Pushpit aerials

Graham_Wright

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Favourite place for the like of Navtex and GPS aerials is on the pushpit.

It seems to me that in that location they provide excellent grab handles for coping with lurches.

Is there any reason why they could not be mounted on the spreaders (apart from issues of cable length). They should be protected from lines there by the shrouds. Perhaps they are also protected there form radio signals?

If ok, will they work upside down?
 

Stemar

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I have a big lazarette. My gps antenna lives under the grp lid, so it's well protected from ropes, clumsy oafs like me. /forums/images/graemlins/blush.gif

The position doesn't seem to have affected signal strength and it's not advertised to the light fingered brigade, which I'm quite keen on not doing!
 

Oldhand

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GPS antennas should be kept low so that they don't swing in big arcs in a seaway which would produce unstable SOG/COG output. In the worst case, a GPS might not compute a fix at all if antenna motion is causing severe instability in the "reasonableness" of the fix calculations, depending on how the software works. They also need an unobstructed view to maximise the number of satllites in the constellation which can be used in the position fix calculation for best accuracy, although its a bit more complicated than that when you start considering geometry. On a spreader it would both have too much motion and the mast, being close, would cast a significant "shadow".

Navtex antennas can be mounted at any height and one may indeed get better reception with a high antenna away from possible interfering sources and electrically conductive clutter. That said, on a spreader the proximity of a metal mast is likely to degrade antenna performance so it should be at the masthead to avoid this.

Long cable runs will attenuate signals received but are not critical if active antennas are employed with at least pre-amplifiers within the antenna, if not the whole receiver front end.
 
G

Guest

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Navtex will normally work inside cabin unless cabin is particularly bad for signals ... eg steel hull / deck etc.

GPS is better at lower where rolling / pitching do not create such large swings upsetting the internal calculations .... and also GPS will often work in 'under-cover' locations ..... ie under Sprayhood, in Pilothouse window etc.
 

[2574]

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Graham,

I had a short (1m) aerial mast made to lift the aerials away from the pushpit rail and slightly astern. It's worked well. The GPS beacon on the pushpit was always being pushed over by oafs like me to 90 deg or more and then losing it's signal.
 
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