AIS & DSC Dipole Aerials

[roland stockham]

Wondering if any of you have done something like this and can make a useful comment. Preparing for trip Aruba/Panama/Hawaii and have been on the AIS threads. This is more specific to installation so starting a new thread.

I now have the following
Vespa Watchmate 850 transponder
Icom M501 VHF radio
Icom DSC100 controller (NMEA 1803 but appear only for GPS position input, not output)
2off Standard Horizon HX851 DSC enabled handheld VHF (these have NMEA 1803 output via charger at 4800baud)
Garmin GPS152 with external aerial
Raymarine autopilot with 10Hz heading sensor linked to NMEA 1803 network via multiplexer
Shipmodul Miniplex-BT/ 4 chanel + AIS @ 38400baud/ integrates GPS, wind & heading data and sends it via blue tooth to laptop (runs SOB software) (over saturation issues?)

Looking to integrate AIS data for display on laptop + DSC contacts to display on laptop (and/or Watchmate). 'autodial' DSC contacts would be nice but not essential

There are a few option, can simply plug Watchmate and mobile cradle into miniplex
Could use the USB cable from Watchmate direct to laptop
Could hook the charger to the Watchmate and use USB output
Could hook GPS direct to Watchmate the watchmate to miniplex
Probable some others I haven't thought of?

Also
I need antenna for both the Icom (old one disintegrated) and the Watchmate. I am intending on using a pair of dipoles hoisted to near the masthead with 3ft from mast and 1ft vertical separation between aerials. I also have a long wire SSB aerial from the masthead. (better signal and much cheaper than commercial aerial/splitter, also masthead currently has main VHF so no space. need total of 3 areals so cant simply use 1 splitter)

If I rig the VHF aerials on the same side (give min run for coax) they will be close to the SSB (about a ft). In theory there should be little interaction between VHF and HF/MF because of the frequency difference, what about the real world?
If this is going to be a problem I can move either VHF or probably MF/HF to behind the backstay but it means an additional 20ft run below deck. The MF/HF is currently behind the backstay but wanted to move it to where Starboard lower are attached to reduce the Cable run (will then only have about 2ft from tuner to aerial and a connection to ground plane that is clear of bilge water. Current one is suffering corrosion problems as it is in the lowest part of the bilge.

Any comments from the radio experts on here

Thanks

[Goudurix]

Hi Roland,

a bit difficult to visualise your situation at the masthead.

Also your (wire) dipoles for VHF hung there do not sound as very sturdy installation.

I would not worry so much about VHF antenna's being a few feet away from SSB (MF/HF) antennas. I suspected my Raymarine AIS receiver getting damaged because I installed a dedicated VHF RX aerial at the transom about 9 feet away from the base of my SSB sloping wire but many people replied this was really very unprobable.

If you really want cheap/DIY VHF antennas still installed quite high up for reach, I would suggest you make the so called "coaxial sleeve" type of dipole by folding back 1/4 wave of the mantle of a 50 Ohm coax (leaving extended 1/4 wave of the still insulated inner lead). Cover the 1/4 wave of the woven mantle with shrink tube. Seal the top of the inner lead and also where the shrink tubing starts. Put this inside a small diameter PVC tube with a cap on the top, and install this both sides of the first or second spreaders.

Remark: bear in mind you will have to do some pruning and the starting value for the 1/4 length will be:
75m divided by AIS target frequency (162 Mhz) * 0.95 (velocity factor) giving 0.46 m or 460 mm. But putting that inside a PVC tube will change the reactance so some extra pruning until reaching optimal VSWR might be needed (a VSWR of 1:1,5 is more than enough).
However DIY'ing the antenna bases to be able to fix them well to the spreaders or any other location will take some effort so maybe it is still worhtwhile to buy simple Glomex Marine VHF aerials instead.....

Jan

[transmitterdan]

I am not able to visualize VHF dipoles. Are you sure you are going to use dipoles for VHF band gear (radio and AIS)? Most VHF antennas are some sort of monopole with a ground plane. Internally some may have dipole type structures but you can't tell that from the outward appearance. These are rare to find on a sail boat.

Normally I would recommend against locating a SSB antenna less than 1 meter from a VHF antenna. Even 2 VHF antennas should be separated by 1 meter. Even though they are on different frequencies the VHF antenna will couple energy from the HF band into the receiver electronics. The electronics have to filter this out which is not easy and it has to survive the possibly high voltage and/or current caused by the HF energy. Were it my boat I would not put SSB and VHF antennas within 1 foot of one another. I would strive for a minimum of 1 meter.

[roland stockham]

Interesting points about using coax to increase strength however getting fully tinned coax (ie inner & outer) id difficult whereas plain tinned cable is cheap and readily available. Yes I was planning to enclose the wire in 1/2" plastic tube for strength and to attach the lanyard to haul up to the masthead. Will fit a pulley at the masthead so aerials can be run up or lowered if there is a problem.
I hadn't realize the tube would effect tuning so thanks for that and will trim accordingly.
Sounds like it would be better to run one set from aft.
Which would you suggest moving (and therefore having a longer cable run) VHF or SSB. With the SSB there is no ground plane connection available in the aft cabin so either means an extra 15ft on the earth strap or feed line?

[ka4wja]

Roland,
To be honest, I'm not clear on what you are trying to accomplish here!!!
If you could explain things more clearly, I'm sure we could help you....

But 'til then, here are a few things that might help...

1) Separation between a marine VHF antenna and a marine HF antenna, should be about 3' (1m), or so....
(note that closer is usually okay, but no closer than 1'!!!, and I always recommend 3' or more....)

2) Separation between two marine VHF antennas should be at least 3'!!!
Although I recommend 6'+ horizontal separation, or 3' - 6' vertical separation, some have found no issues/damage with as little as 3' horizontal separation (but not my recommendation)....

{I used a separate VHF antenna, mounted at the masthead, just 1' away from my primary VHF antenna, for my dedicated AIS Receiver for almost 6 years with no problems....but when I upgraded to a Class B AIS transponder a few years ago, I changed this approach...
I went with a stern-rail mounted VHF antenna as my original AIS transponder antenna, before relegating it to being my "back-up" / redundant antenna....and using the Vesper SP-160 "splitter"/"relay" in the Nav Station, allowing me to use the primary masthead antenna for both my Icom M-602 VHF-DSC Radio and my Class B AIS transponder....(but, I still have the stern-rail mounted antenna wired-up and ready to plug-in, in < 30 seconds, if ever needed...}




3) I've written about all of the above, in great detail, before....
If you wish to read more, have a look...

Look at post #35 here....
http://www.cruisersforum.com/forums/...-102165-3.html

And, have a look at this thread, particularly Ross' and my comments / experiences further down...
SSCA Forum • View topic - "Vessel Name" programming into AIS Transponder





4) Designing / Building your own antennas is a fun hobby....BUT...
But, with the cost of a good Shakespeare VHF whip, LESS THAN 10% of the cost of an AIS Transponder....and less than 20% of the cost of a new full Class D DSC-VHF Radio....and with the reliability required of your primary VHF system on-board, I cannot think of any good reason to "build your own"!

PLEASE consider buying a good antenna!!!!

(besides, if you wish to build a "coaxial dipole" / "sleeve dipole", be sure you understand that you will have very poor antenna pattern unless you eliminate all feedline radiation by using significant VHF chokes / VHF ferrites on the coax, etc...and even then they're really not good for much other than temporary/emergency antennas...)






5) Specifics here in red....

Originally Posted by roland stockham

Preparing for trip Aruba/Panama/Hawaii....
For a voyage like you're planning, please don't skimp, buy a new VHF antenna...


I now have the following
Vesper Watchmate 850 transponder
I great unit!

Icom M501 VHF radio
Icom DSC100 controller
Wow, I've never seen one in person!
A pretty old VHF, with the add-on DSC....
Why not buy a new VHF???
(NMEA 1803 but appear only for GPS position input, not output)



I need antenna for both the Icom (old one disintegrated) and the Watchmate. I am intending on using a pair of dipoles hoisted to near the masthead with 3ft from mast and 1ft vertical separation between aerials.
While technically this would be a bare minimum of vertical separation (assuming you were able to eliminate all feedline radiation, which you will not be able to do)....
The fact that you mention "hoisting" them, AND having them "near the masthead with 3 ft from the mast".....tells me that you will have serious antenna pattern issues, as well as poor reliability....
Not to mention the antennas not being rigidly mounted being a VERY bad idea!!!


I also have a long wire SSB aerial from the masthead. (better signal and much cheaper than commercial aerial/splitter, also masthead currently has main VHF so no space. need total of 3 areals so cant simply use 1 splitter)
While technically there are "splitters" that would allow you to send VHF signals down the same coax used to send the HF (SSB) signals down, this is NOT a practical approach for our marine radio systems, as you want the VHF coax going to the top of the mast, and the HF (SSB) coax going to the remote auto-tuner (usually mounted aft, below decks)....
So, your mention of using a "splitter" here is a bit of a Red Herring...

As for using a "splitter" to allow your primary VHF-DSC radio and your AIS Transponder to use the same masthead VHF antenna (and coax), while some will tell 'ya that it's "not a good idea", many have found that IF YOU SPEND THE MONEY and use a HI-QUALITY "splitter"/"relay" (such as the Vesper SP-160), it is a VERY reliable and fail-safe solution...
But, that'll cost you ~ $250.....about $150 more than a second antenna and second run of coax...
And, with most also wanting the redundancy of a second antenna....many opt for a second VHF antenna, mounted on the stern rail, or bimini-top frame, etc....and they usually find this adequate for their AIS transponder, with the primary VHF-DSC Radio connected to the masthead VHF whip...



If I rig the VHF aerials on the same side (give min run for coax) they will be close to the SSB (about a ft).
I have run many 1000's of watts of power on HF (and >1000 watts on VHF), with antennas just a few feet away...
And, in a pinch, you might not have any major issues with VHF-to-HF antenna separation of just 1'....BUT...
But, you CAN make the darn HF wire a couple feet shorter, and gain a couple feet more separation....and all will be fine!!!
So, go with 3' sep as your minimum....


In theory there should be little interaction between VHF and HF/MF because of the frequency difference, what about the real world?

If this is going to be a problem I can move either VHF or probably MF/HF to behind the backstay but it means an additional 20ft run below deck.
Again, what you write is a bit confusing...
An addition run of 20' of COAXIAL CABLE for HF is absolutely NO ISSUE AT ALL!!
BUT...



The MF/HF is currently behind the backstay but wanted to move it to where Starboard lower are attached to reduce the Cable run (will then only have about 2ft from tuner to aerial and a connection to ground plane that is clear of bilge water.
BUT>>>
But, this here is the real confusing part!!!
You write about "moving the MF/HF", but are you referring to the external antenna wire, the remote auto-tuner, or the radio itself??????????


Current one is suffering corrosion problems as it is in the lowest part of the bilge.
And, here again I'm confused....
What part of your "MF/HF" is corroded, and in the bilge???
I'm assuming you were referring to your grounding strap / foil??? (I assume foil, as strapping will last decades even without being painted/coated!!)


Any comments from the radio experts on here
My comments:
Please explain what it is you have and exactly what you are trying to accomplish....
And, then I can help....
'Til then.....this is all I can come up with!!

Originally Posted by roland stockham

Which would you suggest moving (and therefore having a longer cable run) VHF or SSB.
Again, assuming we're discussing coaxial cable here.....the answer is easy....
Move the HF system....

With the SSB there is no ground plane connection available in the aft cabin so either means an extra 15ft on the earth strap or feed line?
Again, this is confusing....
Assuming you have a remote tuner, you place it near the base of the antenna....and run any extra coaxial cable from there to the radio....
As for RF Grounding / Antenna Grounding, while that is a WHOLE discussion onto itself, suffice to say that there are ways to make it work...
BUT...
But, until I can get some clarification from you on what you have, and what you desire, I cannot give further advice...

Fair winds...

John, KA4WJA
s/v Annie Laurie, WDB6927
MMSI# 366933110

[Goudurix]

Roland,

John-KA4WJA's reply is quite detailed.

If your SSB wire antenna (from your info I gather you have a seperate sloping end-fed wire and are not using an insulated backstay) works OK I would not touch it.

If I understand well how you will hoist 2 VHF wire dipoles up they will probably be quite close to the mast and close to the upper parts of the side stays. Not ideal.
That is wy I proposed to install each one on a spreader, neatly in the middle of the spreader, of course this would mean a "rigid" type of antenna. You might even hang them FROM a spreader but this all seems quite complex and you should also run both coaxes horizontally away from the vertical dipole for several feet.

If you do make vertical dipoles out of zinked steel wire I don't see the need to weatherize them by running them inside a plastic tube which seems rather complicated sine you will have to lead the coax out in the middle. You would be better off buying a wire dipole center insulator that also connects to a PL259 plug. (plenty to find in HAM stores or internet). You can weatherise this type of construction.

The reson why I proposed a sleeve type of dipole made from coax is because with that on you'll have the actual coax running "inside" the lower leg of the dipole and no need to run it away horizontally from the center of the dipole. This is your typical emergency coax wire antenna. If however you put it inside a pvc tube you'll end up with a rigid vertical dipole with the feed coax coming out of the antenna base. That could be installed vertically and freestanding eg. on both spreaders.

But I still think you'd be better of buying 2 basic marine vhf whip antennas.

About $ 120 max I would guess.

Jan

[ka4wja]

Roland,
Aside from the need for GPS position info for their DSC functions, the VHF and HF radio systems have nothing else in common, and therefore should be dealt with separately...
(I might be wrong here, but I suspect some of your confusion/concern is because you are trying to deal with them together, and of course that you chose the one odd VHF radio which required an external DSC controller and its own separate DSC antenna??)
So, let's deal with them separately....(actually would be better in separate threads, but we'll make it work here...


1) First off the HF (SSB) Radio system....
a) I still have no idea of what radio you have, what remote tuner you have, nor where/how they are installed and wired...
So, all I can do is guess, and give you generic advice...

b) A copper wire end-fed vertical (suspended in a rope) is a great antenna....(just remember that like all HF vertical wire antennas on-board, it WILL be effected by all the other rigging, etc...)

c) Understand that your HF antenna actually starts at the remote tuner, not above decks....
This is why mounting the tuner close to where you have the lower end of your external vertical wire, is so important....and having as short of a run of GTO-15 antenna wire running inside your boat as possible....
Although running a long copper strap all-the-way forward to a keel bolt, also compromises the system.....usually this compromise is accepted, as keeping the radiating antenna as far away from other on-board systems as possible is almost always a much better installation approach....

d) The subject of providing an adequate RF Ground / Antenna Ground for an HF vertical antenna system on-board has been beaten-to-death on-line!!! So, I won't delve into it in great detail here....
Suffice to say, that if you are using the 3" wide strapping you mention, to run from the tuner to the keel bolt, this should work okay for you...
{Although, you may wish to also consider experimenting with using additional metallic objects as part of your RF/Antenna Ground system, such as running some copper strapping to the stern rail / pushpit, lifelines, alum toerail (you'll need to thru-bolt/screw-into-it, and connect to bare alum, not try to use a contact with the anodized surface), etc....or even adding some wire radials along the underside of the deck or cabin sole....or even tying-in large metal tanks, etc....}


e) There is NO need at all for the radio and remote tuner to be close to each other....
Rather conversely, since your antenna starts at the remote tuner, it is preferable/recommended to keep the tuner (and antenna) as far as practical from the radio itself....
There is NO noticeable loss in 20 extra feet of coaxial cable on HF freqs....and no reason for any concern here at all...

f)
---Mount the HF radio where you can best use it...
---Connect the HF radio directly to a stiff 12vdc battery bank, using adequately sized wiring to allow a maximum of 3% voltage drop with 30 amp of current draw....(not thru a breaker or distribution panel)
---Mount the remote tuner as close to the lower end of your external wire vertical as you can practically accomplish...
---Use GTO-15 wire to attach the tuner antenna output to your external vertical wire...
---Connect the radio and tuner together using good quality coaxial cable (and tuner control/power wiring), using a coaxial line isolator at the tuner end of the coax, and ferrites on the tuner control/power wires (also at the tuner end of the wires)....
---Connect the copper strapping (and any other RF/Antenna Ground system) directly to the tuner ground lug ONLY (do NOT connect them to the radio ground lug!)
---Keep this primary HF antenna a few feet away from ANY other metallic objects, and keep it at least one to two feet away from the mast / other rigging / other antennas...
---Whatever the manuals say, understand that most remote tuners will actually provide a tune/match with very short antenna wires....so no worries there...(and remember that the antenna starts at the tuner, so the length of GTO-15 is part of your antenna!)

If you do all of the above your HF installation should be okay!!
(but, not knowing what radio/tuner you have, nor where/how they are currently installed and wired....all I can do is be generic!)

----If you have an HF-DSC-SSB Radio (such as an Icom M-802), then you will of course also need a separate HF-DSC RECEIVE-ONLY antenna....(see other posts for more details about this as well...)




2) Now as for your VHF, VHF-DSC, and AIS....
You must decide for yourself if you wish to use the complicated set-up that you have chosen!!
I cannot find any rationale that makes sense to me, for use on a small cruising boat, for you to actually complicate your set-up by choosing a marine VHF radio, with an external DSC-controller needing its own DSC antenna...but if this is your final choice, then you must accept the compromises that this choice forces on you...(there is nothing I can do about that...)


EDIT:
I'm even more confused now....

I see that you have listed a "ketch/yawl" as your vessel type???
If this is the case, why not just use the mizzen masthead for an antenna support, for your AIS antenna, and keep whatever earlier arrangement you had on the main masthead the same???

Sorry about my confusion, but you haven't really explained things well...



I assume that you have a sloop (one mast), but also see that you have a radar pole on the stern???
If this is the case....you have a few options...

Option A:
--- You can simply mount a good quality marine VHF antenna, out in-the-clear, on-top-of your stern pole...

--- Install a good quality VHF marine antenna at the masthead...

--- Install a 3rd good quality VHF antenna on one of your spreaders, keeping it 30" away from the mast and NOT running parallel to any other metallic objects (shrouds?) closer than 30"....(not easy to do on many boats...)


Option B:
--- You can simply mount a good quality marine VHF antenna, out in-the-clear, on-top-of your stern pole...(for you AIS)

--- Install a good quality VHF marine antenna at the masthead...(for your primary VHF)

--- Install a 3rd good quality VHF antenna at the masthead...(for your separate VHF-DSC controller)...mounting it on the other side of the mast, or on an fiberglass mast/antenna extension, etc. (and accept the pattern distortions and any interferences...)


Option C:
--- You can simply mount a good quality marine VHF antenna, out in-the-clear, on-top-of your stern pole...(for your separate VHF-DSC controller)

--- Install a good quality VHF marine antenna at the masthead...and install a Vesper SP-160 "splitter"/"relay" at the Nav Station (for your primary VHF and AIS)


~~~~~~~~~~~~~~


Or, Option D:
You can decide to get a modern Class D VHF-DSC Radio, which does NOT require a separate DSC antenna....

And, be back to what everyone else struggles with....that is, whether to install a separate / isolated antenna (such as on the stern rail or radar pole) for their AIS transponder, or use a Vesper SP-160 "splitter"/"relay".....



3) As for home-brewing VHF-marine antennas.....
I do NOT recommend that at all!
And, certainly would never recommend "hoisting" a vhf antenna up the mast on a halyard!!! (NOT going to work well at all....with extremely poor reliability/longevity...and where do run/secure the coax???)
We could delve into this in depth, but I don't have the time...sorry!!
What you propose is NOT a good idea....NOT even close to being acceptable, in my 40 years of experience...

Simply spend the $$ and buy good quality Marine VHF Antennas....

If you take a direct lightning strike to the masthead, you'll need to replace the VHF antenna, but other than that, a good quality antenna will last a couple decades!!
And, IF you install it and most importantly install the coaxial cable and connectors, properly....and weather-proof them well....you will not have any troubles for at least 10 years of heavy offshore sailing!! (so no need to worry about "antenna maintenance" here...)

BTW, if you've never designed/built VHF antennas, now is NOT the time to try it out!!!





4) Finally, in complete honesty, I think you are way over-thing all of this....
It has all been done before, with success, 1000's of times...
(and except for your VHF radio needing two antennas, nothing else is different here...)
Follow the recommendations/advice of those you have been doing this for decades, and don't over-think this, and you'll be fine!!



5) Regarding your confusing/frustrating experience communicating with Herb...
As I have written before, Herb's signal (and especially his received signals) were NOT very good....especially in the final 3 - 4 years he ran his net!!

While many write this off as "propagation", this is only a small part of the issue...


Please understand I mean NO offense to him at all, he is a genius when it comes to small, "point forecasts", of offshore weather....and there will never be another guy with either his expertise, nor dedication!!!

[And, I consider him a personal friend, as we correspond about our families, etc. regularly]

But, after his main antenna (and secondary antennas) came down in a fierce storm (about 2008, I think), his replacement antenna was seriously compromised....
And, the growth of all the electronic devices around him in the past 5 years or so, seriously hindered his reception as well...

And....as politely as I can write, Herb was not a great "radio guy", he's a great "weather guy"!!
His radio ability was about average, and while he tried to find the best times for his net, he did schedule his net around his life, so what might be a better time might not have been possible....
And, while 12.359mhz is a great all-around freq for Transatlantic comms, many times 16mhz would have been much better!!
And his radio (an Icom M-710) and antennas were also compromised, compared to other shore stations....

And lastly...his location....400 miles inland, near Toronto, placed him a disadvantage as well...

As you see, the list can go on and on....
But, the bottom line is: If you had trouble connecting with Herb in the past, that does not mean there was/is a problem with your system, as there can be many reasons...




6) I hope you don't mind the above generalities are the best I can do at the moment!!



Fair winds...

John, KA4WJA
s/v Annie Laurie, WDB6927
MMSI# 366933110

[roland stockham]

Hi all and thanks for the advice, now sorted what I am going to do
The explanation from KA4WJA about the problems with communications from Herb was very reassuring, it was what got me wondering if I had a problem with the SSB. So given that I have had no problems with other stations will leave that as it is.
On the VHF side I am not concerned with maximum range on the AIS, if a ship is over the horizon it is not a collision risk. This should give me 6-7miles range for small baots and 10-15 for ships as a min. So will mount a good aerial on top of the radar mast for AIS.
I did some more checking in the manufacturers documentation about how the DSC controller works. Turns of that Tx is through the main VHF radio so uses the masthead antenna anyway. The separate feed is because it has its own ch70 receiver. Since it is Rx only the aerial is much less fussy so will mount this on the spreader. That keeps everything simple, no splitter and a backup aerial if anything goes on the masthead one.
Again thanks for your patience and advice. Sometime a "little knowledge can be a dangerous thing" rather out of my depth on this stuff but have always been facinated by the idea that a bit of wire can connect you to anywhere on the planet. One day when I have time will join the ham radio scene and learn to do it properly!

PS the SSB tranciever is an Icom 700pro with the matching Icom tuner (KA4WJA asked)

[Goudurix]

Roland,

I have since many years replaced the fiberglass-tube type of marine VDF antenna's (they are usually either a form of a J-Pole anetnna or a dipole, inside the plastic tube) by base-coil loaded stainless steel whip antenna's from Glomex (Italy).
They are not that expensive and have very low wind-resistance because of thte whip shape. They are also flexible so anything hits it eg when stepping down the mast of when installed on a spreader, or stern pole, and they don't break.

Glomex Leisure - RA106SLSSB25 - VHF - 3DB - 900 mm (35'') - Stainless Steel - 25 m (82') Coaxial Cable

Jan

[ka4wja]

Roland,
Looks like you've gotten things figured out well...and are on the right track!

Fair winds...

John, KA4WJA
s/v Annie Laurie, WDB6927
MMSI# 366933110