Usefullness of Second Receiving SSB Antenna

[ka4wja]

Wow, such a heated discussion for such a simple question.....
Perhaps I can add some clarity and answer RDW's (the original poster's) questions....

1) First off, in addition to 35+ years in HF radio and communications (both maritime and ham, on-board and on-shore), I've owned/operated an M-802 on board my vessel for 6+ years now.....and I HAVE used its DSC functions, quite a bit....

2) Secondly, Eric's info is accurate....


3) Third, it is not my intent here to write a treatise on the M-802's operation, but since the M-802 manual is pretty crappy, and since there seems to be so much mis-information out there, I'm going to try to cut through the BS, and give you the straight scoop...

For clarification, the M-802 has built-in to it, a separate, dedicated, DSC receiver which (as long as the M-802 is switched ON) is CONTINUOUSLY monitoring all 6 Int'l GMDSS Mf/HF DSC freqs.....
(2187.5, 4207.5, 6312, 8414.5, 12577, and 16804.5 Khz)
No matter what mode or freq is selected on the M-802, it's dedicated DSC receiver IS constantly monitoring these freqs, completely independent from the "Main Transmitter/Receiver", and "in the background".....meaning that you have NO idication that this is actually going on, but it IS.....

From the M-802 manual:

•

Monitoring the frequencies, 2187.5, 4207.5, 6312.0,

8414.5, 12577.0 and 16084.5 kHz, for distress, urgency,
etc., no operation is necessary with the transceiver.

These frequencies are monitored at all times.

{Please understand that this is NOT the "DSC Watch Mode", which use the "main receiver" to "scan" 6 DIFFERENT MF/HF DSC freqs, searching for "routine" / "individual" / "group" messages, etc.....unfortunately, you, the average cruising sailor, probably has nobody sending them any of these messages, so the "DSC Watch Mode" is unlilely to be used by those here on this forum....but some (like myself) might find it useful / fun to "call" another vessel (you MUST have their MMSI number), or wait for a call from another vessel, without listening to static or scanning a few different freqs trying to find the best freq for the propagtion of the moment...sort of like a poor man's ALE....}

This separate, independent, dedicated DSC receiver does NOT use the main antenna, but rather is only connected to the "DSC Antenna" jack on the rear panel of the M-802's main unit......

The DSC messages sent on these freqs are NOT just "Distress", but rather ARE a combination of "Distress", "Urgency" ("Pan Pan"), or "Safety" ("Sec-ur-itay") and "Distress Relay" messages......and, some "routine" (position requests, etc.) calls, although these "routine" calls should not normally be on these 6 exclusive Int'l GMDSS DSC freqs, it has been my experience that they ARE.....

So, if you do wish to receive any DSC messages on these freqs, then a separate antenna is "required"......
But, if you have no desire to receive any DSC message on these freqs, then a separate antenna is "not required"....

As you can see, the answer to the "requirement question", depends on what you want to do with the M-802.....

{If you wish my opinion here.....I DO think it IS a requirement, since I cannot think of a reason one would buy/install an M-802 and not wish to fully utilize the MF/HF DSC fuctions.....but, that is my opinion.....to form your own, please read the above factual info and decide for yourself.....}



4) As for RDW's questions.....

Originally Posted by RDW

I am new to all. I have an Icim 802 that I am just learning. From my reading and talking, I think that you can attach a second antenna to the receiver. It would function as a alternate or second DSC receiver antenna, allowing the radio to receive DSC messages and/or distress messages while doing other receiving and transmitting functions.

a) For the details, see info above....

b) Yes, the "second" antenna that you're querying about, IS for receiving DSC messages.....and an effective HF antenna, mounted in the clear IS important for optimal DSC operation....
But, this is NOT an "alternative" or "second" DSC antenna, it is THE DSC Receive Antennna.....
(the "main antenna" is NOT connected to the DSC receiver, and does NOT allow for any receiving on the 6 Int'l GMDSS MF/HF DSC freqs...)

c) Although, because of the reduced bandwidth of DSC (100-baud SITOR) compared to SSB (voice), there is a theoretical S/N advantage of about 15db (500hz vs. 2500hz bandwidth), this doesn't always show-up in the "real world", so while using a lesser-efficient / lesser-effective antenna for DSC-reception, compared to your "main antenna", will work....using a very-inefficient antenna, will provide you with only marginal DSC reception....

Originally Posted by RDW

I have also been told that this can be a simple 6-8 foot wire run horizonally in side the hull of my fibergalass boat and soldered to a pl259 conector and then connected to the second antennae connection on the receiver.

d) Whoa, Nelly!!!
This is where you need to heed some learned and experienced advice....
While this DSC antenna does NOT need to be a "purpose built" antenna, and it can be a whip, stay, or random wire, etc....
It cannot be a "6' - 8' wire run horizontally inside the hull of your boat", unless you want a ineffective antenna and one that receives lots of internally generated noise.....

For a few months, > 6 years ago, I tried the Mertz antenna myself.....and while it worked, I did not find it very effective.....and since then, I've been using an insulated lower shroud for the past 6 years as my DSC Receive antenna....
It is about 23' from chain-plate / feed-point, to the insulator.....it's fed with coax....center cond. to chain-plate....and shield to a 3" wide copper strap, run to a keel-bolt, about 8' - 10' away....
And, it works GREAT!!!!
DSC-test calls are ACK qiuckly, and I regularly receive DSC calls, etc....

You'll notice that my insulated shroud DSC antenna is coax-fed ....which means that the "antenna" is the shroud, not the wire (coax) running to it.....
And, the Mertz "DSC antenna" (49" whip) is also coax-fed, and therefore it's whip is the antenna, not the wire (coax) running to it....

If you were to simply run a short wire inside your boat, and plug it into the M-802's DSC antenna jack, it woiuld receive something, but it would NOT be very effective, and the odds are slim that you'd ever receive any DSC messages with it.....
Sort-of like using a short telesopic whip on a portable HF receiver inside the cabin of your boat.....not very effective....
(And, in addition to the low signal strengths, etc. you'd also have a much higher liklihood of receiving lots of RF noise from other on-board systems, further reducing your DSC received S/N ratios.....the worst of all possibilities...)

Originally Posted by RDW

Any comments on the usefullness of doing this set up?

e) Usefulness of MF/HF DSC??
Remember DSC is part of the GMDSS system.....and is very effective....

{Yes, "Sat C" / INMARSAT C terminals are also part of the GMDSS system, but they're pricey......and for SOLAS / "required vessels", VHF-DSC is required for Sea Area A-1, MF-DSC (2187.5khz) is required for Sea Area A-2, and for high latitude areas (Sea Area A-4) where INMARSAT practicality / usefullness / coverage isn't good, or non-existant, HF-DSC is required......so, having a highly-effective MF/HF-DSC system (and antenna) installed on a cruising sailboat is very viable and useful!!!}

And, although I'm in the minority here-abouts, I think it can be very useful!!!!
For "Distress" situations, sending out a "Distress" DSC call will most likely get you a response from vessels in your area!!!!
{IMO/GMDSS regualtions state that all required vessels (SOLAS, etc.) must maintain a continuous watch on 2187.5khz, 8414.5khz, and "one other GMDSS DSC frequency".......}
While many US-based cruisers see "Distrees" DSC signaling as just a way to get in-touch with the USCG (while you're getting your ditch-bag, fire extinguishers. liferaft, EPIRB, etc.)......
BUT, please remember that the "G" in GMDSS stands for "Global", and that MF/HF-DSC is international and a very important part of the GMDSS system.....
And, if you're in need to assistance, and there are vessels within a few hundred miles of you, that IS who's going to be coming to your recuse first.....and quite possibly the ONLY assistance you're going to get....
Yeah, if you're a couple hundred miles into your passage from the US to the BVI, etc. AND you're within range of a USCG helo, then you may get a visit from them....
But, in most situations, you're more likely going to get assistance from a merchant vessel IN YOUR AREA.....
If you're lucky they may be < 20 miles away, and your VHF-DSC signal would be useful, but don't count on anyone being that close....and that's what the MF/HF-DSC system is for!!!!



5) Although, it wasn't really asked.....you may be wondering how effective is HF-DSC in the real world????

a) First, off, let me give you my personal observations, from on-board my boat, with my M-802......
I quite regularly receive HF-DSC messages.....

Typically I get an "All-Ships" call, almost everytime I've had the M-802 turned on for more than an hour or so.....(in order of regularity, on 8414.5khz, 12577khz/2187.5khz)
{My most recent experiences, from just last week:
I was on-board 3 times, over 3 days.....and only had the M-802 turned-on for about an hour or so each day.....tied to the dock
And, each day, I received one "All ships" call.....
One on 8mhz from a ship in the Gulf of Mexico, one on 8mhz from a ship near Port of Spain Trinidad, and one on 12mhz from a ship in the Med....
I'm in south Florida, and my DSC receive antenna is my 23' insulated lower shroud...
The 12mhz call from the ship in the Med was bizarre, as they spec'd 12577khz as their "traffic freq" (but that is the DSC freq), and after monitoring 12290khz for > 5minutes heard nothing.....so, I suspect an inexperienced operator, and/or a new install under going testing/commissioning....}

And, occassionally I get "Distress Relay" calls (almost always on 2187.5khz).....


b) If you wish to evaluate your own DSC-Receive antenna, do NOT start trying DSC-Test Calls....but, rather try a few easy tests WITHOUT transmitting.....

Using your "main antenna" and "main receiver", listen to some empty / clear channels in the 2, 4, 6, 8, 12, and 16mhz marine channels (preferably the exact GMDSS freqs) in USB (SSB) mode....and observe whatever noise-level you have....
Then un-plug the "main antenna" coax from the back of the M-802, and plug-in your DSC antenna coax into the "main receiver" jack.....and observe what noise-level you have.....(hopefully the same or lower)

If you find lower noise levels, that's great....if you find higher noise levels, you're going to need to check the coax run and its location, possibility of adding a balun and additional grounding, etc. and/or relocating of the DSC antenna.....


Then, after plugging your "main antenna" back into the "main antenna" jack, tune into some active HF frequencies on as many bands as you can.....(such as USCG / WLO weather broadcasts, ham radio nets, etc.)....and observe your received signal strengths AND readability....
(The READABILITY is the most important part)
Then, change over to your DSC-receive antenna again, and observe your received signal strengths and readability, on those same broadcasts, etc....

If you find similar (or slightly lower) signal levels, and similar (or just slightly lower) readability of signals, then your DSC-Receive antenna is pretty good, and should be effective.....
If you find poor signal levels, or more importantly poor readability, then you're going to find your DSC-receive antenna to be less effective than desired....




6) RDW, I do hope that in addition to answering your questions directly, I was able to put into context the factual info that you can use to make your own decisions.....


Fair winds....

John
s/v Annie Laurie

[barnakiel]

We use just a length of coated wire along say again along the mast and no problem receiving whatsoever. Now we got ourselves an active antenna yet to be tried out.

Offshore. In the marina something (the other masts, the shore?) make the remote signals all but disappear or very noisy though.

b.

[ka4wja]

Originally Posted by RDW

It is my understanding that if you do not have a DSC receiving antenna and do a distress call, if another party contacts you buy voice (there by occupying your send and receive functions) you will be unable to monitor and receive information that the Coast Guard might send, i.e. acknowledgement.
Is that not correct?
rdw

RDW,
I just now saw your further questions....
Please read over my earlier post for the details....

But, in a nutshell, if you do NOT have a DSC-receive antenna:
a) you're NOT going to receive any ACK (acknowledgement) of your DSC-Distress Call.....no matter what channel / freq, no matter how you've got your M-802 configured.....
You're just NOT going to get an acknowledgement.....
b) and, therefore, you will need to manually switch your M-802 to a voice channel...
c) and, then, you would need to know what channel to switch to, to contact someone.....whether they be someone who received your DSC-Distress call or not...
d) this has NOTHING to do with "occupying your send and receive functions", since the M-802's built-in DSC-receiver is separate and NOT connected to the "main transmitter/main receiver", nor "main antenna"....


I've been doing all of this for a LONG time (35+ years).....and I've even taught Icom techs more than a few things over the years....
And, I've got 6+ years experience with my own M-802 (and ist DSC functions) across the Atlantic twice, in the Med, Carribean, Bahamas, Florida, etc.....
So, I hope that my thoughts will be taken seriously....

I'm not arguing opinions on antennas, etc....just telling you how the M-802 operates, and what my experiences have been...


Fair winds...

John
s/v Annie Laurie


P.S. PLEASE take one important piece of advice.....
Please do NOT start sending DSC messages / DSC Calls out there into the air, just to "see what works", etc. or to evalute things.....
Please use the tests I outlined in my earlier post.....
Those that go around sending unnecessary messages on these Int'l GMDSS - DSC freqs, clog-up the freqs and can distrupt important / Distress messages....
PLEASE, PLEASE, heed this advice....

[RDW]

Thanks again for all the information. Your idea about testing your DSC antenna by alternating with the main back stay antenna is an excellent way to see how well the DSC antenna is working. I will do the test and follow your advice on not sending test distress messages.

As far as your set up is concerned, can you tell me more. I may very well want to set my boat up just like yours. I have a 46 foot Morris sloop. When you say insulated shroud, is this insulated like a back stay antenna is or is most any shroud already insulated, i.e. would I have to modify my shroud or can I use it as it stands? Also exactly how did you connect to your chainplate? My goal is to do some major off shore cruising so I am trying to learn as much as possible and to be fairly self sufficient. Is this something the average person can do or do I need professional help? If the shrould does not need to be modified, the most skill would maybe be making good connections with the coax, chainplate and cooper ground.

I am interested in your thoughts and thanks again for a very thoughtful and to the point reply.
RDW

[fairbank56]

Originally Posted by ka4wja

RDW,
You're just NOT going to get an acknowledgement.....
b) and, therefore, you will need to manually switch your M-802 to a voice channel...
c) and, then, you would need to know what channel to switch to, to contact someone.....whether they be someone who received your DSC-Distress call or not...

All good information John except for this. After the DSC distress message is sent (it is repeated 5 times in succession), your 802 will automatically switch to the emergency phone frequency while the DSC receiver is still monitoring for the ACK. In a simple distress call where you just press/hold the red button, the distress call is sent on the default freq of 8414.5Khz and after it is sent, it switches to 8291.0Khz for voice operation even though the manual says it switches to 2182.0Khz. The manual is wrong. According to the manual, even if an ACK is received, you must still press the cancel button to stop the alarm. I'm not sure I believe that one as pressing the cancel button will send a cancel alert packet. Seems to me you shouldn't touch the cancel button until you have established voice comms. I do not believe that after the 802 receives an ACK to your distress alert, that the radio sends another DSC packet ACKing the ACK, so to speak, as suggested by Seahunter. I'm with you in that you should have a DSC antenna but I have seen many 802 installs that do not have one and it is absolutely not neccessary in order to get a SAR response from the coast guard.

Eric

[osirissail]

My question is "why" would anybody use HF to send a distress call the the USCG? If you are in an emergency situation, playing around with an HF radio and trying to get contact established, tuned and being able to understand the other side through the hash and static is rather time consuming. That is why EPIRB's were invented.
- - If you are in range of VHF signals (range is dependent totally upon your radio and your antenna situation) then using VHF DSC Distress can efficiently and quickly enable you to talk to responding boats and get assistance.
- - Hooking up the secondary antenna to the ICOM Hf radio is fine but cruisers do not leave that radio turned on unless they are actively trying to communicate on a HF cruisers net. Not to mention the 12VC amps that radio draws in transmit mode. VHF DSC is wonderful, useful for many purposes beyond/besides Distress, and a definite improvement, but HF DSC is of no practical value to the cruiser. So why bother hooking it up?

[ka4wja]

Eric,
I was trying to not complicate matters too much here, in this forum....as many will find them too cumbersome, and I'm afraid they'd just forget about the DSC functions....which, in my opinion, would be a mistake....

Originally Posted by fairbank56

After the DSC distress message is sent (it is repeated 5 times in succession), your 802 will automatically switch to the emergency phone frequency while the DSC receiver is still monitoring for the ACK. In a simple distress call where you just press/hold the red button, the distress call is sent on the default freq of 8414.5Khz and after it is sent, it switches to 8291.0Khz for voice operation even though the manual says it switches to 2182.0Khz. The manual is wrong.

I have done HF-DSC calls on the M-802, but since I've never done a HF-DSC Distress call on the M-802, all I can do is try to believe the manual.....
And, while I do agree with / understand what you wrote regarding a single freq DSC Distress message......I know that, when I need to send a May Day, I'm more likely to do an "all channel-type" DSC Distress Call...
And, according to my understanding of the manual, if you do a DSC Distress call on all 6 Int'l exclusive GMDSS DSC freqs, then the 802 waits for a ACK in order to know which voice freq to switch to?????
Or, in the event of no ACK, it switches to 2182khz????
Is this not correct????
(I'm currently 200 miles from my boat and M-802, so I'm going from memory.....but, am I not correct here????)

Originally Posted by fairbank56

According to the manual, even if an ACK is received, you must still press the cancel button to stop the alarm. I'm not sure I believe that one as pressing the cancel button will send a cancel alert packet. Seems to me you shouldn't touch the cancel button until you have established voice comms. I do not believe that after the 802 receives an ACK to your distress alert, that the radio sends another DSC packet ACKing the ACK, so to speak, as suggested by Seahunter.

I;m with you here.....and, I'd need to have another look at the manual, but I believe that once the ACK is rec'd the "Cancel" button would not send a "cancel DSC Distress" message????

But, to be blunt about all of this, I suspect that having this detailed discussion may have a negative effect.....making some question the "usefullness" of HF-DSC (which already has enough nay-sayer's...mostly those that don't understand it and have never used it...)


John
s/v Annie Laurie

[fairbank56]

Originally Posted by ka4wja

Distress call on all 6 Int'l exclusive GMDSS DSC freqs, then the 802 waits for a ACK in order to know which voice freq to switch to?????
Or, in the event of no ACK, it switches to 2182khz????
Is this not correct????

Correct. After sending on all freqs, it switches to 2182 while waiting for an ACK and I assume the radio will then switch to the appropriate freq although the manual isn't clear on that.

The problem here is that with a simple distress call, all you have to do is press/hold the red button and that's it. You can walk away if you have to. To make the six frequency call you have to go through several steps. Push DSC to select DSC watch mode, push MODE to select the DSC menu, rotate the channel knob to select DISTRESS and then push ENTER, rotate the channel knob to select the desired nature of distress, then push ENTER, verify the position and UTC time data, then push ENTER, rotate the channel knob to select SIX FREQUENCY, then push ENTER. Now you can press/hold the red button.

I;m with you here.....and, I'd need to have another look at the manual, but I believe that once the ACK is rec'd the "Cancel" button would not send a "cancel DSC Distress" message????

That would make sense but again, the manual isn't real clear on that either. Icom manuals are the worst. I have already confirmed that with the simple distress call, the DSC packet is sent on 8414.5Khz and then switches to 8291.0Khz voice regardless of ACK, not 2182.0Khz as stated in the manual.

Eric

[ka4wja]

Oh boy.....I know that I'm in the minority....and I do NOT wish to imply that cruisers need to have MF/HF-DSC on board, that was not my intention.....rather I was answering a question about the what the "second" HF antenna on the M-802 is for, and it's usefullness.....

If you do not have (or use) an M-802, and/or have not used HF-DSC, some may question "usefullness" of this discussion....
But, for those looking to expand their knowledge and understanding, this should be of great use!!!!

Please understand that I'm not trying to say / imply that you need an MF/HF-DSC rig.....
And, I do not wish to get into a long argument about its merits.....
But, do to quite a bit of mis-understanding of how it all works, I thought it prudent to take a few minutes to "explain" some of the mis-understood points.....
Everyone has their own opinions.....and nobody's is more valid or less valid than anyone else's......I just hope that opinions don't get confused with facts....(I try to specifically differentiate the two...)


Although a bit off-topic, osirissail asks a good question.....

Originally Posted by osirissail

My question is "why" would anybody use HF to send a distress call the the USCG? If you are in an emergency situation, playing around with an HF radio and trying to get contact established, tuned and being able to understand the other side through the hash and static is rather time consuming. That is why EPIRB's were invented.

a) For the past 20+ years, the use of remote "auto-tuners" takes the "tuning" problems out of the equation altogether....
b) While, as I wrote earlier, signalling the USCG is the commonly-understood method of dealing with a "distress" (especially for those US-based / originated cruisers), it is NOT the primary function of MF/HF-DSC Distress signalling......
Which is to get asistance from vessels in your area.....as well as alerting a RCC of the Distress, and providing a two-way comm link to the vessel in distress...
(yes, triggering an EPIRB, will get the RCC alerted, and they will send messages, via INMARSAT, to to vessels reported in the area of the EPIRB.....but this isn't an exact science, since nobody knows all of the vessels' positions, all the time.....as well as this taking quite a bit of time....)
c) Forgetting the red herring of "why" EPIRB's were invented.....
Nobody ever suggested thet an MF/HF-DSC radio was a substitute for an EPIRB....
d) MF/HF-DSC actually takes the "being able to understand the other side" completely out of the equation....
As it sends your GPS position, along with your MMSI, with your "digital" May Day, over and over again, on 6 exclusive int'l GMDSS freqs, AUTOMATICALLY.....with no real issues over "hash" and "static".....
All you do is flip up the little spring-loaded door with your thumb, and press-and-hold the "Distress" button for 5 seconds.....and everything else is done automatically......sending the distress signal out on 6 different bands, waiting for a "reply", and switching / tuning to the correct/proper channel for further communications......
This can / typically does alert many vessels (and a couple RCC's), and can provide assiatance to your vessel in distress much quicker and much more precisely (getting the assistance you need) than with an EPIRB.....
(again not a sustitute, but an addition to or refinement of, a vessel's distress signally system...)

Originally Posted by osirissail

- If you are in range of VHF signals (range is dependent totally upon your radio and your antenna situation) then using VHF DSC Distress can efficiently and quickly enable you to talk to responding boats and get assistance.

This is actually what MF/HF-DSC gets you, with longer range.....as well as the ability to contact/speak with both vessels in your area coming to your assistance, and the RCC covering your area (such as the USCG, etc.)

Originally Posted by osirissail

- Hooking up the secondary antenna to the ICOM Hf radio is fine but cruisers do not leave that radio turned on unless they are actively trying to communicate on a HF cruisers net. Not to mention the 12VC amps that radio draws in transmit mode. VHF DSC is wonderful, useful for many purposes beyond/besides Distress, and a definite improvement, but HF DSC is of no practical value to the cruiser. So why bother hooking it up?

As, I wrote above (and many times in the past) everyone's opinion is valid....and, I agree that most cruisers (me included) do not leave their HF rig turned unless using it.....(but, I do have mine on a lot!!!)
Although, if underway, I DO leave the VHF-DSC rig turned-on 24/7.....
But, if I was in distress, I WOULD switch-on my M-802, and use BOTH VHF-DSC and MF/HF-DSC Distress signaling!!!
And, I'd not have any concern of the "amps" being used by my radios, since getting help would be my primary goal....

I do understand osirissail's opinion, but some of us have actually seen a value to MF/HF-DSC and, in my opinion, if you buy/install a radio that has that capibility, to paraphase other great minds, "why not bother hooking it up???"
And, if you do find a practical value (as I have) why not do it correctly???


Again, we all have our opinions, and I'm fully aware that most cruisers do not have MF/HF-DSC equipment or capabilities, and even those that do, do not currently use them, but that doesn't mean that I cannot do so.....and also doesn't really address the issue of mis-information which started this whole thread/discussion....


Fair winds...

John
s/v Annie Laurie

[ka4wja]

Originally Posted by fairbank56

Correct. After sending on all freqs, it switches to 2182 while waiting for an ACK and I assume the radio will then switch to the appropriate freq although the manual isn't clear on that.

Yep, that's the way I understand it as well....

Originally Posted by fairbank56

The problem here is that with a simple distress call, all you have to do is press/hold the red button and that's it. You can walk away if you have to.

I just took another look, and see that I was mixing up "simple distress call" with "regular distress call".....
Yeah, the Icom manual sucks....

Originally Posted by fairbank56

To make the six frequency call you have to go through several steps. Push DSC to select DSC watch mode, push MODE to select the DSC menu, rotate the channel knob to select DISTRESS and then push ENTER, rotate the channel knob to select the desired nature of distress, then push ENTER, verify the position and UTC time data, then push ENTER, rotate the channel knob to select SIX FREQUENCY, then push ENTER. Now you can press/hold the red button.

Yeah, a bit more complex....but after selecting Distress in the DSC Menu, you just press ENTER 3 times and then press-and-hold DISTRESS....assuming that your okay with a generic "undefined" distress, and that you position is correct, and that you do want to use all 6 freqs....


John
s/v Annie Laurie

[ka4wja]

Originally Posted by fairbank56

According to the manual, even if an ACK is received, you must still press the cancel button to stop the alarm. I'm not sure I believe that one as pressing the cancel button will send a cancel alert packet. Seems to me you shouldn't touch the cancel button until you have established voice comms. I do not believe that after the 802 receives an ACK to your distress alert, that the radio sends another DSC packet ACKing the ACK, so to speak, as suggested by Seahunter.

Although the manual does suck....it does "clarify" this issue.....and, you're cirrect that the 802 doesn't send an ACK to the ACK....but, according to the manual, if you don't get an ACK, pressing the CANCEL button does send out another message....

When receiving an acknowledgement, push [CANCEL/

CALL] to stop the alarm then reply to the connected

station via the transceiver’s microphone.

CAUTION!

DO NOT

push [CANCEL/CALL] while waiting for an
acknowledgement, otherwise the distress call repeat
is cancelled.
Push [CANCEL/CALL] only when you want to cancel

repeated transmission.

So, if you get an ACK, all is well with pushing the CANCEL button.....


But, assuming the manual is correct (BIG assumption), if no ACK is received. pushing the CANCEL button cancels repeated transmissions and sends another message...

The cancel acknowledgement is automatically
transmitted when the [CANCEL/CALL] is pushed.

Is this a "Cancel Distress" message or a "Cancel ACK message"????
It is not clear.....




And, "Canceling" a DSC distress call is explained (somewhere, perhaps the USCG site???), as using voice transmissions on the recognized distress/calling freqs, stating the cancelization of the distress.....
So, there is even more confusion.....

John
s/v Annie Laurie

[ka4wja]

Originally Posted by RDW

As far as your set up is concerned, can you tell me more. I may very well want to set my boat up just like yours. I have a 46 foot Morris sloop. When you say insulated shroud, is this insulated like a back stay antenna is or is most any shroud already insulated, i.e. would I have to modify my shroud or can I use it as it stands? Also exactly how did you connect to your chainplate? My goal is to do some major off shore cruising so I am trying to learn as much as possible and to be fairly self sufficient. Is this something the average person can do or do I need professional help? If the shrould does not need to be modified, the most skill would maybe be making good connections with the coax, chainplate and cooper ground.
I am interested in your thoughts and thanks again for a very thoughtful and to the point reply.

RDW,
I'm flattered that you wish to duplicate my set-up, but I'd be remiss if I didn't confess to being a longtime radio nut and making it clear that you do not need to use a shroud for your DSC antenna....

Okay, now that's out-of-the-way....onto the details...

{For additional clarification, I also use this shroud antenna as my We Fax receive antenna.....I use a coaxial "Tee", allowing me to connect both the M-802 DSC antenna jack and my Furuno FAX-408, at all times....and it does work great for both.....I've found 4, 6, 8/9, 11/12, and 17mhz FAX reception to be very good from 600 - 4000+ miles away....}

1) Every boat is different.....where the Nav station is located, where your rigging is loacted. where your chainplates are, etc. etc.....
So, while I did what I did, you may find your situation different...

2) You may find rigging a vertical wire (such as an "alternative" stay) just for DSC reception to be easier and cheaper than rigging an insulator on a shroud, and coax-feeding it, at the chain-plate.....
Any, length of wire will do.....from 15' - 40'.....

3) Whether you decide to "ground" the shield, or not, might not make much of a difference.....
If you do not, you simply have a un-balanced random wire vertical.....and it will work fine....although, grounding may reduce noise pick-up, or not....so don't sweat it much....

4) If you do decide on using a shroud, simply run some coax to the chain-plate, disconnect any "bonding wiring" there, and connect the center-cond of the coax to the chain-plate.....use a small screw, etc...

You may find that's all you need to do, and you'll not add an insulator at the mast end of the shroud.....depends on how well this antenna preforms....test it and see.....

However, in my case, after a few months of using the Metz DSC antenna, with disappointing results, I decided to go all out.....and that's when I changed my DSC antenna to my starboard-aft-lower shroud, and added an insulator at the top of the shroud.....
Yes, I DO have a rigging insulator on the top-end of the shroud...

(My mast has 8 shrouds and 2 backstays, forestays....supporting it....and with the insulators and Sta-Lock fittings being stronger than the SS wire, and with the Hi-Mod insulators being "fail-safe", I have no qualms about using rigging insulators......and, in the past 40 some years, I've seen my share of de-masted sailboats and rigging failures, but never saw a insulator failure.....lots of other failures, but never a rigging insulatir failure....)

5) Here are some links to some photos of my set-up....

4705902 (see the insulator on the upper end of the shroud, on left-hand side of photo...)

4711201 (see Hi-Mod backstay insulator)

Nav Station (Nav Station set-up)


I hope this helps you out....

John
s/v Annie Laurie

[Wotname]

Originally Posted by ka4wja

Eric,
.......
But, to be blunt about all of this, I suspect that having this detailed discussion may have a negative effect.....making some question the "usefullness" of HF-DSC (which already has enough nay-sayer's...mostly those that don't understand it and have never used it...)


John
s/v Annie Laurie

John (and Eric),

IMO, you could not be more wrong about your information having a negative effect.

While obviously I can only speak for myself, I really appreciate your information and I thank you both for taking the time to share it.

I find it especially useful because as we all know, the 802 manual "could do better". Reading your posts is much easier than reading the manual and gives real life practical experience of using the 802. I learn more about the 802 on CF than many nights of ploughing through the manual and especially about the DSC functions.

And if I am not sure about a particular point I can ask you guys which IME is much easier than asking Icom.

For the record, although I have been involved professionally (hands on) in radio communication all my working life, my marine HF experience is limited to being a recreational boat user. Thus I find your posts very helpful especially with respect to DSC. And I can confess to being more at home with a manual tuner and (say) a 12 channel crystal controlled SSB than my bright all singing all dancing 802.

Keep sharing the 802 secrets please

[Wotname]

Originally Posted by osirissail

My question is "why" would anybody use HF to send a distress call the the USCG? If you are in an emergency situation, playing around with an HF radio and trying to get contact established, tuned and being able to understand the other side through the hash and static is rather time consuming. That is why EPIRB's were invented.
- - If you are in range of VHF signals (range is dependent totally upon your radio and your antenna situation) then using VHF DSC Distress can efficiently and quickly enable you to talk to responding boats and get assistance.
- - Hooking up the secondary antenna to the ICOM Hf radio is fine but cruisers do not leave that radio turned on unless they are actively trying to communicate on a HF cruisers net. Not to mention the 12VC amps that radio draws in transmit mode. VHF DSC is wonderful, useful for many purposes beyond/besides Distress, and a definite improvement, but HF DSC is of no practical value to the cruiser. So why bother hooking it up?

Originally Posted by ka4wja

.........
Although a bit off-topic, osirissail asks a good question.....

a) For the past 20+ years, the use of remote "auto-tuners" takes the "tuning" problems out of the equation altogether....
b) While, as I wrote earlier, signalling the USCG is the commonly-understood method of dealing with a "distress" (especially for those US-based / originated cruisers), it is NOT the primary function of MF/HF-DSC Distress signalling......
Which is to get asistance from vessels in your area.....as well as alerting a RCC of the Distress, and providing a two-way comm link to the vessel in distress...
(yes, triggering an EPIRB, will get the RCC alerted, and they will send messages, via INMARSAT, to to vessels reported in the area of the EPIRB.....but this isn't an exact science, since nobody knows all of the vessels' positions, all the time.....as well as this taking quite a bit of time....)
c) Forgetting the red herring of "why" EPIRB's were invented.....
Nobody ever suggested thet an MF/HF-DSC radio was a substitute for an EPIRB....
d) MF/HF-DSC actually takes the "being able to understand the other side" completely out of the equation....
As it sends your GPS position, along with your MMSI, with your "digital" May Day, over and over again, on 6 exclusive int'l GMDSS freqs, AUTOMATICALLY.....with no real issues over "hash" and "static".....
All you do is flip up the little spring-loaded door with your thumb, and press-and-hold the "Distress" button for 5 seconds.....and everything else is done automatically......sending the distress signal out on 6 different bands, waiting for a "reply", and switching / tuning to the correct/proper channel for further communications......
This can / typically does alert many vessels (and a couple RCC's), and can provide assiatance to your vessel in distress much quicker and much more precisely (getting the assistance you need) than with an EPIRB.....
(again not a sustitute, but an addition to or refinement of, a vessel's distress signally system...)
This is actually what MF/HF-DSC gets you, with longer range.....as well as the ability to contact/speak with both vessels in your area coming to your assistance, and the RCC covering your area (such as the USCG, etc.)................
.

John
s/v Annie Laurie

Whiled I believe that John has addressed the EPIRB vs HF-DSC question quite well, I would add (for clarity) that it isn't either / or situation, rather they are two separate systems. If you have little need for HF in general cruising, you will probably not have any need for HF-DSC.

However, in this part of the world, HF remains a primary communication tool and HF-DSC is a great addition, especially in situations that might not warrant EPIRB activation (i.e. grave and immediate danger to ship and crew) but still warrant establishing communications with a RCC (typically a PAN PAN situation).

[fairbank56]

Originally Posted by Seahunter

Eric, when the AK comes in the 802 responds in kind, that's how they know.

I have confirmed using two 802's in a controlled bench test that an 802 receiving an acknowledgment to it's own distress call DOES NOT respond with another DSC transmission. The only way for others to know if you received the ACK is by further voice comms or the fact that you are no longer transmitting the DSC alert, although that in of itself does not neccessarily mean you received the ACK. If the Coast Guard receives your distress call either directly or via relay and there is no further communication, they will initiate a response.

Eric