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The Android head unit is equipped with an FM antenna filter, a rear SAM transmitter, and an output for activating the antenna.


Adv3nture

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Hello, the first question is somewhat technical. The year 2012 (R350CDI LWB W251). I am new to Mercedes, having been a Saabs for years. However, MBWorld, the platform I joined, seems to be hesitant in offering a mentor.

I replaced the Comand 2.5 with a cost-effective Aliexpress Android head unit, which I found to be of high quality. All components are functioning well, with the exception of FM reception. I have identified an output (actuator) on the back SAM that seems to deactivate the antenna using a mechanism sometimes referred to as a 'antenna filter'. I believe it serves as both a power switch and a filter.

Are the outputs of SAM characterised as open drain or open collector? Alternatively, are they combined? One potential interim solution may include the application of either 0V or 12V to the 'filter' pin3. Alternatively, it may be more accurate to use a CANBUS tool to force a SAM output. The GPS system is functioning well, but, I am uncertain about the power source for the component located on the top.

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Typically, the FM antenna amplifier is supplied with power from the HU rather than the SAM.

The Chinese HU's output consistently appears as blue. However, if your Ali express unit is specifically built to be plug and play for your model, the ISO connection will handle this issue.

It is fairly uncommon for these devices to come defective. The first step would include verifying that the blue output attains a voltage of 12 volts (+ve) when selecting the tuner.
At the ISO, I anticipate a voltage of 12 volts in blue, whereas the extra blue voltage would be associated with one of the other plugs. There is no issue with using it to power the amplifier if necessary.
Alternatively, verify that the amplifier has a voltage of 12 volts when required. However, if the FM was satisfactory before, it should be sufficient at this point.

PS. The GPS would lack power, hence I concur with your assumption that power is absent, however it would be located at the amplifier.

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Hello, I appreciate your prompt response! I verified the presence of the antenna power on the connection of the auxiliary head unit in the automobile, but it is nonexistent. In my vehicle, I own a mere two twisted pairs for the twin microphones. These pinouts are not the typical Comand 2.5 pinouts seen online, but they are specifically designed for the R class in WIS.

I am using the head unit to provide power to a pair of FAKRA adaptors, since I believed that the FM amplifier obtained its power from the coaxial cable. That is not true. Indeed, the power outputs of the head unit ant and amp auxiliary are indeed 12V, as anticipated, when activated on the head unit side. It is quite likely that there is no traditional head unit power switch on the automobile side, and instead, the power is sent by CAN to the back SAM. The N10/8 connection activates the amplifier.

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Does the FM amplifier have a canbus connection?

Although it is conceivable that it is under the direction of SAM, I fail to see a rational justification for that particular design.
Derived from the HU, this approach is straightforward.
It seemed odd for the HU to instruct the SAM to regulate the amplifier, even for MB.

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Instances have occurred when the central core of a coax has fractured, resulting in a solitary and fragile strand.
It is fair to exclude it by verifying the presence of 12 volts at the amplifier.

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I did not want to dismantle the boot in order to reach the SAM today. I intended to do a task of lesser complexity. The mag mount DAB antenna should be positioned on an oven tray located on the rear seat, with a total of 85 stations reported. Additionally, a DIY centre loaded dipole should be placed in the A pillar trim. The dipole consists of a 345mm stripping of the coaxial cable, with the centre exposed and the copper material folded back. The lead undergoes two turns of 50mm precisely at the junction. The automobile is capable of detecting 95 stations. Indeed, the mag installation on the expansive steel roof performs much more well from an exterior perspective.

The process of removing the A Pillar trim. Wow. The upper clip exhibits visibility and robustness, while the remaining two clips are concealed below the air bag and its firing canister, demonstrating exceptional strength. Crowbars are unnecessary for removing this. The provided loop aids in facilitating the execution of the task, but in a rather arbitrary manner.


I have adjusted the metal clamps to reduce their firmness and reattached the fabric edge that was inadvertently adhered to the winscreen. The cars are constructed with robust construction, and the trim is designed to endure the impact of a train.

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To connect the antenna amps, you want a 'power insert' adapter that supplies power to the coax. This adapter is necessary since you have an NTG2.5 antenna, which is equipped with a double white fakra for both FM and AM frequencies. It is advisable to use the adapter with the locking tab, or one that can be used for both types of antennas. For example: The Fakra to Male DIN aerial antenna adapter cable, equipped with a 12v phantom power, serves as an adapter for either the InCarTec or VW aerial. The use of phantom power in Fakra to din - InCarTec

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I own one of those devices, with a measured voltage of 12V on both central pins. Please refer to the image provided below.

image.png.43d47a4c0cc5ebc8a0a5e84190594808.png

??? Why is there a link between the SAM (represented by the transistor) and the 'FM filter' (also represented by the transistor), unless it is a switch?

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The ML, specifically the R class, has the capability to alternate between the rear window antenna and roof antenna pack. However, it is important to note that this assumption may be incorrect, as shown by the pre-facelift vehicle, which had a separate power line for activating antenna amplifiers. In my recollection, the roof antenna pack is responsible for the actual switching process, however I am unable to remember the reason for its switching.

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