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Old 17-07-2013, 10:31   #1
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Amazing Power of Good Antennas

As part of my mast-out refit this winter, I replaced my VHF antenna with a Shakespeare Galaxy (as recommended by Nick of Jedi) and added a Diamond vhf/uhf ham antenna on my first spreader (10 meters or 33 feet above the water) for amateur radio plus AIS.

Both connected with fat low-attenuation RG213 cable in place of the old thin coax.

I had some initial problems with a Type "N" connector which I bungled, but now everything is working fine.

I am really amazed at the difference it makes to VHF comms. I now hear calls from all up and down the English Channel, from far beyond line of sight range (which I had thought was a natural limitation). From L' Aber Wrach'h, I got a "loud and clear" radio check report from Falmouth Coast guard, more than 100 miles away! I have had to start using the "LO/DX" switch on the radio (an Icom M604) to filter out very distance calls, and I am now using the low power setting (1 watt instead of 25 watts) for most calls. 1 watt is plenty to be heard very well up to 20 miles or so. I had no idea the antenna would make such a difference.

I received a DSC distress call from next to Hurst Castle in the Solent -- from Ushant -- 120 miles away! And that was from a small yacht, so not a high antenna like the Coast Guard has.

Likewise, with AIS, although the antenna is only 10 meters above the water. I see ships all the way across the English Channel, routinely more than 100 miles away.

I don't yet know from how far other vessels can see my AIS transmissions -- I will start checking that soon.

I always thought that VHF was strictly line of sight, so never thought it was worth spending a lot of time or money on antennas. Boy, was I wrong.
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Old 17-07-2013, 10:36   #2
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Re: Amazing Power of Good Antennas

you might be seeing a bit of "ducting" maybe, conditions at the moment do show show VHF ducting , UK/France

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Old 17-07-2013, 10:37   #3
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Re: Amazing Power of Good Antennas

Quote:
Originally Posted by Dockhead View Post
As part of my mast-out refit this winter, I replaced my VHF antenna with a Shakespeare Galaxy (as recommended by Nick of Jedi) and added a Diamond vhf/uhf ham antenna on my first spreader (10 meters or 33 feet above the water) for amateur radio plus AIS.

Both connected with fat low-attenuation RG213 cable in place of the old thin coax.

I had some initial problems with a Type "N" connector which I bungled, but now everything is working fine.

I am really amazed at the difference it makes to VHF comms. I now hear calls from all up and down the English Channel, from far beyond line of sight range (which I had thought was a natural limitation). From L' Aber Wrach'h, I got a "loud and clear" radio check report from Falmouth Coast guard, more than 100 miles away! I have had to start using the "LO/DX" switch on the radio (an Icom M604) to filter out very distance calls, and I am now using the low power setting (1 watt instead of 25 watts) for most calls. 1 watt is plenty to be heard very well up to 20 miles or so. I had no idea the antenna would make such a difference.

I received a DSC distress call from next to Hurst Castle in the Solent -- from Ushant -- 120 miles away! And that was from a small yacht, so not a high antenna like the Coast Guard has.

Likewise, with AIS, although the antenna is only 10 meters above the water. I see ships all the way across the English Channel, routinely more than 100 miles away.

I don't yet know from how far other vessels can see my AIS transmissions -- I will start checking that soon.

I always thought that VHF was strictly line of sight, so never thought it was worth spending a lot of time or money on antennas. Boy, was I wrong.
Wow, now that is excellent info, thanks. Glad you doing so well with it.
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Old 17-07-2013, 10:39   #4
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Quote:
Originally Posted by goboatingnow
you might be seeing a bit of "ducting" maybe, conditions at the moment do show show VHF ducting , UK/France

dave
Yes, maybe. It's really hard to credit the range Im seeing.
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Old 17-07-2013, 11:18   #5
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Re: Amazing Power of Good Antennas

AIS at that range is remarkable. Ecelent work on the instalation

Time and again people who do not have AIS say its range is 4 or 5 miles. Its not. Its much further. On my antenna on the back rail (normally I have it mast head) it shows all ships at over 23 nms.... theres a shipping route there.

Giving AIS a good antenna setup is a wonderful safety plus.
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Old 17-07-2013, 12:43   #6
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Re: Amazing Power of Good Antennas

Yes, this is almost certainly due to ducting. Ducting propagation can be somewhat seasonal, and will vary over hours / days / weeks. I've seen ducting beyond 1000 miles, and ranges beyond 200 miles for a week or two. Expect your range to get back to "normal" before too long.

But, the good news is that your new antenna setup is obviously working well. Ducting can bring in signals from way over the horizon, but these distant signals are still weaker than the typical local signals. Good job!
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Old 17-07-2013, 13:42   #7
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Re: Amazing Power of Good Antennas

Dunno why everyone always slags AIS! Its got me stuffed.
So 100 nms may be on a great day, but that means on an average day you are going to get excellent range and on a poor day still very good range.

Much better than dying from a ship-hit because you believe AIS doesnt work.... its just atmospherics, a bit of luck and a few beers at Raymarine when they spudded your box....

I get every big ship at 40 nms from the mast top with a little cheap $60 antenna. I dont see why Dockhead cant get as much or better range with a full size expensive antenna picking up every floating digital package.

Also, the Radar Horizon is 6% further than the visual horizon (Info Furuno), and the VHF horizon would be the same or further again with 15% common.

Line of Sight from a 20 meter mast high antenna to a ship antenna at 60 meters high is 31nms
Plus 6% = 33nms
Plus 15% = 36nms

What that all means is that Dockhead, me and everyone with a good AIS setup should be getting 30nms before we start getting serious!

Getting 100 nms shows his set up is good becasue, sure as hell, someone who normally receives 5 nms wont get 100nms when theres a temperature inversion.


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Old 17-07-2013, 14:32   #8
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Re: Amazing Power of Good Antennas

Dockhead, at those distances, it is ducting (aka "skip") but yes, a good antenna and good cable make an incredible difference. Since VHF is an FM radio and all FM radios work based on what is called "the capture effect" it also means that if your signal is slightly stronger than other signals in your area? YOU will get through, the others won't. An invisible but important advantage, even locally.
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Old 17-07-2013, 15:43   #9
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Re: Amazing Power of Good Antennas

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Dockhead, at those distances, it is ducting (aka "skip")
Tropospheric ducting is not also known as "skip". Two entirely different things.

Eric
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Old 17-07-2013, 15:58   #10
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Re: Amazing Power of Good Antennas

Actually, it could be either ducting or skip but one thing it definitely is not is the antenna.
All properly functioning resonant antennas are functionally equivalent with only minor difference due to overall length which can shape the radiation pattern.

In this case, it sounds more like good quality coax and new, properly attached coax connectors than anything to do with the antenna.
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Old 17-07-2013, 16:03   #11
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Re: Amazing Power of Good Antennas

Eric, throw away your licenses and pretend you are a layman. Tropospheric ducting and ionospheric skip become all one and the same. "Something in the air" changes the normal signal path and gives you impossible distance. All same same and many folks will use the terms without any real objective confirmation of which they are experiencing. And if you are simply "dealing with it" as opposed to trying to make dx contacts by pursuing it, they pretty much are the same thing.

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Old 17-07-2013, 16:15   #12
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Re: Amazing Power of Good Antennas

Yellow canary, green canary, all same...eat cat!

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Old 17-07-2013, 16:27   #13
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Re: Amazing Power of Good Antennas

Why not use the proper term, instead of one which may give the wrong impression to non-techies?

There's no "skip" going on. It's tropospheric ducting AKA "Tropo" pure and simple.

It is very common on VHF frequencies in that region at this time of year. From Rabat, Morocco I used to regularly work stations in Portugal on the ham 2-meter band (just below the VHF marine band).

The guy who mentioned before that you cannot expect these unusual distances to become routine is right: what you're experiencing is exceptional, not routine.

I agree that it sounds more like good cabling and connections than a specific antenna effect.

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Old 17-07-2013, 19:21   #14
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Re: Amazing Power of Good Antennas

Quote:
Originally Posted by btrayfors View Post
Why not use the proper term, instead of one which may give the wrong impression to non-techies?

There's no "skip" going on. It's tropospheric ducting AKA "Tropo" pure and simple.
----
I'm a totally incompetent non-techie so proper terminology is a help in keeping me from getting even further misguided.
Thanks btrayfors.
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Old 17-07-2013, 19:29   #15
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Re: Amazing Power of Good Antennas

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Originally Posted by hellosailor View Post
Tropospheric ducting and ionospheric skip become all one and the same. "Something in the air" changes the normal signal path and gives you impossible distance. All same same and many folks will use the terms without any real objective confirmation of which they are experiencing.
I prefer to educate rather than perpetuate misinformation. As far as "impossible distance"? I routinely (daily) communicate around the world on HF using skywave propagation (aka, skip). Tropospheric ducting is entirely different. Skywave propagation via VHF is possible via sporadic-E (aka, skip) but not routine and/or reliable.

Eric
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