Nasa Clipper Navtex Antenna

Emmet

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Anyone know if the antenna will work if mounted inside, away from any possible interference. Havent had a chance to test it yet so just asking the forum for your thoughts.
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thalassa

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Mine worked perfectly in the transom of my old boat. Present situation is in a locker, with some instruments less than a metre away. Both are GRP boats.
 

Jonny_H

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Yes - you can mount inside - mine is behind the instrument panel and works fine.

When you test it - you may gets lots of £$%^&*)(!@?>< etc, this is likely due to being connected to shore power - if you disconnect then this should resolve the problem!

Jonny
 

noswellplease

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Navtex works on the medium frequency band. 518khz for english. For those who can remember pre vhf or fm days the reception sometimes improved if you moved the tranny about to get a better signal. On a boat with constant motion this is happening all the time so unless you place your aerial in a sealed lead casket I don't think it will matter at all where you site it. Good luck.
 

alan

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Yes, will work inside. Should be mounted vertically, but will probably work on its side as well and you are not likely to notice the difference in reception quality.

Alan.
 

Oldhand

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Can I ask what you mean by "work" with reference to antenna positioning? An antenna will work to a degree in any above water location as long as it isn't in a metal box. How well do you expect it to work needs to be asked before answering your question.

A very short active MF antenna, which is what I believe yours to be, will work best if it is at height clear of all nearby metal work and as far away from any possible source of MF interference as you can get within the constrains of the boat (masthead is a good place). So it may well "work" inside and receive your nearest Navtex station reasonably well if your vessel is not moored in an area closely surrounded by hills or metal buildings. However, it will "work" better in difficult locations or for more distant stations if mounted in a more ideal location.

Quite a few forumites have expressed disappointment with Navtex reception over the last couple of years, so think about a good installation option rather than the easiest. I would suggest the latter requires a degree of luck, so you could try it first and see if it meets your requirements and if not be prepared to do somthing better.
 

William_H

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MF signals tend to be a lot less critical of polarisation matching ie vertical or horozontal than VHF so it probably doesn't matter.
Mounting on the mast top will not give a great advantage like VHF compared to lower down. I appreciate Oldhand is advocating mast head to get away from interference however the transom or cabin top should also be remote from interfereence.
Try switching other devices off (including engine) to check for interference problems. Inside the cabin may be adequate for your purpose but best range would be outside and clear of rigging etc.
So just try it. olewill
 

Robin

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I have had mixed results with Navtex antenna positions.
On our last boat I laid the aerials horizontally under the cabin headlining, under the sidedeck area and they worked fine on both frequencies.

When we bought our current boat I fitted the aerials (I opted for 2 separate ones) vertically behind a panel at the nav table, against the ply lining side of the grp hull. In this position Navtex was effectively off the menu, it didn't like being plugged in to shorepower, the engine running, being in harbour or pretty well anything! Because I fitted the aerials whilst the panels were out for other reasons and they were difficult to replace, I left them there and didn't bother about Navtex unless I specifically wanted it when I used our laptop and SSB combination to get it (as well as RTTY/Fax).

Early this season however I had cause to remove the panels around the nav station again and took the opportunity to remove the Nasa aerials, in case I decided to mount them outside. However come one wet day I thought to give the aerials a test run in a different location below and just wedged them up by a coachroof window, whereupon they sprang to life! So now they are fitted just 3ft away from where they received zilch on the wood panelling surrounding the aft coachroof window and just about 18" away from the set from where they have worked faultlessly in harbour, at sea, plugged in, engine running no matter. It is still a 'temporary' location so the coiled cables are hidden behind a plotter but my guess is it will stay like that for some time!

If it can be made to work with the aerials below, you avoid IMO the most frequent reason for failure, damp or corrosion, which Nasa aerials are very prone to. By the same token we had a Raymarine dGPS fail through damp, so when we fitted a Navman 5600 the aerial/GPS for this was (after checking and comparing signal strengths over several days with an external GPS) also mounted in the dry down below. There is an added bonus for us in this too, because running cables to the antenna perch on our stern gantry meens a) standard cables are not long enough b) plugs have to be removed (or the cable cut/rejoined) in order to get through the conduits, most of which are already full, or gantry tubes, this is major bad language time.

BTW a friend told me at the weekend that his external NASA aerial had failed through corrosion and instead of buying a new one at around £50 bought a new pcb from Nasa for £9 or so and just had to swap them over and solder the new one in place. Marine gear that doesn't like damp is a pet hate of mine.
 

DaveS

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A shore power connection shouldn't of its self cause interference, so it's probably worth a little investigation. I discovered after fitting a Sterling battery charger that Navtex reception was almost completely blocked. Clipping ferrites to the charger's output wires fixed it fairly easily, though.
 
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