On Sat, 17 Jan 2004 06:01:33 GMT, (Larry W4CSC) wrote:

All these numbers mean NOTHING if you pull foam cable around a CORNER.
The solid center conductor migrates through the flimsy foam that gives
it such a great set of numbers and it goes all to hell......

Solid center conductors also BREAK if you bend them back and forth as
the loose cable in the mast moves back and forth and back and forth on
every wave.

RG-58A/U has the same loss AFTER you pull it than when it was on the
reel. It's very flexible, finely stranded center conductor and very
hard polyethelene dielectric will take a helluva beating with no
migration around tight turns.

Most boats I know have no room for inch and a half hardline from the
radio to the mast......dammit. 58A/U (not 58/U which is solid
centered) works great for years and years......It's made for MOBILE
service.

Gee, thanks, Larry...here I thought I was screwing up...

My radio experience is painfully limited...as a teen in the '70s I ran
a 40 channel CB base station and used RG-8U...soldered my own
connections and all and put up a free-standing 30 foot tower and
directional antenna (squeaky pulley!). I know 58U was for cars, and
there was no way I was running expensive and heavy 8U up my mast, so I
used 58A/U for the 50 foot run from mast head to a splitter (for AM/FM
radio) under a settee and a further 10 feet to my VHF unit at the nav
station.

I tried a "real world" test with local Coast Guard (5x5 to receivers
about 1,200 higher than me 20 miles away) and with my wife talking to
me in a Zodiac from the boat at dawn some 7 miles away (reckoning by
GPS) over some intervening low land. I could hear her on my handheld
quite well, and she could hear me weakly, but clearly.

So I have no qualms about the 58A/U, the ICOM base unit and the old
whip antenna on a Metz mount...standard coaster rig and good for my
end of Lake Ontario, it seems.

Most of the time I use the handheld (a Standard Horizon 260S with
which I am quite pleased) in the cockpit anyway and save the base unit
for American WX and ship/bridge traffic and whatnot.

My .02 (1.4 U.S)

R.

On Sun, 18 Jan 2004 16:44:18 -0800, wrote:

Every time you double the height of your VHF antenna you gain 6 db in
signal strength

On Sun, 18 Jan 2004 23:46:55 GMT, Gary Schafer wrote:

Never heard this...any sources I can refer to? None of my books suggest this.
///
6 db signal strength increase at 30 miles accounts for about 3 extra
miles in range.

Can you please show the calculations? Or a pointer?
Thanks,
Norm

This is what he had in mind:
If you increase an antenna's height from 40 feet to 80 feet you
increase its line of sight range to the horizon by 3 or 4 miles
( root 2)

And, if you are in free space and are power limited, then doubling the
power transmitted will increase the range by root 2 using the
ordinary inverse square law of surface area [ = power density]
versus radius from a point

So, the argument continues....if the power limited range were 9 miles
and you doubled the power, the power limited range would increase to
12 miles about.
OR
if you doubled the antenna height, the line of sight to the horizon
would increase by about the same amount.
SO
you break even if you lose three dB for an extra 40 feet of height,
and you win if you use less lossy cable than that.

Now in fact, in some cases, VHF communications is not power limited,
but line of sight limited, and it takes MORE than twice the power to
reach an extra 1.4 range or three miles "round the corner" [i.e.
below the horizon]

But using this straight-forward model, you are led towards using
cable which loses less than 3dB per 40 feet or about 7 dB/100 ft.
because that is the breakeven point.

Take home message at VHF:
try to place the antenna as high as possible
and don't kill yourself worrying about cable losses, unless money is
no object. But on a tall boat, better to avoid RG58 if posssible, if
it loses 6 or 7dB per 100 feet.....

Brian W

On Sun, 18 Jan 2004 16:44:18 -0800, wrote:

Every time you double the height of your VHF antenna you gain 6 db in
signal strength

On Sun, 18 Jan 2004 23:46:55 GMT, Gary Schafer wrote:

Never heard this...any sources I can refer to? None of my books suggest this.
///
6 db signal strength increase at 30 miles accounts for about 3 extra
miles in range.

Can you please show the calculations? Or a pointer?
Thanks,
Norm

This is what he had in mind:
If you increase an antenna's height from 40 feet to 80 feet you
increase its line of sight range to the horizon by 3 or 4 miles
( root 2)

And, if you are in free space and are power limited, then doubling the
power transmitted will increase the range by root 2 using the
ordinary inverse square law of surface area [ = power density]
versus radius from a point

So, the argument continues....if the power limited range were 9 miles
and you doubled the power, the power limited range would increase to
12 miles about.
OR
if you doubled the antenna height, the line of sight to the horizon
would increase by about the same amount.
SO
you break even if you lose three dB for an extra 40 feet of height,
and you win if you use less lossy cable than that.

Now in fact, in some cases, VHF communications is not power limited,
but line of sight limited, and it takes MORE than twice the power to
reach an extra 1.4 range or three miles "round the corner" [i.e.
below the horizon]

But using this straight-forward model, you are led towards using
cable which loses less than 3dB per 40 feet or about 7 dB/100 ft.
because that is the breakeven point.

Take home message at VHF:
try to place the antenna as high as possible
and don't kill yourself worrying about cable losses, unless money is
no object. But on a tall boat, better to avoid RG58 if posssible, if
it loses 6 or 7dB per 100 feet.....

Brian W

On Sun, 18 Jan 2004 21:38:20 -0500, wrote:


My radio experience is painfully limited...as a teen in the '70s I ran
a 40 channel CB base station and used RG-8U...soldered my own
connections and all and put up a free-standing 30 foot tower and
directional antenna (squeaky pulley!). I know 58U was for cars, and
there was no way I was running expensive and heavy 8U up my mast, so I
used 58A/U for the 50 foot run from mast head to a splitter (for AM/FM
radio) under a settee and a further 10 feet to my VHF unit at the nav
station.

The various CB myths and cult followings wreaks havoc marine VHF is my
experience. Man, they got some strange physics education on CB....(c;

The gain in altitude (altitude is very important and the reason TV
stations have 2000' tall towers) is FAR more important than a few dB
loss in any kind of cabling. One of these days, I'm going to put up a
Metz on top of a 50' mast fed with RG-174/U, the tiny coax cable used
for connecting internal cables of equipment. Back 20 years ago, I got
a free 1000' roll of it from some ham or another. I never turn down
free stuff. The house is full of it, a regular packrat. Anyways, I
needed an extra antenna centered on 4585 Khz to use for the local CAP
squadron's HF comms I'd gotten my self mixed up in because a good
friend was the squadron commander and had no radio ops. Hell, it's
only 4.5 Mhz and only 100 watts of power, so use what's available. I
hung an inverted-V (dipole) from a pine tree by shooting an arrow over
a high limb with a borrowed bow....after many attempts, I might add.
The tiny RG-174 simple fed the center insulator. To my amazement, it
worked great on 4585 USB. Way early in the mornings, I could check
into the CAP net in Hawaii, causing quite a ruckus of Hawaiian
stations wanting to try to work SC DX. I got to using this big roll
for portable antennas at the local ARRL Field Day when hams camp out
on generators to see how many stations we can contact in 24 hours, a
contest.

The reality of it is a compromise between practicality and function.
Look at any receiver that has a calibrated S-meter. Notice the
calibrations are in 10 dB increments. 3 dB isn't much difference
indeed. Back to the chart someone quoted, the difference on 156 Mhz
between 8X and RG-58, which is so much easier to thread through a
boat, is less than 2 dB per HUNDRED ft. 1 dB for half of that. The
guys at the receiving end won't tell the difference.....er, ah, unless
you short out that big cable trying to bend it too sharp around the
corners...(c; It's fine....



Larry W4CSC

On Sun, 18 Jan 2004 21:38:20 -0500, wrote:


My radio experience is painfully limited...as a teen in the '70s I ran
a 40 channel CB base station and used RG-8U...soldered my own
connections and all and put up a free-standing 30 foot tower and
directional antenna (squeaky pulley!). I know 58U was for cars, and
there was no way I was running expensive and heavy 8U up my mast, so I
used 58A/U for the 50 foot run from mast head to a splitter (for AM/FM
radio) under a settee and a further 10 feet to my VHF unit at the nav
station.

The various CB myths and cult followings wreaks havoc marine VHF is my
experience. Man, they got some strange physics education on CB....(c;

The gain in altitude (altitude is very important and the reason TV
stations have 2000' tall towers) is FAR more important than a few dB
loss in any kind of cabling. One of these days, I'm going to put up a
Metz on top of a 50' mast fed with RG-174/U, the tiny coax cable used
for connecting internal cables of equipment. Back 20 years ago, I got
a free 1000' roll of it from some ham or another. I never turn down
free stuff. The house is full of it, a regular packrat. Anyways, I
needed an extra antenna centered on 4585 Khz to use for the local CAP
squadron's HF comms I'd gotten my self mixed up in because a good
friend was the squadron commander and had no radio ops. Hell, it's
only 4.5 Mhz and only 100 watts of power, so use what's available. I
hung an inverted-V (dipole) from a pine tree by shooting an arrow over
a high limb with a borrowed bow....after many attempts, I might add.
The tiny RG-174 simple fed the center insulator. To my amazement, it
worked great on 4585 USB. Way early in the mornings, I could check
into the CAP net in Hawaii, causing quite a ruckus of Hawaiian
stations wanting to try to work SC DX. I got to using this big roll
for portable antennas at the local ARRL Field Day when hams camp out
on generators to see how many stations we can contact in 24 hours, a
contest.

The reality of it is a compromise between practicality and function.
Look at any receiver that has a calibrated S-meter. Notice the
calibrations are in 10 dB increments. 3 dB isn't much difference
indeed. Back to the chart someone quoted, the difference on 156 Mhz
between 8X and RG-58, which is so much easier to thread through a
boat, is less than 2 dB per HUNDRED ft. 1 dB for half of that. The
guys at the receiving end won't tell the difference.....er, ah, unless
you short out that big cable trying to bend it too sharp around the
corners...(c; It's fine....



Larry W4CSC

On Mon, 19 Jan 2004 03:35:58 GMT, Brian Whatcott
wrote:

On Sun, 18 Jan 2004 16:44:18 -0800, wrote:

Every time you double the height of your VHF antenna you gain 6 db in
signal strength

On Sun, 18 Jan 2004 23:46:55 GMT, Gary Schafer wrote:

Never heard this...any sources I can refer to? None of my books suggest this.
///
6 db signal strength increase at 30 miles accounts for about 3 extra
miles in range.

Can you please show the calculations? Or a pointer?
Thanks,
Norm

This is what he had in mind:
If you increase an antenna's height from 40 feet to 80 feet you
increase its line of sight range to the horizon by 3 or 4 miles
( root 2)

And, if you are in free space and are power limited, then doubling the
power transmitted will increase the range by root 2 using the
ordinary inverse square law of surface area [ = power density]
versus radius from a point

So, the argument continues....if the power limited range were 9 miles
and you doubled the power, the power limited range would increase to
12 miles about.
OR
if you doubled the antenna height, the line of sight to the horizon
would increase by about the same amount.
SO
you break even if you lose three dB for an extra 40 feet of height,
and you win if you use less lossy cable than that.

Now in fact, in some cases, VHF communications is not power limited,
but line of sight limited, and it takes MORE than twice the power to
reach an extra 1.4 range or three miles "round the corner" [i.e.
below the horizon]

But using this straight-forward model, you are led towards using
cable which loses less than 3dB per 40 feet or about 7 dB/100 ft.
because that is the breakeven point.

Take home message at VHF:
try to place the antenna as high as possible
and don't kill yourself worrying about cable losses, unless money is
no object. But on a tall boat, better to avoid RG58 if posssible, if
it loses 6 or 7dB per 100 feet.....

Brian W


It is not a linear function though. The amount of additional range
that you get is in the area of 10% to 30% depending on the heights
that you start at.

True line of sight loss (free space) is equal to 6 db every time you
double the range.

When figuring maximum range when changing antenna heights, refraction
of the signal is involved. The above formula also comes into play
slightly too. But it works out to around 6 db of signal increase at
the maximum range when ever you double the antenna height.


Doubling the power and doubling the antenna height do not give the
same results. Doubling the power results in an increase of 3 db in
signal strength. Doubling antenna height results in a 6 db increase in
signal strength. So you would have to increase the power by 4 times to
equal a doubling of antenna height.

Below is a link to a line of sight calculator.
http://www.vwlowen.demon.co.uk/java/horizon.htm


Here is a path loss calculator. It uses 20 miles as a default for the
range.
You can put in some heights and note the amount of path loss in DB
that you get. Then double the height of one of the antennas and note
that the path loss you get decreases by 6 db.


http://www.decibelproducts.com/Calculators/qegli.htm


The "break even point" in cable loss is also a non linear function.
With a moderate loss cable it does not "catch up" to the height
increase until you have reached a couple of hundred feet. With a high
loss cable it can "catch up" at a much lower height. Giving you a
negative return as you go higher with the antenna.

But the point is that the worse the cable loss the more percentage of
power and range you are giving away the higher you go.

Regards
Gary

On Mon, 19 Jan 2004 03:35:58 GMT, Brian Whatcott
wrote:

On Sun, 18 Jan 2004 16:44:18 -0800, wrote:

Every time you double the height of your VHF antenna you gain 6 db in
signal strength

On Sun, 18 Jan 2004 23:46:55 GMT, Gary Schafer wrote:

Never heard this...any sources I can refer to? None of my books suggest this.
///
6 db signal strength increase at 30 miles accounts for about 3 extra
miles in range.

Can you please show the calculations? Or a pointer?
Thanks,
Norm

This is what he had in mind:
If you increase an antenna's height from 40 feet to 80 feet you
increase its line of sight range to the horizon by 3 or 4 miles
( root 2)

And, if you are in free space and are power limited, then doubling the
power transmitted will increase the range by root 2 using the
ordinary inverse square law of surface area [ = power density]
versus radius from a point

So, the argument continues....if the power limited range were 9 miles
and you doubled the power, the power limited range would increase to
12 miles about.
OR
if you doubled the antenna height, the line of sight to the horizon
would increase by about the same amount.
SO
you break even if you lose three dB for an extra 40 feet of height,
and you win if you use less lossy cable than that.

Now in fact, in some cases, VHF communications is not power limited,
but line of sight limited, and it takes MORE than twice the power to
reach an extra 1.4 range or three miles "round the corner" [i.e.
below the horizon]

But using this straight-forward model, you are led towards using
cable which loses less than 3dB per 40 feet or about 7 dB/100 ft.
because that is the breakeven point.

Take home message at VHF:
try to place the antenna as high as possible
and don't kill yourself worrying about cable losses, unless money is
no object. But on a tall boat, better to avoid RG58 if posssible, if
it loses 6 or 7dB per 100 feet.....

Brian W


It is not a linear function though. The amount of additional range
that you get is in the area of 10% to 30% depending on the heights
that you start at.

True line of sight loss (free space) is equal to 6 db every time you
double the range.

When figuring maximum range when changing antenna heights, refraction
of the signal is involved. The above formula also comes into play
slightly too. But it works out to around 6 db of signal increase at
the maximum range when ever you double the antenna height.


Doubling the power and doubling the antenna height do not give the
same results. Doubling the power results in an increase of 3 db in
signal strength. Doubling antenna height results in a 6 db increase in
signal strength. So you would have to increase the power by 4 times to
equal a doubling of antenna height.

Below is a link to a line of sight calculator.
http://www.vwlowen.demon.co.uk/java/horizon.htm


Here is a path loss calculator. It uses 20 miles as a default for the
range.
You can put in some heights and note the amount of path loss in DB
that you get. Then double the height of one of the antennas and note
that the path loss you get decreases by 6 db.


http://www.decibelproducts.com/Calculators/qegli.htm


The "break even point" in cable loss is also a non linear function.
With a moderate loss cable it does not "catch up" to the height
increase until you have reached a couple of hundred feet. With a high
loss cable it can "catch up" at a much lower height. Giving you a
negative return as you go higher with the antenna.

But the point is that the worse the cable loss the more percentage of
power and range you are giving away the higher you go.

Regards
Gary

On Mon, 19 Jan 2004 19:06:06 GMT, Gary Schafer
wrote:
....
Here is a path loss calculator. It uses 20 miles as a default for the
range. You can put in some heights and note the amount of
path loss in DB that you get.
Then double the height of one of the antennas and note
that the path loss you get decreases by 6 db.

http://www.decibelproducts.com/Calculators/qegli.htm

Regards
Gary

This caculator gives the following caution:

"Note: The Egli model is based on data measured over radials mainly in
the eastern US seaboard and central plains states. It gives an overall
propagation loss over gently rolling terrain with average hill heights
of approximately 50 ft. "

You may have noticed that at sea, you hope to avoid regions with
gentle hillocks of 50 ft wave height. :-)

Brian W

On Mon, 19 Jan 2004 19:06:06 GMT, Gary Schafer
wrote:
....
Here is a path loss calculator. It uses 20 miles as a default for the
range. You can put in some heights and note the amount of
path loss in DB that you get.
Then double the height of one of the antennas and note
that the path loss you get decreases by 6 db.

http://www.decibelproducts.com/Calculators/qegli.htm

Regards
Gary

This caculator gives the following caution:

"Note: The Egli model is based on data measured over radials mainly in
the eastern US seaboard and central plains states. It gives an overall
propagation loss over gently rolling terrain with average hill heights
of approximately 50 ft. "

You may have noticed that at sea, you hope to avoid regions with
gentle hillocks of 50 ft wave height. :-)

Brian W