Garmin Antenna

[RetArmy]

I have a Garmin 2610 GPS. Is it necessary to use an external antenna when traveling on my ST or is the signal strong enough using the internal antenna? I use a RAM mount between the handle bars.

[Marshal_Mercer]

I have a Garmin 2610 GPS. Is it necessary to use an external antenna when traveling on my ST or is the signal strong enough using the internal antenna? I use a RAM mount between the handle bars.
You don't "need" an external antenna, but it really helps where signals are weak. I was surprised how many weak areas there are, especially on stormy days. I use a Gilsson. Its not that expensive, works well, and mounts easily on the stock, curved shelf (cowl) below the wind shield.

Marshal

[Blrfl]

The position of your receiver matters, too.

The integrated antennas in the 26xx and 27xx have a small ground plane underneath them that can block the antenna's view of satellites that are behind you and to the sides and at low elevations if the unit is tilted back to make the display readable. Depending on where you and the satellites are, this contrubutes to a problem called geometric dilution of precision, where you don't get as good a fix because you're looking at a cluster of satellites all in the same place.

--Mark

[Blue STreak]

The only time I find an external antenna makes a significant difference is in the canyons, either real or concrete. Actually, any place where you have a significantly obstructed view of the horizon it can help. But it's much less necessary on a bike than in a car, where the roof can block the signal from multiple satellites.

Actually, there's another time: If you're using the locking mount from Touratech, because that blocks a good part of the internal antenna.

If you DO decide to buy one, I recommend the Gilsson, too. It's cheaper than the Garmin, works the same, and is available with a 1 meter cable, which leaves you a lot less wire to try to hide / control.

[Marshal_Mercer]

The only time I find an external antenna makes a significant difference is in the canyons, either real or concrete. <snip>

At least where I live, there is another condition that reduces/blocks satellite signals. It can be found at the base of some hills. I don't recall the technical reason for this, but in essence, the signal shape cancels itself; kind of like cancelation waves in fluids. I recall that this is a WAAS (ground station) problem but the fact that the signal is weakened is real. Telephone signal repeater stations also experience this.

An external antenna minimizes the signal reduction. Canyon riding applies somwhat the same condition as the signal "bounces". Adding to the mystery, I have seen GPS signal loss at the same time XM radio is solid, and vice versa. Wierd.

Marshal

[RetArmy]

Thanks for all of the information. I plan on getting the antenna. For the cost of the antenna, it makes sense to have it to eliminate any potential problems.

[Blrfl]

At least where I live, there is another condition that reduces/blocks satellite signals.
In RF terms that's called destructive multipath, and it's similar to what happens in fluids. It's caused by direct and reflected signals making it to your antenna at the same time. The reflected one arrives a bit later than the direct one, and sometimes it works out that the peak of the direct one and the trough of the reflected one arrive at the same time and cancel each other out. The opposite can happen, too, in which case you see a stronger signal. (But nobody ever complains about that...)

All radio signals behave this way, but at higher frequencies the wavelengths are shorter and the chance of having cancellation occur increases.

Adding to the mystery, I have seen GPS signal loss at the same time XM radio is solid, and vice versa. Wierd.
That has more to do with the arrangement of the GPS constellation at the moment, where you are relative to the XM satellites (which don't orbit) and what's obstructing your view of the horizon. The differeing wavelengths used by the two services (GPS on 1.575 GHz or about 19 cm, XM is centered around 2.338 GHz or about 12 cm) also mean that signals from one may pass through an obstruction but not the other. Believe it or not, foliage is a big problem.

--Mark