GPS Antenna

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I am trying to hook up a GPS Patch antenna with LNA up to a GPS module
without a lot of luck.  Its actually rather strange, If I hook the patch up
with a 5m long cable that it came with ( I pulled apart a normal GPS
antenna) it works fine but when I detach the cable and use a shorter one
(5-10cm) it won't work.

Does anyone have any suggestions



Re: GPS Antenna

reduce the voltage to the lna?
add a small risistor in series with the coax?
maybe the lna is unstable?

Re: GPS Antenna

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Does it work with a 5m lead made of your cable? Otherwise is the group delay
change affecting the module operation?

Alternatively, is your short cable just plain faulty?



Re: GPS Antenna

Thanks for suggestions guys,

I have tried a 1R resistor in series with the signal wire, do you think it
would be a good idea to add one to the GND rail as well to isolate it a bit?
I have tried a few different cables and im sure I don't have a faulty one..
I have even tried cutting a piece of the original cable to try but no go.  I
am working on 2 of the same units, I managed to get one to work with a 1R
resistor in series but its operation is not as good as norml... I have put
it to rest for today, a fresh start tomorrow.



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Re: GPS Antenna

If it is very close (< a metre??) , the module could be re-radiating
the signal and it is being picked up by the patch antenna, causing
overload and signal distortion. You may be able to confirm this by
experiment. eg. shielding the module, moving the antenna around.

A normal one ohm resistor could have enough inductance (a few nano
Henries) to significantly attenuate the 1.5GHz signal.


AJ wrote:
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Re: GPS Antenna

Hi Glenn

Actually it is very close, about 3 cm.  I have been testing with
re-radiating antenna and moving it away a bit form the antenna doesn't seem
to make a lot of difference.  I will try some shielding today to see if that
makes any difference.  I have also ordered a few inductors to see if that
will help at all!

Thanks for your suggestion



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