[time-nuts] GPS Antenna Voltage-Dropping

Brucekareen at aol.com Brucekareen at aol.com
Fri Sep 4 18:50:56 UTC 2009

Thanks to all for your comments and suggestions.  In a private message 
James Miller  advised that while constructing a splitter, he discovered tubular 
ceramic  capacitors have significant self-inductance at 1.5 GHz.  Then Warren
’s suggestion that the VSWR  meter (PRD 2919) might not  like  unbiased 
diodes caused me to re-measure the adapter with a bias-T and forward  bias.  
The VSWR dropped to about  1.9.  It appears the self-inductance  of the 
capacitor is causing part of the RF current to flow through the  diodes.   With 
forward biased diodes,  the capacitor may be unnecessary.  The remaining VSWR 
is likely caused by  the coaxial line impedance of the internal parts being 
other than 50  ohms. 
I will try the antenna with the adapter.  If it fails to work, and the 
antenna can  be readily opened, Bert’s suggestion of putting the diodes in there 
(past the  bias-T) sounds good, as does the eBay lead for an inexpensive 
external  bias-T. 
Bruce Hunter 

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