DIY GPS Module & QFH Antenna :)

Thread Starter

Art

Joined Sep 10, 2007
805
Hi Guys :)

I have just completed my first hand wired GPS module
and DIY QFH backfire antenna for 1575 MHz,
and thought I’d share my project and sources.

The Ublox GPS module (LEA-5T) has options specifically for timing
which I intend to use to set the time for another clock project.

The PCB has a solid thin copper sheet ground plane a little larger than the GPS module,
and a thin insulator between the module and the ground plane.
The module is wired for minimal UART configuration with no battery backup
and no EEPROM memory for almanac or configuration retention.
I will be happy with all default settings, but have wired an EEPROM breakout board
just to test the feasibility of adding the surface mount chip by hand (it’s feasible).

The antenna is based on the example in the link. The feed line in the stem is rigid coax,
and the stem is 3.1mm brass tube from a local hobby store.
The thicker copper lobes are 2.8mm copper tube, and the thinner lobes (inner lobes)
are formed with solid 1mm enamelled copper wire.

The yellow LED is connected via 390R resistor to the module’s frequency output
which defaults to a 100ms pulse at 1Hz when sufficient accuracy is attained.
By default, there is no synthesised frequency available at boot time prior to a GPS fix.

The unit was tested indoors last night for a period of several hours,
which is also the first time I have been able to monitor the serial UART.
It maintained at least a 2D position fix the whole time monitoring the
$GPRMC NMEA sentence.
My iPhone at the other end of the desk reported anything from good to poor accuracy.

Cheers, Art (VK4FAST).


Online QFH antenna calculator here:
http://www.jcoppens.com/ant/qfh/calc.en.php

Based on Quadrifilar Backfire Helix antenna design by Matjaz Vidmar (S53MV):
http://lea.hamradio.si/~s53mv/navsats/analog.html

Short YouTube Video (GPS lock acquired) :












 
Last edited:

Thread Starter

Art

Joined Sep 10, 2007
805
Man I had a go at copper electroplating the bracket (made of standoffs)
and it turned out like this! Not to say I won’t be using it!! :D

 

Thread Starter

Art

Joined Sep 10, 2007
805
Thankyou :)

I’ve since learned that metho is good for cleaning leaded solder resin :D
and also since these pics have added an SMA connector for frequency output for the rest of the clock.
I will seal the rest of the seams when I’m sure it’s finished.



 
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