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Old 25-06-2010, 14:54   #1
RDW
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Usefullness of Second Receiving SSB Antenna

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.
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.
Any comments on the correctness of my information?
Any comments on the usefullness of doing this set up?
I await your informed kind reply.
Be nice, I am a learner.
RDW
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Old 25-06-2010, 15:52   #2
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Your information is correct. You don't need a fancy antenna for the DSC receiver in your M802, since all it is doing is receiving. To an extent, the longer it is the better. Try to run the antenna away from potential sources of RF interference, and use insulated wire for corrosion protection and to prevent accidental shorts or grounding the antenna itself.

I still need to do the same thing myself.
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Old 26-06-2010, 01:48   #3
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Metz supply a neat HF whip with optional rail mount.



Since ICOM have gone to the trouble of installing a separate DSC receiver it seems sensible to hook up an antenna to it.
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Old 26-06-2010, 07:04   #4
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I'm sure that Metz antenna works fine and looks good, but it isn't likely to perform significantly better than a straight piece of wire also mounted clear of other conductors. If I had one I would certainly use it, but I'm also disinclined to spend the $60 or so on it when its easy enough to get the same results with $5.
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Old 26-06-2010, 11:36   #5
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It is REQUIRED not optional! DSC receive will NOT work without it. All you'll be able to do without it is send the DSC transmission and there will be NO AK! It NEEDS to be either the Metz #201 or a 17+' fiberglass SSB antenna not just a length of wire laying on the rail or hull as it needs to receive in the 2-16 MHz range. ICOM fails to include this info in the manual except on pages 5 #4 and 54, 56, which is incomplete information. From experience the rail mounting of the Metz 201 is not a good idea on sail as it will give spotty reliability and you'll not be able to receive either group or individual calls nor will the DSC WATCH receive any transmissions. From Metz themselves as high as possible; astern of the tuner. My recommendation; a FG whip on davits. This way you will have a backup antenna if the backstay fails. All you need to do is is switch antenna plugs and you'll have both send receive capabilities. The Metz will not be capable of this as it is a receive ONLY antenna.
If there are any doubts, try sending a "TEST" transmission; AK is automatic; if no response, it's NOT working.
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Old 26-06-2010, 11:56   #6
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Quote:
Originally Posted by SoonerSailor View Post
I'm sure that Metz antenna works fine and looks good, but it isn't likely to perform significantly better than a straight piece of wire also mounted clear of other conductors. If I had one I would certainly use it, but I'm also disinclined to spend the $60 or so on it when its easy enough to get the same results with $5.
Makes you wonder why radio HAMS spend all that money on towers & fancy antenna's
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Old 26-06-2010, 14:31   #7
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Hams, like me, need to transmit without having large amounts of power reflected back into their transmitter final amplifiers, that is one reason why they need antennas tuned to the bands they are interested in.

For RECEPTION ONLY, which is what the DSC antenna on the M802 is used for, you absolutely do not have to have a specialized antennna, and any good length random wire will provide that reception. That is why ICOM doesn't make a big deal out of DSC antenna requirements in the M802 manual.

Have you ever had a decent portable shortwave radio with a whip antenna? What limits your ability to hear stations in the 2 to 16 mHz range? It is background QRN or atmospheric noise that is well above the noise floor of the radio. Having a fancier antenna in this frequency range is not going to help reception much, unless it is directional, and you don't want a directional DSC receive antenna.

No doubt that Seahunter's setup is best, who wouldn't want a backup transmitting antenna too?

Chip
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Old 26-06-2010, 18:26   #8
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SoonerSailor, in the US under the Rescue21 system the DSC antenna is REQUIRED. This is the DSC's ONLY receiving antenna; so you will NOT receive DSC transmission to your radio's MMSI number if you do not have one. The M802 has 2 (two) receivers). This information is directly from Icom (the manual and technical support) . More information can be found at Icom SSB Radio Kits
and page 19 of the "Icom Radio manual for ID-Yachts".
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Old 26-06-2010, 18:59   #9
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There is no requirement to have a DSC receive antenna. Rescue 21 is a VHF radio based system that provides coverage out to 20nm. It has nothing to do with long range HF communications.

Eric
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Old 26-06-2010, 19:10   #10
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Quote:
Originally Posted by fairbank56 View Post
There is no requirement to have a DSC receive antenna. Rescue 21 is a VHF radio based system that provides coverage out to 20nm. It has nothing to do with long range HF communications.

Eric
This is true in part. This is from the DSC page of the Rescue 21 site.
"No new equipment is needed for you to benefit from Rescue 21. The new system will increase the Coast Guard’s ability to respond to distress calls in the coastal zone. However, you can help us improve response time by using a marine-band VHF-radio equipped with digital selective calling (DSC)."
The official stand of the USCG is that channel 16VHF will become unmonitored sometime in the future and that all emergency call will be DSC; meaning VHF DSC (channel 70) or HF SSB channels. They support both right now and in the very near future commercial traffic will not be live monitored on ANY channel whether LF/MF/HF and all emergency traffic will be digital.
If you want the right stuff go here:
http://www.uscg.mil/acquisition/resc...CFactSheet.pdf


By the way DSC on the ICOM can be as far away as 800nm not 20nm. DSC on VHF is 20nm. The M802 transmits on HF channels; it receives on the DSC receiver. Ergo, if you send a DSC emergency call on your Icom M802; a receiving antenna is REQUIRED.
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Old 26-06-2010, 19:16   #11
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SeaHunter - I don't understand why you think I'm saying not to put an antenna on the DSC connector? A random length of wire IS an antenna, just not a store-bought one. I'm only making the point that this random length of wire is likely to function every bit as well in the receive only function as a pretty little manufactured antenna marketed for that purpose and sold for a handsome profit. And if having HF DSC function is important to the sailor, he should certainly test and confirm the function of whatever he installs.

I'll certainly concede that your recommendation for a separate 17' SSB whip for DSC receive, that could also function as a backup transceive antenna is a nice idea for those with the desire, space, and wherewithal to add it to their vessel.
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Old 26-06-2010, 19:30   #12
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A DSC receiving antenna is not required on your M802. You can still send an emergency transmission. You won't get an ack but you may not anyway even if you do have a DSC receiving antenna.

Eric
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Old 26-06-2010, 19:57   #13
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Yes guys I understand what you're both saying. Eric; there's absolutely no point to a DSC emergency transmission if you don't get an AK. Firstly, you wouldn't know if was even received and secondly you would be spending valuable prep time trying to save the boat. You would be better in that scenario to just do an emergency call directly on the USCG HF channel and talk to someone directly. It's the whole point of DSC to do everything automatically.
SS; yes a random piece of wire should work, but it doesn't. I even made a matched antenna with wire and it didn't work. I also tried a second backstay wire, that actually worked, however my point was to have a backup SSB antenna and removed it. I even have issues with the Metz 201 mounted to the rail (I ended up mounting it mizzen mast where it works perfectly). I went with a Shakespeare 171/2' SSB antenna mounted to the davits as my emergency/backup. I'm actually thinking of adding a second for the DSC receive as the backup receive, (I strung the cable already) but as with all things on boats $300+ here and $300+ there adds up.
It's funny when I spoke with ICOM support they initial told me they liked the 27' Shakespeare for the receiver but I was thinking like you; "why the hell spend that kind of money...I can make that".
Anyways the point was to answer the question posed in the thread and after messing around with so many options this is where it ended.
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Old 26-06-2010, 20:15   #14
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Eric; there's absolutely no point to a DSC emergency transmission if you don't get an AK.
Sure there is. That's the point of the red button. It's automatic. You can press the red button and walk away to attend to your emergency if need be. It will continue to send until you get an ACK. With HF, you may not get one anyway even if your transmission was received due to the nature of HF propagation and the fact that your DSC receiving antenna is likely much less efficient than your tuned transmitting antenna. Obviously, it is a good idea to have the receiving antenna so that you can monitor the DSC channels as well as receive an ACK to your own transmissions, but it is certainly not a requirement.

Eric
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Old 26-06-2010, 22:11   #15
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Oh boy. Let's make it clear, Eric. If you hit the red button on the ICOM IC-M802 and there's no digital receive response from your radio (because you don't have a receive antenna to receive the packets), the USCG does nothing except report your call to the FCC. There's a USCG bulletin on this and I'm not going to take the time to look it up again, so you can do some research of your own. Oh what the hay... http://www.uscg.mil/directives/ci/16...CI_16121_1.pdf , Digital Selective Calling - USCG Navigation Center
If you hit the red button on your ICOM IC-M802 without the receive antenna hooked up you might as well be on the bow taking a P into the wind.
On the ICOM IC-M802 without a DSC receive antenna you cannot: Hear ANY DSC traffic, including making a position, induvidual, test, all ships call, distress relay call, or group call as well as use your DSC Watch mode.
I don't know about other SSB radios but I do know the ICOM IC-M802.
On VHF DSC radios the send and receive are both done on channel 70 and there is no voice option. It's all digital. So yes, when you hit the "panic button" on your VHF radio; you're right it doesn't matter; however, on the ICOM IC-M802 it does.
On the ICOM IC-M802 none of the DSC features works without a receive antenna.
That's it.
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