[time-nuts] GPS Antenna Voltage-Dropping

WarrenS warrensjmail-one at yahoo.com
Thu Sep 3 17:45:06 UTC 2009


Nigel

Ummmmm is right,
One of us is missing something, I wonder which one, I think I know.
He has a good bypass cap across all that, The RF is not going to see the diodes.
ws

-----------------------
Ummmmm
 
Not really a very good idea, we're talking about two silicon diodes in  
series with each other and then used as the central conductor of a coax adapter 
 at nearly 1600MHz.
Aside from the discontinuity caused at the diode junction itself, consider  
how fine the wire might be inside that diode and consider the magnitude of  
the uncompensated impedance changes caused by this, the high VSWR shouldn't 
come  as too much of a surprise.
Then consider what two rectifying diode junctions are going to do to your  
RF signal regardless of the VSWR.
 
Burt's suggestion of  fitting the diodes inside the antenna  stands more 
chance of success, assuming they are fitted correctly,  but I would still 
suggest an external biased T as the most  practical answer if one still insists 
on using the 3.6v antenna.
With 5v antennas so widely available though there really doesn't seem to be 
 much good reason for doing this anyway.
 
regards
 
Nigel
GM8PZR

*****************

In a message dated 03/09/2009 17:04:50 GMT Daylight Time,  
warrensjmail-one at yahoo.com writes:

Seems  like a good idea, a lot simpler and cleaner than the other  
suggestions.
Sounds like a data problem, I'd suspect your VSWR meter or  cabling first. 
Maybe your VSWR meter does not like diodes especially if it  is not running 
current thru them.
And if you are running current thru them  to approximate the GPS antenna, 
whatever you're doing to run the current  thru them is making the reading 
unhappy.
Did you try just the BNC adapter  with just a short inside?  And with just 
the cap inside?  Better  cap?
And the finial test does it work OK despite the VSWR  reading?




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