Insulated Back Stay

[rrees]

I am looking to recieve Weather form the German Transmissions on SW
I have looked at the Weatherman system and Nasa say the reception would be better with an insulated back stay that the active antenna
The boat is a GRP do I need to install an insulator or could I connect directly up to one of the back Stays as I will not be transmitting and will not need to tune the Antenna length.
I am dropping the mast this winter so it would be an ideal time to modify one of the Back Stays

 

[Talbot]

For the extra money that this will cost, I would be looking for comments on the ability of the active antenna to do the job in the area you want to cruise.

 

[shmoo]

If the chainplate at the bottom is not connected to anything there is the possiblity of running as a loop: up the backstay, down the mast with a wire from the base of the mast back to the set earth side of the input. Could be noisy since connection at top of backstay to mast is not optimised for electrical contact.

But insulated backstay or loop I suspect your biggest problem will be getting the signal back to the set. Without a tuner you have no real idea of what impeadance the aerial is presenting to the feeder cable which means that you may a) lose a lot of signal through mismatch and b) if the feeder runs through an electrically noisy area (such as the nav station or near NMEA cables) it will pick up noise.

At least the active antenna will be properly matched to the feed cable even if it pulls down less signal because its smaller.

(My experience of DWD is limited to use with a transeiver and a tuner at the base of an insulated backstay with earth radials which, needless to say works just fine)

Regards
Peter

 

[TigaWave]

Before you start spending try with just the wire antenae wrapped around the backstay.

I've found the Target HF3 had good reception with coax run to the transom then the bit of wire supplied with the set wrapped up the backstay, I could get weather fax and rtty from one side of the Atlantic to the other, and very good reception from UK to Canaries. But it wont work in harbour with interference from a mains charger running.

 

[jerryat]

Agree with Tigawave. Try the simple things first! It is probable that you'll get perfectly adequate reception for what you need. IMHO, the active antenae are substantially a waste of money.

We tried one for a couple of years but, as we'd been advised before we fitted it (and ignored!) whilst the aerial will boost the signal you're after, it also of course, boosts the extraneous 'noise' you DON'T want. Frankly, even with high quality kit (Lowe 150 receiver etc) the result was very poor.

In the end, and also because we were changing to a transceiver, we put Norseman insulators on the backstay. Expensive but perfect!!

However, do try the simple form first, it works more often than fails!

 

[shmoo]

I am interested in the experiences of you folks who have used a "length of wire" round the backstay for HF reception. It seems to have worked for you. What about noise? If as in most cases the RX is mounted in or near the nav station then the route out to the open is through a pretty noisy environment. Did you have to turn all the instruments, computer, NMEA senders etc off to get a clean signal? Or did you get enough signal to rise above that stuff? What did you do about earth/counterpoise?

Certainly a sailing boat, sailing, with all its electrics shut down and way out to sea is a wonderful quiet platform for HF reception but that situation is something of an exception, isn't it?

I'm not trying to start an argument: I've never tried what you suggest. I would just like a slightly fuller understanding of your experiences.

Regards
Peter

 

[Benbow]

I too agree that running a wire up the backstay is likely to work perfectly well for receive only. However, on a GRP boat I think it is unlikely to be any different from simply taking a wire to the base of the backstay. This is because the insulation on a wire wrapped around a backstay is invisible to radio frequencies. In effect your entire rig becomes the antenna and this may be why results are unpredictable.

If I was dropping the mast anyway I would fit insulators top and bottom of the backstay. That way you also have the option of moving to a transmitter later.

As for radio noise on the feeder, suck it and see. There should not be too much noise from your electronics, it's motors like fridge compresssors and gennies that will cause grief. If you do get noise, a simple ferrite or two can be very effective.

HTH

 

[jerryat]

Hi shmoo and Benbow!

I only tried the direct connect with a bit of wire to the backstay (not run up it) using co-ax centre core only. Whilst reception was 'irregular' it did work. Part of the problem was, as has been mentioned, the effect that connecting to the overall rig has in different conditons. For example, when it rained it was worse and sometime the boats heading had an effect. Running the instruments/engine made no discernable difference, though using the laptop with the charger running via an inverter wiped out reception. The latter happens whatever system you use though.

The inconsistancy was the reason we then changed to an active aerial.

In our experience, the AA wasn't a much of an improvement (hence my comments earlier) since it too had a very variable performance, the worst being the amplified 'noise' that often drowned out the signal we were really after and often made fax reception impossible.

We stuck it for a couple of years, but seeing/hearing the results our cruising friends were getting with a properly insulated backstay, we swallowed hard and went that route about 9 years ago. Excellent results and total consistancy, but at a cost then of about £75.00 per insulator (though we fitted them ourselves) it's a hell of a chunk of money.

Worth every penny though, because we were than doing transats and wanted an SSB tranceiver.

I suspect we are basically staring at the same songsheet - try a connection the bottom of the backstay, try a wire wound up it, or fit insulators. Personnally I wouldn't recommend the AA route (though this might be better if it's sited at the masthead rather than the pushpit as in our case) as you can buy an insulator for the cost, so are halfway to the best solution already!

 

[rrees]

Thanks all have a lot to think about
I was looking for an alternate backup to Mobile Data / Inmarsat connection for internet forcasts in case I have a problem with these.

 

[Oldhand]

The isulated backstay should have a balun (balanced to unbalanced transformer) at its feed point and the connection to the the receiver is then made with impedence matched co-axial cable. The latter provides a screened feed through the boat.

 

[Sailorbuoy]

Forget the 'balun' I have my antenna permantly connected to the backstay of a 35' plastic insulator (and a good earth to the keel) I get very good signal reports from Med to UK and have 'worked' Japan two way on 5 Wats power. Rtty on your receiver no problem. Some help and schedules on www.walterreed.co.uk