Navtex reception

[ParaHandy]

Just tested (prior to fitting) a Nasa HF3M with shareware Navtex de-coder. It picks up Niton with no apparent errors on 518khz at +100miles range with 30' wire aerial and will be fitted to the boat with an active (stub type, not whip) aerial. The HF3 picks up Northwood's weatherfax transmissions OK and in early evening can decode Offenbach RTTY weather reports (but not Offenbach's weatherfax, yet).

It's good stuff the HF3 - won the IEEE medal and the Institute don't hand their gongs out readily.

Could any of you, please, who have fitted a Navtex receiver let me know if they can pick up Corsen or Oostende transmitters in the Solent area and, particularly, the aerial type and position and whether they grounded it to the anode (and has their propellor halved in size!)? I have heard and read many reports about how critical aerial position and grounding is and anybody who's picking up these stations must have a decent installation but, equally, anybody else's experience would be helpful.

 

[steve_cronin]

You will get sick....

... of Ostend messages in the Solent. They are to say the least "prolific". We had a Navtex on out last two boats right from 1984 and had no problems with Niton or Ostend with the active antenna in a saloon locker. Later with it on the taffrail we got Corsen occasionally and of course all the time when in Brittany waters. Well that is not quite true. I remember the summers of 1999 & 2000 when the jamming from the French military in the Rade de Brest made it indecipherable as it did Radio4.

I am a fan of Navtex and am fitting a Nasa Clipper to the new boat out in Greece in a few weeks time. I prefer NASA's as you don't need to mess around with damp paper although I conceed that having hourly position printouts is a plus with the IC3 etc.

Steve Cronin

 

[ParaHandy]

I\'m a fan of Nasa....

as well. They seem to be v. good and British. Agree about paper and IC3 - bound to run out just when you need it.

Did shifting the aerial out of the locker onto the stern rail cause reception to deteriorate and can you recall where it was earthed?

Many thanks.

 

[steve_cronin]

Re: I\'m a fan of Nasa....

No it improved things a lot. Less asterisks as the NASA LCD (& old Video) navtex sets have programmed into them to show doubtful characters. The new sets didn't require an earth but the old video set was earthed to a convenient skin fitting until i later fitted an earth stud because the (then) early first GPS i bought needed one and I was starting to get concerned about creating a galvanic cell.

Are you using a laptop for a display?

Steve Cronin

 

[ParaHandy]

Laptop

Yes, ancient Compaq Contura which runs Windows 3.1 but all weather software runs under DOS. Quite happy with that.

Tried "modern" laptop (Dell) but it didn't get hold of the serial port when in DOS mode. Could have got Nasa HF3P (with audio output - HF3M has demodulator to generate mark-space as digital RS232 o/p) which requires a computer with sound card (or decent digital signal processor) which would run under Windows 98 etc. However wasn't prepared to risk DSP on Dell not working and software is v. expensive - as is the Dell to leave on a boat.

 

[ParaHandy]

Re: Laptop

I had another reason for using that laptop - the AC charger generates max +16v which might mean that the boat's 12v could be sufficient.

Otherwise, modern laptops have 3 pin chargers which I assume require two DC voltage levels and, probably, need the expense (and power loss) of a DC-AC convertor to keep it running.

 

[extravert]

I fitted a Nasa Navtex for a trip round Britain last summer, and it picked up all the stations you mentioned, and a whole load others too. The installation was just following the manual, there was no ground other than the negative power supply. Reception of the nearest station was nearly always good, better out at sea than in docks and harbours. Strangely we couldn't get any reception in Portpatrick harbour at low tide, despite being only half a mile from the transmitter, must have been the high dock walls. I tried to persuade a crew member to run up the hill to get a forecast directly from the man in the shed typing it in, but he didn't fall for it.

The time of the transmissions is not always spot on, you have to wait a minute or two sometimes, making you think it's not working. If the stations are a long way off sometimes the text comes through a bit garbled, up near Cape Wrath we had drozzle forecast (which came too), so for the rest of the trip any rain was called drozzle.

The best use I got from it was the inshore waters and 5 day forecast, which is much more useful than radio 4's now much reduced marine weather broadcasting.

 

[Bergman]

Probably the best improvement you could make would be to the aerial.

Don't know your arrangement but 30ft is a long way short of a resonant aerial on 518kc/s.

Some sort of tuning unit would help. I believe Maplins do one specifically for Medium wave which would probably meet your needs.

The aerial itself will benefit if you can get a horizontal section in it, particularly after dark.

As for earthing - apply the earth to the tuning unit if you try one, otherwise apply to receiver. There should not be a problem with electrolysis, but if you are concerned get hold of a 1000pf mica capacitor and connect it between the receiver and earth. Not particularly good practice but it will break any DC path.

Hope this helps

Best of luck

 

[steve_cronin]

I think...

you might have just given a new lease of life to my old 486 laptop!!

Steve Cronin

 

[alex_rogers]

I have a Furuno NX300 Navtex receiver which picks up Corsen perfectly in the Solent but has problems with Niton!

My HF3M radio has a mast head active antenna and picks up Northwood weatherfax very well. I made a small circuit to convert the signals from the HF3M serial port level ( just a capacitor and a couple of resistors ) and enable it to be plugged into the line input of the sound card. The difference in weatherfax quality compared to using the serial input is enourmous.