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Sensitivity
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Jay1967
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Joined: Mar 01, 2006
Posts: 75

PostPosted: Sun Jan 06, 2008 5:42 pm    Post subject: Reply with quote

mikealder wrote:
You need to host the image on the net then link to it on the forum, image shack is a good free site that supports forum links and accepting uploads.

As you had two GPS devices on the table were they close together? if so I am not surprised the reception is poor, close proximity causes interference and will result in a longer time to acquire a position fix, or under poor reception conditions you might never get a lock on either device. Even with a fix two devices close together will compromise the accuracy.

If you don't believe me get both devices showing a position fix, watch the SNR on both devices as you draw them closer together - Mike


I had the SatMap acquiring Sats about 2 mins before I placed the 60CSx next to it. With regard to interference, one would get no less interference if they were to put their leather wallet next to it! They are both receivers and NOT transmitters. The electronics in both have to by nature of the device have minimal radio interference therefore a non issue in a test such as this.
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mikealder
Pocket GPS Moderator
Pocket GPS Moderator


Joined: Jan 14, 2005
Posts: 19638
Location: Blackpool , Lancs

PostPosted: Sun Jan 06, 2008 5:57 pm    Post subject: Reply with quote

Try doing the test and watch the SNR, this can be seen on every GPS device I have used - yes they are receivers, but you might be surprised at the findings when you actually try it - Mike
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martin_b
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Joined: Mar 02, 2006
Posts: 36

PostPosted: Sun Jan 06, 2008 6:21 pm    Post subject: Reply with quote

I wonder if mine is slightly defective then?




Jay1967 wrote:
martin_b wrote:
Just tested mine again,

Standing outside in the "same position" as it was last used, ( in a wide open space) my unit took 4mins 45 sec to get a fix. this is with new batteries. In comparison my Nuvi unit inside the car takes about 30sec.

If I hadn't battered mine about a bit I'd send it back! What i will say though is once it has a fix it seems pretty good at keeping it.


stood outside in my garden, house 10m behind me, 6 foot fence 4 m to my right, 30ft trees 30m infront of me. SaMap was unused for 12 hours. Cold start and locked position in 1m 50s. Powered off, off for 10s, powered on, got lock 40 seconds.

When put in heading Up position, maps span for over 2 mins.. very disconcerting. SNR reading between 30-35.

This is not as good as the Garmin 60CSx.
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Jay1967
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Joined: Mar 01, 2006
Posts: 75

PostPosted: Sun Jan 06, 2008 7:35 pm    Post subject: Reply with quote

martin_b wrote:
I wonder if mine is slightly defective then?




Jay1967 wrote:
martin_b wrote:
Just tested mine again,

Standing outside in the "same position" as it was last used, ( in a wide open space) my unit took 4mins 45 sec to get a fix. this is with new batteries. In comparison my Nuvi unit inside the car takes about 30sec.

If I hadn't battered mine about a bit I'd send it back! What i will say though is once it has a fix it seems pretty good at keeping it.


stood outside in my garden, house 10m behind me, 6 foot fence 4 m to my right, 30ft trees 30m infront of me. SaMap was unused for 12 hours. Cold start and locked position in 1m 50s. Powered off, off for 10s, powered on, got lock 40 seconds.

When put in heading Up position, maps span for over 2 mins.. very disconcerting. SNR reading between 30-35.

This is not as good as the Garmin 60CSx.


Martin, it would be very difficult to determine whether or not your satmap is defective just based on this. There could be any number of reasons why yours took longer as satellite geometry, weather conditions, environment are all parameters in acquisition time. But I would say that if you are continually getting these long acquisition times especially from a warm start, I would call SatMap. Im yet to do a proper test with mine, but will likely post further thoughts about my SatMap later in the week (if Iíve still got it!!!)
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FrequentFlyer
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Joined: Jun 12, 2006
Posts: 960
Location: London

PostPosted: Mon Jan 07, 2008 1:41 pm    Post subject: Reply with quote

Question. I'm off for the best part of a days walk...not exactly sure of the route, but I just want Satnav to keep tabs on me/it, so that when I get home I will be able to superimpose my walk over to the SouthDowns internal map, so that I can decide whether to save/edit it for future use. If I stop for lunch for an hour or so, should I turn it off....completely or somehow, standby ? Will it pick up again from where I left off ?
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Jay1967
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Joined: Mar 01, 2006
Posts: 75

PostPosted: Tue Jan 08, 2008 12:23 pm    Post subject: Reply with quote

FrequentFlyer wrote:
Question. I'm off for the best part of a days walk...not exactly sure of the route, but I just want Satnav to keep tabs on me/it, so that when I get home I will be able to superimpose my walk over to the SouthDowns internal map, so that I can decide whether to save/edit it for future use. If I stop for lunch for an hour or so, should I turn it off....completely or somehow, standby ? Will it pick up again from where I left off ?


turning the satmap or any gps off (power off) means that you will lose satellite lock. Depending on your environment and satellite geometry, simply turn on the gps to reacquire acquisition. If conditions are good, you'll probably get a lock right away, if not, then your gonna have to wait! This waiting might not be acceptable to you?!

When using my Garmin 60CSx I often turn it off during breaks (particularly long ones) because im confident it will require satellites quickly assuming environmental conditions are as normal. Even in very dense tree cover my 60CSx has not yet let me down (touch wood)!

Now.. with my SatMap itís a little different. Im not entirely confident (yet) that satellite reacquisition is as good, so I tend to leave it on standby. My settings are POWER ALWAYS ON; BACKLIGHT OFF AFTER 30 SECONDS. I believe its true to say that any GPS hunting for satellites is going to use slightly more power (just like a mobile phone searching for cell sites) so power times are quite difficult to determine.

Slightly off topic here .. my advice to anyone who wishes to purchase a GPS merely to record tracks for later map superimposing on a pc, should seriously look at buying a GPS data logger and not a handheld GPS/GIS (Graphical Information System i.e a GPS device with a map screen etc.).

Cost of a top rated Data logger about £60
Size: less than 3Ē some of the best ones
Power: last 40hrs plus (mine is rated 50hrs continuous)

WHY?: for when I want to record very long trips. The unit (in my case) measure only 3 inches (about 7cmís), can record over 100,000 positions, and continuously tracks for over 40hrs! I can upload and see my tracks on Google earth and have the ability to output to almost every known GPS format!
After all these GPS devices I have my wife still tries to give me directions!
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