GPS not working with tauglas external antenna

bani_j · October 23, 2017, 2:14pm

I am trying to replace the on board GPS antenna with an active antenna(Taoglas AP.25E).i have followed the instructions mentioned in the application note “Adding U.FL Antenna Connectors to DragonBoard 410c and Validating GPS on Android”. application note link . After soldering the mentioned components, i have taken following steps to start the ON board GPS module.

sudo apt-get install gpsd-clients gnss-gpsd
sudo systemctl start qdsp-start.service

Below are the system logs (when i executed the command " cat /dev/ttyGPS0")
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS] send LOC_REG_EVENT to (0:14)
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS] send LOC_START to (0:14)
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS] packet; from: 0:14
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0000: 04 01 00 26 00 1c 00 01 19 00 24 47 50 56 54 47 …&…$GPVTG
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0010: 2c 2c 54 2c 2c 4d 2c 2c 4e 2c 2c 4b 2c 4e 2a 32 ,T,M,N,K,N2
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0020: 43 0d 0a C…
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS] packet; from: 0:14
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0000: 04 02 00 26 00 21 00 01 1e 00 24 47 50 47 53 41 …&.!..$GPGSA
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0010: 2c 41 2c 31 2c 2c 2c 2c 2c 2c 2c 2c 2c 2c 2c 2c ,A,1,
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0020: 2c 2c 2c 2a 31 45 0d 0a ,1E…
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS] packet; from: 0:14
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0000: 04 03 00 26 00 1d 00 01 1a 00 24 47 50 47 47 41 …&…$GPGGA
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0010: 2c 2c 2c 2c 2c 2c 30 2c 2c 2c 2c 2c 2c 2c 2c 2a ,0,
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0020: 36 36 0d 0a 66…
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS] packet; from: 0:14
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0000: 04 04 00 26 00 1c 00 01 19 00 24 47 50 52 4d 43 …&…$GPRMC
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0010: 2c 2c 56 2c 2c 2c 2c 2c 2c 2c 2c 2c 2c 4e 2a 35 ,V,N5
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0020: 33 0d 0a 3…
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS] packet; from: 0:14
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0000: 04 05 00 26 00 1c 00 01 19 00 24 47 50 56 54 47 …&…$GPVTG
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0010: 2c 2c 54 2c 2c 4d 2c 2c 4e 2c 2c 4b 2c 4e 2a 32 ,T,M,N,K,N2
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0020: 43 0d 0a C…
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS] packet; from: 0:14
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0000: 04 06 00 26 00 21 00 01 1e 00 24 47 50 47 53 41 …&.!..$GPGSA
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0010: 2c 41 2c 31 2c 2c 2c 2c 2c 2c 2c 2c 2c 2c 2c 2c ,A,1,
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0020: 2c 2c 2c 2a 31 45 0d 0a ,1E…
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS] packet; from: 0:14
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0000: 04 07 00 26 00 1d 00 01 1a 00 24 47 50 47 47 41 …&…$GPGGA
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0010: 2c 2c 2c 2c 2c 2c 30 2c 2c 2c 2c 2c 2c 2c 2c 2a ,0,
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0020: 36 36 0d 0a 66…
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS] packet; from: 0:14
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0000: 04 08 00 26 00 1c 00 01 19 00 24 47 50 52 4d 43 …&…$GPRMC
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0010: 2c 2c 56 2c 2c 2c 2c 2c 2c 2c 2c 2c 2c 4e 2a 35 ,V,N5
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0020: 33 0d 0a 3…
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS] packet; from: 0:14
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0000: 04 09 00 26 00 1c 00 01 19 00 24 47 50 56 54 47 …&…$GPVTG
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0010: 2c 2c 54 2c 2c 4d 2c 2c 4e 2c 2c 4b 2c 4e 2a 32 ,T,M,N,K,N2
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0020: 43 0d 0a C…
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS] packet; from: 0:14
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0000: 04 0a 00 26 00 21 00 01 1e 00 24 47 50 47 53 41 …&.!..$GPGSA
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0010: 2c 41 2c 31 2c 2c 2c 2c 2c 2c 2c 2c 2c 2c 2c 2c ,A,1,
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0020: 2c 2c 2c 2a 31 45 0d 0a ,1E…
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS] packet; from: 0:14
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0000: 04 0b 00 26 00 1d 00 01 1a 00 24 47 50 47 47 41 …&…$GPGGA
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0010: 2c 2c 2c 2c 2c 2c 30 2c 2c 2c 2c 2c 2c 2c 2c 2a ,0,
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0020: 36 36 0d 0a 66…
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS] packet; from: 0:14
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0000: 04 0c 00 26 00 1c 00 01 19 00 24 47 50 52 4d 43 …&…$GPRMC
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0010: 2c 2c 56 2c 2c 2c 2c 2c 2c 2c 2c 2c 2c 4e 2a 35 ,V,N5
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0020: 33 0d 0a 3…
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS] packet; from: 0:14
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0000: 04 0d 00 26 00 1c 00 01 19 00 24 47 50 56 54 47 …&…$GPVTG
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0010: 2c 2c 54 2c 2c 4d 2c 2c 4e 2c 2c 4b 2c 4e 2a 32 ,T,M,N,K,N2
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0020: 43 0d 0a C…
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS] packet; from: 0:14
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0000: 04 0e 00 26 00 21 00 01 1e 00 24 47 50 47 53 41 …&.!..$GPGSA
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0010: 2c 41 2c 31 2c 2c 2c 2c 2c 2c 2c 2c 2c 2c 2c 2c ,A,1,
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0020: 2c 2c 2c 2a 31 45 0d 0a ,1E…
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS] packet; from: 0:14
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0000: 04 0f 00 26 00 1d 00 01 1a 00 24 47 50 47 47 41 …&…$GPGGA
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0010: 2c 2c 2c 2c 2c 2c 30 2c 2c 2c 2c 2c 2c 2c 2c 2a ,0,
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0020: 36 36 0d 0a 66…
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS] packet; from: 0:14
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0000: 04 10 00 26 00 1c 00 01 19 00 24 47 50 52 4d 43 …&…$GPRMC
Oct 17 13:29:52 linaro-alip gps_proxy[3523]: [GPS <-] 0010: 2c 2c 56 2c 2c 2c 2c 2c 2c 2c 2c 2c 2c 4e 2a 35 ,V,N5

Do I have missed any step. In the open air environment dragonboard was able to receive the GPS data through onboard antenna.

ljking · October 24, 2017, 2:53pm

Hi @bani_j

The Taoglas AP.25E is an active antenna with a 15dB gain stage, this should increase your sensitivity. However because it is an active antenna, it needs power. First thing to check is that you have all of the components for an active antenna correctly soldered on the board (they are pretty small), specifically L19 and C216 really need to be on the board. I would suggest that you ensure that R126 is removed, but since C216 and R126 share a pad in the physical layout, there is no way you could install C216 without removing R126. C217 will improve the signal by blocking electrical noise from the board…

The second thing to check is that VREG_L7_1P8 is actually turned on with a voltmeter (or scope probe). Since this supply is used by a bunch of other circuits on the board I suspect it is turned on, but if those circuits are not in use, it may have shut down to save power.

Finally it is possible that you are picking up a noise source in the GPS band and this is jamming the received signal. Testing for this requires some sophisticated test equipment. If you have access to this kind of equipment you could also tune C216 to optimize response for your antenna and physical configuration.

When I wrote the App Note I tested it with an (old) Android build. I haven’t tested with the latest Linux builds. Since I haven’t heard of anyone using an external active antenna for GPS, it is possible that the Linux builds don’t turn on VREG_L7 and nobody would have noticed.

Full disclosure: I am an employee of Qualcomm Canada, any opinions I may have expressed in this or any other posting may not reflect the opinions of my employer.

bani_j · October 24, 2017, 9:29am

Hi @ljking
Thanks for your response.

I verified that VREG_L7_1P8 is 1.79 V. I also verified this voltage at the UFL connector pins 1 and 4. So it confirfs that L19 is soldered properly. I cannot see any component with designator L7 in the GPS circuit. As mentioned in the datasheet AP.25E datasheet link This antenna works between 1.8V MIN and 5.5V MAX with a typical voltage 3.3V.

My doubt is if VREG_L7_IP8 is 1.79V, will the antenna function properly.

ljking · October 24, 2017, 3:10pm

Hi @bani_j

Oops, I made a typo in my original posting, L7 should be L19. I have corrected the original post.

1.79V and 1.8V are almost the same thing, in fact you need to look at the accuracy of your measuring instruments, this 0.56% error could easily be measurement accuracy of your measuring instrument. Another possible source of measurement error is the choice of “ground reference point”. Did you measure the voltage from the barrel to the pin of the connector (which is what the antenna sees), or did you measure from some other point on the board like the USB connector body to the pin? In general I would say that 1.79V should be OK, although it is on the bottom edge of the specification.

As to why it is not working at all, I am at a loss.

The next thing I can think of is the choice of inductor and capacitor (L19 and C216), did you use the parts recommended in the app note, or did you use something else from your parts bin?

Other things to check:

Do you have a microscope to visually inspect the soldering of C216? Is there a solder bridge to the R126 pad?
Based on the fact that you measured 1.79V at the connector pin, I would believe that L19 is installed correctly.
now that you have make the changes and can easily connect any antenna, did you try a Taoglas passive antenna? (a passive antenna will work fine with L19 installed)

Full disclosure: I am an employee of Qualcomm Canada, any opinions I may have expressed in this or any other posting may not reflect the opinions of my employer.

bani_j · October 26, 2017, 2:07pm

Hi,

@ljking I have measured the voltage(1.79) at the UFL connector pins. You are right, It may be due the accuracy of the measuring voltmeter. I have a inspected the components visually through magnifying glass.They are properly soldered.
I am able to make the antenna work through the below mentioned arrangement.
I have detached the VREG_L7_1P8 and created a jumper arrangement to create a similar LC circuit but in place VREG_L7_1P8 we have supplied 5 V. Now this Taoglas AP.25E antenna is working properly.

rvl · November 3, 2017, 2:04am

I just received my board and intend to try the GPS with external antennas, so I’ll add the UFL and C216, once I have got more familiar with using the board in general first.
For active antennas I’ll go for an external splitter, with DC block in the DragonBoard branch and DC supply for the active antenna in the other, where I also can put another GPS receiver for comparison.