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Old 07-12-2014, 07:46 PM   #21
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Full wavelength antennas are difficult if not impossible to match. There is also a problem with the phase angle. Most 8' antennas are either 1/2 or 5/8ths wavelengths. The shorter 4' fiberglass antennas are typically the 1/4 wave antennas.
The reason for the great performance sailboats get is many masts are Aluminum so they have a ground plane and your height above average terrain is far better than most Trawlers. 8' and 16' VHF antennas are used to get additional height for the typical mode of VHF Marine FM line of site (aka LOS).
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Old 07-12-2014, 07:59 PM   #22
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The 16-22 foot antennas are usually 10db where the 8 footers are 6db.

While VHF is usually regarded as line of site...and terrain is different than curvature just of the earth blocking....VHF can and often exceeds 100 miles with enough power.

In the Cape May area...USCG stations in Massachusetts to North Carolina can be heard transmitting..my personal best was from a USCG Helo in a 50' hover over a cruise ship and talking to Cape May about 120NM away.

35-40 NM with a 10db antenna and a good receiving antenna is pretty common in my experience.

Again...my experience is discussing "open water" reception.
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Old 07-12-2014, 08:14 PM   #23
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While VHF is usually regarded as line of sight...and terrain is different than curvature just of the earth blocking....VHF can and often exceeds 100 miles with enough power.
Absolutely true. But it cannot be depended upon, because there are so many variables. And so LOS is better to take as a baseline.

Anyway, I do not like to get involved in discussions, so will back out of here. Been fun, y'all. :-)
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Old 07-12-2014, 08:26 PM   #24
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It's not unusual to get an ionosphere 'skip' on VHF and intermittently receive a transmission from well beyond line of sight, but it doesn't make for reliable communication. It happened frequently in air traffic control. When I was an Air Traffic Controller in San Diego, we would occasionally receive transmissions in the control tower from an ATC facility in Central CA.

In fact, the FAA has a Frequency Management office which deals with assigning and protecting communications and navigation signals from interference from distant sources on the same frequency. The area of protection, called a service volume, is MUCH greater than typical line of sight for that reason, plus the fact that aircraft at altitude can receive at much greater distances than land-based radios.
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Old 07-13-2014, 12:58 AM   #25
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All I know is that higher the antennae, the longer the range.

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Old 07-13-2014, 06:39 AM   #26
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The 16-22 foot antennas are usually 10db where the 8 footers are 6db.

While VHF is usually regarded as line of site...and terrain is different than curvature just of the earth blocking....VHF can and often exceeds 100 miles with enough power.

In the Cape May area...USCG stations in Massachusetts to North Carolina can be heard transmitting..my personal best was from a USCG Helo in a 50' hover over a cruise ship and talking to Cape May about 120NM away.

35-40 NM with a 10db antenna and a good receiving antenna is pretty common in my experience.

Again...my experience is discussing "open water" reception.
Quite true but not reliable past LOS. The method that allows VHF signals to propagate like you mention is called tropo ducting. It's usually caused by a stagnant high pressure system where the gradients stack up. There is also a temperature component to it where this causes a duct in the atmosphere hence the term ducting.
I have heard it numerous times over the years and the 1st clue is my AIS screen populating with stations from areas not normally seen and at distances greater than 60 miles. Last year we heard USCG Jacksonville, Fla from Little Egg Bay, NJ. That's about as far south as I have ever heard on the VHF marine band.
It is possible for E Skip to happen in our VHF band but that is extremely rare and it is very short duration and usually limited to one area. Tropo usually opens up the entire coast in the direction of the ducting. The morning we heard Jacksonville we also heard Charleston, SC along with many far but still distant USCG stations along the coast to the south.
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Old 07-13-2014, 09:18 AM   #27
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All I know is that higher the antennae, the longer the range.
But to get the benefit of the higher antenna and to get the longer range you need to be using bigger coax to reduce signal loss. Using RG58-U cable with a 40' run, you loss about -2.4dB vs if you used RG213 you only loose -1.0dB.
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Old 07-13-2014, 09:23 AM   #28
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For shorter runs it's pretty hard to beat RG-8X losses at 156.8MHz. I prefer LMR400 over UG-213 either is excellent at VHF frequencies.
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Old 07-13-2014, 01:52 PM   #29
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But to get the benefit of the higher antenna and to get the longer range you need to be using bigger coax to reduce signal loss. Using RG58-U cable with a 40' run, you loss about -2.4dB vs if you used RG213 you only loose -1.0dB.
Very true and for some reason it has just now occurred to me that maybe that is why it is so hard to get some sailboats to answer a VHF call? (;o) All this time I thought it has something to do with that Maple Leaf flag flying off the back causing some sort of interference...
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Old 07-13-2014, 01:54 PM   #30
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George I have seen many sailboats where the VHF radio is in the cabin not at the helm.
That could be part of the problem as well?
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Old 07-13-2014, 03:19 PM   #31
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And like in the Biscayne Bay collision...the skipper of the sailboat said he had to have someone turn it on.
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Old 07-13-2014, 05:02 PM   #32
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There's no requirement for a recreational boat to have a VHF transceiver on board and if there is one on board there is no requirement that it be turned on.

If it is turned on, there is a requirement to monitor channel 16 but commercial operators are apparently exempt from the requirement to monitor channel 16.

So who is running this zoo?
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