GPS aerial inside console

[Chris Murray]

I have an option to include a Lowrance 3600c on my console, close to the top of the console. (Scorpion)

This has a built-in aerial.

I would be interested to hear your views on the likelihood of receiving sGPS signals through both the equipment case (which should not be a problem, as this is what it is designed to do) and through the fibreglass console.

The alternative is a 3500c, which is identical, except that it has an external aerial.

Thank you for your thoughts!

Chris.

[Richard B]

Originally Posted by Chris Murray

...through the fibreglass console.

Hi Chris, I'm fairly sure this won't work. The GPS signal transmitted from satellites is very low power. Our receiver is on top of our console, and it's OK if obscured by a paper chart, but anything more substantial stops it working. Placing a mobile 'phone in an aquapack on top of it is usually the reason for it displaying "No GPS signal"!

[Chris Murray]

Hello Richard,

Thanks for your comment. This is pretty much what I would expect. However, if there was a reasonable chance that it would be OK, then it means that I would not need to have an aerial on the console.

My main GPS antenna will be on the radar arch. This will be my back-up but it really does need to work! I am tying to avoid a second aerial on the radar arch on the basis that if a wave takes out the main aerial, then the back up may still be intact on (or inside) the console.

I would welcome other views and experiences, in the hope that someone can tell me that they have tried it and it is useless! That way, the choice becomes obvious.

Whilst writing, Aries IV ("Quick One" didn't look right) is due to be completed in late April. It's already out of the Jelly mould!

Best wishes,

Chris.

[codprawn]

My GPS works fine inside a car - glass and metal etc in the way.

I have also had signal through an asbestos sheet roof and inside a plane so try it and see is the best advice!!!

[jwalker]

Sorry Richard but I don't agree. I have 3 antennas inside the cabin and they're all ok. I tried them inside and out before deciding where to mount them and the signal strength displayed by the units appeared unaffected. In use, there's not been a problem. However, if there is anything metallic above then that is a different story.

[Scary Des]

Originally Posted by codprawn

My GPS works fine inside a car - glass and metal etc in the way.....

they work through glass but not metal and metalised windows stop them working too Des

[Mark Halliday]

My old Garmin GPS3+ works below deck on yachts. I found that aquisition was a bit iffy but if you powered it up on deck the took it below it worked fine. Signal is degraded but there is still enough for a low DOP. Flash it up and then try different positions whilst watching the signal bars. Mount it where the signal is strongest.

Des. Add heated front screens to your list of "no work" situations.

[Jon Brooks]

I have recently assited with the fit of DSC radio's to PWC's.
We mounted a Garmin GPS antenna inside the ski, not exrternal.

Works fine with no problem at all.

Not exactly the same but nearly.

Regards

[roycruse]

If you have a Sirf III chipset the GPS will work inside an office block - but they are not common on marine gps.

the older gps receivers where "tuned" to reject signals below a certain level as this was the only way they separate out a direct from a reflected signal when in urban or mountainous conditions.

modern GPS chipsets work out your likely position based on your last position, speed and heading and then reject signals based on the likely hood of them being reflected. This means that they can still use weaker signals to get a fix which is why they now work indoors.

your best bet would be to power it up inside the console and check if it works - unlike when in a car you will be driving under trees etc you are in open water 99% of the time so you may get away with it - it will depend on quality and type of receiver, thickness of console grp, and what else you have or put on top of the console.

[roycruse]

Originally Posted by Richard B

Placing a mobile 'phone in an aquapack on top of it is usually the reason for it displaying "No GPS signal"!

A mobile phone will drown out the GPS signal rather than block it.

I think if you take a handheld vhf over to your antenna and key up it will also drop all the satelites.

even though frequencies are not the same a strong enough signal of any band near enough to a reciever will cause drop out.

[Downhilldai]

From what's been posted on this thread, it seems that integral GPS antennae are ok in an open cockpit. Are there any disadvantages over an ext. antenna, if the GPS unit is mounted on the top of the console?
Curious, as I'm thinking of getting a GPS chartplotter and was wondering whether it's worth going to the additional expense and trouble (No A-frame) of the ext. antenna.
Your views/experiences would be appreciated.

[roycruse]

If you are mounting your gps on top of the console - best go for integral antenna as its one less wire to sort out. - unless you are planning to take the thing with you to your next boat and theres a chance it might need to be flush mounted.

[Downhilldai]

Thanks Roy - no noticeable loss in signal quality then? I'm thinking of a Garmin 172C - quite cheap at the moment - just over £300. Anyone know of any better deals?
Also, any good deals on Garmin charts around

[roycruse]

If £300 is including the VAT then I'd say thats a very good deal.

[codprawn]

It is very easy to jam a GPS signal - worrying!!!

Even an active TV aerial can cause block out a wide area.

http://www.gpsworld.com/gpsworld/art...3404&&pageID=1

It has been possible for some time to buy jammers that will take out quite a wide area - same with mobile phones. The joys of digital - with analogue something usually gets through!!!

[jwalker]

Originally Posted by roycruse

A mobile phone will drown out the GPS signal rather than block it.

Must be more to it that that, roycruse, or my Garmin Navtalk phones wouldn't work.

I can see, as Richard said, putting a mobile phone on top of a gps will likely block it's signal cos the mobile will have a good deal of copper circuit inside and that'll likely also include a ground plane. Plus there will probably be other metal inside it too.

[DGR]

Originally Posted by roycruse

I think if you take a handheld vhf over to your antenna and key up it will also drop all the satelites.

My main VHF antenna is only a couple of feet from my GPS antenna - the only time I lose satellite signal is when it is physically blocked by something (i.e. people leaning over it, or a structure of some sort). Using the radio doesn't affect it.

D...

[jwalker]

Just did a wee experiment....it's best to know for sure.

Putting my mobile phone at the side of, at the end of, underneath, on the top of but not covering the antenna of the gps, made no difference to the gps. Putting it on top of the antenna section halved the reception indicator bars. But there was very good reception so with poorer satellite recepiton the gps may well loose it's signal.

Calling the speaking clock while the phone's antenna was adjacent to the gps antenna appeared to shorten the bars by just a tad but it was difficult to tell for sure whether it was just the normal movement of the bars or not. My feeling is that there was a very small effect. The phone didn't appear to be bothered by any of this.
This was indoors in a conservatory and so shielded by glass and a plastic roof.

[roycruse]

Ok ill shut up

but try it with you VHF...

[Roy Smith]

Chris why not buy a good hand held gps, then you have a completly seperate
backup with its own power supply (batterys)