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Old 12-11-2016, 10:48   #1
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SSB DSC antenna idea

Hi,

I'm installing a new Icom M802 right now, replacing a failed 20+ y/o SEA unit. So most of my installation issues are easy, except the old unit did not have DSC capability.

I've read many threads here about the DSC receive antenna, so I feel well informed (despite the real lack of info from Icom). In thinking about various ways to install a passive DSC receive antenna I had an idea that I'd like feedback on.

I'm looking at the stainless steel strip on my rub rail that runs about 44 feet along my boat. I've checked continuity and it is not grounded or otherwise connected to the boat. I could very easily remove one of the screws, drill a skinny pilot hole through the rub rail and hull (right at the deck/hull joint), pass an unshielded antenna wire through and connect to the stainless steel strip. I can do this right where the SSB transceiver box is mounted, so it would be extremely simple to do. Maybe ten boat minutes (ok, an hour).

Is there any reason not to? The only thing that I can think of is that when sailing with the rail in the water (I have a somewhat low freeboard) then it's possible the rail would ground out with the boat and then not receive DSC calls. Seems like a very minor concern, but maybe not. Any other reason?

Thanks,

JR
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Old 12-11-2016, 11:24   #2
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Re: SSB DSC antenna idea

A horizontal strip just a few feet above the water line will not make a very effective HF antenna in my experience. A vertical whip will receive much better.
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Old 12-11-2016, 11:29   #3
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Re: SSB DSC antenna idea

Quote:
Originally Posted by jr_spyder View Post
Hi,

I'm installing a new Icom M802 right now, replacing a failed 20+ y/o SEA unit. So most of my installation issues are easy, except the old unit did not have DSC capability.

I've read many threads here about the DSC receive antenna, so I feel well informed (despite the real lack of info from Icom). In thinking about various ways to install a passive DSC receive antenna I had an idea that I'd like feedback on.

I'm looking at the stainless steel strip on my rub rail that runs about 44 feet along my boat. I've checked continuity and it is not grounded or otherwise connected to the boat. I could very easily remove one of the screws, drill a skinny pilot hole through the rub rail and hull (right at the deck/hull joint), pass an unshielded antenna wire through and connect to the stainless steel strip. I can do this right where the SSB transceiver box is mounted, so it would be extremely simple to do. Maybe ten boat minutes (ok, an hour).

Is there any reason not to? The only thing that I can think of is that when sailing with the rail in the water (I have a somewhat low freeboard) then it's possible the rail would ground out with the boat and then not receive DSC calls. Seems like a very minor concern, but maybe not. Any other reason?

Thanks,

JR
The rub rail would probably work just fine. Two thoughts, though:

1. You don't need to pass a wire thru the hull. Rather, when you remove the screw for the rubrail and drill a hole, use an appropriately sized s/s bolt to pass thru the hull, and attach the antenna to that bolt. You could very easily seal that connection with marine sealant.

2. The rub rail would make an excellent radial for the SSB. If you need to improve your RF ground on the SSB, try that first and if it works well then find another solution for the DSC antenna.

Bill
WA6CCA

PS - transmitterdan is right...it wouldn't be the best DSC antenna but, then, you don't need much of one....unless you're into receiving DSC calls from the Med. :-)
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Old 12-11-2016, 13:37   #4
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Re: SSB DSC antenna idea

I'm giving this a try: http://www.made-simplefor-cruisers.c...ade%20DERA.pdf. I bought a premade 12' pl-259 cable on ebay, stripped suggested 6', connected to the radio and snaked the cable inside towards the cockpit. For $8, it is worth a try -- I'm waiting to see how this works.
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Old 13-11-2016, 08:27   #5
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Re: SSB DSC antenna idea

Sorry Pal I do not see the point.

The Manual says:
Frequency coverage
Rx
0.5 29.9999 (continuous)
Tx
(unit: MHz)
1.6 2.9999, 4.0 4.9999, 6.0 6.9999
8.0 8.9999, 12.0 13.9999, 16.0 17.9999
18.0 19.9999, 22.0 22.9999, 25.0 27.5000

Looks like a perfect unit. So, a perfect unit requires a perfect antenna.
It is common to have an antenna at the aft-stay with a baloun and a coax-cable and not something. Do not forget to ground your tx to get an ultimte dipole. And please invest th same money you paid for the tx for the antenna baloun and an professional to mount and adjust it. It is worth the money.
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Old 13-11-2016, 09:46   #6
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Re: SSB DSC antenna idea

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Originally Posted by moseriw View Post
Sorry Pal I do not see the point.

The Manual says:
Frequency coverage
Rx
0.5 29.9999 (continuous)
Tx
(unit: MHz)
1.6 2.9999, 4.0 4.9999, 6.0 6.9999
8.0 8.9999, 12.0 13.9999, 16.0 17.9999
18.0 19.9999, 22.0 22.9999, 25.0 27.5000

Looks like a perfect unit. So, a perfect unit requires a perfect antenna.
It is common to have an antenna at the aft-stay with a baloun and a coax-cable and not something. Do not forget to ground your tx to get an ultimte dipole. And please invest th same money you paid for the tx for the antenna baloun and an professional to mount and adjust it. It is worth the money.
I think the OP is referring to the dedicated DSC receive antenna required for the M802, not the main RX/TX antenna.
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Old 13-11-2016, 10:09   #7
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Re: SSB DSC antenna idea

Yes, this is about the dedicated SSB receive-only antenna (which is meant to be kept simple and is rarely critically used). I have an insulated backstay for the normal SSB Tx/Rx antenna. Also, the boat was built with SSB in mind with copper strips laid into the hull fiberglass, and a ground plate installed. The only new challenge I'm trying to solve is for the DSC receive-only antenna.
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Old 13-11-2016, 11:37   #8
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Re: SSB DSC antenna idea

I think you are entirely over-thinking the issue. ALthough probably workable, I would prefer not to use something horizontal. Do you have a FM radio/stereo - how about tapping into it's antenna. Is your mast grounded? - if not it makes for a good DSC antenna. Your side stays will likely work too.
Touch your general receive terminal on the radio to anything you think will work and if your noise level jumps up substantially you have found a good DSC antenna.
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Old 13-11-2016, 18:15   #9
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Re: SSB DSC antenna idea

Quote:
Originally Posted by jr_spyder View Post
Hi,

I'm installing a new Icom M802 right now, replacing a failed 20+ y/o SEA unit. So most of my installation issues are easy, except the old unit did not have DSC capability.

I've read many threads here about the DSC receive antenna, so I feel well informed (despite the real lack of info from Icom). In thinking about various ways to install a passive DSC receive antenna I had an idea that I'd like feedback on.

I'm looking at the stainless steel strip on my rub rail that runs about 44 feet along my boat. I've checked continuity and it is not grounded or otherwise connected to the boat. I could very easily remove one of the screws, drill a skinny pilot hole through the rub rail and hull (right at the deck/hull joint), pass an unshielded antenna wire through and connect to the stainless steel strip. I can do this right where the SSB transceiver box is mounted, so it would be extremely simple to do. Maybe ten boat minutes (ok, an hour).

Is there any reason not to? The only thing that I can think of is that when sailing with the rail in the water (I have a somewhat low freeboard) then it's possible the rail would ground out with the boat and then not receive DSC calls. Seems like a very minor concern, but maybe not. Any other reason?

Thanks,

JR
Another option is to get some 6 or 8mm double braid line. Expose the inner, push a length of 1.5 or 2.5mm2 insulated, stranded wire up inside the inner braid for 100 - 200mm, then bind down tight on it with whipping thread. At the other end you can now quite easily pull the wire through by pulling out the inner core, while working the outer up to keep it loose.

When through, you will have a nice length of insulated wire protected and strengthened by an outer fabric braid. Seal the wire ends, put a soft eye in the far end, and as part of the process bind down tight on the inner wire (with a cable-tied loop or a knot in it to ensure it will not slip inside).

At the lower end, exit the wire through the outer, and put another soft eye in the cord.

You will then be able to hoist this wire-cored, braided line up into your rigging,, and lead the deck-end wire through a gland to your radio.

Just another way.

David
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Old 14-11-2016, 11:54   #10
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Re: SSB DSC antenna idea

JR,
As well all know, just about anything metallic can be used as an antenna....and for HF-DSC Receive-only, it doesn't need to be complicated, resonant, etc...
But, I'm with Bill and Dan on this...
Using your SS rub rail would work....but, not great....(Bill is quite correct that this better used as part of your main transmit antenna's RF ground / counterpoise....but, probably mot needed in your case)

You'd be better off just running a coax from the M-802's DSC receive antenna jack, to a shroud chainplate, and just attaching the center-conductor of the coax to that chainplate (thereby using that shroud and your whole rig, as your HF-DSC receive antenna)....using a balun at the shroud, and attaching only one wire from the balun to the chainplate (which is what I do), or attaching the other wire from the balun to a keel bolt (made no difference in my case), is a good idea....(or at least a few ferrites on the coax, at the chainplate end of the coax)
As you're using your entire rig as a receive antenna, it is possible that you may have some added receive RFI with this antenna, but the narrow-bandness of the DSC signal and its robust nature of demodulating, should compensate for this...

{A good way to tell is to tune into an open band (such as 12mhz daytime or 6mhz or 8mhz at night and swap between your main antenna (backstay and tuner), and your "HF-DSC receive antenna" (your coax coming from the shroud/stay chainplate), simply swap the coax on the back of the radio and compare the noise levels....
And, then tune into a station live on-the-air, such as the USCG weather broadcast or WLO's, etc., and compare reception....swap them back 'n forth a few times over a few minutes, and make note of any differences, on both noise levels and overall signal-to-noise levels...
(you may be surprised to hear the "compromise antenna" sounding as good or better, since the untrained human ear has difficulty with noise.... ) }


Also, as HF-DSC is a fairly robust mode of communications and has a significant advantage over SSB Voice (of at least 12db - 15db)....this allows you some margin to use rather inefficient / compromise antennas, and still receive signals....BUT...
But, since MF/HF Maritime DSC takes place between 2mhz and 16mhz, with most on 2mhz, 8mhz, and 12mhz, using a short antenna is a compromise you should be aware of...

So yes, a short end-fed whip (such as the 54" HF-WeFax / HF-DSC-Receive antenna marketed by Metz) can work...
Metz Communication General Coverage/WeatherFax Antenna
As can the simple, home-made 6' wire antenna made from coax, understand that they are compromise antennas...
AND...

And, please be aware that this "you can mount in a closet" statement is BS!!
(I've actually seen/heard people do this! And, have actually read this being recommended by so-called experts!!)
Yes, here again....anything will work to some extent....
But, the more in the clear the antenna is, the better!!
And, the farther it is away from any on-board RFI sources (and their wiring), the better!!


FYI, for the first few months I had my M-802 on-board (spring/summer 2004), I used this Metz 54" antenna, mounted in the clear, on my stern rail and I was able to complete a "test" DSC call, once....but, then in the fall of that year (fall 2004) changed over to using a 22' section of rigging (an insulated aft lower shroud, fed from the chainplate) as my HF-DSC receive antenna, and not only have I used this successfully ever since then, I regularly receive "all-ships" HF-DSC calls on 8mhz and 12mhz, almost everytime I'm on-board (and have received a couple DSC-Distress calls as well), many while I'm just sitting at the dock...
{BTW, the first MF/HF-DSC Distress Call I received (actually a Distress Relay Call) was in summer of 2007...at night, rafted to the quay in Horta, Azores....I was listening to some SW stations (with headphones on), and the damn Distress Alarm went off...scared the crap out-of-me!! and woke my crew up, thinking we were on fire or something!! }



Hope this helps...

John
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Old 15-11-2016, 07:56   #11
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Re: SSB DSC antenna idea

John,

As always thanks for your thoughtful expert advice. Especially debunking some other opinions.

I wanted to use a lower diagonal shroud off my rig but I thought that was a non-starter since the whole rig is grounded (shouldn't they all be in case of a lightening strike? Maybe too much thread drift to answer this...). I get continuity to ground at the chain plate. Or does it not matter? I know I can have the shroud removed, the rod cut, an insulator installer, the shroud reinstalled, and my rig retuned (phew...) and I'd have the perfect HF-DSC receive only antenna, but I confess, I was looking for a shortcut. That said I'll probably go in this direction.

Could you give an example of the right kind of balun to use? I see very cheap ones used for TV aerials, to expensive ones used on ham antennas. Sorry for my rookie learning curve on this, but I don't see how to sort out balun types.

Very funny about that first alarm you received! That said, does it become irritating to have such a good antenna and receive all the distress calls from far away with no means to help?



Oh - Jd1 - you pegged me, I overthink a lot. Easy to do when my body is off the boat but my brain is still there, and I don't actually have tools in my hands to do the work. It usually serves me well, but not always.

JR
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Old 15-11-2016, 11:10   #12
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Re: SSB DSC antenna idea

jr,
As always, you're welcome!

Please remember I'm a radio nut and make my living in the electronics industry, so many things I do are a bit overboard....but, they work well...


First off, usually when most speak of "ground" / "grounded", we're speaking of DC ground (or very low freq AC), not RF ground....
So, while your rig (shrouds, stays, mast, etc.) are "grounded", they can still function as an antenna....especially for HF reception...

Secondly, while the potential is there for this "whole rig" antenna to pick up RFI from systems on-board, this is not due to it being at DC ground, but rather due to the proximity of these other systems on-board to this antenna (which is in effect the entire rig, chainplates, bonding wires, etc.)....as well as any RFI flowing on the DC ground system...
(do the tests I mentioned above, and you'll probably be good to go)

Third, nobody has anyway of knowing what antenna pattern (both elevation and azimuthal) of the entire rig will look like....nor what various resonances (if any) it may have....

So, taking this approach may work well....or may be a bit of a compromise...(and again, why I recommend the simple tests above)


Myself, I decided to insulate an aft lower shroud, for use as my HF WeFax reception antenna / HF-DSC reception antenna, as I did not wish to deal with any RFI issues nor any antenna pattern issues....and it has worked well for me...
Others have simply attached their coax center-conductor to a chainplate and used the whole rig as their HF-DSC reception antenna, and apparently has worked well for them....
If you do the tests I prescribed above, you can easily see how well it will work for you...


{Please note my reasoning for doing what I did was both serendipitous (my aft lower shroud allowed me a good length for what I wanted, about 20' - 22'), and met my easy / no-muss (and no failure) design criteria....
My design thoughts were: with my primary WeFax freqs being 8.5-9mhz and 12.7mhz (with some daytime 17mhz and some nighttime 4mhz and 6mhz)...and with 8414.5 being a primary HF-DSC freq, (with 2187.5khz being a secondary, and a primary in Europe), and end-fed vertical antenna of 30' or less would do well, and provide a decent low-angle....and an end-fed wire of 18' - 27' long would be excellent, easy / low-loss match to 50-ohm coax on 12mhz thru 8mhz freqs, and still not be that low impedance on the lower freqs....and since atmospheric noise rises significantly on these lower freqs, any possible (and small) mismatch loss would actually be a positive....
So, in my case, my aft lower shroud worked perfectly for my application...}


Again, you do not need to do what I have done....you can do what others have done....and chances are, it will be fine...
(but, I still recommend the tests above....
And, while technically just attaching the coax center-conductor to the shroud chainplate is a short-cut, it's not a bad approach...it does work!


And, BTW, no matter what DSC receive antenna choice you make, you do not need to "retune the rig", and please never attempt to do so!
These various antennas will all work, and the HF-DSC receiver built-into the M-802 has 4 tuned input networks (2-7mhz, 8mhz, 12mhz, and 16mhz) combined together and then connected to an RF input amp ("pre-amp" if you will), so there is NO need to fret over the minutia of an HF-DSC receive antenna....(okay, I confess....I went overboard in my design thoughts, but again I'm a nut!!



Oh, as for the balun...
Probably unnecessary....and a waste of money....but, they're less than $50....so, why not???

For an insulated stay, receive-only antenna it's not needed...in my testing on received signals (with no RFI on my boat), I found no difference....
But, I left it there anyway....my thinking was it did isolate the coax / stopped common-mode RF (whether my transmit RF or on-board RFI) from coming back to the radio...

For a grounded stay, receive-only antenna, it can provide some significant isolation....stopping all common-mode RF (again, both your transmit signal and on-board RFI) from coming back to the radio, which can be greater when using the whole rig as your receive antenna (HF-DSC receive antenna)...and since you'd be attaching only one wire to the chainplate, the balun may also provide some differential-mode RF isolation from any strong out-of-band RFI (low-freq noise, etc.) that may be flowing on the DC ground system (although, I've never measured it's possible)

Just about any decent HF "current balun" will work fine....
No need to spend $100+ on my fav big transmit baluns!!

Radioworks, Balun Design, DX Engineering, etc...all sell excellent current baluns....buy one of theirs and you'll be fine...

B1-2K Current Balun
http://www.radioworks.com/cb1-200.html

If you want a balun for this (probably unnecessary), then Radioworks is fine!!



Model 1110 - QRP 1:1 Isolation/Choke balun 1-54 MHz - Balun Designs

https://www.dxengineering.com/search...uns-and-chokes





As for HF-DSC reception being "irritating"??
To me, not at all....
I can tell you my experiences and you decide for yourself...

FYI...
Most cruisers will not have their HF radio on all day long (as they do their VHF radio)...although some sailing hams do...

So, for the short time you'd have your M-802 on, it's not likely that you'll receive an HF-DSC Distress call (which will trigger the alarm!)....but you may get an occasional HF-DSC "all-ships" Securite or Routine call (neither will trigger an alarm, nor disrupt your use of the radio)

But, be aware that you may in fact be of some assistance to others at sea, even if a few hundred miles away...(both by communicating with them when others might not be able to, and/or relaying their emergency traffic to appropriate authorities....and/or you being in a position to provide some search and rescue assistance yourself...)
Remember, each year we loose a couple boats (and a few lives) from our cruising community on ocean passages where their "distress call" is either never heard, never sent, or an EPIRB signal is received but nobody is found in time...
AND...

And, with the new "regional" HF-DSC Groups, where you can signal an MMSI # that corresponds to your present NAVAREA, and all vessels with this group call MMSI# programmed into their radios will automatically receive this "Group Call"....
Note that this is not for DSC-Distress signaling, but rather for non-distress signaling (such as Securite or Routine), where you may require some assistance from someone, etc., but not be in an emergency situation...
So, you having a decent HF-DSC receive antenna can be of assistance to others...

So, in a nutshell...it's doubtful that this would ever rise to even the nuisance level...let alone be irritating...

Quote:
Originally Posted by jr_spyder View Post
Very funny about that first alarm you received! That said, does it become irritating to have such a good antenna and receive all the distress calls from far away with no means to help?
Here has been my personal experience with my HF-DSC reception...
A couple years ago, I spent 3 - 4 hours each afternoon, for a couple months in the spring and fall, on-board with the M-802 (and wefax unit) on....(and sometimes my laptop, etc.)...
I was helping out Herb on his weather net on 12.359mhz...(a great experience, BTW...) from my dock here in S. Florida...

And, each day I'd tune in the Australian HF weather broadcasts on 12.362 and 12.365mhz to see how good the long-range propagation was (these stations are about 9000 and 10500 miles from me)....as well as tune in WLO and USCG HF Voice broadcasts....as well as pull down a wefax chart or two....
And, then as it got within 30 minutes of check-in times, I'd just monitor 12.359mhz for the next couple hours...

And, on average about once a month I'd receive an HF-DSC-Distress Alert....and the damned loud alarm!
And, on average about once every few days (and sometimes a couple a day, and then nothing for a week), I'd receive an HF-DSC "all ships" Securite or Routine call...no alarm...
Now a couple years later, there is more routine HF-DSC traffic, but it is mostly point-to-point (rather than "all ships")...so, I suspect about the same amount of HF-DSC calls received, for most cruisers....




I do hope this helps...

Fair winds

John
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Old 15-11-2016, 14:02   #13
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Re: SSB DSC antenna idea

Big lesson for me here. I really thought the ground just killed the idea of using a shroud. Now I know better, and that's what I'll do. It's kind of too easy to be true when it comes to boat stuff, so I was searching for something more complicated. I'll order a balun just for the extra clarity it may provide.

One comment about "retune the rig." I was referring to the sailing rig, not the HF rig. Once a shroud is removed and put back on, as I 'm sure you know, the mast has to pulled into optimal shape/alignment for sailing performance. Not difficult, just one more thing...

I agree with your advice about helping others. On a sail from Bermuda to Newport last year, about halfway across, I received a mayday call over VHF from a boat only ten miles away. I was able to reach the Coast Guard on my sat phone and relay info with the distressed boat. Felt good to be able to help.

Now I can't wait to finish my SSB re-install and get on the air. Hopefully that will happen in the next two weeks, otherwise it will wait until next Spring.

Thanks,

JR
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Old 15-11-2016, 20:38   #14
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Re: SSB DSC antenna idea

jr,
Oppsss...
Quote:
Originally Posted by jr_spyder View Post
One comment about "retune the rig." I was referring to the sailing rig, not the HF rig. Once a shroud is removed and put back on, as I 'm sure you know, the mast has to pulled into optimal shape/alignment for sailing performance. Not difficult, just one more thing...
Sort of a "Duh!" moment for me...
I was thinking "radio"....and forgot about the "rig"!
But, depending on your boat / rigging...measure tension (loos gauge), and then loosen the two corresponding / opposite stays the same amount, add insulator, and then re-tension both to the same tension as before, and you're done...
(those with racing boats, fractional rigs, those you desire a precise mast bend, etc...yeah, you all will want to re-tune the whole rig....but, for most of us cruising boats, we're good-to-go as long as the mast is pointing up...







BTW, I probably shouldn't have mentioned the balun, as probably won't be necessary...but, it's cheap!



Fair winds..

John
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Old 25-12-2016, 12:15   #15
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Re: SSB DSC antenna idea

I#m in the process of buying all components for my SSB equipment (M-802). So I understand putting a dedicated DSC Antenna as the Metz or use a schroud and insolate it. That results in addtional Insolators and rerigging (Cost appr. 700). A Metz antenna: cost of 150) but adding further X-Mas tree equipment, which I dislike, but the easiest way.
Who knows an alternative to the Metz in Europe ?
Next item: GPS Signal: looking for alternatives: I have a GPS in my Raymarine equipment, and a 2nd GPS for My AIS.
Question: Anyone can advise me if I should install an additional GPS rteceiver or can I easily take the signal from the NMEA Bus and use this signal to the SSB radio?
Should these coax cables be equippped with ferrite cores on one or both ends?

Next question: there are ferrite cores made from Ni-Sn ferrite or from Mn-Sn ferrite.
Which ones should I buy or does it make no difference? Which supplier (obtainable in Europe is for me the easiest, but not obligatory.
Last question: I bought the M802 in Canada. Can somebody tell me if apart from the marine bands, also the HAM bands are open.
Thanks for your advise. Habe a nice X-Mas, wherever you are

Theo
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