[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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