Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 17-04-2015, 07:17   #1
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,737
DSC Receive Antenna for SSB?

I bought the Metz special antenna for DSC receive for my M802, which I am only just now getting around to installing.

However ---

I have been reading that for receiving HF radio, that an uninsulated stay or shroud works just as well (or even better?).

I have a shroud chainplate almost next to my HF radio, so this would be simplicity itself to connect.

Does it make sense? And could people do the same thing for dedicated Navtex receivers and the like?

I've actually got a Navtex antenna on my pushpit, with cable run, but if I use shrouds for Navtex and DSC, I could replace that antenna with a regular VHF antenna, and have a spare not dependent on the mast being up -- something I have kind of wanted for a while.
__________________

__________________
Dockhead is online now   Reply With Quote
Old 17-04-2015, 07:56   #2
Registered User

Join Date: Sep 2008
Location: Camden, ME
Boat: A Thistle and a Hallberg-Rassy 36
Posts: 661
Re: DSC Receive Antenna for SSB?

Give the shroud a try. If you want to experiment, connect your shroud to the normal txcvr input of your m802 and tune around. You should pick up stations just fine. Also, If when you attach that shroud 'antenna' to the normal txcvr input and you hear an increase of noise (atmospheric not onboard rf interference) you can feel pretty sure your shroud is going to receive DSC about as well or better than a short little whip. That is what I did anyway, and it works fine for the DSC receive only antenna connection.


Sent from my iPhone using Cruisers Sailing Forum
__________________

__________________
SoonerSailor is offline   Reply With Quote
Old 17-04-2015, 08:20   #3
Senior Cruiser
 
Roy M's Avatar

Cruisers Forum Supporter

Join Date: Feb 2007
Location: Southwestern Yacht Club, San Diego, CA
Boat: Searunner 40 trimaran, WILDERNESS
Posts: 3,041
Images: 4
Re: DSC Receive Antenna for SSB?

Dockhead, I noticed that requirement for the DSC antenna while reading the instructions for installing my own M-802. I have an "antenna farm" atop my sterncastle that I keep for my AIS, VHF (plus one at the masthead, planned, using a selector switch), GPS (times two) and FM radio antennas. What model Metz are you using?
__________________
Roy M is offline   Reply With Quote
Old 17-04-2015, 08:21   #4
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,737
Re: DSC Receive Antenna for SSB?

OK, thanks. That's very useful. Anyone else doing this?

How did you ground the shield, by the way?
__________________
Dockhead is online now   Reply With Quote
Old 17-04-2015, 08:22   #5
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,737
Re: DSC Receive Antenna for SSB?

Quote:
Originally Posted by Roy M View Post
Dockhead, I noticed that requirement for the DSC antenna while reading the instructions for installing my own M-802. I have an "antenna farm" atop my sterncastle that I keep for my AIS, VHF (plus one at the masthead, planned, using a selector switch), GPS (times two) and FM radio antennas. What model Metz are you using?
This one: Metz Communication General Coverage/WeatherFax Antenna
__________________
Dockhead is online now   Reply With Quote
Old 17-04-2015, 08:49   #6
Registered User
 
ka4wja's Avatar

Join Date: May 2007
Location: Florida
Boat: Catalina 470
Posts: 2,033
Re: DSC Receive Antenna for SSB?

Dockhead,
1) I actually have been using an insulated aft lower shroud, as my DSC Receive and WeFax Receive antenna for 10 years now...and it works great...

Yes, mine is insulated at the top with a rigging insulator, and fed at the chain plate with the center-conductor of RG-8x coax....with the shield connected to a simple ground wire, running about 8' to a keel bolt....(actually never noticed any difference whether the shield was connected to the keel bolt or not...)

I realize this is not exactly what you asked, as you were asking about using the un-insulated shroud/rig as antenna....but thought I'd pass this on anyway...
Quote:
Originally Posted by Dockhead View Post
OK, thanks. That's very useful. Anyone else doing this?

How did you ground the shield, by the way?


2) But also important here, is a probable peculiarity of the M-802....
-- We DO know that the separate DSC antenna (and dedicated DSC Receiver) is used to receive your DSC-Distress ACK (a DSC acknowledgement of your DSC-Distress Call), while the main antenna and main receiver is monitoring the corresponding GMDSS SSB-Voice freq...
-- We also DO know that the dedicated DSC Receiver (and the separate DSC antenna) continuously scans all six GMDSS DSC freqs, all the while the M-802 is on, looking for "Safety", "Urgency", and "Distress" calls from others...
From the M-802 manual:
Quote:
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.


-- But apparently, when waiting for a response (ACK) from a DSC Test Call, or DSC Routine Call (both are "individual" calls), the M-802's Main Antenna and Main Receiver is being used for this, while the dedicated DSC Receiver is still scanning the six GMDSS DSC Safety and Calling freqs looking for "Safety", "Urgency", or "Distress" calls...
(note that I have not personally verified this myself, but will do so within the month....this info was posted here recently by another Cruiser's Forum member...)

-- So, while having the DSC Receive antenna working well is important in order for you to receive an ACK from your own DSC-Distress Call, and to receive "Safety", "Urgency", and "Distress" calls from others....it appears to not be used for ACK's when you are making other individual DSC calls....
(again, I have not confirmed this personally....and I just finished some major family business, and now am away from the boat for a week or so....so, it will be a few weeks 'til I do confirm all of this....)



I hope this helps...

John
__________________
John, KA4WJA
s/v Annie Laurie, WDB6927
MMSI# 366933110
ka4wja is offline   Reply With Quote
Old 17-04-2015, 08:52   #7
Registered User

Join Date: Sep 2008
Location: Camden, ME
Boat: A Thistle and a Hallberg-Rassy 36
Posts: 661
Re: DSC Receive Antenna for SSB?

I didnt ground the shield. Of course it grounds at the receiver end, but no need at the antenna end. There is of course a large impedance mismatch (high SWR) between the long wire antenna (shroud) and the 50 ohm receiver/coax on most bands, but that makes little difference to receive strength. If the coax run is fairly short there will be minimal SWR related signal loss at DSC frequencies.


Sent from my iPhone using Cruisers Sailing Forum
__________________
SoonerSailor is offline   Reply With Quote
Old 17-04-2015, 10:35   #8
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,737
Re: DSC Receive Antenna for SSB?

Quote:
Originally Posted by ka4wja View Post
Dockhead,
1) I actually have been using an insulated aft lower shroud, as my DSC Receive and WeFax Receive antenna for 10 years now...and it works great...

Yes, mine is insulated at the top with a rigging insulator, and fed at the chain plate with the center-conductor of RG-8x coax....with the shield connected to a simple ground wire, running about 8' to a keel bolt....(actually never noticed any difference whether the shield was connected to the keel bolt or not...)

I realize this is not exactly what you asked, as you were asking about using the un-insulated shroud/rig as antenna....but thought I'd pass this on anyway...




2) But also important here, is a probable peculiarity of the M-802....
-- We DO know that the separate DSC antenna (and dedicated DSC Receiver) is used to receive your DSC-Distress ACK (a DSC acknowledgement of your DSC-Distress Call), while the main antenna and main receiver is monitoring the corresponding GMDSS SSB-Voice freq...
-- We also DO know that the dedicated DSC Receiver (and the separate DSC antenna) continuously scans all six GMDSS DSC freqs, all the while the M-802 is on, looking for "Safety", "Urgency", and "Distress" calls from others...
From the M-802 manual:


-- But apparently, when waiting for a response (ACK) from a DSC Test Call, or DSC Routine Call (both are "individual" calls), the M-802's Main Antenna and Main Receiver is being used for this, while the dedicated DSC Receiver is still scanning the six GMDSS DSC Safety and Calling freqs looking for "Safety", "Urgency", or "Distress" calls...
(note that I have not personally verified this myself, but will do so within the month....this info was posted here recently by another Cruiser's Forum member...)

-- So, while having the DSC Receive antenna working well is important in order for you to receive an ACK from your own DSC-Distress Call, and to receive "Safety", "Urgency", and "Distress" calls from others....it appears to not be used for ACK's when you are making other individual DSC calls....
(again, I have not confirmed this personally....and I just finished some major family business, and now am away from the boat for a week or so....so, it will be a few weeks 'til I do confirm all of this....)



I hope this helps...

John
My shrouds are massive 16mm cable which is not really realistic to insulate -- do you think this will work ok without being insulated? And in general, do you think this is a good plan, or should I use the Metz antenna?

And should I ground the coax shield?

Grateful as always for your expert advice, which will benefit others on here, too.
__________________
Dockhead is online now   Reply With Quote
Old 17-04-2015, 10:37   #9
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,737
Re: DSC Receive Antenna for SSB?

Quote:
Originally Posted by SoonerSailor View Post
I didnt ground the shield. Of course it grounds at the receiver end, but no need at the antenna end. There is of course a large impedance mismatch (high SWR) between the long wire antenna (shroud) and the 50 ohm receiver/coax on most bands, but that makes little difference to receive strength. If the coax run is fairly short there will be minimal SWR related signal loss at DSC frequencies.


Sent from my iPhone using Cruisers Sailing Forum
Does it work ok?

The coax run will be less than 2 meters if I do it this way.

And it seems to me that I wouldn't actually need coax at all over this kind of distance. I could just use a bit of GTO or even plain copper wire.
__________________
Dockhead is online now   Reply With Quote
Old 17-04-2015, 10:52   #10
Registered User

Join Date: Sep 2008
Location: Camden, ME
Boat: A Thistle and a Hallberg-Rassy 36
Posts: 661
Re: DSC Receive Antenna for SSB?

Yes GTO or insulated wire would be as good or better, unless it runs very close to a source of RFI that coax shield might mitigate. In fact a banana plug will fit into the center of the SO-239 on the m802 so you can solder your wire to that and not bother with using a PL-259 like you need to on your main antenna connection. A 2 meter coax run would not have be any problem though.

It works well on my boat. The shroud is not insulated at the top, and not grounded at the chainplate.


Sent from my iPhone using Cruisers Sailing Forum
__________________
SoonerSailor is offline   Reply With Quote
Old 17-04-2015, 11:17   #11
Registered User
 
ka4wja's Avatar

Join Date: May 2007
Location: Florida
Boat: Catalina 470
Posts: 2,033
Re: DSC Receive Antenna for SSB?

Dockhead,
I do think your plan will work....but, you can just try it and see...use this new antenna as your "main" antenna for receive testing of various signals / compare this to your regular "main" antenna, and you should be good to go...
Quote:
Originally Posted by Dockhead View Post
My shrouds are massive 16mm cable which is not really realistic to insulate -- do you think this will work ok without being insulated? And in general, do you think this is a good plan, or should I use the Metz antenna?

And should I ground the coax shield?

Grateful as always for your expert advice, which will benefit others on here, too.
But, I'm afraid I disagree slightly with SoonerSailor here....
I would not run a simple wire / GTO-15, etc. from the M-802 to the chain plate....
I WOULD use coax....even if all you do is connect the center conductor to the chain plate, I would still use coax....
(a few feet of RG-8x or even RG-58, with a PL-259 on it, is cheap!!!)


Now, having written the above....I need to disclose that I DID use a 35' length of black GTO-15 wire (soldered into the center of a PL-259), right from a radio, out thru a thru-deck fitting, and run up along a shroud (twisted it around the shroud tightly, and secured with some cable ties), and used this for years on another boat as both a WeFax receive antenna, and a SW receive antenna....going to an Alden MarinFAX and to a Yaesu FRG-7 (yes this was 35+ years ago)....and I even had a Palomar Engineering VLF converter to allow LW / 200khz reception of UK shipping forecasts, etc., using this antenna and the Yaesu....
So....

So, not only CAN you run your antenna wire directly to the receiver input, but I've done this on-shore often, as well as on-board years ago...
BUT...

But, again this was years ago....and/or on-shore, where I could control received RFI, etc...

So, I still think feeding the chain plate with coax is the better approach...



I hope this helps.

John
__________________
John, KA4WJA
s/v Annie Laurie, WDB6927
MMSI# 366933110
ka4wja is offline   Reply With Quote
Old 17-04-2015, 11:21   #12
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,737
Re: DSC Receive Antenna for SSB?

Quote:
Originally Posted by ka4wja View Post
Dockhead,
I do think your plan will work....but, you can just try it and see...use this new antenna as your "main" antenna for receive testing of various signals / compare this to your regular "main" antenna, and you should be good to go...

But, I'm afraid I disagree slightly with SoonerSailor here....
I would not run a simple wire / GTO-15, etc. from the M-802 to the chain plate....
I WOULD use coax....even if all you do is connect the center conductor to the chain plate, I would still use coax....
(a few feet of RG-8x or even RG-58, with a PL-259 on it, is cheap!!!)


Now, having written the above....I need to disclose that I DID use a 35' length of black GTO-15 wire (soldered into the center of a PL-259), right from a radio, out thru a thru-deck fitting, and run up along a shroud (twisted it around the shroud tightly, and secured with some cable ties), and used this for years on another boat as both a WeFax receive antenna, and a SW receive antenna....going to an Alden MarinFAX and to a Yaesu FRG-7 (yes this was 35+ years ago)....and I even had a Palomar Engineering VLF converter to allow LW / 200khz reception of UK shipping forecasts, etc., using this antenna and the Yaesu....
So....

So, not only CAN you run your antenna wire directly to the receiver input, but I've done this on-shore often, as well as on-board years ago...
BUT...

But, again this was years ago....and/or on-shore, where I could control received RFI, etc...

So, I still think feeding the chain plate with coax is the better approach...



I hope this helps.

John
As always, it helps a lot, of course!

There's no cost issue -- I have tons of coax lying around. I just want the best solution. It seems to me that coax might cause impedance problem which GTO or plain wire wouldn't. Or maybe it doesn't matter, since it's a run of less than 2 meters?

What concerns RFI: I have a blessedly quiet boat. I have a couple of rogue LED lighting unit which put out a little RFI which sounds like white noise, but that's it (and I'm going to hunt those down and kill them eventually). I doubt if 1.5 meters of GTO inside the cabin is going to make much difference in RFI.
__________________
Dockhead is online now   Reply With Quote
Old 17-04-2015, 11:41   #13
Registered User

Join Date: Sep 2008
Location: Camden, ME
Boat: A Thistle and a Hallberg-Rassy 36
Posts: 661
Re: DSC Receive Antenna for SSB?

Your Coax impedance is same as the radio's input impedance if you are using the right stuff. Even if the shroud happens to be exactly 1/2 wave at a frequency of interest, with an SWR of 40:1 (a worst case scenario), and that frequency is 16 mHz (highest of the DSC frequencies I think), your 2m coax SWR loss would only be about 1 dB if using RG8x, a trivial figure. At lower frequencies loss is even less. If you use RG-8 losses would be half of those figures, but I wouldn't bother. Bottom line is dont worry about coax loss on such a short run.


Sent from my iPhone using Cruisers Sailing Forum
__________________
SoonerSailor is offline   Reply With Quote
Old 17-04-2015, 13:08   #14
Registered User

Join Date: Sep 2008
Location: Camden, ME
Boat: A Thistle and a Hallberg-Rassy 36
Posts: 661
Re: DSC Receive Antenna for SSB?

On top of that, when you talk of coax losses on receive, both signal AND noise are attenuated that little tiny bit - the signal to noise ratio is unchanged, which figure is by far going to be the limiting factor at the HF frequencies used by DSC.


Sent from my iPhone using Cruisers Sailing Forum
__________________
SoonerSailor is offline   Reply With Quote
Old 17-04-2015, 20:19   #15
Jd1
Registered User

Join Date: Aug 2011
Location: Victoria, BC
Boat: Catalina 36 MKII
Posts: 1,095
Re: DSC Receive Antenna for SSB?

Quote:
Originally Posted by Dockhead View Post
OK, thanks. That's very useful. Anyone else doing this?

How did you ground the shield, by the way?
I am using a side stay for my DERA. I do not run coax but just a straight 18 ga marine wire. This works reasonably well when connected to the primary antenna input so I assume it is fine for the DERA. I have NOT been able to verify correct operation though!!!
Please note, only emergency related DSC messages go through the DERA. Although the 'test' function of the M802 DSC system is supposedly going through the DERA, I was able to verify that I can get an Ack to a test call without the DERA connected.
Testing the DERA system remains a project in progress.
Late addition:
the stay is grounded at the mast (not the chain plate)
RFI is generally not an issue unless you run your cable right past a big source of RFI. The stay that is your antenna will pick up any significant RFI even if you use coax for the lead-in of the DERA
__________________

__________________
Jd1 is offline   Reply With Quote
Reply

Tags
antenna, dsc, ssb

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
SSB Current Draw - Both Transmit and Receive tedcoats Marine Electronics 32 16-01-2015 09:37
SSB weatherfax receive only antenna csmithers Marine Electronics 3 25-02-2013 16:48
Where to Mount Antenna For SSB DSC Dockhead Marine Electronics 31 14-01-2013 09:59
Raymarine AIS250 receive fault due to SSB? Goudurix Marine Electronics 4 02-10-2012 02:54
Weatherfax Receive-Only Antenna Routing akio.kanemoto Marine Electronics 8 20-09-2011 17:39



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 05:18.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.