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Old 09-06-2015, 08:42   #1
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Wire antenna for HF DSC

As a non electronics kind of Guy i am looking for a simple solution to installing an Icom 801 HF and AT140 in a catamaran.

I dont want to have a big whip antenna that can catch reef lines and such and read here that for the antenna I can just use a length (23ft I guess?) of HT wire secured to the main stay (which is insulated Kevlar)

As the 801 requires a seperate DSC watch antenna, could I just use a similar 2Mtr length of wire on the other mainstay? and how best to connect it.
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Old 09-06-2015, 10:43   #2
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Re: Wire antenna for HF DSC

Pacey,
I'm not completely sure how you have your boat rigged, or wired up.....nor exactly where these "stays" are??
Are they the "main backstays"???

This has been discussed in detail in the past, so I'll give you the highlights here and refer you to some other threads for further details....


1) If I understand what you wrote correctly (?), the primary HF antenna you describe here, using a non-conductive stay / rope to support a copper wire antenna, is known generically as a "rope-tenna", and as long as you consider/design its length (approx. 40' - 45' in total wire length, is typical) based on the primary frequencies you desire to use most, it is an excellent primary HF antenna for you....

Although, I'm NOT familiar with anyone using a Kevlar stay, I'm wondering if this is a language/terminology confusion on my part, or just that I haven't seen anyone with Kevlar rigging holding up their mast...

But whatever the case, yes you CAN use a copper wire (preferably a high-voltage insulated, tinned-copper, wire) inside a non-conductive rope, just fine!!!

If you have two Kevlar backstays, you COULD do this, with some caveats, assuming these are non-conductive stays (and in this case, using ONLY GTO-15 wire, in order to protect the Kevlar stay from the high RF voltages which could represent a problem when wet with sea water...)
But, not sure if the typical plastic cable-tie-wraps, that most would use to secure the wire to the non-conductive stay, would survive long enough to be practical....
But, "electronically", this is do-able!!

Quote:
Originally Posted by Pacey16 View Post
As a non electronics kind of Guy i am looking for a simple solution to installing an Icom 801 HF and AT140 in a catamaran.

I dont want to have a big whip antenna that can catch reef lines and such and read here that for the antenna I can just use a length (23ft I guess?) of HT wire secured to the main stay (which is insulated Kevlar)
As I wrote, this general subject (not using backstay insulators to create an HF antenna) has been discussed in detail in other threads....have a look...
SSB Antenna without a Backstay

SSB antenna for a ketch.

Optimal SSB Antenna(e)

and
Optimal SSB Antenna(e)

Recommended coax for triatic stay HAM antenna




As for the M-801's DSC Receive antenna....yes, you could do this....but, you'd probably be better off using a LONGER wire than this "2m length", I would recommend a 6m - 7m length).....or you may wish to look into a 2m SS whip antenna designed just for this purpose...such as the Metz..
Metz Communication General Coverage/WeatherFax Antenna
Quote:
Originally Posted by Pacey16 View Post
As the 801 requires a seperate DSC watch antenna, could I just use a similar 2Mtr length of wire on the other mainstay? and how best to connect it.



I do hope the above helps....but if it doesn't and/or if the other threads do not provide you with adequate info, please ask more here and provide us with some more info on your boat, your electronics, and how you have everything wired up...

Fair winds...

John
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Old 09-06-2015, 10:59   #3
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Re: Wire antenna for HF DSC

Quote:
Originally Posted by Pacey16 View Post
As a non electronics kind of Guy i am looking for a simple solution to installing an Icom 801 HF and AT140 in a catamaran.

I dont want to have a big whip antenna that can catch reef lines and such and read here that for the antenna I can just use a length (23ft I guess?) of HT wire secured to the main stay (which is insulated Kevlar)

As the 801 requires a seperate DSC watch antenna, could I just use a similar 2Mtr length of wire on the other mainstay? and how best to connect it.
There is a reason so many marine ssb installations use an insulated backstay as a robust antenna option. Reliability and perfirmance.

Sure you can just use a 'length of wire' but its not ideal. A great emergency antenna though.

HF SSB and DSC is not a cheap option. Are your antenna concerns related to cost? Do you have a decent ground plane setup? HF is high power so you need to be aware of RF energy from a safety perspective.

You state you're not an electronics guy. Shortcuts dont tend to end well with HF installations.

The advice given by others here is well worth adopting.



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Old 09-06-2015, 11:34   #4
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Re: Wire antenna for HF DSC

I might have posted this once before in one of the referenced threads. If so, my apologies. I've had good success using the traditional insulated backstay for transmit and receive, but for HF DSC receive I use another shroud that is easily accessible near the radio. This shroud doesn't have any special fittings or insulators, but works well for receive only. The one caveat is to please make sure that your backstay is properly insulated from the rest of the standing rigging.
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Old 09-06-2015, 15:35   #5
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Re: Wire antenna for HF DSC

I can't imagine how the Metz DSC antenna can perform better than a 2m copper wire. Its specs claim 2 to 30 mHz coverage, which suggests it isn't tuned to any particular band.

I wish I had one to sweep with my antenna analyzer, just curious to see what it would show.

The single advantage I can see to it is that it makes mounting some kind of antenna a bit easier.

Chip


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Old 09-06-2015, 21:29   #6
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Re: Wire antenna for HF DSC

Guys, Thanks for your informative responses.

So after reading these posts I plan to run a 45' GTO 15 wire on the outside of one mainstay and a 7 Mtr length on the other mainstay, I will feed them both through the chainplates. I can not see a risk as no one would be touching a chainplate at any time.

The mainstays are Kevlar line covered in a plastic jacket so I should have no issues with interference? I can replace the cable ties periodically while up there inspecting the rigging. The chainplates are not earthed or bonded to anything.

Just no sure how to connect the DSC receive wire to the chainplate as it is a CoAx coming out of the radio, do I connect the core and leave the armour disconnected?

If this can work I will be happy not to have stupid looking antenna's whipping around catching lines and getting broken.
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Old 10-06-2015, 09:37   #7
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Re: Wire antenna for HF DSC

Have this, easy install , works!!!!!!!!!
Have large steel boat and don't rust the insulation part of an insulated back stay. Removed mine ! Russ

GAM / McKim Split Lead Antenna | GAM Electronics
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Old 10-06-2015, 10:25   #8
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Re: Wire antenna for HF DSC

Quote:
Originally Posted by Pacey16 View Post
As a non electronics kind of Guy i am looking for a simple solution to installing an Icom 801 HF and AT140 in a catamaran.

I dont want to have a big whip antenna that can catch reef lines and such and read here that for the antenna I can just use a length (23ft I guess?) of HT wire secured to the main stay (which is insulated Kevlar)

As the 801 requires a separate DSC watch antenna, could I just use a similar 2Mtr length of wire on the other mainstay? and how best to connect it.
Hi Pacey,

I'm preparing to do something similar [I'm replacing an ICOM M710 with an M802] so I have been researching DSC Antenna options. [Otherwise know as DERA: DSC Emergency Reception Antenna.]

Paraphrasing from the book Icom IC M802 Starting from Scratch:

An unloaded whip 54" long can be used. [e.g., METZ WeFax antenna #201] Or one can be made by removing 72" of the shielding from a piece of coax (leaving the core and its insulation intact.) Connect the other end of the coax to the DSC Antenna input on the transceiver. This home made DERA is reportedly only useful for close range contact.

Have fun with your install.

Cheers!
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Old 10-06-2015, 10:25   #9
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Re: Wire antenna for HF DSC

Pacey,

With regards to the DSC receive antenna, I have the center conductor of the coax attached to one of the chainplate bolts and the outer conductor of the coax attached to a keel bolt. I am by no means an expert, but this seems to work for me.

Fair winds,
Gary
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Old 10-06-2015, 10:28   #10
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Re: Wire antenna for HF DSC

To be very clear, I am not talking about transmitting using such an arrangement. This is receive only for DSC. Also, make sure that the backstay (or whatever you are using for your main antenna) is insulated from the rest of the rigging.
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Old 10-06-2015, 19:02   #11
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Re: Wire antenna for HF DSC

The second antenna for DSC is a receive-only antenna. It can be a random wire, and it doesn't even need to be outside the boat. You can put it under your headliner or in a locker.
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Old 11-06-2015, 06:08   #12
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Re: Wire antenna for HF DSC

Pacey,
1) I think I understand everything now...
And, in general, your plan sounds good (see below for more details)

2) Everyone should understand that your set-up is different that the "norm", and realize that your solutions might not be "normal" either....


{BTW, I am very familiar with plastic-jacket-covered Kelvar "rope", as I've worked with "Philistran guy rope" for radio towers, for many years...so, I am familiar with this type of Kevlar rigging..}


3) Onto some specifics in red...
Quote:
Originally Posted by Pacey16 View Post
So after reading these posts I plan to run a 45' GTO 15 wire on the outside of one mainstay and a 7 Mtr length on the other mainstay, I will feed them both through the chainplates. I can not see a risk as no one would be touching a chainplate at any time.
If you simply use one continuous length of GTO-15, and run it thru-the-deck, you will not have any outdoor connections to worry about, secure, nor weather-proof....and this is what I recommend...(rather than attaching a GTO-15 to the chainplate below-decks and another piece of GTO-15 wire to the chainplate above-decks, as this would have multiple connection points, with one being out in the weather...)


The mainstays are Kevlar line covered in a plastic jacket so I should have no issues with interference? I can replace the cable ties periodically while up there inspecting the rigging. The chainplates are not earthed or bonded to anything.
This seems okay....my only caveat here would be if your sail ever contacts these stays, you will need to make sure that the ends of the cable ties do not snag / chafe the sail....and, of course that the sail doesn't snag/chafe the GTO-15 wire!



Just no sure how to connect the DSC receive wire to the chainplate as it is a CoAx coming out of the radio, do I connect the core and leave the armour disconnected?
Yes, you can do this, and it will work well...

Or, you can connect the coax shield ("armour") to ground/earth (typically a keel bolt, as I've done....or an underwater bronze thru-hull, etc.)...

Either approach should work fine...


If this can work I will be happy not to have stupid looking antenna's whipping around catching lines and getting broken.
I actually think antennas are rather "pretty" and "intelligent"....but that's just me...



4) Now to address some of the others...
--- Chip, you are of course correct that the Metz antenna is not as good as a 20' - 25' vertical wire....but it is cheap, and easy, for most sailors.....and due to the "advantage" of the DSC signals vs. a voice SSB signal (as much as 12 - 15db), the "disadvantage" of the Metz antenna is compensated for, to a good degree...
FYI, I used a 49" Metz WeFax/DSC rec antenna for a couple months, before changing over to my 22' aft lower shroud (insulated, and fed from the chainplate), and found the 22' shroud antenna to be superior...


--- Gary H's approach is VERY valid, and DOES work....
Quote:
Originally Posted by Gary H View Post
I've had good success using the traditional insulated backstay for transmit and receive, but for HF DSC receive I use another shroud that is easily accessible near the radio. This shroud doesn't have any special fittings or insulators, but works well for receive only. The one caveat is to please make sure that your backstay is properly insulated from the rest of the standing rigging.
With regards to the DSC receive antenna, I have the center conductor of the coax attached to one of the chainplate bolts and the outer conductor of the coax attached to a keel bolt. To be very clear, I am not talking about transmitting using such an arrangement. This is receive only for DSC.
The only possible disadvantage, is a possible increase in received RFI from noise pick-up from all the rigging / all other systems on-board....but you can easily try it out, and if you have no additional received RFI (compared to any received RFI from your main antenna is should be LESS), then you're good to go!


--- Russ, the GAM is not needed here as Pacey's stays are plastic-covered-Kevlar.....and besides, we've already discussed the sporadic nature of trying to use a shunt-fed, slant-fed, coupled, antenna as a wide-band antenna....(sometimes it works, but usually not well across widely spaced bands...)

--- Bill, yes, you can make your own DSC receive antenna....and yes, a "coaxial vertical" is a good, cheap, emergency antenna....but not a good idea for a permanent antenna!




--- "Doublewide", I do not wish to be rude in anyway, and I don't wish to start an argument about HF antennas, noise, etc...But, this is bad advice!
Quote:
Originally Posted by doublewide View Post
it doesn't even need to be outside the boat. You can put it under your headliner or in a locker.
Your advice here is VERY VERY bad advice....(and yes, I'm aware that there are supposedly knowledgeable folks who recommend this approach, but they are VERY mistaken!)
PLEASE accept this as bad advice, and poor engineering, etc. and place all antennas (especially HF antennas) as far away from noise sources as possible, as much in the clear as possible, and away from other metallic objects / wiring / electrical circuits / etc. as possible....



I do hope this helps...

Fair winds..

John
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