I used a bias tee with a capacitor block. I varied the resistor until I
could see signals coming from the external antenna, the built in patch was
shielded with aluminum foil and the receiver verified that no signals were
coming from the internal antenna. Some receivers needed only a 10K
resistor, some models needed 220 Ohms.
John WA4WDL
--------------------------------------------------
From: "Brian Kirby" <kilodelta4foxm...@gmail.com>
Sent: Thursday, October 01, 2009 7:57 PM
To: "Discussion of precise time and frequency measurement"
<time-nuts@febo.com>
Subject: Re: [time-nuts] GPS from a window seat
In order to fake out some Garmin units, when using them via splitters on a
external antenna, we put 220 ohm resistors from the center of the coax to
the sheild. The splitters we used were capacitive coupled and this work
fine for the Garmins.
The Garmin units needed to see some sort of DC load, is you wanted to use
the external antenna ports. If you did not pull any current, the unit
stayed on its internal antenna.
Brian KD4FM
Magnus Danielson wrote:
Jim,
Jim Palfreyman wrote:
I've done this with two separate GPS units. One was a basic unit with
no maps - more designed for bushwalking, boating and other direct
navigation. It worked really well.
Mmm. Bushwalking is one of your local specialities I gather...
Just recently (a few days ago) flying to Perth I used my car-designed
Navman. It locked easily and I chuckled as it rapidly swept across
roads and intersection on the ground at 777 km/hr telling me "Go to
nearest road".
That must have been one jumpy ride... 777 km/hr offroad.
Once again I have been forced to invent a DC fake load to handle the case
where the current sensing of the GPS receiver is set higher than the
hooked in GPS antenna consumes. The shot-from-the-hip solution involves a
T-connector, a 10 uH SMD coil and a 470 Ohm SMD resistor. Not ideal in
any sense, but hopefull pulls enought (additional 10 mA) while not
mocking too much with the signal. A similar approach has worked before.
Cheers,
Magnus
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