GPS repeater

[BradC]

I suppose it's time I posted some progress on the GPS repeater project.

The unit comes from E-bay with an external antenna and internal transmitter :
https://www.fnarfbargle.com/private/221109-221109-221109-D3-GPS/s-l1600.jpg

I put the external antenna to one side. Don't need it.

The concept is to split the NAV GPS and feed it to the transmitter. I did this with a Fakra splitter, and Fakra to SMA adapter cable :
https://www.fnarfbargle.com/private/221109-221109-221109-D3-GPS/s-l1600-3.jpg
https://www.fnarfbargle.com/private/221109-221109-221109-D3-GPS/s-l1600-1.jpg

The NAV unit supplies power to the GPS antenna, so does the repeater. So having them both poking volts down the line is likely to end in tears, thus the need for a DC block between the repeater and the remainder :
https://www.fnarfbargle.com/private/221109-221109-221109-D3-GPS/s-l1600-2.jpg
All up it looks something like this :
https://www.fnarfbargle.com/private/221109-221109-221109-D3-GPS/SAM_0245.JPG
https://www.fnarfbargle.com/private/221109-221109-221109-D3-GPS/SAM_0243.JPG

Having the DC block seemed like a good idea, but in theory if the repeater is pushing power down the line it can be modified not to :
https://www.fnarfbargle.com/private/221109-221109-221109-D3-GPS/SAM_0214.JPG

Prying the back off saw a module with a GPS patch antenna on the front and soldered metal shield on the back. The shield is held in place with 2 joints, and a hot iron and tweezers saw those loose.

R8 is a 150 Ohm resistor that supplies 5V to the Antenna, and R7 is a 2K resistor that supplies power to the LED. The theory being if the antenna is shorted the led is out. I removed R8 and bodged R7 across to the 5V input to make the LED come on. I could have just removed both.

I soldered the shield back in place and used superglue to stick the back on, holding the module in place. Now I can (and have) remove the DC block.

None of the cables are long enough to allow me to conceal the unit, so initially I ordered a 1M SMA extension. Then I found a place that made me a custom cable. It's a Fakra splitter, with the Fakra->Fakra being 20cm, and a Fakra->SMA at 1.4M.

Fakra ”C“ Male to SMB Female 5005 SMA Male Y Splitter Combined Cable 20cm 140cm | eBay (https://www.ebay.com.au/itm/265967986370)

That will allow me to thread the cable up under the console and put the repeater in top of the center console.

Results wise, it has solved all reception issues I've had with both dashcam and phones in the vehicle. I'm waiting on an additional GPS receiver to arrive to allow me to do quantitative signal surveys, but that's just "for info". The results so far are outstanding.

[BradC]

I have a pretty good view of the sky looking South from my driveway. Here are some raw captures using a GPS receiver on my mobile phone mount.

The numbers to pay attention to are the SNR on the left hand side. (Signal to Noise Ratio). Higher is better.

If you look at the sky map on the top right, the size of the dot indicates the relative signal strength of the satellite. There is a marked change with the repeater turned on. That difference is magnified significantly in areas with "less reliable" reception.

General overviews with repeater off and on respectively :
https://www.fnarfbargle.com/private/221111-221111-D3-GPS/Overview_Raw.png
https://www.fnarfbargle.com/private/221111-221111-D3-GPS/Overview_Repeater.png

Sky map indicating signal to noise ratio with repeater off and on respectively.
https://www.fnarfbargle.com/private/221111-221111-D3-GPS/Sky_Raw.png
https://www.fnarfbargle.com/private/221111-221111-D3-GPS/Sky_Repeater.png

[loanrangie]

Must have been a dark night, no attachment ?

[veebs]

Must have been a dark night, no attachment ?

They are showing for me?

[loanrangie]

They are showing for me?

Yes now i'm at home they are there but not on my work laptop earlier.

[veebs]

Yes now i'm at home they are there but not on my work laptop earlier.

Curses, that office firewall! :)

[BradC]

Curses, that office firewall! :)

It has been pointed out that the issue probably occurs because I use http:// urls rather than https:// when I link the images. I've edited the urls in this post to see if that solves the problem.
I find it bloody annoying personally. There is absolutely nothing wrong with using non-encrypted urls in that context, but peoples over zealous filters/blockers get all upset about it.

I've edited my script that generates the urls when I do an upload to use https so it shouldn't be an issue in future.

[BradC]

Ok, after months sitting on the dash I finally got around to setting this up properly with the new cable and all wired in.
The new custom GPS "Y" cable :
https://www.fnarfbargle.com/private/230226-230226-D3_Elec/SAM_0065.JPG
Running the cable up inside the center console under the passenger cup holder. Fiddly! :
https://www.fnarfbargle.com/private/230226-230226-D3_Elec/SAM_0066.JPG

Wiring connectors. The fig-8 taps off the 5V converter I mounted in the roof for the dash-cam. I used a 6 core cable to get the 12V up, so I had spare cores to get 5V back. The SMA connector is just straight to the end of the custom cable I had made :
https://www.fnarfbargle.com/private/230226-230226-D3_Elec/SAM_0067.JPG

The GPS repeater double-sided taped to a step in the console :
https://www.fnarfbargle.com/private/230226-230226-D3_Elec/SAM_0068.JPG

It has been sitting on the console shelf directly above its current location, so provided that plastic console doesn't have metalized paint it'll be ok. Time will tell.