Bob wrote in
:

On Tue, 06 Apr 2010 00:16:56 GMT, Owen Duffy wrote:
....
I have had sucess with placing a balun of a string of ferrite cores
over the line.

That means literally threading some suitable ferrite toroidal cores over
the transmission line you are measuring.

If you add a separate balun between the analyser and the cable under test,
you introduce an unknown component that will probably disturb your
readings.

Owen

Bob wrote in
:

Anyone know the velocity factor of JSC #1317 450 ohm line, 18 AWG?
Googling seems to give a variety of answers, and it's not posted at
the JSC site.

Wes, N7WS, measured some Wireman lines similar to that above. His
measurements indicated Zo quite different to nominal, and velocity factor
around 0.9.

For applications where velocity factor is important, eg the 'matching
section' of a G5RV, I suggest you measure the actual cable.

Wes's data is included in TLLC (http://www.vk1od.net/calc/tl/tllc.php).
Your cable has similar stranding to Wireman 551, but velocity factor will
depend on the detail of the dielectric extrusion and punching. If JSC is
the manufacturer, they may even be the source of Wireman lines, in which
case Wes's data may be directly applicable.

I have reservations about the adequacy of copper cladding on the cable
such as yours at the lower end of HF.

Owen

On Sun, 04 Apr 2010 20:46:21 GMT, Owen Duffy wrote:

Bob wrote in
:

Anyone know the velocity factor of JSC #1317 450 ohm line, 18 AWG?
Googling seems to give a variety of answers, and it's not posted at
the JSC site.

Wes, N7WS, measured some Wireman lines similar to that above. His
measurements indicated Zo quite different to nominal, and velocity factor
around 0.9.

For applications where velocity factor is important, eg the 'matching
section' of a G5RV, I suggest you measure the actual cable.

I'm plugging the velocity factor figure into Cecil's program for
optimum feedline lengths on a multiband dipole, IMAXMIN.EXE. Given the
approximate nature of this kind of feed, a ballpark figure is probably
okay.

Bob
k5qwg


Wes's data is included in TLLC (http://www.vk1od.net/calc/tl/tllc.php).
Your cable has similar stranding to Wireman 551, but velocity factor will
depend on the detail of the dielectric extrusion and punching. If JSC is
the manufacturer, they may even be the source of Wireman lines, in which
case Wes's data may be directly applicable.

I have reservations about the adequacy of copper cladding on the cable
such as yours at the lower end of HF.

Owen

Bob wrote in
:

....
I'm plugging the velocity factor figure into Cecil's program for
optimum feedline lengths on a multiband dipole, IMAXMIN.EXE. Given the
approximate nature of this kind of feed, a ballpark figure is probably
okay.

Bob,

Have you seen my article "Optimum length of ladder line" at
http://vk1od.net/blog/?p=949 ?

Owen

On Apr 4, 4:19*pm, Bob wrote:
I'm plugging the velocity factor figure into Cecil's program for
optimum feedline lengths on a multiband dipole, IMAXMIN.EXE. Given the
approximate nature of this kind of feed, a ballpark figure is probably
okay.

Yes, given all the variables, adjusting the final length, sometimes by
a few feet (depending on wavelength) is almost always required to
achieve system resonance. Remember that this approach is designed to
eliminate the tuner and therefore eliminate tuner losses and it is
designed to be used with a 1:1 current-choke-balun. Owen's comments
are certainly valid for systems using antenna tuners and 4:1 baluns.
In fact, if one chooses a ladder-line length halfway in between my
"good" (current maximum) and "bad" (voltage maximum) lengths, one will
obtain the odd 1/8 wavelengths points that are recommended for use
with 4:1 baluns. Those points result in a ballpark impedance in the
neighborhood of Z0 +/- jZ0/4, e.g. 400+j100 ohms. For those who
understand a Smith Chart, a picture is worth a thousand words.

http://www.w5dxp.com/smith.htm
--
73, Cecil, w5dxp.com

On Mon, 5 Apr 2010 06:27:54 -0700 (PDT), Cecil Moore
wrote:

On Apr 4, 4:19*pm, Bob wrote:
I'm plugging the velocity factor figure into Cecil's program for
optimum feedline lengths on a multiband dipole, IMAXMIN.EXE. Given the
approximate nature of this kind of feed, a ballpark figure is probably
okay.

Yes, given all the variables, adjusting the final length, sometimes by
a few feet (depending on wavelength) is almost always required to
achieve system resonance. Remember that this approach is designed to
eliminate the tuner and therefore eliminate tuner losses and it is
designed to be used with a 1:1 current-choke-balun. Owen's comments
are certainly valid for systems using antenna tuners and 4:1 baluns.
In fact, if one chooses a ladder-line length halfway in between my
"good" (current maximum) and "bad" (voltage maximum) lengths, one will
obtain the odd 1/8 wavelengths points that are recommended for use
with 4:1 baluns.

The more I look at it, the odd 1/8 wavelengths is probably the way I
will go, connecting to my tuner's 4:1 balun. There will be a 130 foot
flat-top, and the 450-ohm feedline length can be somewhere between 50
to 100 feet or so. Tnx for the input!

Bob
k5qwg

Those points result in a ballpark impedance in the
neighborhood of Z0 +/- jZ0/4, e.g. 400+j100 ohms. For those who
understand a Smith Chart, a picture is worth a thousand words.

http://www.w5dxp.com/smith.htm

Bob wrote in
:

The more I look at it, the odd 1/8 wavelengths is probably the way I
will go, connecting to my tuner's 4:1 balun. There will be a 130 foot
flat-top, and the 450-ohm feedline length can be somewhere between 50
to 100 feet or so. Tnx for the input!

I guess then that you didn't look at the article I quoted.

Typical T match ATU's are lossier on capacitive loads than on inductive
loads.

The odd eighth wave rule of thumb is a popular one. But, alternate odd
eight waves (on a resonant load) assures the highest ATU losses for the
given SWR.

These rules of thumb, and there are plenty that are conflicting, are
usually given without explanation of why they work. We are a gullible
lot!

The same occurs with 4:1 voltage tuner baluns which anecdotal evidence
suggests assist match of a wider range of loads. There is good reason to
think that the mechanism behind this is that their own loss assists, and
it is an inefficient work-around for another problem.

Owen

"Owen Duffy" wrote in message
...

I have reservations about the adequacy of copper cladding on the cable
such as yours at the lower end of HF.

Owen

I have often wondered the same thing. Mainly does the LMR400 center
conductor have enough copper over the center conductor for 1.8 to 7 MHz. I
don't use it at all as I just don't like the cladded cable.

"Ralph Mowery" wrote in
:


"Owen Duffy" wrote in message
...

I have reservations about the adequacy of copper cladding on the
cable such as yours at the lower end of HF.

Owen

I have often wondered the same thing. Mainly does the LMR400 center
conductor have enough copper over the center conductor for 1.8 to 7
MHz. I don't use it at all as I just don't like the cladded cable.




The issue is greater with the CCS conductors in ladder line, because the
strands are thinner in the first place, and the core is steel.

The effect of CCS inner conductor in some types of RG6 shows up as a
departure from the classic loss model at frequencies below 5MHz.

Owen

Owen

On 4 abr, 19:13, Bob wrote:
Anyone know the velocity factor of JSC #1317 450 ohm line, 18 AWG?
Googling seems to give a variety of answers, and it's not posted at
the JSC site.

tnx,

Bob
k5qwg

Hello Bob,

I used the ATLC program to calculate the properties of weird
transmission lines. It accepts arbitrary shaped dielectric material.
It outputs the line properties. When you run two simulations (with
window and without window), you can average them to find the velocity
factor of the ladder line.

The program can be retrieved from atlc.sourceforge.net (also Windows
versions). When you hit the tutorial button, you can check whether it
is worth to spend the time.

Looking to the picture of the line, most important for Zo is the ratio
(bare wire diameter)/(wire + insulation diameter) as E-field is
highest close to the conductors. For a ballpark calculation, I would
use VF = 0.92.

You can also determine the quarter wave resonance length by
measurement and calculate the velocity factor, but then you need
several meters at hand. When you really need VF with high accuracy,
measuring is the best option (around the frequency of interest). As
the separation of the wires is very small (w.r.t. length), it is
probably not necessary to correct for fringing at the open end.

Maybe the vendor cannot guarantee VF, because he receives material
from different sources.

Best regards and good luck with determining VF,


Wim
PA3DJS
www.tetech.nl
When using PM, remove abc before hitting the send button.