Installing an ICOM802 SSB Part 4: Connecting the emergency DSC antenna

So the last thing I had to do to finish off the ICOM 802 install was plug in an antenna to act as an emergency DSC antenna. ‘What – two antennas for one radio?’ I hear you cry? (although that may be the crow that lives on my spreader)

Yes, weirdly. The 802 has a not-very-well-thought-out setup (in my opinion) where the 2nd antenna is used for receiving DSC signals. ‘But what are DSC signals?’

Well, GLAD YOU ASKED steve and jane! DSC signal is basically a pre-defined message, usually containing GPS co-ords, your MMSI number (kind of like a phone number for a vessel) and a channel to switch to. Using it you can call a vessel directly or send a general distress call, which means a DSC message is sent out containing your GPS coordinates and your vessel MMSI so people can look up your details. Anyone who picks up the DSC call and acknowledges it will be switched to your channel so you can talk to them. Obviously, that is quite useful, especially when on fire or something. DSC signals are a lot more noise tolerant as well, being data like, so then can go further and through worse noise and still be legible.

However (and this is where the weird setup comes in), the 2nd antenna is just used to RECEIVE DSC signals. If you are sending one, it goes out the main antenna. Acknowledging a call – the acknowledgment gets sent out the main antenna. Sending a distress call – it gets sent out the main antenna (though you won’t hear any return ack signals and so won’t get auto-switched to a correct channel.) Basically, if you lose your main antenna, you are screwed. Lose the secondary, then all you lose is the ability to receive other DSC calls or hear acks to your own ones.

ANYWAY, for the two people still reading, a lot of people don’t even bother hooking up the 2nd antenna, as that means another antenna and more fiddling. I decided to add it however, as you may as well have it and I’m a borderline obsessive completionist. Ah well.

Since I wouldn’t be transmitting so it didn’t need to be shielded to avoid RF burn and had a lot greater tolerance to receiving shitty signals I just decided the simplest thing would be to connect the damn thing to one of my shrouds (a 30′ long stainless wire). Or more exactly, one of the chainplates connected to the shrouds. Presto, instant antenna.

First thing was to get some coax cable and a PL259. Then I stripped the coax and attached the PL259.

 

Then I plugged in the cable into the back of the radio (I actually added heat shrink to the connector afterwards, just isn’t shown)

The last thing to do was finish the other end and come up with some way to attach it to my chainplate.

I came up with a crocodile clip, and strung the cable along the top of the locker with zipties and sticky pads

In the pic above you can also see the end of the ground KISS radial.

Once everything was hooked up and plugged in, I tested by switching antennas and was able to take part in a radio net using the 2nd antenna. Once I confirmed it was working fine, I switched antennas back over and called it a day.

Cross another thing off the list!

Matt

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