[time-nuts] GPS Antenna Voltage-Dropping

GandalfG8 at aol.com GandalfG8 at aol.com
Thu Sep 3 07:44:26 UTC 2009

In a message dated 03/09/2009 02:05:20 GMT Daylight Time,  
Brucekareen at aol.com writes:

I bought  a 3.6-V Trimble Bullet GPS antenna on ePay and wish to use it 
my  T-bolt.  Rather than try to internally modify the T-bolt to provide  a  
3.6-V antenna feed, I decided to try to build an in-line dropping  adapter. 
I seriesed two Si diodes inside a 100 pf tubular  ceramic capacitor and 
installed  the shrink-wrapped assembly inside a  salvaged BNC-M to BNC-F 
assembly.  Unfortunately the  completed assembly exhibits about a 4-to-1  
VSWR when terminated in a  50 ohm load.  Has anyone else tackled this   

The 3.6-V Trimble antenna has less gain than the 5-V  version which  makes 
my planned antenna rcable run on the edge even  without the high  VSWR..

If you dont want to modify the T'bolt it would probably be easiest to  
derive 3.6v from the 5v supply external to the T'bolt and feed that into the  
antenna line with a blocking T.
In the long run though it might be cheaper just to cut your losses and sell 
 on the 3.6v version, buy a higher gain low cost 5v patch for now if you 
don't  already have one, and keep an eye out for a 5v bullet if that's what 
you really  want.

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