What is the difference between AIS and DSC? They seem very similar,
use VHF etc. Also, is it possible to test a VHF antenna for optimal
performance?

thanks,

Luc

"luc" wrote in message
oups.com...
What is the difference between AIS and DSC? They seem very similar,
use VHF etc. Also, is it possible to test a VHF antenna for optimal
performance?

thanks,

Luc


DSC and AIS are two different systems to meet two different needs. AIS lets
you track all the ships around you for collision avoidance and DSC lets you
"select" which ship to call on the radio.

Digital Selective Calling (DSC) is on marine VHF channel 70 (156.525 MHz)
Automatic Identification System (AIS) broadcasts are on two VHF marine
channels 87 (161.975 MHz) & channel 88 (162.025 MHz).

DSC also has a "panic button" feature that you can push and the radio
automatically broadcasts your GPS position and the fact that you have an
emergency.

Here are some web pages that further describe AIS and DSC

http://www.navcen.uscg.gov/marcomms/gmdss/dsc.htm
http://www.navcen.uscg.gov/enav/ais/default.htm

Here is a link to a popular AIS receiver:

http://www.nasamarine.com/AIS/AISENGINE.html

If you want to use the sound card to decode and display AIS data on your
laptop see this web page:

http://www.coaa.co.uk/shipplotter.htm

Here are a few more interesting links:

http://www.xmradio.com/weather/
http://www.xmradio.com/weather/av_subscription_pkg.pdf
http://www.garmin.com/products/gpsmap376c/
http://www.nasamarine.com/press/pdfs/sx35.PDF
http://www.nasamarine.com/press/pdfs/sx35pract.PDF
http://www.nasamarine.com/press/press.html
http://www.sailmag.com/05feellison.qrk.pdf
http://www.amcom.nl/marine/icom_ic_m421.htm

Re antenna performance: You can make sure that the power you send into the
cable actually end out in the air and not just being reflected to the radio.
To meassure this use a "SWR meter" that can be bought in any HAM shop for
approx 50 dollar (low end but quite OK to meassure a boat antenna).

Eksample: http://www.mfjenterprises.com/produc...rodid=MFJ-812B (maybe
to cheap, ask for advise in a shop or in a ham newsgroup)

Bjarke





"luc" wrote in message
oups.com...
What is the difference between AIS and DSC? They seem very similar,
use VHF etc. Also, is it possible to test a VHF antenna for optimal
performance?

thanks,

Luc

"luc" wrote in news:1144802036.593200.282480
@i39g2000cwa.googlegroups.com:

What is the difference between AIS and DSC? They seem very similar,

DSC is a digital communications mode that has never been implemented on
small boats because of its exhorbitant prices.

AIS is a navigation aid system that allows computers to communicate over
existing VHF marine radio channels to share position and other navigation
information.

The only thing they share is they are on the same frequency band, but not
the same channels. DSC is on 70, AIS is on 86 and 87A.


use VHF etc. Also, is it possible to test a VHF antenna for optimal
performance?



Yes, it's quite easy. I recommend the meter be permanently installed
next to the radio, if the radio is out of the weather and seawater spray.
The simplest, good working one is:
http://www.buyreliant.com/marine/accessories/art2.htm
it is also branded Valor V6050 and is the same meter. They are about
$40, sometimes cheaper if you hunt around Google. I picked this website
solely because its URL was short. Another website at $39 is:
http://www.walcottcb.com/product_inf...50-vhf-marine-
swr-power-watt-meter&cName=radio-accessories-meters
but you'll have to paste the two wordwrapped lines together to get the
whole address. That's the Valor to look for.

On the boat, simply attach two right-angle adapter connectors to the two
SO-239 jacks to route the RF back through the panel, surface mounting the
little meter next to the radio. Two 3/4" holes allow the PL-259 cable
connectors to connect to the adapters. You'll need a short jumper
between the meter and the radio.

Flip the switch to FWD (some say SET) and adjust the little control for a
full-scale reading while holding the mike keyed NOT ON CHANNEL 16 or 13,
PLEASE. Use a channel that's not loaded in your area near the middle of
the numbers. Flip the switch to REF (means reflected power back from the
antenna that's not transmitted). The perfect antenna will show no
reflected power, the meter won't move. The SWR calibrations from 1 (no
reflected power) to mid scale show the condition of the antenna on this
channel. Any readings under 2:1, which means about 10% reflected power,
are acceptable. No antenna is perfect, well, not many. Above 2:1, I'll
want to fix it. 3:1 is 25% reflected. There's a little black range of
"acceptable" SWR on the meter face.

Leave the meter inline and set to the POWER switch setting for normal
use. This lets you know, for sure, the radio is, in fact, transmitting
as the LCD or LED lights on the front of it are a total lie these days.
You'll see the 1W or 25W output. It also helps you to stop forgetting to
switch to high power when you're not near the dock.

The meter runs off the RF power, but uses a tiny fraction of a watt
you'll never miss. It never needs a battery. It has none. Someone
brought theirs to me to have its battery replaced a couple of months ago.
Puzzled, I asked why. "It stopped reading.", he told me. His radio
transmitter had a blown power amplifier IC....(c;

He was hoping, in vain, it was the meter....(c;

"Larry" wrote in message
...
"luc" wrote in news:1144802036.593200.282480
@i39g2000cwa.googlegroups.com:

What is the difference between AIS and DSC? They seem very similar,

DSC is a digital communications mode that has never been implemented on
small boats because of its exhorbitant prices.

What?

Here is a DSC equipped radio for $105 on Ebay

http://cgi.ebay.com/ebaymotors/ws/eB...=mem_guide%3A3

Here is a DSC radio at west marine for $159

http://www.westmarine.com/webapp/wcs...01/3001/0/3000


What is your idea of an "exorbitant" price????

Also, I am told that DSC is a digital CALLING mode only. The actual voice
conversation happens not on channel 70 but on a standard VHF marine analog
voice channel.



AIS is a navigation aid system that allows computers to communicate over
existing VHF marine radio channels to share position and other navigation
information.

The only thing they share is they are on the same frequency band, but not
the same channels. DSC is on 70, AIS is on 86 and 87A.


use VHF etc. Also, is it possible to test a VHF antenna for optimal
performance?



Yes, it's quite easy. I recommend the meter be permanently installed
next to the radio, if the radio is out of the weather and seawater spray.
The simplest, good working one is:
http://www.buyreliant.com/marine/accessories/art2.htm
it is also branded Valor V6050 and is the same meter. They are about
$40, sometimes cheaper if you hunt around Google. I picked this website
solely because its URL was short. Another website at $39 is:
http://www.walcottcb.com/product_inf...50-vhf-marine-
swr-power-watt-meter&cName=radio-accessories-meters
but you'll have to paste the two wordwrapped lines together to get the
whole address. That's the Valor to look for.

On the boat, simply attach two right-angle adapter connectors to the two
SO-239 jacks to route the RF back through the panel, surface mounting the
little meter next to the radio. Two 3/4" holes allow the PL-259 cable
connectors to connect to the adapters. You'll need a short jumper
between the meter and the radio.

Flip the switch to FWD (some say SET) and adjust the little control for a
full-scale reading while holding the mike keyed NOT ON CHANNEL 16 or 13,
PLEASE. Use a channel that's not loaded in your area near the middle of
the numbers. Flip the switch to REF (means reflected power back from the
antenna that's not transmitted). The perfect antenna will show no
reflected power, the meter won't move. The SWR calibrations from 1 (no
reflected power) to mid scale show the condition of the antenna on this
channel. Any readings under 2:1, which means about 10% reflected power,
are acceptable. No antenna is perfect, well, not many. Above 2:1, I'll
want to fix it. 3:1 is 25% reflected. There's a little black range of
"acceptable" SWR on the meter face.

Leave the meter inline and set to the POWER switch setting for normal
use. This lets you know, for sure, the radio is, in fact, transmitting
as the LCD or LED lights on the front of it are a total lie these days.
You'll see the 1W or 25W output. It also helps you to stop forgetting to
switch to high power when you're not near the dock.

The meter runs off the RF power, but uses a tiny fraction of a watt
you'll never miss. It never needs a battery. It has none. Someone
brought theirs to me to have its battery replaced a couple of months ago.
Puzzled, I asked why. "It stopped reading.", he told me. His radio
transmitter had a blown power amplifier IC....(c;

He was hoping, in vain, it was the meter....(c;

In article ,
Larry wrote:

The only thing they share is they are on the same frequency band, but not
the same channels. DSC is on 70, AIS is on 86 and 87A.

Actually, AIS uses the Duplex Receive Frequencies from Vhf Marine
Channels 86 and 87, as Simplex Transmit and Receive Channels......

Bruce in alaska
--
add a 2 before @

In article et,
"Ted" wrote:

What?

Here is a DSC equipped radio for $105 on Ebay

http://cgi.ebay.com/ebaymotors/ws/eB...tegory=31275&i
tem=4582047129&sspagename=mem_guide%3A3

Here is a DSC radio at west marine for $159

http://www.westmarine.com/webapp/wcs...1/-1/10001/148
723/10001/3001/0/3000


What is your idea of an "exorbitant" price????

Also, I am told that DSC is a digital CALLING mode only. The actual voice
conversation happens not on channel 70 but on a standard VHF marine analog
voice channel.

Tom, Larry is talking about the "Totalitly" of DSC, not the very small
Subset, of DSC that is implimented in the radio's you are tallking about.
I would guess that if you were to research the cost of a Full Blown Class
A DSC VHF Radio System, you would consider the price involved,
"exorbitant", in the extreme. What you have been "told" is a very
small subset of the DSC capabilites that were designed into this
antiquated 1980's technology foisted on the ITU/IMO by the Europeans.

Bruce in alaska
--
add a 2 before @

Bruce in Alaska wrote in news:bruceg-
:

Tom, Larry is talking about the "Totalitly" of DSC, not the very small
Subset, of DSC that is implimented in the radio's you are tallking about.
I would guess that if you were to research the cost of a Full Blown Class
A DSC VHF Radio System, you would consider the price involved,
"exorbitant", in the extreme. What you have been "told" is a very
small subset of the DSC capabilites that were designed into this
antiquated 1980's technology foisted on the ITU/IMO by the Europeans.

Bruce in alaska
-

Gotta see one work to see what it can do, Tom....(c;

Just calling one station you key in manually or for help isn't DSC...or
GMDSS...

AIS here in Brazil uses channels 87 and 88, not 86 and 87.

The frequency os AIS can change at every country?



Bruce in Alaska escreveu:

In article ,
Larry wrote:

The only thing they share is they are on the same frequency band, but not
the same channels. DSC is on 70, AIS is on 86 and 87A.

Actually, AIS uses the Duplex Receive Frequencies from Vhf Marine
Channels 86 and 87, as Simplex Transmit and Receive Channels......

Bruce in alaska
--
add a 2 before @

"Pascal" wrote in news:1145139514.303678.7110
@u72g2000cwu.googlegroups.com:

The frequency os AIS can change at every country?



No, it's the same. My mistake. In the USA, one of the channels was a
duplex pair used by the old marine telephone operators so its either 87a or
88a, I forget which, which designates it as a simplex frequency (one
frequency transmit and receive so AIS will work). The whole VHF bandplan
across the planet is stupidly laid out and way out of date...