Stereo Install Questions

[BuzzH3]

Originally Posted by f5fstop

Not sure how a speed sensor could increase accuracy of the GPS system. Especially since most people with calilbratable speedometers will calibrate from a GPS unit.

As to why it takes a while to obtain an accurate fix....

When you first turn on a GPS, the unit must download an almanac from the satellites. The almanac is transmitted every 12 minutes and tells the GPS unit where it should expect to see the GPS satellites. The satellites also transmit what is called ephemeris data which is sent in blocks, each about six second in length, starting every tenth second. Ephemeris data is precise orbit information of the satellites.
If you are traveling cross country with the GPS on, the almanac and ephemeris data is kept up to date. However, if you have the GPS off on a cross-country trip, and you turn it on 3000 miles from where it was last turned on, it is a bit confused, since it retained the last alamanc informaton, so until it downloads the almanac and the ephemeris data, accuracy will be affected.
Almanac data is sent by all satellites and includes information about all the satellites. Ephemeris data in regard to a satellite is only sent by that particular satellite.
If the GPS system is WAAS capable and WAAS is enabled, the GPS needs to download the WAAS almanacs from all Satellites. The WAAS almanacs are transmitted every five minutes. This almanac information is used by the GPS to correct the information received from the other satellites.
Right now, on some GPS units, depending on your location in the USA, having the WAAS disabled may give you better accuracy. The US government last year launched a few more WAAS satellites and they are currently moving the old ones and new ones around to new locations, and testing them.
On Units with the SiRF III chip, the chip will not recognize a test signal from the WAAS satellite. Older non-SiRF III chip models will recognize, but the signal may not be correct.
WAAS satellite 33 is over the Atlantic somewhere near Europe. Number 35 is being moved to the west, and I believe 47 is over the Pacific. Right now, the best areas for reception are the southwest, or so I have been told.

Thank you for the response. That is very interesting.

From my understanding (and this is just from reading info on the AVIC-Z1), the Z1 uses the speed sensor and an internal gyroscope to determine your current location if you lose the GPS signal. Once the signal is reacquired, it syncs to where the satellites are saying you are. It continuously records this information and the unit becomes more and more accurate the more you drive. So if you are driving in a heavily wooded area or in the city with tall buildings it can still maintain a high level of accuracy.

One more quick question. Where in the engine compartment is the PCM located?

[f5fstop]

Originally Posted by BuzzH3

Thank you for the response. That is very interesting.

From my understanding (and this is just from reading info on the AVIC-Z1), the Z1 uses the speed sensor and an internal gyroscope to determine your current location if you lose the GPS signal. Once the signal is reacquired, it syncs to where the satellites are saying you are. It continuously records this information and the unit becomes more and more accurate the more you drive. So if you are driving in a heavily wooded area or in the city with tall buildings it can still maintain a high level of accuracy.

One more quick question. Where in the engine compartment is the PCM located?

Ok, that makes sense for the need of a speed sensor. However, not sure how often it would be used on the main highways of the US. I travel with a Garmin iQue 3600 for the roads, and I have only lost signals in very narrow canyons for a few minutes, or in long tunnels.

PCM is at the left rear of the eingine compartment, by the coolant bottle.

[kodiakz]

Must use a vss for the nav to function properly and for voice guidance to work at all.

[HummerNewbie]

Originally Posted by kodiakz

Must use a vss for the nav to function properly and for voice guidance to work at all.

Does this just apply to the Z1? D1 doesn't have voice commands so that isn't an issue for me and may nav seems to work just fine. Have talked to others that never hooked up the vss and their systems work just fine as well.

[dеiтайожни]

The N2 also uses the VSS to increase accuracy...if you lose signal it will still have a good idea where you are, incase you can get lost in a tunnel I suppose. I never hooked my VSS in the h3, had it hooked up in my last vehicle though. I can't tell a difference. Nav functions properly, and I still get voice guidance. So must be only on the Z1...which sucks.

[kodiakz]

The Z1 and N3 (can't remember on the D2) have voice guidance that will not work if the vss is not connected. Also, your system will be much more 'spot on' when locating using vss instead of just the gps. We have installed many of the new eclipse models that don't require vss and have noticed that they are not quite as accurate as when the vss is used.

[HummerNewbie]

When I read voice guidance, I was thinking voice commands as in you say the address you want. The Z1 has that feature doesn't it? The D1 does have voice guidance and it works fine without the vss hooked up. I know it will increase the accuracy no matter where you are at but I have yet to have an issue without it. I wonder if your location effects the need for vss or not. I can see being in the mountains making it more important. It certainly won't be like being in the rockies but guess I will find out when we head up to Tellico. Every morning it is off by a couple of blocks but is back on track in a couple of minutes. Not going to get lost within a couple of blocks from my house so not too worried about that

[BuzzH3]

Does anyone know how to remove the antenna from the factory XM box? Does it pull straight out or unscrew?

Thanks