| Author | Message | ||
     Rich Zellmer (Personalt) New Member Username: Personalt Post Number: 39 Registered: 11-2002 |
I got a reall cool deal on ebay for a GPS setup that works with my ipaq. It comes with a magnet mount antenna. For testing purposes I put it on the roof and ran the wire out the window. Now that I know things work I want to mount the antenna for good. I have seen some GPS units that just sit on the dash. Does this mean I can put this antenna on the dash and have it work well? I am ok with drilling a hole in the roof. I am more not looking foward to pulling down the headliner to run the wire. Anyone have any ideas or better places to mount it? I have a good 15 feet worth of cable from the brain to the antenna | ||
| Erik G. Burrows (Erik) Member Username: Erik Post Number: 237 Registered: 04-2002 |
I run my Garmin eMap with a remote antenna both on the dash, with the antenna about an inch from the windscreen, so as not to be blocked by the wiper arm. This work exceptionally well for me, I don't get any better reception holding it out the window. | ||
| Streak (Streak) New Member Username: Streak Post Number: 7 Registered: 03-2003 |
Rich, as Erik mentioned most of the modern 12 channel GPS receivers work really well without the need for an external antenna. I have used the Garmin II, II+, III, III+ and now V on the dash with their built in antenna over 1000km drives with no problems. Mounting anything extra externally just invites vanadlism!! By the way, what is the GPS setup that you bought? Some units come with a suction cup extension that you can stick on the inside of the windscreen. Enjoy. www.worst4x4.freeservers.com | ||
| Reed Cotton (Reedcotton) Member Username: Reedcotton Post Number: 164 Registered: 01-2003 |
I mounted my remote antenna on the top of my Safari snorkel. Now when people ask me what it is, I tell them that it is an antenna mast. -Reed | ||
| David Marchand (Dmarchand) Member Username: Dmarchand Post Number: 169 Registered: 09-2002 |
I used an ARB CB antenna mount, mounted on my bull bar. Placed the magnetic external antenna on it, then siliconed it from underneath. It's sturdy, and while not vandal proof, I doubt it's the first thing a vandal will touch. Gets excellent reception. | ||
| Perrone Ford (Perroneford) Member Username: Perroneford Post Number: 158 Registered: 02-2003 |
Streak, I find that those people who've never had external antennas for GPS tend to downplay them. But anyone who's used them, tends to talk them up. External antennas increase signal strength quite a lot. Sometimes over tenfold depending on conditions. You may not use your GPS in heavy cover, but I can tell you, in the deep woods or urban jungle, they help a LOT. Similar theory to fitting an external CB antenna, or an external AM/FM, or external cell-phone antenna. You don't really "need" them, but they make a world of difference. -P | ||
| Streak (Streak) New Member Username: Streak Post Number: 8 Registered: 03-2003 |
Hi Perrone, I have used and tested a number of antennas. Yes they have their application mainly when the GPS is not mounted near the window. You cant compare GPS antennas to other AM/FM etc. antennas. With GPS you either have the signal or you dont. A stronger signal will not give you better performance as with an analogue signal. Also a GPS can receive up to 12 signals from a selection of umpteen satellites. As long as you have at least 3 for 3D navigation then you should be fine. With AM/FM/CB etc. their is only one signal source, the one you are trying to listen to and a good antennas makes a huge difference. Having said all of this, yes there may be certain instances where an external antenna will make a difference but most of the time they are a nice to have as opposed to a need to have. | ||
| Perrone Ford (Perroneford) Member Username: Perroneford Post Number: 159 Registered: 02-2003 |
Streak, In the environments I tend to drive, it is not uncommon to have signficant signal attenuation as I move in and out of certain areas. My problem is also exacerbated by the heating element in my windshield. I find that my unit locks far more quickly with my external antenna, I find that locking more than 3 satellites increases the accuracy projected onto my software, and I find I lose lock less often with the external antenna. If you're in the rocks, or in the desert, you're already locking 8-12 sats without much interference. Much is dependent on GPS placement as you mentioned, terrain traveled, and other issues. I used GPS for about 7 years before I bought my external and for my uses, I'd never go back. I don't expect my uses to mirror everyone elses. But I find for the additional $100, it really makes a worthwhile difference. | ||
| Leslie N. Bright (Leslie) Senior Member Username: Leslie Post Number: 2284 Registered: 02-2002 |
Streak, If you want just a lat/long, 3 is okay, but to get anything even remotely close to 3D you have to have 4 satellites... You're right in that, with a digitial signal, you've got the signal, or not. The problem is, look at a Rover... it's windshield isn't laid back, it's a lot more upright, which means, a lot of the roof is going to block the signals from behind you. You end up having all of your satellites in front of you in the sky, which creates a poor geometry. Another problem that exists are multipaths.... ie, reflected signals bouncing, then hitting the antenna, but with a delay because of the increased travel distance. It's similar to what Perrone is experiencing with his heated windshield, but more pronounced. (Well, maybe not, since the wires in the windscreen end up reflecting the signals off, not to the unit). Anyway, the windshield itself, or the dash, or the hood (bonnet if you prefer), can cause them, too.... external antennas are shielded from underneath, preventing multipaths from being picked up in the first place. Also, a good GPS unit should have an algorithm that can disregard multipaths, but there are some out there that don't. It also depends on where you're driving. If you go on a spirited jaunt here in the southern Appalachians, ie, in and out of forest canopy down in valleys, then quite often a dash-mounted unit is going to not have the ability to see 4 satellites well. Probably not as big of a problem if you're driving across the Plains. If you're in downtown NYC, in Manhattan, then you may be picking up LOTS of multipaths off of nearby buildings, which could really throw off your position, or make it jumpy, at least. FWIW... -L | ||
| Perrone Ford (Perroneford) Member Username: Perroneford Post Number: 161 Registered: 02-2003 |
Yea, what he said! ;) -P | ||
| Tom Hyslip (007) Member Username: 007 Post Number: 173 Registered: 03-2002 |
Your reception will be terrible from inside the vehicle if you have a heated front windshield. I have run mine up to the sunroof and mounted it on the edge of the front rail to avoid the problems with reception from my heated front windshield | ||
| Erik G. Burrows (Erik) Member Username: Erik Post Number: 238 Registered: 04-2002 |
My windsheild is heated, and with the antenna moved back enough to be out of the way of the wiper arms, it works perfectly. I almost never loose 'lock' and aquisition is nearly instantanious. The frequency that GPS signals use have a wavelength that easily fits between the heater elements. One thing that hasn't been mentioned here yet is radio frequency (RF) interference. GPS receivers are VERY sensitive to RF noise. A nearby laptop or inverter can blind them completely. I've even seen two GPS receivers not like to be too close together. If you're having trouble getting a good signal, try moving the antenna. Your sterio, CB radio, CD player, and even AC fan/servos could easily be affecting the receiver. | ||
| Eric Pena (Evalp) Senior Member Username: Evalp Post Number: 551 Registered: 06-2002 |
I ran my wire outside my door molding and sealed it with silicone to prevent leaking. I then mounted it atop my rack with something I fabricated. I was restricted by cable length and I thought maybe it would be a bad location incase a tree branch was to hit it but I have been through some thick bush and branches and it hold up fine.  I am also for an external antennas. I used it for a while without one and it locks sats slower and has less accuracy as I can lock as many as is in the sky over me, up to 12. I noticed that satts behind me it could not see and can't lock. I use the small one for when it goes out of the car. | ||
| Stuart H (Disco_stu) New Member Username: Disco_stu Post Number: 6 Registered: 06-2003 |
FWIW - I made some brackets that my GPS and XM Sat radio antennas sit on that are on the inside of my rear alpine windows. I mounted the bracket to the interior trim piece, and made them of metal so that the antennas would stick to them(because of the magnets on the bottom). I did this because I wasn't to keen on taking the wires outside of the vehicle. I just did this two days ago, and I haven't played with my GPS yet, but my XM seems to work fine. Although I am within range of one of their terrestrial repeaters right now, I will be interested to see how it performs when I am only picking up the sattelite signal. |
