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October 2022 GPS Antenna Interference tests

I noticed something weird in one location while testing the Flex antenna. GPS fix was lost many times in that location, but not always.

Then, I went to one well known track here in Andalucia and noticed the same thing in two different corners. It happened always in those corners and with one specific antenna...

Then, 2 days later, customer reported an issue with this same antenna.

Picture is coming together now, but there must be something common? Common was that all 3 different locations had cell towers close by.

U-Blox ZED-9 GPS receiver is a wonderful device and has a spectrum analyzer for both L1 and L5 bands. So, I took all of my antennas and went to the location where the interference happens. 

Interference Location

Results from all antennas

Results of the test

Antenna in question was Taoglass AA.178. It picks up wide band interference from cell towers and amplifies it. Look at the gallery and the AA.178 picture, wide band interference is clearly visible and ZED-9 jamming indicator in showing critical. 

But, why is AA.178 so bad?

One important thing to remember is that the GPS signal is very low, below the noise floor. Therefore, GPS is very sensitive to interference. Interference can come from cameras and many things with electronics.

AA.178 is a wonderful antenna, when there is no interference,  it is unusable in the real world.

AA.178 is a dual band antenna that supports L1 and L5 bands.

This page in the AA.178 gives a hint why it is so poor. There are 2 things here:

 
  • There is no filter before the LNA's.
  • LNA Gain is 20 across the complete L1 and L5 bands.

If we compare this to AA.200, from the same company:

As you can see, there is a band pass filter before the LNA as there should be.

How about the AA.200 Gain then?

There is no gain between L5 and L1 bands and outside the bands. Great.

Reason why AA.178 is so poor is that all the junk from around L5 and L1 bands get thru to LNA which then amplifies the junk even further. Result is a lot of junk getting to the GPS receiver. Poor thing...

End result in my opinion is that there is no way to fix this antenna without redoing it completely. What they tried to do is an L1/L5 antenna the cheapest way possible.

Response from Taoglass: AA.178 also does not have any filtering on the front-end and so would give poor performance when situated close to cell towers. 

We are not selling AA.178 due to this issue and are testing a new L1/L5 antenna to replace all AA.178 antennas we have sold. New L1/L5 antenna has been tested and worked well in out tests. See Portimao 2022 test

So, what is the best antenna what comes to interference?

Best antenna against interference is clearly Taoglass AA.200, it is a survey grade L1/L2/L5 antenna. Too bad that it is so big that it can't be used on a bike. 

Next is UBLOX L1/L2/L5 antenna, followed by Pulse's GPS0010 which is a very very good L1 band antenna.