Mio c520t connected to car radio antenna

jonasolof

The TMC receiver in the mount was designed by GNS-GMBH in Germany. They also sell Y adapters with Fakra and ISO connectors. The cable to the TMC receiver ends with a three pole 2.5 mm plug whereas the wire antenna for the c520t uses a four pole plug with the wire connected to the base of the plug.

Nevertheless, TMC works perfctly well if one plugs in the three pole connector from the Y adaptor. GNS evidently designed the circuit so that both wire and coaxial antennas could be used. Mio-tech support wrote that GNS-GMBH has a solution for a cabled connection but that Mio "does not support it" which is rather ambiguous.

In the three pole connctor, the coaxial center wire connects to the tip whereas the shield connects to the base of the plug. Inside the bulge on the Y-adapter there is an impedance matching balun and a capacitor, which would prevent 12 volts from an inline antenna amplifier to reach the TMC receiver. There is no DC insulation of the shield though, albeit there is room for the addition of a 100 pF capacitor inside the bulge.

There is a measurable voltage of 63-64 millivolts (varying) betwen the antenna shield and ground inside the mount with the TMC receiver when the 12 volt power adapter for the GPS is conected to a car battery which also connects to the antenna shield. This could be caused by the power adapter itself. The reason that the antenna shield was connected is that I also tested an inline antenna signal amplifier in the antenna cable. It is fed 12 volts plus from the battery over a separate cable, taking minus over the shield.

The result is excellent, TMC is received before I have a GPS fix as I power on.

This was done outside the car. I first didn't use a car battery as a 12 volt source for the Mio but a cheap switching adapter for 240 to 12 volts. No TMC could be recived at all, probably because of interference from the switching adapter.

When fed from a battery instead, TMC reception was good without an inline amplfier and slightly better with it. Thus, one must be aware of adaptors for other devices which could interfere with TMC reception. Interference is probably feed over the power cable.

link: www.gns-gmbh.com

I paid over internet bank after contacting them by email. Ask them to use mail instead of UPS.

Edit: The Y-adapter I got has part number 403 77 35 102 705 which is not among the eight on their shop web site. Could it be a special model for the c520t? I have written to ask them.

According to the answer, the item to order ís the T5 ending with 102 514 if you want ISO and with 102 507 if you want FAKRA. I got both. The 2.5 mm plug is connected the same way in both. If you want to use DIN- connectors, you can get either one and just replace the connectors.

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