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Next: Looking for Tips on buying my first (used) boat
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External
Since: Apr 19, 2006
Posts: 5
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(Msg. 1) Posted: Wed Apr 19, 2006 6:13 am
Post subject: Changing VHF antenna location...?
Archived from groups: rec>boats>electronics (more info?)
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I have a small sail boat (26') used for coastal cruising. It
would probably never be beyond 25 miles from the shore
line (maximum) and normally no more than 1 to 3 miles.
At present... it has a 1/2 wave Shakespeare mounted about
5 feet above the water line on a stern rail. The previous owner
has indicated that this arrangement has worked for him... and
I am assuming the standing wave ratio and that sort of thing is
ok... or must be... if his radio checks/contacts have been
satisfactory.
My question is...
Would I be *much* better off... moving the antenna to the top
of the mast... which would be 30 feet higher than where it is now
situated... based on the aforementioned cruising criteria?
Cause... if the gain won't be that *significant*... I don't want to
go through the hassle of remounting everything. Kind of like...
"...if it ain't broke why am I trying to fix it?" (smile)
Tnx for your help...
73
Bill
Southern California |
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External
Since: Apr 19, 2006
Posts: 4
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(Msg. 2) Posted: Wed Apr 19, 2006 2:28 pm
Post subject: Re: Changing VHF antenna location...? [Login to view extended thread Info.]
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An interesting discussion. A couple of things to consider.
Another reader mentioned that VHF signals are essentially line of sight,
which means that the effective range of your radio is a function of,
among other things, the height of your antenna and the height of the
receiving antenna. Since you dont necessarily know the height of the
receiving antenna, it's hard to predict the range of the radio with any
precision. However, you can get a relative indication of the range of
an antenna mounted at 5' versus, say, 25'. At 5', the horizon is about
2 1/2 miles away. At 25' it's about 5 1/2 miles away. So, all other
things being equal, moving your antenna to the top of the mast should
roughly double your range. However, all other things are not equal, and
this should only be used as the roughest of estimates.
There are a couple other considerations. At 155mhz, there's a
reasonable amount of signal loss in the cable itself. For instance,
let's say that your marine radio is on high power, 25 watts. Let's say
also that you're using relatively low budget Radio Shack RG58, and that
the total cable length from the radio to the base of the antenna is 35'.
That's almost 2dB of signal loss, or roughly 16 watts of power at
the antenna. Obviously the shorter the feed line, the less loss.
The other obvious consideration is what happens if you lose your rig and
need to call for help? An antenna at the top of the mast performs
better, assuming the mast is still standing!
On my last boat, I solved this conundrum by having 2 separate VHF
radios, one with an antenna on the stern rail, and the other with the
antenna at the top of the mast. That way I was protected from a failure
of either of the antennas or the electronics themselves.
On the current boat, I have the luxury of having 2 masts. Each mast has
2 small high gain antennas at the top, offset by about 2'. The four
antennas are all interchangeable, so if one fails I can simply switch to
another. The four antennas are connected to a VHF marine radio, a dual
band VHF/UHF ham radio, an AIS receiver, and to the stereo system.
billwarnock.RemoveThis@earthlink.net wrote:
> I have a small sail boat (26') used for coastal cruising. It
> would probably never be beyond 25 miles from the shore
> line (maximum) and normally no more than 1 to 3 miles.
>
> At present... it has a 1/2 wave Shakespeare mounted about
> 5 feet above the water line on a stern rail. The previous owner
> has indicated that this arrangement has worked for him... and
> I am assuming the standing wave ratio and that sort of thing is
> ok... or must be... if his radio checks/contacts have been
> satisfactory.
>
> My question is...
>
> Would I be *much* better off... moving the antenna to the top
> of the mast... which would be 30 feet higher than where it is now
> situated... based on the aforementioned cruising criteria?
>
> Cause... if the gain won't be that *significant*... I don't want to
> go through the hassle of remounting everything. Kind of like...
> "...if it ain't broke why am I trying to fix it?" (smile)
>
> Tnx for your help...
>
> 73
>
> Bill
> Southern California
> |
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External
Since: Feb 24, 2006
Posts: 35
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(Msg. 3) Posted: Wed Apr 19, 2006 4:23 pm
Post subject: Re: Changing VHF antenna location...? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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wrote in message
>I have a small sail boat (26') used for coastal cruising. It
> would probably never be beyond 25 miles from the shore
> line (maximum) and normally no more than 1 to 3 miles.
>
> At present... it has a 1/2 wave Shakespeare mounted about
> 5 feet above the water line on a stern rail.
>
> My question is...
>
> Would I be *much* better off... moving the antenna to the top
> of the mast...
No.
There would be a small improvement but I don't think you would even notice.
I recommend you leave the antenna where it is and if you ever have an
emergency be sure to point your sailboat (if you can) so that the boat is
not between the antenna and the shore. If you are disabled and adrift off
shore then occasionally your boat will not be between your antenna and
shore. These are the best times to call for help but by all means, call for
help constantly until someone hears you. If you are out of sight from shore
then I recommend you get an epirb.
http://www.sarsat.noaa.gov/emerbcns.html
I also recommend you keep a cell phone aboard. I have found it to be much
more handy than marine vhf radios. >> Stay informed about: Changing VHF antenna location...? |
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External
Since: Jun 24, 2004
Posts: 213
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(Msg. 4) Posted: Wed Apr 19, 2006 6:09 pm
Post subject: Re: Changing VHF antenna location...? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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In article ,
"Ted" wrote:
> wrote in message
>
> >I have a small sail boat (26') used for coastal cruising. It
> > would probably never be beyond 25 miles from the shore
> > line (maximum) and normally no more than 1 to 3 miles.
> >
> > At present... it has a 1/2 wave Shakespeare mounted about
> > 5 feet above the water line on a stern rail.
> >
> > My question is...
> >
> > Would I be *much* better off... moving the antenna to the top
> > of the mast...
>
> No.
>
> There would be a small improvement but I don't think you would even notice.
>
> I recommend you leave the antenna where it is and if you ever have an
> emergency be sure to point your sailboat (if you can) so that the boat is
> not between the antenna and the shore. If you are disabled and adrift off
> shore then occasionally your boat will not be between your antenna and
> shore. These are the best times to call for help but by all means, call for
> help constantly until someone hears you. If you are out of sight from shore
> then I recommend you get an epirb.
>
> http://www.sarsat.noaa.gov/emerbcns.html
>
> I also recommend you keep a cell phone aboard. I have found it to be much
> more handy than marine vhf radios.
>
>
>
>
With both Marine VHF and Cellular Service, you are looking at the maximum
range of transmission being determined by LOS (line of sight) plus a
extending factor of signal bending, which is Frequency dependant, and
which is maybe 5 to 10% more, which makes up the Radio Horizon. USCG
Remote Radio Sites are typically located at high elevation points along
the coastline, so as to maximize their coverage out to sea, where
Cellular coverage is specifically designed to minimize adjacent Cell
overlap but give continious coverage along the coastline. These are
two, basically, Mutually Exclusive determinations.
Moving the Marine VHF Antenna to the top of the mast, WILL certainly
extend the VHF Range for the vessel over an antenna that is 5 ft
above the water. Remember it is just not the distance offshore that one
needs to consider, it is also how far the USCG Site is up or down the
coast from your position as well. Another thing to consider is the
Antenna Gain Specs of the Marine VHF Antenna, which will determine the
3db Vertical Antenna Beamwidth, which intern will affect the ability of
the antenna to communicate to shore stations when the vessel is healed
over while navigating crosswind.
For sail powered vessels, it has always been prudent to have the VHF
Antenna, as high as possible, with no more than 4.5 db of gain in
the antenna, so as to minimize the healing degradation of maximum
effective range. Cellular should NEVER be considered a substitute
for Marine VHF communications, but it can be helpfull as a backup
system.
Also remeber that Marine VHF will allow communications with other
vessels in your area, as well USCG Remote Radio Sites, where Cellular
MUST be able to communicate with the Shorebased Cellsite in order to be
of use in communications. There is no vessel to vessel communications
with cellular, if you are not within cellular coverage.
Bruce in alaska
--
add a <2> before @ >> Stay informed about: Changing VHF antenna location...? |
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External
Since: Nov 05, 2005
Posts: 1367
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(Msg. 5) Posted: Thu Apr 20, 2006 2:18 am
Post subject: Re: Changing VHF antenna location...? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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billwarnock.RemoveThis@earthlink.net wrote in
@i39g2000cwa.googlegroups.com:
> Would I be *much* better off... moving the antenna to the top
> of the mast... which would be 30 feet higher than where it is now
> situated... based on the aforementioned cruising criteria?
>
>
Much better off. Altitude and Power are our friends on VHF, which is line-
of-sight. You climb to the top of the mast, you can see further. So can't
your VHF radio....do it. >> Stay informed about: Changing VHF antenna location...? |
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External
Since: Feb 24, 2006
Posts: 35
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(Msg. 6) Posted: Thu Apr 20, 2006 12:53 pm
Post subject: Re: Changing VHF antenna location...? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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"Larry" wrote in message
> billwarnock.TakeThisOut@earthlink.net wrote in
> @i39g2000cwa.googlegroups.com:
>
>> Would I be *much* better off... moving the antenna to the top
>> of the mast... which would be 30 feet higher than where it is now
>> situated... based on the aforementioned cruising criteria?
>>
>>
>
> Much better off. Altitude and Power are our friends on VHF, which is
> line-
> of-sight. You climb to the top of the mast, you can see further. So
> can't
> your VHF radio....do it.
>
Bill, when was the last time you actually pushed the transmit button on
your marine vhf and who did you try to talk to? >> Stay informed about: Changing VHF antenna location...? |
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External
Since: Feb 24, 2006
Posts: 35
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(Msg. 7) Posted: Thu Apr 20, 2006 1:02 pm
Post subject: Re: Changing VHF antenna location...? line of sight calculator web page [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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Here is a line of sight calculator
http://homepages.nildram.co.uk/~vwlowen/java/horizon.htm
"Ted" wrote in message
>
> "Larry" wrote in message
>
>> billwarnock DeleteThis @earthlink.net wrote in
>> @i39g2000cwa.googlegroups.com:
>>
>>> Would I be *much* better off... moving the antenna to the top
>>> of the mast... which would be 30 feet higher than where it is now
>>> situated... based on the aforementioned cruising criteria?
>>>
>>>
>>
>> Much better off. Altitude and Power are our friends on VHF, which is
>> line-
>> of-sight. You climb to the top of the mast, you can see further. So
>> can't
>> your VHF radio....do it.
>>
>
> Bill, when was the last time you actually pushed the transmit button on
> your marine vhf and who did you try to talk to?
>
> >> Stay informed about: Changing VHF antenna location...? |
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External
Since: Aug 23, 2005
Posts: 35
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(Msg. 8) Posted: Thu Apr 20, 2006 1:24 pm
Post subject: Re: Changing VHF antenna location...? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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In article , Bruce in Alaska wrote:
>In article ,
> "Ted" wrote:
>
>> wrote in message
>>
>> >I have a small sail boat (26') used for coastal cruising. It
>> > would probably never be beyond 25 miles from the shore
>> > line (maximum) and normally no more than 1 to 3 miles.
>> >
>> > At present... it has a 1/2 wave Shakespeare mounted about
>> > 5 feet above the water line on a stern rail.
>> >
>> > My question is...
>> >
>> > Would I be *much* better off... moving the antenna to the top
>> > of the mast...
>>
>> No.
>>
>> There would be a small improvement but I don't think you would even notice.
>>
>> I recommend you leave the antenna where it is and if you ever have an
>> emergency be sure to point your sailboat (if you can) so that the boat is
>> not between the antenna and the shore. If you are disabled and adrift off
>> shore then occasionally your boat will not be between your antenna and
>> shore. These are the best times to call for help but by all means, call for
>> help constantly until someone hears you. If you are out of sight from shore
>> then I recommend you get an epirb.
>>
>> http://www.sarsat.noaa.gov/emerbcns.html
>>
>> I also recommend you keep a cell phone aboard. I have found it to be much
>> more handy than marine vhf radios.
>>
>>
>>
>>
>
>With both Marine VHF and Cellular Service, you are looking at the maximum
>range of transmission being determined by LOS (line of sight) plus a
>extending factor of signal bending, which is Frequency dependant, and
>which is maybe 5 to 10% more, which makes up the Radio Horizon. USCG
I would say this is definately for reliable transmission.
I always get cellular service around 60 mi up at lake Erie. Its hard not to
keep out of the Canadian stations on the US side, in fact its hard to get in the US
sites on the US side from the coast. I always think of an article or rig named Puddle Jumper.
This was a 2 meter superregen rig, mabe by Heathkit, not
sure. They talked about talking out over one of the Great Lakes I always think of this.
Of course, heat and cold air over the lake do wonderfull things.
greg >> Stay informed about: Changing VHF antenna location...? |
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Since: Nov 05, 2005
Posts: 1367
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(Msg. 9) Posted: Thu Apr 20, 2006 7:26 pm
Post subject: Re: Changing VHF antenna location...? [Login to view extended thread Info.]
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szekeres DeleteThis @pitt.edu (GregS) wrote in
> This was a 2 meter superregen rig, mabe by Heathkit, not
> sure. They talked about talking out over one of the Great Lakes I
> always think of this. Of course, heat and cold air over the lake do
> wonderfull things.
>
>
We call them the "Lunchbox" because Heath's cabinet looked like a kid's
metal lunchbox...which also makes a great homebrew cabinet..(c;
Not sure how many I built from the time I was 11. People used to bring me
Heathkits and pay me to build them all through middle and high school. The
reel-to-reel tape recorder Heath had as a kit was a real challenge....
They also made lunchbox CB regen sets. They'd only transmit on one channel
from the xtal plug on the front of it, but we kept the xtals on the desk
nearby..(c;
Ahhh...the incessant hiss of a sensitive regen receiver waiting for 6 meter
AM to open up in the middle of the night (1957 was a great sunspot maximum,
an all-time record. Great time to get your first ham license, like I did!) >> Stay informed about: Changing VHF antenna location...? |
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External
Since: May 23, 2006
Posts: 1
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(Msg. 10) Posted: Tue May 23, 2006 6:00 am
Post subject: Re: Changing VHF antenna location...? line of sight calculator web page [Login to view extended thread Info.]
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So,
antenna height feet, horizon miles
Boat Coast Horizon
6 100 17
30 100 22
The range with the coastal stations doesnt change so much and the DSC calls
will be received from much further away. For emergency calls to the coast
the antenna difference is not so much, boat to boat is a different story.
J >> Stay informed about: Changing VHF antenna location...? |
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External
Since: Nov 05, 2005
Posts: 1367
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(Msg. 11) Posted: Wed May 24, 2006 10:53 pm
Post subject: Re: Changing VHF antenna location...? line of sight calculator web page [Login to view extended thread Info.]
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"Jester" wrote in
> For emergency calls to the coast
> the antenna difference is not so much, boat to boat is a different story.
>
And you have to factor in the damned marinas and their 70' antenna towers
running 25 watts to talk to the motoryacht 200 ft away coming towards their
docks. FCC should restrict marinas to antennas 20' off the water running
1/2 watt.....or walkie talkies. >> Stay informed about: Changing VHF antenna location...? |
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External
Since: Aug 07, 2004
Posts: 171
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(Msg. 12) Posted: Thu May 25, 2006 8:01 am
Post subject: Re: Changing VHF antenna location...? line of sight calculator web [Login to view extended thread Info.]
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Larry wrote:
<snip>
> And you have to factor in the damned marinas and their 70' antenna towers
> running 25 watts to talk to the motoryacht 200 ft away coming towards their
> docks. FCC should restrict marinas to antennas 20' off the water running
> 1/2 watt.....or walkie talkies.
?? You're joking right? Did you know that more Watts gives them more
range? And that people can sometimes reasonably expect to communicate
with things that are beyond their visual (not radio) line of sight?
What would really make more sense to me is to make everyone have a radio
that shifts to the low power transmit mode when they transmit after a
received signal had a power level above a certain point. Add a LED so
the people can tell which mode they are transmitting in. And also give
them a power over ride control that will let them cancel the automated
feature when they feel the extra power is appropriate.
Someone is always going to be "too close" and someone else is always
going to "too far away".
And how about this? A radio that will not transmit if the antenna loop
shows an resistance above a certain level. That would get the folks
with bad installs and weathered connectors off the air.
Oh yeah, and add a SWR monitoring circuit too! If the SWR is more than
1.5:1 it won't transmit.
Jack
--
Jack Erbes in Ellsworth, Maine, USA - jackerbes at adelphia dot net
(also receiving email at jacker at midmaine.com) >> Stay informed about: Changing VHF antenna location...? |
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Since: Nov 05, 2005
Posts: 1367
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(Msg. 13) Posted: Thu May 25, 2006 6:40 pm
Post subject: Re: Changing VHF antenna location...? line of sight calculator web page [Login to view extended thread Info.]
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Jack Erbes wrote in
> ?? You're joking right? Did you know that more Watts gives them more
> range? And that people can sometimes reasonably expect to communicate
> with things that are beyond their visual (not radio) line of sight?
>
>
I'm not joking at all. Marinas have no need to transmit further than the
end of their docks. They certainly have no need to transmit 100 miles from
tall antenna towers way over their buildings. Channel 16 isn't "The Marina
Channel", it's for calling and emergencies, not selling dock space.
Maybe FCC needs to designate one of the unused telephone company channels
"The Marina Channel" and make them all go over there. If you want to call
a marina, you go to "The Marina Channel", like you do now with "The Bridge
Channel", 9. >> Stay informed about: Changing VHF antenna location...? |
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Since: Jun 11, 2004
Posts: 68
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(Msg. 14) Posted: Thu May 25, 2006 7:53 pm
Post subject: Re: Changing VHF antenna location...? line of sight calculator web page [Login to view extended thread Info.]
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In article ,
Larry wrote:
> FCC should restrict marinas to antennas 20' off the water running
> 1/2 watt.....or walkie talkies.
Nope, the Marinra Operators just need to be EDUCATED, on how to use
the 1 Watt switch on their radios, when talking to a vessel they can see
out the window........
Me Educated = 2X4 up the side of the opoeraters head....... >> Stay informed about: Changing VHF antenna location...? |
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Since: Nov 05, 2005
Posts: 1367
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(Msg. 15) Posted: Thu May 25, 2006 7:53 pm
Post subject: Re: Changing VHF antenna location...? line of sight calculator web page [Login to view extended thread Info.]
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Me wrote in
@netnews.worldnet.att.net:
> Nope, the Marinra Operators just need to be EDUCATED, on how to use
> the 1 Watt switch on their radios, when talking to a vessel they can see
> out the window........
>
>
One watt from a 9db antenna at 70', used to advertise the marina simply by
it telling boaters their name, is of no use. Marina operators are teenage
kids from the local college working the docks, here. They need WALKIE
TALKIES in the 100 milliwatt range, not 1 watt radios with 70' towers and
high gain antennas. >> Stay informed about: Changing VHF antenna location...? |
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