Can an SSB receiver pick up Navtex messages?

[DavidMcMullan]

I've rigged up a NASA HF3 SSB receiver on my boat with the aerial strapped alongside the backstay and the output connected to a laptop loaded with SeaTTY software.
Reception has not been particularily good, probably due the location of the aerial, but I have been able to pickup some weather charts.

Question 1: Should I be able to pickup Navtex broadcasts on 518kHz with this set-up? The software has an option for Navtex, but should I be able to pick it up with the HF3 & standard wire aerial?

Question 2: any SeaTTY experts out there, who I can PM with specific queries on correct set-up?

David.

 

[Oldhand]

The answer to question 1 is yes. However, an aerial "strapped alongside the backstay" is unlikely to work due to the influence of the backstay itself being a conductor. I am assuming from your description the aerial is insulated from the backstay and not connected to it. A long wire antenna needs to be as far away as possible from other metallic structure and you might have better results actually conncting your aerial wire to the backstay, even though the latter is not insulated from the mast and hull. However, assuming your hull is GRP or wood and the mast is not electrically bonded, water on the hull surface will change the hull's insulation properties and any movement or poor metallic conctacts in the rig will degrade reception for a number of reasons

That said, unless you are at a long range (60nm +) from the Navtex stations you wish to receive, any old bit of insulated wire located as far above water as possible and away from other wiring and metal structure should suffice. However, be aware that boat electronics often generate interference at Navtex frequencies, so if nothing is decoded try switching everything else off.

In respect to question 2, tune your receiver to 516.3kHz, USB. If Navtex mode is selected in the software, then you should get successful decoding. For 490kHz reception, tune the receiver to 488.3kHz USb.

 

[TigaWave]

I tried but never managed to get the navtex broadcasts, I also found that reception of rtty and weatherfax was far better once you were a few miles offshore, we had good clear reception all the way across the pond, but often found that in marinas we could only get interference.

We just had the wire on a coax to the transom, then wrapped up the backstay.

 

[PembrokeshirePromise]

I played with your exact setup just the other day. Remember your ground is just as important as your aerial.

I got fax and Navtex OK

I connected the aerial cable that came with the NASA box to metal straps in the cabin that attach to the metal rigging and the mast etc etc.

I attached the ground to a keel bolt (which I trust is still well embedded in my lead keel). Boat is GRP.

This instantly gave me better reception than I'd been getting messing around at home (which made me think presumably there is no earthing for lightening strike from mast to keel - but having read thread on here the other night I no longer know if thats a good or a bad thing /forums/images/graemlins/confused.gif!)

I was using the SeaTTY software and your welcome to PM me - not that I'd consider myself an expert - but had it working.

Best wishes
James

 

[alex_rogers]

I've used SeaTTY and and NASA HF3 SSB to recieve Navtex. I have a small active antenna on the masthead but have experimented with a wire antenna and it doesn't seem to make too much difference to Niton Navtex reception (I'm in Southampton).

I find that the sound of Navtex is less distinctive than weatherfax and it is a bit more problematic since you have longer to wait between transmissions. But once a transmission has started, you should be able to play with the tune and fine tune control until it receives okay.

 

[steverow]

Should be OK, but NASA do an active stubby antenna for about £35 which will probably be better.

As well as navtex you should be able to RX weather faxes.

Good software is the key here.

JVcomm32 is the best there is available, downloadable free from www.jvcomm.de
This is widely used in the radio amatuer world as well as commercial radio industry.
It wil do everything you will need it to do, and comes broadly set up with it's default parameters.


Steve.

 

[constajc]

I use the NASA SSB set with JVcomm32 with excellent results. The long wire antenna is coiled around the chain plate in the main saloon which in my case is a stainless rod and (electrically) connected to the shrouds. The long wire should not be directly connected, so take care to ensure the bare wire at its end does not make contact (small piece of insulating tape that can also double as the mechanical fixer to stop the coil unwinding). This means the signal picked up by the standing rig is inductively coupled to the antenna input of the set. As I say it works very well for me on both Navtex frequencies and for weather fax from Northwood and Germany. Hope this helps.