good/cheap GPS with external antenna?

skywise · 07-06-2009, 04:27 PM

I'm in the middle of installing a fresh build of my carputer (using a eeepc) and am in need of a GPS that either is/can have an external antenna.
The antenna will be mag mounted to the trunk so one of those 5' USB GPS units won't work (the eeepc is stashed under the front passenger seat)
I don't really care if the unit has a display or not since it'll also be under the seat (or stashed elsewhere) but if there's a cheap tomtom-ish unit with serial and external antenna that will just throw out serial when plugged into 12V of the car I wouldn't mind.

A side question:
How is the triple threat roof antenna for sale on mp3car?
Work well? What GPS units does it's connector fit? (FME female)

rodweb · 07-06-2009, 07:46 PM

Why don't you get a USB GPS receiver and run a software solution?

I use one of these:

Wrong country I know but I got it bundled with Odyssey Navigator software from here (prices in AUD):
http://www.twig.com.au/store/index.php

I fitted this under the plastic cowling where the windscreen wipers are. It works a treat. I had to daisy chain it via a Hub as the Car PC is behind my back seat and the cable length was too long for USB to work without a hub. I cut the USB connector off and fed the cable through the firewall and resoldered the connector back on.

Details in my buildup, see link below.

skywise · 07-06-2009, 09:18 PM

I don't mind a USB solution, except for the cable length issue.
I don't get along with USB hubs, they have a habit of getting weird on me.

skywise · 07-07-2009, 11:48 AM

Any word on the merits of sirf II VS sirf III ?
Ebay has a nice cheap sirf II unit for a total of ~$30

(item number 220444692367)

skywise · 07-09-2009, 02:01 PM

I've grabbed the sirf II unit, will see how well it works.

DarquePervert · 07-09-2009, 03:10 PM

You should be fine. Sirf III touts faster lock times and more sensitivity.

skywise · 07-28-2009, 03:31 PM

Got the sirf II unit last week and finally got to installing it.
Works just fine, the combo of it's cord and supplied serial-USB dongle were almost long enough to reach from the trunk lid to under the front seat. (I put in a short USB extension cord to make up the slight gap)
The receiver works fine, can even grab (barely) 3 sats inside my metal clad garage.
Outside it sits at a min of 5 sats and up to 9 locked sats.
I'm more than happy with the unit, now to see if it minds living outside in the cold winnipeg winter.

skywise · 08-12-2009, 02:05 PM

Ok, went on a trip with the new carputer/GPS.....
Generally it worked fine, good signal...
It was quite rainy in Calgary and downtown we started losing signal.
No big deal, tall buildings N all that, but when we got away from them, signal didn't come back. We navigated using my wife's iPhone and I attacked the GPS..
It sloshed. The poor thing was 1/2 full of water. Seems water affects the ability of the unit to function correctly

After taking it apart and blow drying the unit, it's still not quite right.
I think there's a bit of corrosion on the circuits and the super cap discharges in no time flat, every power on is a cold start, a 20 minute cold start.

Sooooo, back to Ebay and now I have a Holux GR-213 on it's way for $28US, shipping included. This one IS waterproof.

(being sirf III isn't a bad thing either)

Moral of the story, don't put that sirf II unit outside, it may look mostly waterproof but it isn't.

Sky

DarquePervert · 08-12-2009, 09:45 PM

The construction of the GPS unit is what determines how watertight it is, not the chipset.

skywise · 08-12-2009, 10:36 PM

Oh, I totally agree, it's the build of the case that determines watertight.
That's why I worded it "That sirf II unit", this was sortof a review of a specific sirf II GPS from ebay.
Or maybe a review of my luck getting a GPS unit from Ebay

Punky · 08-12-2009, 10:56 PM

is the newer gps worth the upgrade? Mine is working fine, but it does jump around a bit in area with lots of high rise (downtown) or large trees.

DarquePervert · 08-13-2009, 06:51 AM

Quote: Originally Posted by Punky

is the newer gps worth the upgrade? Mine is working fine, but it does jump around a bit in area with lots of high rise (downtown) or large trees.

A newer unit won't help with that.
The trees and/or buildings are blocking the GPS signal from one or more satellites, so you see your position jumping around.

Punky · 08-13-2009, 06:39 PM

my current system has 12 satellite max, which i thought cause the weak signals.
newer ones seems to have something like 32 satellite? you don't think that'll fix the problem?

UN5T0PP4813 · 08-13-2009, 07:57 PM

i've been using the Ambicom GPS-USB.. it's been working for me far almost 2 years now.. i think i only paid 25 at frys electronics

skywise · 08-14-2009, 12:57 AM

Quote: Originally Posted by Punky

my current system has 12 satellite max, which i thought cause the weak signals.
newer ones seems to have something like 32 satellite? you don't think that'll fix the problem?

From what I've read, about the max number of sats in the sky at one time is about 12, and the gps wiki has a nice animated globe with sats in view and it's usually max 10 with blips of 11 or 12.

Sooo, a 32 channel receiver sounds cool, it's probably not much practical use.
(it would be of some use for the next sat coming up after the last heads down, but don't think it'd help that much)

Now, what may be of some use is receiver sensitivity.
You'd have to look up the specs on your current unit, and the specs of a current chipset to see how much better.
But....
You're talking about tall buildings... Doesn't matter how sensitive the chipset is, a full block of concrete N steel, nothing is going to get through that.
A busy downtown will get you a street wide peek forward/back of your car and tiny peeks to the side. Not many sats will be lined up exactly right to get to you.
Trees on the other hand, a sensitive receiver will help. The trees are cutting down the signal, but there's probably still some left to be found.

(overly) long story short: Check the specs and see if the new chipset is alot better than the old.

Sky

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