DSC HF Antenna design

[Cruisingscotts]

Ok John, here you go........

Below is what I have. Radio is a Icom 802

All advice on reliable DSC HF setups appreciated.

[Cruisingscotts]

And...............to make things more intersting....

I currently have a main mast head morad VHF whip that is used for the Icom 504 and AIS.

The foremast has two masthead mounts. Both have Morad VHF whips whic hat some point, pre main mast existing, made sense. Also on the foremast below the VHF whips is a Wave Wifi antenna.

So....what I dream of having all working in harmony on the above rig without it looking like something out of a Terry Gillian movie is...

HF longwire
HF DSC
VHF-AIS primary
VHF-backup fixed
2 meter whip (I also have a Icom 2300)
Wave Wifi antenna

[smac999]

you can buy short whips for HF DSC. I don't think you need to rig up a huge long line.

[Cruisingscotts]

Smac999,

I did look at the metz weather fax whips recommended in the other DSC thread. My goal in this thread is to try and bring together some ideas on "by the numbers" calculated instals and practical expieriance intals that people have found succesful. I have read multiple threads on here as well as ham forums and manufactures reccomendations. Unfortunately as with most things "boat" there is alot of contradictory information. Shakespear for example does not reccomend using the same antenna for VHF and AIS. Our local marine electronics guy who is a ham did in my case so?? My goal is optimum functionality based on priority of all equipment without the possiblilty of one damaging the other. Hopefully the DSC portion of the SSB will be the least or never used part of all the equipment, however it is probably at the top of the list as far as priority for functionality. With the schooner rig I have decent horizontal and vertical seperation so there shoudl be lots of options for doing it right

[smac999]

the DSC ant is only for receiving calls. you will transmit DSC help via the main antenna.

so it's receive only and won't interfere with other things on the boat.

lets face it. if you are getting DSC help calls via HF on a sail boat you won't be helping them.

maybe VHF DSC in VHF range.

I bet a lot of them are not even hooked to anything. I have certainly seen that on 802's.

[RDW]

I am not very experienced so that this with a grain of salt.
I have just a 12-15 foot wire laid horizontal in the boat behind the cabinets. To test if it was any good I listened to come communication on ssb channels using the back stay antenna. Then I switched this wire antenna to the main antenna connection and listened to the same channels. If I have similar reception I think that told me it was working fairly well. I am sure there are much better ways but this sounded reasonable to me for a starter.
rdw

[Cruisingscotts]

Originally Posted by smac999

the DSC ant is only for receiving calls. you will transmit DSC help via the main antenna.

so it's receive only and won't interfere with other things on the boat.

lets face it. if you are getting DSC help calls via HF on a sail boat you won't be helping them.

maybe VHF DSC in VHF range.

I bet a lot of them are not even hooked to anything. I have certainly seen that on 802's.

Ok...I downloaded the 802 manual, which is at home, and I have to admit I'm feeling pretty dumb......unless I'm missing something, yes it appears that the DSC ports sole purpose is recieving so the Metz is probably fine as a working channel would be used in any distress situation..........

If this thread could crawl in a courner thats where it would be heading.......

On a UP note I did manage to procrastinate another 12hrs from studying for my ham test, 100t masters and 1st unlimited so YAY. This time was spent OCDing antenna instals and I did actually learn something. For the most part I can't see any reason not to use the existing VHF AIS combo setup I have. The 2 meter will be a working radio cruising for boat shore communications to it will live happily by itself on the foremast. A rail or spreader mount 2nd VHF and HF DSC seem the most approprite without re-inventing the wheel.

I came across a post in the wood boat forum by Paladin (Chuck) RIP, the former electronics guru. This was trying to convince someone to not put a 8' VHF antenna on a very small boat. Makes 3db vs 6db gain antenna more clear See below.

From WBF Archives Paladin

hi Donnwest.....I ain't trying to start an argument about radiation patterns.......But....
I have worked extensively in anechoic chambers and with extensive modelling programs on this very subject...including a PhD paper on elimination of multipath in similar situations.....
In a perfect world......imagine a donut shaped balloon....nice and fat with a small hole as the radiation pattern emitted from the antenna. Radiation reflects from metal surfaces so let's put the donut on a metal plate. Thennn use a nice pyrex dish set on top of the balloon (donut) to compress it slightly...the donut flattens a fixed amount. Take the initial area covered by the donut and press until the donut covers twice the NUMBER OF SQUARE INCHES...which isn't really that much more in the sense of radiation diameter....you have just amplified your signal 3 dB. Press some more to squash the balloon to again cover twice the square inch area of the 3 dB pattern....for anothr 3 dB or 6 dB total. We will stop at 6 dB for some practical purposes.
Since the metal plate was very rigid the pattern flattened top and bottom with no apparent loss in energy....but wait...the plate was thin material and the pressure from the first 3 dB compression forced the center of the aluminum plate down in the center, forming a depression and creating a cone shaped radiation pattern...it will still flatten out somewhat...making a signal perhaps heard an additional10 miles away....but creating a dead spot between (example only) 14 to 18 miles away...still heard at 22 miles. When you compress the balloon for the 6 dB compression the center depression in the metal plate becomes more severe and there are more "holes" or Dead spots as the reflected signal is raised from the apparent radio horizon. The radio horizon will be at approximate right angles to the physical direction the antenna is pointing.....The metal plate acts as a counterpoise....you do not want a flat counterpoise on a marine antenna unless it is a powerboat and sits perfectly flat all the time.
One solution is an antenna counterpoise constructed of several wires or elements beneath the antenna at a 45 degree angle. This will lower the radiation angle, which is what most manufacturers hope to do with several pieces of metal foil inside your 8 foot antenna...a poor compromise...........So...mount the little 3 dB antenna at the masthead....above the rigging wire, save bucks, headaches etc and forget what I just wrote above 'cause it causes long winded discussions.......
uh....did you just miss-speak.....a 3 dB increase doubles the APPARENT signal strength and a jump from 3 dB to 6 db further doubles it again or Quadruples the APPARENT signal strength....the energy is concentrated...in realitey the energy must come from somewhere as the antenna does not amplify.. it merely redirects the energy from one direction to another......

[wrwakefield]

Originally Posted by Cruisingscotts

Ok John, here you go........

Below is what I have. Radio is a Icom 802

All advice on reliable DSC HF setups appreciated.

Thanks for starting this thread, Jake.

After reading John's mention of using an insulated shroud for MF/HF DSC in his recent DSC Explained post, it peaked my interest as well.

I know the Metz antenna is adequate for Emergency DSC comms, but we are extending DSC on HF to non-emergency comms as well thanks to another great contribution from John.

We want to hail select friends[and be hailed by same] on HF/SSB using DSC per John's explanation and guidelines.

If an insulated shroud improves reception over the Metz, then we will make that primary and keep the Metz as back-up.

I will watch with interest.

Cheers!

Bill

[Cruisingscotts]

Hi Bill,

I'm not ruling out a tuned antenna like John has, right now it's a little over my head, budump shhhh....no pun intended. I emailed Morad and will see what they say after the weekend. They are next door to our wh in Ballard so I will stop by when I'm home. It looks like they will build small custom whips which might be another option, I don't know if they will be that much more money than the standard ones which are about $110-$140 for VHF and 2 meter. I have 2 hayne insulators I bought to do a longwire on the back stay so there is really no cost for me in setting up a tuned antenna jsut a matter of what will work right. As joh npointed out in the other thread it's sort of a ideal situation due to the fact you are dealing with a very specific frequancy, you can full on nerd out on the setup. I can definately see the benifit of being able to ping a friend outside of VHF range with very good reliablity and low power low tech. And the best part is the phone does ring with the extremely annoying DSC alarm going off!! If you were buddy boating with one or more boats and were not interested in by the minute FB updates of their day via nets you could set up a working channel and protocal that if something worth talking about is going on you ping the group or the individual boat and have a chat.

[SoonerSailor]

For the HF DSC receive antenna connection on the M802 you don't need a tuned or resonant antenna - which would only be resonant on a single band anyway. Any random wire located away from sources of potential RF interference will work. There is nothing special about the METZ HF DSC receive antenna, except that it is convenient to install. It won't receive better than a similar length of bare copper wire. Believe me.

Put a banana plug on one end of some copper wire (insulated) and plug that into the HF DSC receive socket on the M802 and run the wire where you will. Above the water line, and away from things that radiate, like Danfoss compressor controllers and other electronics. I attached mine to a shroud chainplate.

If your M802 is too close to things that emit RFI, then use a length of coax with a PL259 plug on the M802 end, and run the coax to a point away from the noise sources, then attach the coax center conductor only to a length of wire or a shroud.

If you would rather spend the money, buy a Metz HF DSC receive antenna. While you are at it, buy a KISS counterpoise too......

Chip

[Cruisingscotts]

I mispoke on the tuned part, only meant long wire or sim setup.

[knockabout]

pc navtex receiver is a small hairspray can white plastic cylinder that is screwed to the push pit / earth independent (receive only) / doesn't look much bigger than a digital phone arial .


the barrett hf different story / we are a small wooden sail boat / after some experimentation we ended up with a kiss counterpose earth system purchased online from experienced yachties from over your way somewhere / works excellent and doesn't foul the hull / the arial ended up vertical whip similar to that used by
cb-ers / it looks too frail but forgot to take it off last cyclone near miss and thankfully it survived 50kts wind / the vhf shares the ais through an antenna splitter
and is the same / takes up very little room and works well / if you look up the brand of your hf receiver the maker should have instructions, diagrams to help you resurrect your equipment /

[knockabout]

for cruisingscots/ 802 dsc receiver arial pdf
DSC-Antenna.pdf

[Cruisingscotts]

Knockabout, very interesting antenna will have to look into it as it looks promising. Also in regards the 802 primary antenna I am happy with the setup I have, but thanks for the info and feedback.


Smac999,


You bring up a couple interesting points. The first would sort of be the crux of this thread, however ill conceived, the functionality of HF DSC antennas. As stated above the antenna and port in question is for recieving only. It's entirely possible some people don't bother hooking it up as it does not effect the ability to use the radio or send a distress DSC or otherwise. A weather fax antenna will work, why put effort into making sure this particular antenna is as good as it can be other than pinging friends boats. This got me thinking, as a professional mariner, albeit in the bottom end of the boat I have been around through the comms shuffle from SSB and HF only to $11.00 a min Sat phone to GMDSS being required. Probably the biggest fault of the GMDSS system is that it is all encompassing, every couple hrs or so the alarm goes off the button gets hit the printer spits out a report and it noted a vessel 6,000 miles away is in distress of some kind. People get numb to it and it becomes background noise. I thought of this and our VHF DSC, when we leave the dock the VHF stays on 16 all the time, at anchor or not, with the volume up enough to hear in the cabin. Around may 1st in the San Juans the DSC alerts start rolling in. For the most part I do the same thing as the guys at work, I look I clear I move on. With 16 going and the USCG local as well as Victoria there is pretty much always something being reported and I always listen. The VHF DSC alerts however are back ground noise that I have not paid much attention to other than reading. So this really got me thinking. I'm all set up and I can hit the Oh Sh@t button on both radios VHF and HF and the cavalry will come. This is when it dawned on me that however unlikely at some point our boat may be the only available cavalry. Yes a big old sail boat is not going to be making tracks anywhere fast but in a big crossing even beating to weather for 4 or 5 days at a snails pace might be the best "worse" option for a fellow mariner. So the question is if you have safety gear that goes both ways, as a prudent mariner are you obligated to ensure it is functioning at it highest level whenever possible. I think everyone would agree the answer is yes.


Soonersailer,


In researching your points, and by research I mean a search on eham.... there was a very good thread backing up your comments on a random wires effectiveness and the importance of isolating noise. I did find it interesting that the general concensous was that a random wire lacking noise will be heard just as effectively as a dipole, however a properly setup dipole with a balum will be louder. So does this make a difference on a short data burst or not? I would guess maybe this is the reason John was fiddling with this route? Or maybe not.


I am interested to read more about he antenna knockabout linked. In "reading" the 802 manual further I saw something curious, that when sending a routine messege you could direct enter or pick from a programmable list. I wonder if you intend to send to a specific boat will it go out only on this frequency and do they need to have that plugged in? More reading required for sure, I most likely missed something.

[Cruisingscotts]

A little bit of groundhog day. Seems that this is a ongoing topic..


http://www.cruisersforum.com/forums/...nna-10542.html