GPS Antennas: Can You Use Multiple on a GPS?

Hello.

First, the case:

A customer has installed the factory-installed navigation system in their 2007 T5. The original GPS antenna on the roof needs to be removed. However, the MFD (Multi-Function Display) should still maintain good GPS reception.

The idea is to install 4 GPS antennas inside the bus (one in the center of the dashboard, one on the right side window trim, one on the left side window trim, and one on the rear door trim) so that at least one antenna is always free from being blocked by the roof.

Therefore, the question is: Is it possible to operate multiple GPS antennas simultaneously on a navigation device? Are there even ready-made adapters for this?

GPS operates in the so-called L-band, at slightly below 1.6 GHz. This frequency band is quite robust for this purpose, but precise engineering is required. Having multiple antennas connected to a single input is not feasible due to timing errors caused by cables of unequal lengths; even the smallest inaccuracies would cause them to cancel each other out. I am not familiar with any civilian GPS receivers that have multiple antenna inputs and diversity functionality.

The GPS roof antenna may look unsightly, but it's the best option for its purpose. It's positioned high and exposed, allowing it to receive signals from as many satellites as possible. This results in faster and more accurate calculations. An antenna located behind a window simply can't achieve the same level of performance; the device would have to work at full speed while simultaneously being severely limited. That's a shame!

Hutfahrer wrote:

...due to runtime errors caused by cables of unequal length...

Well, no one is forcing me to use cables of different lengths, are they?

Quote:

The GPS roof antenna may look aesthetically unpleasant, but it is the best option for the purpose.

If you distribute multiple GPS antennas and simply connect their cables together, it will likely result in a degradation of performance rather than an improvement.

What's wrong with discreetly mounting the GPS antenna on the dashboard, just like the climate control's sunlight sensor? I've never had any reception problems with my windshield-mounted navigation system.

Best regards, Rainer.

Even with your carefully measured cables, you won't have worked accurately enough. In the L-band, a millimeter is already too coarse for measuring.

Here are a few more ideas: You could have the roof antenna housing painted to match the car's color. This might look a bit better and would still allow you to use the good antenna. If it absolutely has to be removed, you could potentially hide a GPS antenna under plastic covers, as some cars have space for it in the area below the windshield. Be careful, though, as this area needs to be kept clear of snow and ice in the winter! Rear spoilers, roof edge spoilers, or exterior mirror housings have also proven to be viable options.

Small patch antennas can actually be hidden in many places. They should be mounted flat and have as unobstructed a view as possible to large parts of the sky. Plastic provides very little shielding, the amount of metallic pigments in paints can be disruptive, and glass also dampens the signal significantly. Heating elements can worsen or completely prevent reception, as can metallic windshield coatings. The French had something like this, and it made it impossible to use a suction cup navigation system without an external antenna.

Okay, to start with: It's not about the aesthetics; the antenna has to be removed because otherwise the bus would constantly have to book a height of over 2 meters on the ferry. With 2-3 trips every month, this quickly adds up to a significant cost.

I once tried setting it up in the center of the dashboard, and it worked, but in some cases, you only get 2-3 satellites, while the roof antenna receives 9.

Okay, but if it's not possible with multiple antennas, then I'll probably have to find an optimal location and make do with that.

Thank you very much for the remaining tips, nonetheless.

Okay, I installed two antennas on my G4.
Eine Dachantenne und eine auf dem Armaturenbrett. Ich muss allerdings umstecken. Bei beiden Antennen ist der Empfang erstklassig. Es gibt empfangsmäßig keinen Unterschied. Glas ist nämlich kein Problem. Das Problem liegt wo anders ... Punkt 3, bottom.

However, there are a few pitfalls to be aware of when mounting it on the dashboard.
- Is the glass coated with a metallic layer? -> Not possible.
- The mounting must not be positioned too close to the (metal) frame of the glass, otherwise there will be significant performance losses.
- A metal plate placed beneath the antenna significantly increases the reception strength, achieving the same effect as a metal roof.
Consequently, Philips Navigation always included a metal plate beneath the Trimble antenna.

I once installed a GPS antenna directly below the dashboard in an aftermarket factory navigation system, and it worked perfectly.

Unlike a smartphone or portable navigation device, a built-in navigation system requires significantly less signal strength because it has the advantage of receiving speed and steering rate data from the ABS/ESP system. Therefore, after an initial signal lock, it should be able to operate "blind" for a period of time without getting confused.

We live in the countryside, so we're not blocked by tall buildings or anything like that. But since it's the most discreet solution, I'd at least like to try it out temporarily.

Greetings.
Guste.

If I'm not completely mistaken, the RF signals are completely processed within the antenna itself. Only the data, similar to how a GPS receiver sends data to a laptop via NMEA, is then transmitted to the navigation module.
Therefore, that won't work if the navigation module doesn't explicitly support it.

christians wrote:

If I'm not completely wrong, then they will completely evaluate the HF signals within the antenna.

Unfortunately, you are completely wrong (at least when it comes to Volkswagen).

A coaxial cable is connected to the navigation module.
NMEA data is transmitted via a serial interface. You don't need a coaxial cable for that.

The 2007 T5 should have an RNS510 system, and that system has the Trimble Lassen SK3 module installed.

Yes, you're right. The antenna is active, but that's all it is.