[time-nuts] Galvanic decoupling of GPS antenna

[Didier Juges]

Yuri,

It is not clear to me why the antenna should be isolated from the receiver, I would prefer to keep the antenna and receiver on the same return, and isolate that assembly from the rest of the world.

It is much easier to provide isolation on the supply, RS-232 and 10MHz (if you use it) than on the antenna, in my opinion, at least as much as it is less likely to have a negative performance impact, and you can do it with off-the-shelf parts.

There are dc blocks available that will work at the GPS frequency to isolate the antenna from the receiver, but they are expensive and do not resolve the issue of power to the antenna.

Didier

------------------------ Sent from my BlackBerry Wireless thingy while I do other things... 

-----Original Message-----
From: Yuri Ostry <yuri at ostry.ru>
Date: Thu, 17 Jun 2010 01:09:34 
To: <time-nuts at febo.com>
Subject: [time-nuts] Galvanic decoupling of GPS antenna

Hello,

I'm trying to put gps (for a coarse timing sync and RTC
auto-setting) to a small controller that must be completely
galvanically decoupled from outside world. Antenna power must be
supplied from separate power source (ground potential of isolated part
of circuit can slowly float up to +/- 250 volts referenced to ground
of antenna power supply).

First thinked about using some choke to inject power, then DC-blocking
capacitor around 20-30 pf and then smt 1:1 wideband transformer, but
looks like Mini-Circuits don't make standard models for frequencies
over 1200 MHz, their search engine give me some part numbers that looks
like special order ones, and cannot be found in their catalog.

Is there any chances to get decent performance if I'll simply split
stripline (both ground and signal traces) by dc-blocking caps? Idea
looks not very good to me, of course, I suspect that i'll get all
sorts of interference right to GPS LNA input...

Maybe there is some well proven solution with easily obtainable parts?

-- 
Sincerely,
 Yuri                          mailto:yuri at ostry.ru



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