

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
>
>