I am revisiting the B5C GPS blockage problem from nearby FM broadcast signals and curious if anyone has isolated the B5C in a shielded enclosure or moved indoors and feed a GPS signal from a quality outside GPS antenna, kinda like a re-radiation scenario? Seems odd that there are 5 other GPS systems at the same site with no problems at all.
I did a simple bench test with a +18dBm signal generator and 30" whip adjacent to the B5c case, no modulation, simulating a carrier only local “FM Station”. I started at 88.1 and incremented 200 kHz up to 107.9 allowing the GPS signal to stabilize at each step . What I found was the GPS reception was mostly good except when the simulated FM station came up on a few frequencies, it totally wiped out all satellites. I am making up an Excel graph to show results.
Finally finished graphing the GPS reception vs Simulated FM signals and here is how it looks.
The blue line is total GPS satellites and the rust line is GPS dB reading. Just my dumb luck to have a co-located 92.9 translator and a 88.1 AUX not to mention a 95.1 translator. Next will try adding self adhesive 3" wide copper shielding inside the plastic cover so it will bond to the back chassis posts and also add snap on ferrite cores on all leads. Stay tuned for updates…
At least you know where your interference is coming from, I spent months hunting with Mimosa for what could be causing my interference and still no dice…
Thank you very much for this info, I am sure it will help other people in the future.
Here is what the B5c looks like before shielding measures have been applied.
The Ethernet cable, LED board and rubber grommets have been removed for clarity.
Here is after the copper self adhesive 3" foil has been applied with a 2" gap on top edge for the GPS signal to get through. Snap on ferrite cores have been attached to both ends of all cables except the LED ribbon cable has only one. When the case is closed, the copper shield bonds to the back case in 8 places when o-ring screws are secured. Next will be another round of simulated FM signal testing.