vhf radio

[willk]

Originally Posted by SPR

Only the colours /colors, the shapes are the same...

S.

D@mn! You cunningly neutralised/neutralized my intended riposte regarding spelling

[smiffysteve]

it all makes sense now

[jyasaki]

Originally Posted by Rokraider

It has a guideline range of 1 mile per watt, depending on how high the antenna is, so I could reasonably expect a range of 25 miles with my setup.

I'd be suspect of your expectations. Unless you're on a ship, or some other vessel that puts the antenna way, way above the waterline, you're probably looking at something more like 7 to 10 miles max on a good day, when communicating with another small craft.

jky

[smiffysteve]

with an antenna on the top of a 30ft mast surley 25 miles should be achievable

[Salty John]

Range in nautical miles equals 1.4 times root of the height of the transmitting antenna plus the root of the height of the receiving antenna. Heights in feet.
If your antenna is at 30' and the other boat has an antenna at 6' the range is just over 11 miles.
If the other boat has an antenna also at 30', the range is just over 15 miles.

You need at least one of the antennas to be really high to get 25 miles, fortunately Coast Guard stations are located very high above sea level.

[smiffysteve]

so does that equation apply to the way dsc works too?

[Pikey Dave]

I have had clear comms with Solent coastguard from Grandcamp-Maisy in France, about 90nm. Probably due to the quality & height of the coastguards kit than ours.

[Pikey Dave]

Originally Posted by smiffysteve

so does that equation apply to the way dsc works too?

Yup! dsc uses the VHF band, iirc channel 70, but it only transmits at 2w, not the 25w of full power vhf, so that's also a consideration.

[smiffysteve]

so as previously discussed if you have a series of boats using dsc over a 30mile distance,say 10 boats 3 miles apart will that not get 30mile using the others as a repeater

[Salty John]

Originally Posted by Pikey Dave

I have had clear comms with Solent coastguard from Grandcamp-Maisy in France, about 90nm. Probably due to the quality & height of the coastguards kit than ours.

There's a phenomenon known as tropospheric ducting that allows huge distances, but you can't rely on it. I think the record is about 600 miles!

[smiffysteve]

that must get carried by some other frequency or somthing to travel that far

[Salty John]

Originally Posted by smiffysteve

so does that equation apply to the way dsc works too?

Yes. The digital signal actually has slightly more range than the analog voice signal, about 15% or so.

[Salty John]

Originally Posted by smiffysteve

that must get carried by some other frequency or somthing to travel that far

This occurs in certain atmospheric conditions - when there is a high pressure system in place and there is little wind. The radio signal gets trapped below a certain altitude, about 1000' if I remember correctly, and this allows it to travel further. It involves temperature inversions and super-refraction - gobbledegook to most people, including me.

[smiffysteve]

so basicly the same as an am signal using the ionisphere to bounce off,i believe charged from particles that have been discharged by solar flars from the sun? thus carrying it further,

[Pikey Dave]

Originally Posted by smiffysteve

so as previously discussed if you have a series of boats using dsc over a 30mile distance,say 10 boats 3 miles apart will that not get 30mile using the others as a repeater

Class D dsc sets can't relay messages

[martini]

Originally Posted by Pikey Dave

Yup! dsc uses the VHF band,... but it only transmits at 2w

I can't argue this as I don't have any evidence to the contrary but I've never heard this before and it sounds extremely daft IMHO

[Pikey Dave]

Originally Posted by martini

I can't argue this as I don't have any evidence to the contrary but I've never heard this before and it sounds extremely daft IMHO

I might be getting confused with AIS which is 2W, so I'm willing to stand corrected

[martini]

Originally Posted by Pikey Dave

I might be getting confused with AIS which is 2W, so I'm willing to stand corrected

Originally Posted by Wiki

To prevent overloading of the available bandwidth, transmission power is restricted to 2 W, giving a range of about 5–10 mi.

Consider yourself corrected

[Pikey Dave]

Originally Posted by martini

Consider yourself corrected

See, you CAN educate pork after all

[Copinsay]

Hello

From my recent experience I'd certainly go for DSC unit if you can.

The point above about the DSC data signal going further seems very true here, where we have patchy VHF coverage due to cliffs and a fragmented pattern of islands.

I've just set up the DSC unit on my RIB and the DSC signal got through to both Aberdeen and Shetland coastguards 100% even in places where my voice signal was weak.

In an emergency, that DSC distress data packet (complete with the GPS locational data from the chart plotter) could I'm sure be a life saver, especially as all you need is that long press of the red button, even where a voice signal may be unreadable. Plus if I came to grief, it's great to know there's such an easy way for crew to call for help too when they may be flustered.

Plus the DSC "test call" function is a really quick and easy way to be reassured that the system is working in a discreet way.

Of course, it depends where you are, but I'm sure pleased I went for a DSC unit.

Hope this helps

Steve