Sat nav speed pulse ..how come portable units dont need one ?

mapleleaf

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just an observation and not sure if this has been brought up b4 but,

Comand & all the other head unit based sat nav systems need a speed pulse to work properly and finding said speed pulse wire on some cars has been a much discussed topic.

So, how come portable sat navs work fine in the car with no speed pulse?

is there any noticeble difference in accuracy ?

I dont seem to have an analoge speed pulse in the mustang so may go the TT 700 route. any advise or comments welcome. thanks
 
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PJH

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Does Command keep working correctly in tunnels ? My TTG switches to ASN when it looses the satalite signals and the display can hop about a bit if the signal less period lasts too long. eg Dartford tunnel.
 

fuzzer

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yep , its purely for when there isnt a good sat lock and going through tunnels etc :)

Its really weird with the sat nav showing your in the water :)

on another note ... has anyone else noticed their TMC dropping off today ?
 

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steve_bcs said:
just an observation and not sure if this has been brought up b4 but,

Comand & all the other head unit based sat nav systems need a speed pulse to work properly and finding said speed pulse wire on some cars has been a much discussed topic.

So, how come portable sat navs work fine in the car with no speed pulse?

is there any noticeble difference in accuracy ?

I dont seem to have an analoge speed pulse in the mustang so may go the TT 700 route. any advise or comments welcome. thanks
I think you will find the COMAND is more accurate than non OEM units as it uses the combination of speed pulse and the gyroscope to compensate when there are no satellites (tunnels etc) or less than three satellites available. Also, the COMAND definately compensates for your speed when issuing instructions. For example my COMAND normally says '....in 200 yds ' or that sort of distance. Today travelling on the M40, it issued statements like '...in 3/4 of a mile) I was travelling significantly faster than usual (until that accident at High Wycombe!).
 

tim.100

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steve_bcs said:
just an observation and not sure if this has been brought up b4 but,

Comand & all the other head unit based sat nav systems need a speed pulse to work properly and finding said speed pulse wire on some cars has been a much discussed topic.

So, how come portable sat navs work fine in the car with no speed pulse?

is there any noticeble difference in accuracy ?

I dont seem to have an analoge speed pulse in the mustang so may go the TT 700 route. any advise or comments welcome. thanks
Blaupunkt sell at least two models of Travel Pilot. A comparison of each may answer your questions. I have installed both to family cars:

- Travel Pilot E1
- Travel Pilot Freestyler

They look identical, but the E1 is cheaper and has a speed sensor. The Freestyler is sold specifically for cars where the speed sensor signal is hard to get at.

The Freestyler needs more satellites to operate, as stated in the manual (can't remember how many). It is slightly slower to find its position on start-up.

However, in the suburban areas where I tested both units, they worked to a similar standard of accuracy. I suspect the inherent weaknesses of the Freestyler become more apparent in places like the City, with its underpasses and limited view of the sky. It will get lost more often!

Brilliant web site for finding speed sensor signals: www.tachosignale.com (translation may be useful).

Hope this confirms your question / assumptions above.

Regards,

Tim
 

tim.100

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A quick follow-up, following the simultaneous post.

1) Both Travelpilots use gyroscopes. Hard cornering upsets them!!! :eek:

2) Differential GPS is incredible technology. A vessel in the North Sea can sail half-way to Norway, then lower a hook onto a rig's anchor chain using GPS. With DGPS, you can plan exactly which link in the chain you want to pick up.

However, DGPS is not available in cars AFAIK.
 

nickmann

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I have found that the speed sensor and gyro makes a big difference. I use Satnav to get me to mountainbike races. The courses are usually in the middle of nowhere, often in forests, and forests are not GPS-friendly.

I used a Garmin eMap for a couple of years, but it often let me down in the last few miles of the journey - when the tree cover gets thicker the GPS signal gets lost.

Then I got a TravelPilot E1. It never gets lost as when the signal goes it uses the speen sensor and the gyro. It does get a bit confused when I get of the ferry because it wakes up 80 miles from when it went to sleep. It takes about 3 or 4 mins to sort itself out, but I've never had a GPS that didn't do that when faced with a bit of sky comnpletely different from what it was expecting.
 

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tim.mcd said:
Both Travelpilots use gyroscopes. Hard cornering upsets them!!!
Do they use mechanical gyros? :eek:

My 'other hobby' is r/c planes. Gyros are used in virtually all r/c helicopters to stabilise the yaw axis, and solid state (electronic) ones have been standard for years now. I assume that's what the TTG 500 and 700 contain (to drive the 'assisted navigation') ... the only problem with hard cornering might be the windscreen mount coming off?! :D
 

GrahamC230K

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I had a problem with my GPS aerial (my fault really) in the early days of owning my Panasonic system. I navigated my way part round Coventry using the data from the Gyro and the speed pulse alone. I was very impressed.
 

prprandall51

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GrahamC230K said:
I had a problem with my GPS aerial (my fault really) in the early days of owning my Panasonic system. I navigated my way part round Coventry using the data from the Gyro and the speed pulse alone. I was very impressed.
The first commercially available navigation systems didn't use GPS at all. You can navigate all day on gyro and speed pulse alone.

Sat Nav is a misnomer - GPS is not that critical to its operation, especially on systems engineered before the removal of Selective Availability in 2000.

Philip
 

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prprandall51 said:
Sat Nav is a misnomer - GPS is not that critical to its operation, especially on systems engineered before the removal of Selective Availability in 2000.
I believe that COMAND only uses GPS for initial location and then only for about 10% of it's navigation, with no speed pulse comand is practically useless (I have seen this).
 

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Shude said:
........................................................................................................................... with no speed pulse comand is practically useless (I have seen this).
I can confirm this as when I installed my COMAND it had no idea where I was, where I was going and wouldnt update my position until I connected up the speed pulse.
 

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prprandall51 said:
The first commercially available navigation systems didn't use GPS at all. You can navigate all day on gyro and speed pulse alone.

Sat Nav is a misnomer - GPS is not that critical to its operation, especially on systems engineered before the removal of Selective Availability in 2000.

Philip
This is indeed true as many many airliners used to use inertial navigation systems (based on gyro's) to navigate all over the world before the advent of GPS. They are amongst the most accurate systems around.
 

calum

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and submarines still have to use INS, of course, with only the occasional GPS update.

I think that COMAND also has a snap-to-street feature, whereby since it's knows you're following roads it can constantly fine-tune things accordingly.
 
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mapleleaf

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Thanks guys, so the upshot I guess is basically go for a unit that needs a speedpulse for the best directional accuracy accross the majority of situations. and in my case - do whats necessary to find an appropriate speed pulse signal on the car.
I've been used to comand & Becker traffic pro so I would probably find the limitations of the portable units a pain to use every day as most of my navigating would be in build up areas. You've helped me to decide the way to go.

On a side note - having been a member here for a little now I never cease to be impressed at how quickly the replies come back. In comparison, my Mustang Forum take a lot longer to respnd if at all. especially in the car electrics department.

thanks again.
 

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