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Old 24-02-2013, 04:24   #16
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Re: ICOM M802 DSC antenna?

The shroud is probably grounded and as a result would not be a good choice. The Metz and Gam weather fax antennas are probably the best solution. I have the instructions on my web site for making a simple DSC antenna that I actually call the DERA (DSC Emergency Reception Antenna). The weather fax antennas are simple. They are a coax to a coil of wire to about a 4 foot stainless rod. Since this is only a reception antenna, you could get a ~100 to 150 feet of say number 22 wire, wrap all but 5-6 feet on a something round like a dowel and string the 5-6 feet vertically someplace. Run a coax to the radio using a PL259 connector. The coil should be at the vertical piece. Another option is a stainless or fiberglass CB antenna. They are cut for the high end instead of the low end of the HF Band, but they should work fine. Some of the folks in Asia are using a splinter off their AM/FM antennas.

You can test the antenna with another cruiser (not next door but a few miles away so you are still using the ground wave) Have them call you on your radio say on 2A, 4A, 8A, 12A, and 16A. Assuming good contact, connect the home made antenna to the main antenna jack ***DO NOT TRANSMIT on this antenna***. The other party could repeat the calls on the same channels. If that works, it should work for the DSC antenna. Still the easiest is to buy a Gam or Metz. I know they work.

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Terry L Sparks
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Quote:
Originally Posted by Tip View Post
Any thoughts on using a shroud as the DSC antenna? I have rather easy access to the chainplates inside the boat and am thinking of hooking up to this. Does the shroud need to be insulated for any reason? I'm using an insulated backstay antenna.
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Old 24-02-2013, 07:05   #17
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Re: ICOM M802 DSC antenna?

Quote:
Originally Posted by Tip View Post
Any thoughts on using a shroud as the DSC antenna? I have rather easy access to the chainplates inside the boat and am thinking of hooking up to this. Does the shroud need to be insulated for any reason? I'm using an insulated backstay antenna.

This is what I have done. Primary drawback might be that it would be close to noise sources in the boat. Try it and see. Temporarily hook it up to the regular tx/rx antenna input on the 802, and use it as a receive antenna to see if it picks up signals and not lots of noise. If it sounds good, it will be a good DSC antenna.

Chip
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Old 24-02-2013, 21:08   #18
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Re: ICOM M802 DSC antenna?

Tip,
What Chip wrote....+1!!!
Quote:
Originally Posted by Tip View Post
Any thoughts on using a shroud as the DSC antenna? I have rather easy access to the chainplates inside the boat and am thinking of hooking up to this. Does the shroud need to be insulated for any reason? I'm using an insulated backstay antenna.
In my set-up, I've been using a lower shroud (starboard, aft, lower) as my ~ 24' vertical DSC-Receive (and WeFax Receive) antenna for 8+ years, and regularly receive "All-ships" DSC Calls when just sitting around talking on the radio.....
It's a great DSC-Receive antenna....

Although it does not need to be insulated.....I did mine this way....
For my set-up, I reduced (removed???) the possibility of direct-coupled RF noise ingress into the antenna from other systems on-board, by insulating the top of my shroud (see left side of photo, just below the spreader...)
And, further wanted to be able to easily use this antenna as a back-up transmit antenna without significant RFI into other systems on-board....so here again, the insulator....

However, over the years, I've heard from others who have simply attached a wire to their chainplate and have used that as their DSC antenna, and have good results....
So, saving the couple hundred dollars on an insulator is a workable plan....
Best to try it and see....if you're picking up too much noise, then consider another antenna (perhaps a short whip on the stern rail)....






I hope this helps...

Fair winds....

John
s/v Annie Laurie



{BTW, Terry, wrapping 100' of wire helically around a 4' long form, to use as a vertical receive antenna is not only a waste of wire, and not work any better than a simple 4' piece of wire / 4' ss whip / etc....it will perform worse!!!
I haven't posted anything in contrary to some of your other posts, as I didn't wish to be thought of as "rude".....but a friendly note here that quite a bit of your writings, while creative, are based on incorrect facts, misunderstandings, and poor theory......I mean this as no insult, and I'm aware of the qualifications you've posted, but then you'd be aware of many of these quite simple falsehoods....}
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Old 25-02-2013, 04:19   #19
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Re: ICOM M802 DSC antenna?

Quote:
However, over the years, I've heard from others who have simply attached a wire to their chainplate and have used that as their DSC antenna, and have good results....
So, saving the couple hundred dollars on an insulator is a workable plan....
Best to try it and see....if you're picking up too much noise, then consider another antenna (perhaps a short whip on the stern rail)....
IN my experience, virtually any length of wire will work, remember its really like your old LW radio , Ive used a car antenna to good effect. Theres no transmission on it.

DSC over HF has even more problems then DSC over VHF, if it doesnt work well it dosnt really matter. You can still make DSC calls and distress alerts , just you may never get the ACK, ( but in reality who cares, theyll come in over voice anyway).

Dont fuss about it too much.

Dave
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Old 25-02-2013, 07:33   #20
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Re: ICOM M802 DSC antenna?

John,

No offense taken, there are many things that should not work that actually do work with HF and for that matter, radio communications. I have in fact recommended clipping onto a stay for a portable HF receiver to enhance the signal. There are no grounding issues to consider.

It is actually good to find out that it is working for at least two boats. There are a lot of folks that do not have DSC antennas down here in Mexico and no place to buy one. So I would like to know more about this approach.

Did you do any testing with someone else using it as a receive antenna to make sure you had good/similar copy on 2-16MHz with a boat a few miles away?

Electrical/electronic facts are not necessarily the bottom line for radio communications and especially not for HF. Many things work that should not in theory.

I am still a bit uncomfortable recommending an approach that will bring another ground into the 802. The RF connectors are connected to the chassis and the chassis is connected to neg DC or basically DC ground.

On some boats I have found folks have tied the RF ground into other DC ground(s) giving two or more separate points grounded to the chassis. Adding another ground through a stay just sounds like it is asking for many ground loops. Since each different grounding source has a different resistance and reactants back to the radio, ground loops can generate additional noise in the system as well as pick up the noise from your system as you have pointed out.

I have a Metz antenna and I do know I get Safety calls that people with short pieces of wire do not get. However they are usually from a thousands of miles away. I had one Distress Acknowledgement from Norfolk VA when I was in La Paz MX the short wires did not get. So if you are coastal sailing probably would be no worries.

If any one has gotten a safety/distress type call on a stay from say 3,000 miles it would be good to know. I am in PV right now with several puddle jumpers that need DSC antennas and if the stay works, it is better than nothing for sure. I just want to make sure they will receive a distress acknowledgement when the are 1/2 way to the South Pacific.

By the way my 100+ foot of wire antenna is based on the design for a typical base loaded antennas similar to what you get when you buy a Metz and Gam weather Fax antenna.

By the way it is not a 4 foot form but a 4 inch to creating the base load coil so the antenna is tuned within the HF band. This will work, but to your point is well taken. Since this is digital and receive only signal, it may not work significantly better than just a piece of wire.

The other method I have used that works well for OK range is take a piece of coax with a PL 259 on one end and strip off the outer insulation and shield off the other end leaving the insulated center conductor. String the center conductor in a vertical locker in the (fiberglass or wood) boat or even topside if possible. That works OK and does not add a ground to you radio.

Quote:
Originally Posted by ka4wja View Post
Tip,
What Chip wrote....+1!!!

John
s/v Annie Laurie
{BTW, Terry, wrapping 100' of wire helically around a 4' long form, to use as a vertical receive antenna is not only a waste of wire, and not work any better than a simple 4' piece of wire / 4' ss whip / etc....it will perform worse!!!
I haven't posted anything in contrary to some of your other posts, as I didn't wish to be thought of as "rude".....but a friendly note here that quite a bit of your writings, while creative, are based on incorrect facts, misunderstandings, and poor theory......I mean this as no insult, and I'm aware of the qualifications you've posted, but then you'd be aware of many of these quite simple falsehoods....}
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Old 25-02-2013, 08:23   #21
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Re: ICOM M802 DSC antenna?

just to be sure everyone is one the same wavelength!!. The Class D 802 has a seperate DSC only MF/HF receiver. This is there to comply with the requirement that CLass D radios listen for DSC alerts continuously, irrespective of transmit and rx of voice.

Why you would want to receive Distress alert acknowledgements from 3000 miles away is strange. Since all DSC working is backed up by voice and anyway DSC Tx takes place on your main HF antenna, then the DSC Rx antenna is not a key component. A simple AM radio antenna mounted on the radar arch is enough.

Once you receive the voice acknowledgement you can always cancel your own distress. Anyway in theory only Class A MF/HF sets and coast stations issue distress ACKs. ( and ship based ones only do after ensuring no coastguard station responded, since GMDSS requires that the Alert , both voice and DSC must/should reach a shore station first).

This is being over thought here

Dave
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Old 25-02-2013, 10:10   #22
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Re: ICOM M802 DSC antenna?

Has anyone tried this?

ICOM MN-100L

$309.95

Antenna matcher. Matches the transceiver to a long wire antenna. Covers all HF bands from 1.5 to 30mhz. One 15m antenna comes standard.
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Old 25-02-2013, 11:08   #23
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Re: ICOM M802 DSC antenna?

tampahokie,
This is nothing new.....there have been many models designed and sold over the past 60+ years....(B&W has been marketing their terminated folded dipole longer than I've been alive!!!)
Like all "resistive matching devices", for all practical purposes this is "radiating dummy load"...
Quote:
Originally Posted by tampahokie View Post
Has anyone tried this?
ICOM MN-100L
$309.95
Antenna matcher. Matches the transceiver to a long wire antenna. Covers all HF bands from 1.5 to 30mhz. One 15m antenna comes standard.
It's specs are a bit "generous", but Icom specs it as having 6db off LOSS....(I'd think it closer to 6db - 10db, compared to the same wire antenna fed with an auto-tuner/coupler....but that depends on how/where it is installed...)
Remember we may never hae much "gain" out of our antennas, but you don't want to start off with "loss"!!!

http://www.thiecom.de/ftp/icom/mn100l/mn-100_l.pdf

In non-technical terms, it is big resistor and heat sink (dummy load), connected to a balun/unun, connected to a wire (antenna).....
And, in the commercial world, these are collectively know as "terminated-feed antennas"....but in common parlance, they're known as "radiating dummy loads"...


I hope this helps...

John
s/v Annie Laurie
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Old 25-02-2013, 14:39   #24
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Re: ICOM M802 DSC antenna?

Terry,
Please understand I mean no offense in anything I write here....I'm just in a rambling mood today...



1) Testing....
Quote:
Originally Posted by TLSparks View Post
Did you do any testing with someone else using it as a receive antenna to make sure you had good/similar copy on 2-16MHz with a boat a few miles away?
Just Briefly.....(read the SSCA disc boards and/or e-mail directly for more details....)
Yes, I've done extensive testing on-air, with vessels 3 - 4 miles away, and vessels 3000 - 4000 miles away....(usually using a coax switch, to instantly switch back/forth while receiving....but also switching during a pause between words while transmitting and getting descriptive signal reports back...)
As well as with commercial and gov't shore stations....

Original testing was in 2004, here in S. FLA....using WLO - Mobile, AL and NMN - Chesapeake, VA as my "control" DSC and Voice shore stations, for 4, 6, 8, 12, and 16mhz...DSC and Voice comparisons...
I used the Metz 49" whip, mounted on my stern rail....vs. my ~24' shroud....vs. my ~64' backstay antenna....
I also used USCG Miami on 2mhz DSC and Voice....(not much of a test, as they're only 100 miles away...)

I did further tests, comparing HF signals from various sources, such as NMF - WeFax, NMG - WeFax, as well as doing "A/B" comparisons (using the coax switch), while on the ham bands....
(perhaps you should peruse the SSCA disc. boards "communications" forum, and if you wish some details of my experiences with DSC over the past 8-9 years, or my HF comms experience over the past 40+ years, send me a message and we'll talk...)

Bottom line....
Shroud antenna MUCH better than Metz whip....and backstay better than shroud on 8mhz and below, and about equal 12mhz and above....

{Note that I DID use the AT-140 tuner, "tuned", on the backstay...and have NO tuner (direct coax connection to the chain plate and insulator at top of shroud) on "shroud antenna"....
Although I DO have an old MFJ tuner on-board at the ready, to use with my "emergency antenna" (25' length of GTO-15 wire, and a fishing rod), and have jumpers to allow use of shroud antenna as back-up transmit antenna as well....
Heck I've got TWO remote auto-tuners (Icom and SGC) and TWO Icom M-802's on-board, and a dedicated WeFax Rec (Furuno FAX-408), and a portable shortwave/SSB receiver, as well as a Sony AM/FM/CD player w/ HF/Shortwave reception built-in...so, depending on how you count 'em, I've got 4 HF transmit/rec antennas on-board, and 5 HF receivers, etc....
Yeah, I'm an "HF Nut", but in addition to making a living in microwave / satellite comms for 30 years, I've been in HF, private and commercial (at sea and on land), for ~ 40 years.....so, if I'm not a "nut" by now, I wouldn't worth listening to.... }







2) Terry, again forgive my bluntness.....but Huh???
Quote:
Originally Posted by TLSparks View Post
Electrical/electronic facts are not necessarily the bottom line for radio communications and especially not for HF. Many things work that should not in theory.
In 40 some years working in HF communications (and 30 years in microwave/satellite comms), in all my years of education, in all my real world experiences and experiments, in the 100's of systems (1000's ???) I've worked on, designed, and consulted on, etc. etc. I have NEVER found any that "work that should not in theory"!!!!
Nor ones that "didn't work, but should have"....except, of course, if there were construction anomalies (short circuits, etc..)
Perhaps we are working with different theories???

I see these sorts of statements, along with the "HF radio is more 'art' than 'science'", etc. all the time.....and the fact is just the opposite!!!
(Yes, when it comes to OPERATING a radio there is some "art" to being in the top percentile of good operators, but even these "arts" are based on fairly simple facts...)
There are basic scientific facts that govern how HF radio wave propagate, how the electrical energy of a transmitter is changed into the electro-magnetic energy in the antenna system, and how that energy is coupled/radiated into the ether...(and vice versa, on receive)....
This is NOT new science (been understood, written about and taught since before I was born), and I've taught some of these basics myself....

I won't ramble on-and-on here....but the bottom line appears to me (my opinion here), that since many do not know / understand the underlying theories, they assume some "myths" they read/hear are the facts/theories, and that's how these statements propagate....
(heck, I listened to "experienced radio engineers" spout off complete falsehoods like Moses himself came down the mountain with them!!! and when questioned, they turn a bit red-in-the-face....)

Now, in all humility, I freely admit I don't "know it all"!!!
I still remember listening to Walt Maxwell (W2DU) discuss one of his IEEE papers (later a book, I think), about 30 years ago, and trying to fully grasp what he was talking about!!! (and I was a physics major!!)
Walt became an acquaintance of mine (I think maybe he originally thought of me as a "pest"....but he always was willing to answer my questions...), and while I miss him, he left behind some of the most extraordinary work in antennas, transmission lines, etc. in history.....
And, while L.B. (W4RNL) and I never met face-to-face (we corresponded via e-mail during his last 10 years or so), I consider him the greatest teacher of modern antenna modeling, etc. and that of understanding how what we see in the real world relate directly to the theories!!!

So, while I still think I better than 99% of the RF Communications Engineers / Consultants out there.....compared to those two guys.....I'm just a novice...
What's that old saying....."they've forgotten more than I'll ever know"

So, in addition to the Radio Engineering Handbooks, and the ARRL Handbooks and Antenna Books, and ON4UN's books....once you've mastered/conquered all of those, you may want to look at Walt's and L.B's writings....

{Sorry, I know I wrote I was going to be brief....but I can't help myself when talking about Walt....and I've got a GREAT story about RCA SATCOM satellites, Cape Canaveral launches, waveguides and coax, etc....that should probably never been told publicly....but maybe I'll relate one-on-one....}








3) Direct-coupled RFI can be an issue to worry about....and I simply didn't want to worry about it....hence I insulated my shroud....
But, others have had no issue when using a dc-grounded shroud, so on a case-by-case basis, this is an idea to try....(and perhaps we'll find that there is little to be worried about???)
Quote:
Originally Posted by TLSparks View Post
I am still a bit uncomfortable recommending an approach that will bring another ground into the 802. The RF connectors are connected to the chassis and the chassis is connected to neg DC or basically DC ground.
Understand that "radiated RFI" is usually what causes reception issues on-board, and it is this RFI that needs 95% of the attention.....direct-coupled RFI and "ground-loop" caused RFI are both rare....


????
Quote:
Originally Posted by TLSparks View Post
On some boats I have found folks have tied the RF ground into other DC ground(s) giving two or more separate points grounded to the chassis. Adding another ground through a stay just sounds like it is asking for many ground loops. Since each different grounding source has a different resistance and reactants back to the radio, ground loops can generate additional noise in the system as well as pick up the noise from your system as you have pointed out.
Terry, while noise pick-up (RFI ingress) is an issue to worry about on-board, and YES, ground loops are BAD!!!!
I think you may be misunderstanding the way a "grounded" shroud is being used....
It is DC-grounded, but like all conductors can still radiate (or receive) RF signals (at least to some extent), think of shunt-fed or slant-wire fed verticals, which can be made to work effectively for single-band / single-freq operation, but are notoriously poor at multi-band/multi-octave applications (in addition to the theory, I've personally tried multi-band/multi-octave shunt-feeding and have found the books/equations/theory to be correct...)

While antennas and feed systems are reciprocal, receivers are more forgiving than transmitters.....and since all HF receivers that we are using have a couple orders of magnitude more gain/sensitivity than ever needed (20db+), especially below 10mhz, than losing a few db in a receive antenna system isn't too critical....
(Sorry again....I need to learn how to be brief!!!_







4) While I appreciate your efforts, and I suspect that you are helping some of those other boaters/cruisers, please remember that anecdotal reports are often times misleading.....Heck, even "scientific" testing has errors....
So, unless you can do "instantaneous" (within one second) switching and compare signal strengths between two different antenna systems that are quite close ( ~ 1/4 wavelength distance), then most tests results have VERY large +/- variables, along with errors....(and that's not even considering the limited ability to read signal strength variations down to +/- 1 to 2 db!!!!)
Quote:
Originally Posted by TLSparks View Post
I have a Metz antenna and I do know I get Safety calls that people with short pieces of wire do not get. However they are usually from a thousands of miles away. I had one Distress Acknowledgement from Norfolk VA when I was in La Paz MX the short wires did not get. So if you are coastal sailing probably would be no worries.






5) Not only have I received All-Ships "Safety" DSC Calls from 1000's of miles away, one of the first ones I did receive was from the Eastern Med (about 5500 - 6000 miles from me) on 12mhz....that was about 8 years ago....
Quote:
Originally Posted by TLSparks View Post
If any one has gotten a safety/distress type call on a stay from say 3,000 miles it would be good to know. I am in PV right now with several puddle jumpers that need DSC antennas and if the stay works, it is better than nothing for sure. I just want to make sure they will receive a distress acknowledgement when the are 1/2 way to the South Pacific.
I believe it was with my current insulated shroud....as I know the furthest DSC signal I ever received from the Metz antenna was about 1000 miles away....


Most importantly here is not what my anecdotal results have been, but how the DSC-distress system works and who/what will respond!!!!

I cannot write a detailed treatise here, but in brief...

--- So, if the "fit hits the shan" and you need rescue, you'll trigger your EPIRB, AND hit/hold the "Distress" buttons on your DSC radios....(sending out a "6-freq Distress Call" from your M-802")

AND/OR....

--- If you're in need of assistance (not an "abandoning-ship" rescue), such as fuel, food, water, navigation, medical emergency, etc....and you need to establish contact with vessels nearby and/or shore stations, you will probably NOT trigger your EPIRB, but you WILL want to send out a "6-frequency DSC-Distress" call....

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....
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....


All SOLAS vessels are "required" to monitor 2187.5khz DSC, 8414.5kz DSC, and "one other DSC channel" (to be determined by their voyage/route/time-of-day/etc.), however in actual practice most have GMDSS consoles (or other DSC-watch receivers) that scan all 6 int'l GMDSS DSC freqs, so no need to worry about "which channel do I use"....BUT....

But, knowing that vessels closest to you will usually be those able to render assistance first/best, then it makes sense use an HF antenna system (for Voice and DSC) that is designed to be effective ( or even optimal) on MF and lower HF freqs.....and this means the biggest/tallest antenna you can fit onto our typical cruising boats....
So, while a 40' - 65' backstay is great, a 4' whip isn't so great....

Although, since MF/HF-DSC is 100-baud ascii FEC SITOR in a 500hz rec bandwidth, it is a VERY robust communications mode!!!! (it is, after all, designed as one of the 3 primary communications modes in the GMDSS!!, so it better be robust!!!)
In the real world, it is easily 10-12 db better (in S/N department) than SSB-Voice....so a DSC receive antenna that is even down 10 db compared to your backstay WILL work adequately....

And, while signaling for assistance via MF/HF-DSC isn't thought of as "common" by most cruisers, remember that this part of the GMDSS and is considered a "confirming source" when EPIRB activation alone sin't sufficient to trigger a SAR response (as IS the case in many far-flung/remote areas, covered by some 2nd and 3rd world nations!!!)
So, having an effective transmit antenna, that works well on the lower HF freqs is also an important consideration here!!

Bottom line:
Use as big/tall of an antenna (up to a reasonable height of 60' - 65') as you can rig.....
I'm a fanatic, and I don't mind spending some $$$ on comms.....but you don't have to be like me....a 20' - 30' long wire, strung from a flag halyard is a pretty good temporary HF-DSC receive antenna, and it'll cost you little....
Or, try using a grounded shroud....

And, do some tests/comparisons on-air, BEFORE you head out to sea....
If you're in Mexico, use NMC, Pt. Reyes, CA and NMO, Honolulu as test stations.....

Again, I need to be brief...but I hope this helps...

For some more details on the M-802 DSC functionality, be sure to look at the SSCA disc boards as well as look at the info Eric provided here a few years ago....
SSCA Forum • View forum - Communications

SSCA Forum • View topic - Routine HF-DSC Frequencies/Icom M-802 "DSC Watch Mode" Freqs


Usefullness of Second Receiving SSB Antenna


Just some tidbits....
Quote:
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.....
Quote:
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...

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....

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????
Quote:
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.


Quote:
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.
Quote:
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.....

Quote:
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.....
Quote:
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....


Quote:
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...)




Quote:
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) No need to wind a coil and try base loading for a short HF rec ant....losses in the coil out-weigh any advantages of attempts at imped match.....
Quote:
Originally Posted by TLSparks View Post
By the way my 100+ foot of wire antenna is based on the design for a typical base loaded antennas similar to what you get when you buy a Metz and Gam weather Fax antenna.




7) Terry, this approach works.....but works much better if you get the "antenna" up....
Quote:
Originally Posted by TLSparks View Post
The other method I have used that works well for OK range is take a piece of coax with a PL 259 on one end and strip off the outer insulation and shield off the other end leaving the insulated center conductor. String the center conductor in a vertical locker in the (fiberglass or wood) boat or even topside if possible.
String it up from a flag halyard, and you've got a great temporary HF receive antenna, whether for DSC, WeFax, or Voice!!




Okay, how's that for brief...
Enough ramblings....gotta go....

Fair winds..

John
s/v Annie Laurie
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Old 25-02-2013, 16:24   #25
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Re: ICOM M802 DSC antenna?

The last Distress Ack I heard was from Norfolk VA to a Turkish vessel in the Black Sea. I was in Mazatlan MX at the time using a Metz antenna.

While you are correct that if you get a voice acknowledgement, you can stop your display the automated frequency change by pressing and holding the Call Cancel button, a Distress Acknowledgement contains the frequency they want to talk to you on. If you have already (automatically) shifted to the next frequency when they acknowledge the shore station acknowledges via voice you could easily miss the acknowledgement. If your system will antenna is adequate to receive the DSC Acknowledgement, you will be directed automatically, by pressing enter to the Traffic Frequency.

The 3000 miles is how far a puddle jumper could be from a CA shore station sending the ACK. It is close to 3K to the SP and 2K to Panama. The last safety call I received was from Panama so I am reasonably sure a base loaded whip works.

What has been your experience connecting to a grounded a stay?

You are correct Dave, I understand folks in the Western Pacific have had good luck with AM radio antennas. A metal close hanger hanging of the jack in the back of the radio would probably get most calls.

Just to clarify what you said, It is true that the ships do not respond directly until it is clear no one is responding on shore. However they are required to send a Distress Relay if no contact is heard within 5 minutes.

What you use is probably over thought as you stated. The importance of having a good DSC antenna is usually understated in the cruising community so I am happy something is being discussed!

Terry

Quote:
Originally Posted by goboatingnow View Post
just to be sure everyone is one the same wavelength!!. The Class D 802 has a seperate DSC only MF/HF receiver. This is there to comply with the requirement that CLass D radios listen for DSC alerts continuously, irrespective of transmit and rx of voice.

Why you would want to receive Distress alert acknowledgements from 3000 miles away is strange. Since all DSC working is backed up by voice and anyway DSC Tx takes place on your main HF antenna, then the DSC Rx antenna is not a key component. A simple AM radio antenna mounted on the radar arch is enough.

Once you receive the voice acknowledgement you can always cancel your own distress. Anyway in theory only Class A MF/HF sets and coast stations issue distress ACKs. ( and ship based ones only do after ensuring no coastguard station responded, since GMDSS requires that the Alert , both voice and DSC must/should reach a shore station first).

This is being over thought here

Dave
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Old 25-02-2013, 17:39   #26
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Re: ICOM M802 DSC antenna?

Terry,
I've never received a "Distress ACK" DSC message....(as I've never sent a DSC-Distress message..)
Quote:
Originally Posted by TLSparks View Post
The last Distress Ack I heard was from Norfolk VA to a Turkish vessel in the Black Sea. I was in Mazatlan MX at the time using a Metz antenna.
Although, I have received many DSC messages and have received "ACK" from WLO and NMN to my "test" calls, I've never received someone else's "Distress ACK" on my M-802...
Just wondering if you are using some decoding software???


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Old 25-02-2013, 20:24   #27
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Re: ICOM M802 DSC antenna?

Not using anything special John. Just my 802 with a Metz antenna on the arch. I do keep my radio in DSC watch most of the day just in case someone is in trouble and needs help.

What are you using for an antenna?

Were your tests using individual/group or are you talking about a the actual DSC test call?

I have received 3 distress calls and Acks over the past couple of years as well as many Safety calls. I have gotten the distress calls in port so was able to look up the MMSI as well as take a look at where the vessel was at. The one from the Black Sea, I never heard the call, just the ACK.

I have also received around a dozen Distress Relays for the same calls above. The first distress I heard was in the Atlantic off Columbia when I was in La Paz MX. Someone fell overboard. I had no idea what to do so I called San Diego SAR. I could hear the Distress Relays going off in the background. That gave me a very good feeling about the power of HF DSC.

Regards
Terry

Quote:
Originally Posted by ka4wja View Post
Terry,
I've never received a "Distress ACK" DSC message....(as I've never sent a DSC-Distress message..) Although, I have received many DSC messages and have received "ACK" from WLO and NMN to my "test" calls, I've never received someone else's "Distress ACK" on my M-802...
Just wondering if you are using some decoding software???


John
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Old 26-02-2013, 08:01   #28
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Re: ICOM M802 DSC antenna?

Quote:
Originally Posted by goboatingnow View Post
Why you would want to receive Distress alert acknowledgements from 3000 miles away is strange.
Agree. I can make 6 knots in most conditions, 8 and a bit when everything is perfect. I can't help someone more than a few hundred miles away and even then there is almost always someone better positioned.

If the antenna system on my boat hears a distress call there WILL be others better configured on commercial and government platforms that hear too.

Do I listen? Of course! Will I help if I can? Of course! Do I want to hear Med DSC traffic when I'm between Newport and Bermuda? No.
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Old 26-02-2013, 10:49   #29
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Re: ICOM M802 DSC antenna?

Quote:
I had no idea what to do so I called San Diego SAR. I could hear the Distress Relays going off in the background. That gave me a very good feeling about the power of HF DSC.
Actually GMDSS procedure now is that Distress Relay is not to be used. Relays are to communicated by voice , or at very best using a standard DSC call to a HF/MF coastguard station. The automated or semi-automated use of DSC relays is being removed and abandoned as it has produced vast quantities of DSC alerts bubbling up from one source.

SO the rules is relay all distress alerts by voice
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Old 26-02-2013, 10:59   #30
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Re: ICOM M802 DSC antenna?

Terry,
I think I detailed my set-up quite well in the posts above....(~24' insulated shroud as my DSC-rec and WeFax-rec antenna...)
And, I made indiv calls to both WLO and NMN, and a couple to large ships (QM2, etc.), and a few to other pleasure boats w/ M-802's.....
Sorry, if I didn't detail that clearly...


When I've received "DSC-Distress" calls (only 3 in the past 8+ years) and one "Distress-Relay" call (while in port in Horta, in 2007), I've hit cancel right away to spot the deafening alarm, and switched immediately to the voice ("traffic") channel, so I've never waited to see if I'd receive a "Distress ACK"......

I always figured that the "Distress ACK' was directed at the specific MMSI that sent the "Distress" call in the first place....and that's why I never waited to see if I'd receive one.....now I know different...
So, Terry, thanks for the new info!!!

~~~

As for others comments on not needing to receive DSC calls from 1000's of miles away, you all DO have a point....but since I'm a "radio nut" and since this ability has not been detrimental to me (nor a bother to me or crew), and since it is possible that someday I might wish for this capability, I figure why not!!!
And, in my case, I use this same antenna (using a simple coax "Tee") to feed both my M-802 DSC-rec antenna jack, AND my Furuno FAX-408 WeFax-rec (and my old Alden MarineFaxIV before that)......and it works GREAT for both applications....


Fair winds to all....

John
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