[time-nuts] Z3801A & ThunderBolt USING SAME ANTENNA?

Bruce Griffiths bruce.griffiths at xtra.co.nz
Tue Jul 8 22:58:00 EDT 2008


jshank wrote:
> Bruce,
>
> Do I need to spend the extra $ for LMR400 cable or could I just use 
> rg58 for a total run of 60 feet.
> Jeff
Jeff

A conservative approach would be to use a cable that has an attenuation 
of no more than 10dB (the attenuation of the cable supplied in the 
Trimble Thunderbolt starter kit).
For standard RG58 this can mean no more than about 30ft.
This only applies if the antenna preamp gain is similar to that of the 
Trimble bullet antenna.

_Minimum Antenna gain for Thunderbolt_

http://trl.trimble.com/docushare/dsweb/Get/Document-30908/Product 
Bullentin 200213.pdf 
<http://trl.trimble.com/docushare/dsweb/Get/Document-30908/Product%20Bullentin%20200213.pdf> 


Above link specifies a minimum of 20dB gain at Thunderbolt input.

Thus with 23 dBattenuation (cable plus active splitter) you would need 
to use an antenna with at least 43dB gain preferably a little more.
With 10dB of cable attenuation and 3dB maximum splitter loss the antenna 
preamp gain should be at least 33dB.

The 5V Bullet III antenna has 35dB gain and thus allows a maximum 
attenuation (cable plus splitter) of about 15dB, preferably a little 
less, when used with a Thunderbolt.

GPS Timing antennas with higher gains (50dB) are available.

Bruce



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