"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;