navtex wiring connection problem

[duke]

Hi,

recently purchase Nasa clipper navtex.

I cut the cable plug approx. 1 metre from inner end to feed the cable through bulkheads and then hopefully reconnect at the chart table.

The antenna aeriel cable is approx. 10 metres long -- 75 ohm coaxial.

However the cable supplied with the Nasa clipper navtex is smaller in diameter than standard 75 ohm cable ( clipper navtex cable diameter is more like satellite dish cable).
Also the central wire is "stranded" rather than a single solid wire.

I'm finding it impossibe to get a good rejoin of this cable.

Cant find a connector to join this cable - the "stranded" central core is very fragile and breaks very easily.

I've tried using a " satellite cable connecting kit' but this is designed for use with a single( solid wire) central core and the "stranded" core won't push into it and just breaks.

Has anyone had a similar problem and any suggestions as to solution.

Am seriously thinking of purchasing new antenna and drilling bigger holes in bulkheads to accomodate cable plug and avoid cutting it.

Regards,

Duke.

 

[wotayottie]

sounds as if the navtex has decent quality RF cable which likely will be 50 ohm not 70. you will need to buy some connectors like the PL259 and solder the wire to the connectors. maplins can supply all you need. rg58 cable 2 x PL 259 male plugs, and a female joining plug ( http://www.maplin.co.uk/Module.aspx?TabID=1&DOY=9m7&ModuleNo=1638&criteria=) looks like the right one but I'm not sure.

any doubt, call nasa - very helpful.

 

[mikejames]

I wouldnt use big heavy connectors like pl259 on thin cable.

How about using Phono connectors, a male and inline female as these should be compatible with the 75 ohm/ audio type of coax used.

Or soldered TV aerial connectors (some have screw terminals in which case you solder 'tin' the stranded inner core to make it a bit stiffer.

Navtex is not very high frequency. In fact twisting the wire ends together and soldering them will work, provided you dont short the inner to the outer. Best to twist and solder inner, wrap in a couple of layers of PVC tape. then twist and solder the outers and then wrap the whole lot in tape


Buy a rope cutting/soldering gas iron or a 12 volt soldering iron so you dont need mains power (although a soldering iron will work off an inverter )

If you cannot manage to succesfully join the ends find someone who can do it and give them a sail or a few pints to come aboard and do it.

 

[Greenwichman]

Hello - just been through similar hoops because the distance between antenna and unit was greater than length of wire supplied. After some very delicate (sharp knife) trimming of insulation, and following precisely the instructions that came with the coax connector, I managed to fit two plugs and an interconnector. It helped to cut the centre strand longer than necessary and bend it back and twist it on itself. NAVTEX works well and I especially appreciate having the dual frequency capability. Good luck. /forums/images/graemlins/smile.gif

 

[duke]

Hi Greenwichman,

I see you used coaxial connectors. I understand these would be standard TV cable connectors.
Did you find any problem due to the diameter of the navtex cable being smaller than standard TV cable?

Regards,

Duke.

 

[DaveS]

This is a delayed reply since I lost my internet connection last night, so some of this has been covered by others, however...

If this joint is not to be dismantled then I think, before buying any more bits, I would at least have a try with a low tech solution. Strip back the outer sheaths and tease back / twist together each screen. Carefully trim back a few mm of dielectric (inner insulation). Solder together the cores. Wrap the soldered core with insulating tape, building up to the original dielectric diameter and with a layer of tape overlapping the dielectric by about 10 mm at each end. Solder together the screen wires, using a bit of bare, stranded wire to bridge the gap if necessary. Wrap a couple of turns of aluminium kitchen foil over the soldered screen wires to restore a continuous screen, and give it a squeeze to "fix" its shape. Wrap insulating tape over all, overlapping the undisturbed sheath by about 30 mm at each end.

After a few years the tape might go a bit sticky...

 

[lw395]

Navtex operates at around 500kHz, and the NASA receiver has the front end built into the 'active' antenna. Therefore you don't need to worry about good coaxial connections, apart from perhaps screening from interference.
My NASA navtex is 2ch version, this has a third wire to the antenna, where the channel switching is done. I assume the others are similar.
By the way worst source of Navtex interference is mobile phone charger imho.
Hope that helps,
Chris