Originally Posted by Captain Bill
I'm looking at buying
a hand held VHF with GPS capability. The advice given by the FCC is that they should be programmed with the same MMSI as the primary radio, unless they are to be used often on other boats. Under normal circumstances I would want the hand held to have the same MMSI as the primary, since I want it to be the backup in case of a failure of the primary. I would also like to use it on the dinghy
. My question is what will happen if I send out a position request from the primary radio to the MMSI number that is programmed into the unit. Will the primary radio report its own position or will the hand held respond with its position? I can see that since reception
is inhibited during transmission
that if the primary radio just blindly sends out the request for a position from the inputed MMSI number the primary will never receive the request and the response will be from the hand held. However if the primary recognizes its own MMSI it may never send out the position request and simply report its own position. My experience is that marine electronics
are not overly smart and it will probably just transmit the position request. I figure that someone on this forum must have tried this by now. So has anyone tried this and what was the result?
I have done it.
I have a two Standard Horizon radios, a handheld HX-851 and a fixed mount GX-2150, both programmed with the same MMSI designating my boat.
I use the HX to test the fixed GX and vice versa.
When I initiate a position report from the handheld, it reports the GPS position that the HX receives and computes from its GPS fixes. I send it to my own call sign/MMSI. Since it is transmitting on CH70, it's not receiving on Ch70, but the fixed unit IS. It accepts the PR from the handheld and then sends the position to my chartplotter
and displays it as a waypoint with the handheld's MMSI (which is the same as the fixed unit's).
If you send a Position Report from the fixed unit to the handheld, the handheld will show the GPS fix from the chartplotter interface to your fixed mount radio.
If the fixed unit sends a Position Request, the handheld will respond with its own GPS position.
The fact that they share the same MMSI doesn't interfere with the handheld and fixed unit interaction, at least none that I've seen.
If I send a DSC Test message to, say, a Coast Guard MMSI, the acknowledge I get back will show up on both the handheld and on the fixed unit, assuming they are both in coverage. When the DSC Test addressee is far away, only the fixed unit will indicate receipt of the acknowledgement, since it has a lot more antenna
gain that the little rubber ducky antenna on the HX.
I'm the guy Eric is referring to on the Hull
Truth forum. I did think the fixed unit would relay a distress call from the handheld. If not, at least the handheld's GPS position can be shown on the chartplotter through a position report. I would also hope it would show through a distress alert, since distress alerts carry the position if the sender's got it set up right.
I'm disappointed to hear that the alert will not be relayed and will be digging in to understand that situation. Unfortunately, there is no way to test distress alerts that are not official distress alerts, so some things could be tested if that was allowed, but currently there is no provision to do that other than DSC Test.
I believe nearby boats will receive position info from the distress alert, since I have seen that myself on the only DSC distress alert I've ever received this past season. So while my handheld's distress alert appears that it won't be automagically forwarded, nearby boaters will receive the info and could relay it on CH16 by voice in a pinch.
Unfortunately, not many people know how to use DSC functionality, so that is far less reliable than auto-forwarding would be.