Owen Duffy wrote:

Cecil Moore wrote:
If 100m (325 feet) of ladder-line results in 6dB loss, then a more
realistic 75 feet of ladder-line will result in about 1.4 dB of loss.

Close, I make it 2.2dB.

What matched line loss are you using? The wireman says that line
has about 0.2 dB of matched line loss per 100 ft at 30 MHz. According
to the chart in my ARRL Antenna Book, an SWR of 25:1 at the load
would cause about 1.5 dB loss in 75 feet.

... waiting for me to forget to cross an 'i' or dot a 't'.

Cecil, people often employ long runs of open wire feed on HF ...

Did you miss the humor?
--
73, Cecil http://www.qsl.net/w5dxp

On Tue, 08 Nov 2005 15:33:01 GMT, Cecil Moore wrote:

Owen Duffy wrote:

Cecil Moore wrote:
If 100m (325 feet) of ladder-line results in 6dB loss, then a more
realistic 75 feet of ladder-line will result in about 1.4 dB of loss.

Close, I make it 2.2dB.

What matched line loss are you using? The wireman says that line
has about 0.2 dB of matched line loss per 100 ft at 30 MHz. According
to the chart in my ARRL Antenna Book, an SWR of 25:1 at the load
would cause about 1.5 dB loss in 75 feet.

I am using Wes's characterisation of Wireman 551. Dan's TLDETAILS prog
or my online calculator ( http://www.vk1od.net/tl/tllce.php ) both use
(slightly different) models derived from Wes's published measurements.

I don't have the ARRL Antenna Book with me at the moment, but I
suspect it is not based on the same Matched Line Loss model, and does
not estimate loss from the actual reflection coefficients but from an
"average SWR" model which gives an averaged loss per unit length that
doesn't take account of the fact that loss is usually highest in the
region of current maxima.

My calculator produces a figure of 2.2 dB for your example. I haven't
rechecked Dan's this morning, but it is close.

Grab Dan's calculator or mine and try it out. Dan's is really neat and
a stand-alone Windows app, my online calc has less graphics, doesn't
display (or even calculate SWR), knows about more transmission lines,
and only needs a browser to access it. I use them both.

In my 100m of W551 with a 16+j0 load at 30MHz, the loss in one metre
of line nearest the load is over 4%, the good news is that since 75%
of the transmitter power is already lost, the weighted effect of that
4.3% is nearer 1% of tx output.


... waiting for me to forget to cross an 'i' or dot a 't'.

Of course I don't, otherwise I would have mentioned ...!

Did you miss the humor?

Must have.

73
Owen
--

Owen Duffy wrote:
In my 100m of W551 with a 16+j0 load at 30MHz, the loss in one metre
of line nearest the load is over 4%, the good news is that since 75%
of the transmitter power is already lost, the weighted effect of that
4.3% is nearer 1% of tx output.

What the heck is one "metre"? Netscape says that is misspelled and
probably should be corrected to "metro". Why aren't you guys on
the English system?

If the loss in each meter is 4%, wouldn't the loss in 100 meters
be 400%? What am I missing?
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:

Owen Duffy wrote:

In my 100m of W551 with a 16+j0 load at 30MHz, the loss in one metre
of line nearest the load is over 4%, the good news is that since 75%
of the transmitter power is already lost, the weighted effect of that
4.3% is nearer 1% of tx output.


What the heck is one "metre"? Netscape says that is misspelled and
probably should be corrected to "metro". Why aren't you guys on
the English system?

If the loss in each meter is 4%, wouldn't the loss in 100 meters
be 400%? What am I missing?

C'mon Cecil, you know it's an exponential decay.

I just started reading this thread. Is the loss in a 'per meter' or 'per
wavelength'? In the olden days, we quoted loss as Nepers per
wavelength. When did it change to 'percent per meter'?

AK

Amos Keag wrote:

Cecil Moore wrote:
If the loss in each meter is 4%, wouldn't the loss in 100 meters
be 400%? What am I missing?

C'mon Cecil, you know it's an exponential decay.

The maximum HF current point could exist in the first foot of
feedline at the source. Why would the HF losses in the transmission
line at the load ever be greater than at that maximum HF current point?
--
73, Cecil http://www.qsl.net/w5dxp

At the same time velocity factors were converted to furlongs per
fortnight... :)

"Amos Keag" wrote in message
. ..
I just started reading this thread. Is the loss in a 'per meter' or 'per
wavelength'? In the olden days, we quoted loss as Nepers per
wavelength. When did it change to 'percent per meter'?

AK

On Tue, 08 Nov 2005 23:09:51 GMT, Cecil Moore wrote:

Owen Duffy wrote:
In my 100m of W551 with a 16+j0 load at 30MHz, the loss in one metre
of line nearest the load is over 4%, the good news is that since 75%
of the transmitter power is already lost, the weighted effect of that
4.3% is nearer 1% of tx output.

What the heck is one "metre"? Netscape says that is misspelled and
probably should be corrected to "metro". Why aren't you guys on
the English system?

Met The fundamental base of the metre is the quarter of the
terrestrial meridian, or the distance from the pole to equator, which
has been divided into ten millions of equal parts, one of which is of
the length of the metre.

I think we saw the light before the English, but I think they have a
partial metrication now.

If the loss in each meter is 4%, wouldn't the loss in 100 meters
be 400%? What am I missing?

I did not say "the loss in each meter is 4%", I said "the loss in one
metre of line nearest the load is over 4%".

Firstly, percentage losses on cascaded sections are not additive...
you know that. Losses multiply, dB losses add because adding exponents
is multiply the fundamental quantity.

As I have said before, you seem to be under the misconception that the
overall loss (ie Pin/Pout) per unit length of a transmission line
operating with VSWR1 is constant,

It is not necessarily a constant. It is for a lossless cable, and I
think it probably is for a distortionless cable... but I would have to
check that.

(It is true that the loss per unit length of a transmission line
operating with VSWR=1 is constant.)

We were discussing an example based on Wireman 551 ladder-line. The
dominant factor affecting loss at 30MHz is the series resistance
element. Does it make sense that since in that example, the magnitude
of the current varies by nearly 25:1 along the line, that the I**2*R
loss per unit length along the line is not constant, and will vary by
a factor approaching 625:1?

Owen
--

Owen Duffy wrote:
We were discussing an example based on Wireman 551 ladder-line. The
dominant factor affecting loss at 30MHz is the series resistance
element. Does it make sense that since in that example, the magnitude
of the current varies by nearly 25:1 along the line, that the I**2*R
loss per unit length along the line is not constant, and will vary by
a factor approaching 625:1?

25% of the power is delivered to the load. There are eleven current
maximum points in 100m on 10m. Does that 11% of the feedline really
contribute 59% of the losses? Does the remaining 89% of the feedline
really only contribute 41% of the losses?
--
73, Cecil http://www.qsl.net/w5dxp

On Wed, 09 Nov 2005 05:46:00 GMT, Cecil Moore wrote:

Owen Duffy wrote:
We were discussing an example based on Wireman 551 ladder-line. The
dominant factor affecting loss at 30MHz is the series resistance
element. Does it make sense that since in that example, the magnitude
of the current varies by nearly 25:1 along the line, that the I**2*R
loss per unit length along the line is not constant, and will vary by
a factor approaching 625:1?

25% of the power is delivered to the load. There are eleven current
maximum points in 100m on 10m. Does that 11% of the feedline really
contribute 59% of the losses? Does the remaining 89% of the feedline
really only contribute 41% of the losses?

When I have written about loss per unit length, I have implied "loss
at the rate of y per unit length". If you have tried to apply the 4+%
figure to one meter at each maximum, then you are unlikely to get any
meaningful results for a number of reasons. See the graph I just
posted (our posts crossed in the mail so to speak).

I haven't stated it it the post, but it should be obvious that the
rate of attenuation is the slope of the line in the plot referenced in
the post.

Owen
--

On Wed, 09 Nov 2005 03:25:47 GMT, Owen Duffy wrote:



We were discussing an example based on Wireman 551 ladder-line. The
dominant factor affecting loss at 30MHz is the series resistance
element. Does it make sense that since in that example, the magnitude
of the current varies by nearly 25:1 along the line, that the I**2*R
loss per unit length along the line is not constant, and will vary by
a factor approaching 625:1?

I knocked up a quick graph of the attenuation from point x to the load
for this scenario. (I think / hope it is correct!)

http://www.vk1od.net/lost/W551Example.htm

Is the shape of the curve (the cyclic variation over each electrical
half wave diminishing away from the load, and the general shape of the
curve a surprise? The effects plotted here might not be explained by
the ARRL charts.

Owen
--