[aprssig] GPS Intgrated Engine

Stephen H. Smith wa8lmf2 at aol.com
Tue Mar 28 10:15:05 CST 2006

AA3JY at Winlink.org wrote:
>> What I don't like about integrated GPS receivers is that you still have to
>> connect an external antenna...
> Look at Garmin's Rino 520 and 530....
> Regards,
> Clay AA3JY
> (via WL2K
But that's a *hand held* where the radio is going to probably be 
outdoors.  It would be useless to do that with a mobile rig like a D700 
where the radio chassis is inside the trunk or under a seat.  

The external GPS antennas used with built-in GPS receivers normally 
contain 15-20 dB gain preamps to offset the horrendous loss of 
small-gauge coax at 1575 MHz where GPS operates.  In turn, there is 
virtually no selectivity in front of these high-gain amplifiers -- the 
antenna element is a very broadband patch that is not sharply 
resonant.   These amplifiers often overload and block every time you get 
within a few blocks of a 1900 MHz PCS cell site, causing the GPS 
reception to drop out every time you get near one.  

The combined receiver/antenna puck-type GPS devices don't use active 
pre-amplified antennas because the ant is connected directly to the 
receiver  with no coax at all.  

In real life testing in RF-saturated areas like Los Angeles or Chicago, 
I have seen the inexpensive GPS18 or Deluo GPSes sitting on the 
dashboard inside a car far outperform expensive two-piece "professional" 
units with roof-mounted active antennas.  

Further, a root-mounted GPS active GPS antenna will often overload, 
block, and knock the GPS out of lock every time your own 25-50W two 
meter or UHF rig keys up, if the antennas aren't separated far enough.   
This usually isn't a problem on a ship or aircraft where the antennas 
can be farther apart, but is often a problem on cars.  

The "hockey puck" all-in-one GPS sitting on the dash UNDER the roof of 
the car will experience far less RF from your other transmitters.  

Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
Home Page:          http://wa8lmf.com

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