Help required on the Circuit of a GPS Patch Antenna

Thread Starter

shahrukh1987

Joined Feb 12, 2021
7
Dear Friends.
I am Shahrukh Saleem from Pakistan. I am a SCADA Engineer working on EMS. Recently I have come across a faulty GPS Antenna. I pulled out the pcb from the antenna housing and looking upon the components. Please have a look on the attached snapshot of PCB. I have recognized the Resistors, Inductor, Capacitors and Transistors, but I could not recognize the component labelled SGT 1575c. I know that GPS mean frequency is 1575.42 Mhz so this component deals with the frequency. Is it a band pass filter? Please help me on understanding the circuit. Also please some one explain the working of this circuit. Thank you.

RegardsIMG_20210212_181128.jpg
 

drc_567

Joined Dec 29, 2008
1,110
What does the circuit board cover plate look like?
Is there a cut-out that allows the 1575 chip to receive the GPS signal?
 

Thread Starter

shahrukh1987

Joined Feb 12, 2021
7
The pcb was mounted on a metal plate and was housed in a completely sealed plastic dome shaped casing. Please have a look on the snapshots. Yes the cover plate has cuts. I don't know the purpose of those cuts. Sorry don't have the plate with me at the moment so cannot share the picture of that. But it's a conventional gps patch antenna.2. hopf GPS Antenna 4490 -1.jpeg3. hopf GPS Antenna 4490 -2.jpeg4. hopf GPS Antenna 4490 -3.jpegIMG_20210212_200057.jpg
 

drc_567

Joined Dec 29, 2008
1,110
... I have posted a related link here:
GPS patch problems
As an experiment, you might first try operating the GPS antenna without the protective dome, in order to see if that could make any difference.
The link above suggests modifying the antenna top plate by making small slots, which are supposed to modify the operating impedance in some way. However, it may be prudent to contact the antenna manufacturer, before trying a destructive modification of this nature.
 

Delta Prime

Joined Nov 15, 2019
1,004
Hello there :)
rs and Transistors, but I could not recognize the component labelled SGT 1575c. I know that GPS mean frequency is 1575.42 Mhz so this component deals with the frequency. Is it a band pass filter?
In general you have a antenna terminating to a low noise amplifier that connects to a surface acoustic wave filter at 1575.42
that enters into a phase lock loop then mixes with a fractional" N"synthesizer, . Which provides the LO local oscillator and guess what frequency that is? that's right. 1575c The C stands for custom. Which is a down converter at 1552.82Mhz. which gives the first IF 22.6Mhz balanced IF. ultimately terminating into the Hard-limiting (1-bit ADC);)
 

Thread Starter

shahrukh1987

Joined Feb 12, 2021
7
:)Dear drc_567 sir. Thank you very much for the prompt support. The article shared is very informative. For the time being I am more concerned about the components and working concept of this antenna. I will update you once I try the modifications as suggested by you.
Regards
 

Thread Starter

shahrukh1987

Joined Feb 12, 2021
7
Hello there :)

In general you have a antenna terminating to a low noise amplifier that connects to a surface acoustic wave filter at 1575.42
that enters into a phase lock loop then mixes with a fractional" N"synthesizer, . Which provides the LO local oscillator and guess what frequency that is? that's right. 1575c The C stands for custom. Which is a down converter at 1552.82Mhz. which gives the first IF 22.6Mhz balanced IF. ultimately terminating into the Hard-limiting (1-bit ADC);)
:oops: Delta Prime sir!! may I have some more simple explanation?? You mean this 1575c component is a SAW filter or Local Oscillator or Down Converter?? how you calculated the IF 22.6 MHZ balanced IF???
 

Thread Starter

shahrukh1987

Joined Feb 12, 2021
7
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