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Old 18 August 2018, 14:41   #1
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Sending a test mayday via DSC

I'm tempted to replace the aerial on my handheld DSC VHF with a dummy load that'll mean that the range should be reduced from miles to feet. This should then allow me to familiarise myself with, and test, the red button functions.

I would do it next to my boat with a fixed DSC set. I could put a dummy load on that set too & try in the reverse direction.

Does anyone have any experience in doing this? Does a Mayday acknowledgement alert other users? Are there any pitfalls, other than the blatant one of triggering a response if anyone else receives it?
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Old 18 August 2018, 15:43   #2
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Iirc, there's a facility to send a "test" dsc message without the faff of dummy loads & the risk of alerting the cavalry. Just select "test" for the dsc message type. Or I could be talking bolleaux
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Old 18 August 2018, 16:49   #3
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Don't know if they all have it but my icom has the test facility.

Probably something in your user manual?
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Old 18 August 2018, 17:17   #4
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Quote:
Originally Posted by simonl View Post
I'm tempted to replace the aerial on my handheld DSC VHF with a dummy load that'll mean that the range should be reduced from miles to feet. This should then allow me to familiarise myself with, and test, the red button functions.
What is to familiarise yourself with?

When you walk past a fire alarm do you think I should press that and see what happens?

Quote:
I would do it next to my boat with a fixed DSC set. I could put a dummy load on that set too & try in the reverse direction.

Does anyone have any experience in doing this? Does a Mayday acknowledgement alert other users? Are there any pitfalls, other than the blatant one of triggering a response if anyone else receives it?
You can NOT acknowledge a Mayday with a Class D set. It will sit trying to re-transmit unless you cancel it.

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Originally Posted by Pikey Dave View Post
Iirc, there's a facility to send a "test" dsc message without the faff of dummy loads & the risk of alerting the cavalry. Just select "test" for the dsc message type. Or I could be talking bolleaux
Pikey is right, modern sets have a test function. That allows you to test the digital workings basically it sends a digital call to someone (CG seems sensible) and it auto responds. That will be in a menu somewhere. Wont be via the red button.

Handheld DSC do have a few nuances from my understanding as they often have GPS switch to off to conserve power. For iCom M93:

Hold down Red Button for 3 seconds. It bleeps to say to release it.
Wait while message sent and digital acknowledgement received
Set re-tunes to 16 - transmit voice mayday.

If GPS is off, it will try to get a fix for 15seconds. No position it sends the last known pos from previous 4 hours unless the radio was switched off.

If a pos is then received within next 20 minutes even if already ACK'd it sends a fresh alert (depending on country of set config).

None of that will be obvious on a dummy load.

If you were thinking stuff like selecting type of distress... ...think how likely it is in a distress you are really going to go through a menu selecting the emergency. Imagine if you dial 999 and speak to a person but dial 112 and answer 1 for a fire, 2 for ambulance, 3 for police. Then 1 for cardiac arrest ... 9999 for stubbed your big toe etc... You'll take a person every time.

You can program a soft key on the M93 to get you to the menu pretty quick but from the list:

Undesignated - no change
Fire - If my boat is on fire - I'm not messing with finding the right options on the menu!
Flood - On a RIB?
Collision - Possible. But what does it really add to the distress message, other than there may be 2+ alerts
Grounding - Is that likely to be a Mayday on a RIB?
Capsizing - Possible. In which case it is capsized! Only relevant on a HH.
Sinking -
MOB = Better to use the MOB button on the set which gets you a waypoint but also pre-sets the DSC distress alert...
Abandon Ship - unusual on a RIB
Listing - probably not relevant on a RIB
Disabled and adrift - as a distress?
Piracy - not commonly an issue in the UK

Ultimately the help sent is unlikely to differ much. A drifting boat - needs a tow not a chopper. But why is it a distress. A MOB - probably useful to know the distress may be in a different location to the boat. But the set will do that from the MOB button or when wet.

The rest will either be so catastrophic that you may not have time to send a specific alert or is not urgent enough to mean a voice call cant clarify the needs... If you do use the soft key you select the type then hit the red button as before...
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Old 22 August 2018, 17:27   #5
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Thanks for the replies. It had never occurred to me that my set (Class D) wouldn't be able to acknowledge a Mayday, but makes sense.

I don't subscribe to the fire alarm analogy though. You can't beat regular hands-on training to get to a good level of familiarity. I'm happy that I could work it out, but it may be needed in situations where there is intense pressure and normal behaviour/capability vanishes. I've seen it happen.
Stuff into a freak wave in diminishing light with broken ribs, one person lost overboard, an unconscious child and a handheld DSC with the speaker full of water so you can't hear any beeps. I'm being slightly pedantic, but I'd prefer to understand the nuances.
It would help if the manufacturers put a detailed video of the behaviour of their products in Mayday situations.
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Old 22 August 2018, 17:48   #6
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Simon - I presume youve done the appropriate training course? What did you not do on that which you wish you could now?

The only specific thing I felt was missing (from a distress perspective) was using the actual set I own. I feel having read the manual though gives me that. If I was really worried Id maybe shop around for a vhf school that used my brand and ask if I could do a 1 hr refresher?
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Old 23 August 2018, 08:34   #7
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Simon - I presume youve done the appropriate training course? What did you not do on that which you wish you could now?

The only specific thing I felt was missing (from a distress perspective) was using the actual set I own. I feel having read the manual though gives me that. If I was really worried Id maybe shop around for a vhf school that used my brand and ask if I could do a 1 hr refresher?
I did a course ages ago. My only real memory from that was that the instructor didn't have a clue how DSC works.

Some of my unanswered questions:

If you can reach another boat, but not a Coast station (quite likely if in close) then how do you know when to switch to 16 to use the voice? How do you know if they have received the DSC broadcast? What's the difference between a Coastal Station acknowledgement & another Class D radio 'acknowledging'? If you & the other class D radio go to Ch16, does your set keep sending on CH70 pending acknowledgement by Coastal Station? (Standard Horizon HX870)

Does a chart plotter (Garmin 172C, Bidirectionally DSC compatible) normally automatically create a waypoint & 'goto' it or do you have to dig down to find it?

I'm not worried per se by not knowing this, but I do like to fully understand things & I'd rather know all this in advance than when I'm floating in a rough sea or trying to help a third party in a Mayday Relay situation.
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Old 23 August 2018, 16:34   #8
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Quote:
If you can reach another boat, but not a Coast station (quite likely if in close) then how do you know when to switch to 16 to use the voice?
if it is not acknowledged the radio remains on '70' transmitting the distress data periodically. Manually changing to 16 will stop further transmission on 70. IIRC sets receiving a DSC distress alert will automatically turn to Ch 16, if the user doesn't do anything after about 15 (?) seconds; you radio will not retransmit the DSC message for 4 minutes so you might as well hit red button, wait 15 secs and if not acknowledged by shore station, change to Ch 16 and make your voice call. If that goes unanswered then repeat the process.

Quote:
If you & the other class D radio go to Ch16, does your set keep sending on CH70 pending acknowledgement by Coastal Station? (Standard Horizon HX870)
no your radio can only be tuned to one frequency at a time. If you have two radios there could be an argument for leaving one transmitting the DSC and voice comms on the second one?

Quote:
Does a chart plotter (Garmin 172C, Bidirectionally DSC compatible) normally automatically create a waypoint & 'goto' it or do you have to dig down to find it?
the behaviour of chartplotters is much more manufacturer variable than DSC (which is defined by standards). Since you were talking about fitting dummy loads you are obviously not scared of electronics - it should be easy enough to "mock" a DSC alert going into the plotter to see how it behaves (or spend a weekend in the solent).

I believe that when YOUR plotter receives a DSC position message from the radio it will open a "pop up" on the screen. That pop-up will have an option allowing you to navigate to it. You can send a position DSC message (not distress) and will get very similar behaviour. Its all in the manual.
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Old 23 August 2018, 17:27   #9
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Some of my unanswered questions:

If you can reach another boat, but not a Coast station (quite likely if in close) then how do you know when to switch to 16 to use the voice?
If they are a Class A set they COULD acknowlegde. But lets assume they don't or are Class D. Then OFFICIALLY what they should do is when they receive your alert, and have decided no-one else is acknowledging (quite when - who knows!) they contact you on 16. Your DSC set can cope with that.

I suspect in reality the absolute urgency of your call will define when you decide voice may work when digital doesn't. (Remember not all users have DSC). Unconscious child, person in the water, I wouldn't wait more than a few seconds before going to voice, especially if you think the geography may affect acknowledgement. There is no-one going to tell you off for not getting this perfectly right.

Your HX870 - for an incoming call will auto re-tune to CH16 after 15 seconds. So if your call can wait more than 15 seconds... waiting will mean more people's sets have tuned to 16 to hear you.

Quote:
How do you know if they have received the DSC broadcast?
Your set will say something like "Waiting for ACK" then "ACK received" and return to 16 automatically.

Quote:
What's the difference between a Coastal Station acknowledgement & another Class D radio 'acknowledging'?
Coastguard ACK = "We have received and are handling your call"
Class D - Is a local cancel of the alarm on the set - nothing else.

Quote:
If you & the other class D radio go to Ch16, does your set keep sending on CH70 pending acknowledgement by Coastal Station? (Standard Horizon HX870)
On the SH870 pressing 16 will cancel further retrying.


Quote:
Does a chart plotter (Garmin 172C, Bidirectionally DSC compatible) normally automatically create a waypoint & 'goto' it or do you have to dig down to find it?
It needs both the plotter and the VHF to be bi-directional.
Then behaviour will vary by plotter. The 172C displays a Pop-up Window which tells who the distress boat is and its pos. With a bearing and distance. You can then select "Create WPT" and you can click show on chart...

The 172C has a simulator mode ... ...you can simulate a DSC alert in it.

Quote:
Originally Posted by simonl View Post
Thanks for the replies. It had never occurred to me that my set (Class D) wouldn't be able to acknowledge a Mayday, but makes sense.
That should have been covered on your course. Part of the reason that they will have taught you how to do a MayDay Relay on DSC - with the instruction to send an Urgency Message rather than a distress...

Quote:
I don't subscribe to the fire alarm analogy though. You can't beat regular hands-on training to get to a good level of familiarity. I'm happy that I could work it out, but it may be needed in situations where there is intense pressure and normal behaviour/capability vanishes. I've seen it happen.
Stuff into a freak wave in diminishing light with broken ribs, one person lost overboard, an unconscious child and a handheld DSC with the speaker full of water so you can't hear any beeps. I'm being slightly pedantic, but I'd prefer to understand the nuances.
But it really is no different to a Fire alarm! Ignore all the nonsense about types of distress etc. In panic / flap mode you want simple.
Provided you have a GPS switched on and connected (or it is inbuilt) simply open the protective cover and hold down the red button for 5 seconds. (Some sets are 3 seconds, but I think some are 5 - so just go for it). The screen will say something like "Sending Undesignated DSC Distress Alert 5, 4, 3, 2, 1"
That bit is almost as close to a fire alarm as you can get.

Then Wait.

When the ACK is received - Set re-tunes to 16 and read the prompt card you stick next to the radio with blanks filled in... ...thats probably something like dialling 999 after breaking the fire alarm.

But if what you want is to be familiar with the other aspects of DSC - use it for routine calling, position polling, test calls etc.

Quote:
It would help if the manufacturers put a detailed video of the behaviour of their products in Mayday situations.
What is your radio... Contact SH and suggest it... What is your fixed unit that is interfaced to the Garmin?
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Old 23 August 2018, 19:24   #10
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Thanks for the great & comprehensive answers. Knowing the underlying fundamentals makes dragging through the manual much more productive.
I guess a day in the Solent would have me much more familiar. Having had my ICOM IC-M603 turned on for many hundreds of hours, the only time it has alarmed was whilst refueling in Tesco. It was so bloody loud the woman alongside thought it was a fire alarm & dragged her kids out of the car!
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