"Jason Dugas" wrote in message ...
I'm interested in measuring the velocity factor of some coax I have (more of
an exercise than necessity). In order to do this, the MFJ-259 Operations
...
What would be a good way of making this connection?

Do you have a scope and a pulse generator? If so, just make a simple
TDR (Time Domain Reflectometry) setup to measure the reflection from a
un-terminated or shorted far end of the cable. You will get much more
accurate results with substantially less effort.

Don't get me wrong, the MFJ-259 is a good instrument. It's just that TDR
is so quick and easy and unambiguous for propogation delay measurements.

Tim.

"Reg Edwards" wrote in message ...
"Tom Bruhns" wrote "Reg Edwards"
The velocity factor of ALL solid polyethylene coax cable, regardless of
impedance, is 0.665

================================

And this comes from someone who I could swear posted not long ago a
table that had velocity factors for solid polyethylene cable that were
significantly different from this magic number?
....
===============================

Your para. 1. You can swear till you're appoplectic black and blue in the
face - it wasn't me. I'm not THAT stupid. So who was it then?
....

----
Reg.

Hi Reg...

Well, the Google archive says it was from you. Perhaps you DO have
someone else posting under your name.

See below. Or is the "VF" column not actually velocity factor? OTOH,
I do agree with the posting below, that at low frequencies, beta
becomes dependent more on R than on L, and thus the VF changes.

Cheers,
Tom


From: Reg Edwards )
Subject: Coax Cable vs Freqency

View this article only
Newsgroups: rec.radio.amateur.antenna
Date: 2003-08-12 17:41:24 PST

For anyone who may be interested.

Typical of RG-58 and RG-11 type cables.
Zo = Ro - jXo
Xo is always negative.
Angle of Zo in degrees. Always negative.
VF = relative velocity.

Freq Ro jXo Angle VF
------ ------ ------ ------ ------
50 Hz 967 -965 -44.95 0.034
1 kHz 220 -213 -44 0.151
10 kHz 80 -58 -36 0.41
100 kHz 56 -9.3 -9.5 0.59
1 MHz 52.4 -2.4 -2.7 0.63
10 MHz 50.7 -0.76 -0.86 0.65
100 MHz 50.2 -0.23 -0.27 0.66

Smith Chart calculations begin to be inaccurate around 2 MHz and
below. So
do SWR meters.

"Reg Edwards" wrote in message ...
"Tom Bruhns" wrote "Reg Edwards"
The velocity factor of ALL solid polyethylene coax cable, regardless of
impedance, is 0.665

================================

And this comes from someone who I could swear posted not long ago a
table that had velocity factors for solid polyethylene cable that were
significantly different from this magic number?
....
===============================

Your para. 1. You can swear till you're appoplectic black and blue in the
face - it wasn't me. I'm not THAT stupid. So who was it then?
....

----
Reg.

Hi Reg...

Well, the Google archive says it was from you. Perhaps you DO have
someone else posting under your name.

See below. Or is the "VF" column not actually velocity factor? OTOH,
I do agree with the posting below, that at low frequencies, beta
becomes dependent more on R than on L, and thus the VF changes.

Cheers,
Tom


From: Reg Edwards )
Subject: Coax Cable vs Freqency

View this article only
Newsgroups: rec.radio.amateur.antenna
Date: 2003-08-12 17:41:24 PST

For anyone who may be interested.

Typical of RG-58 and RG-11 type cables.
Zo = Ro - jXo
Xo is always negative.
Angle of Zo in degrees. Always negative.
VF = relative velocity.

Freq Ro jXo Angle VF
------ ------ ------ ------ ------
50 Hz 967 -965 -44.95 0.034
1 kHz 220 -213 -44 0.151
10 kHz 80 -58 -36 0.41
100 kHz 56 -9.3 -9.5 0.59
1 MHz 52.4 -2.4 -2.7 0.63
10 MHz 50.7 -0.76 -0.86 0.65
100 MHz 50.2 -0.23 -0.27 0.66

Smith Chart calculations begin to be inaccurate around 2 MHz and
below. So
do SWR meters.

(Tom Bruhns) wrote in message om...
"Reg Edwards" wrote in message ...
The velocity factor of ALL solid polyethylene coax cable, regardless of
impedance, is 0.665

Even if you just ignore the fact that at low frequencies, R dominates
over omega*L and affects the velocity factor, even if you just say
VF=c/sqrt(LC), I believe there are changes with frequency. That's
because with a good dielectric like polyethylene, C doesn't change
much with frequency (AFAIK), but L decreases as the skin depth
decreases. On large line, it's unlikely to be noticable, but on a
line with an inner conductor radius only a few skin depths at the low
end of HF, the change can be perceptable. Of course, the R term does
dominate over omega*L at low frequencies. If the velocity factor were
independent of frequency, I'd expect no dispersion.

BTW, I'd be a little surprised to find an inexpensive line which did
not have polyethylene dielectric...polyethylene isn't expensive, and
it's a good dielectric except for its low softening/melting
temperature. You should be able to get a pretty good idea what it is
from carefully measured VF, if it's a solid dielectric. There are
very few inexpensive and low-loss plastics with as low a relative
dielectric constant as polyethylene.

Cheers,
Tom

(Tom Bruhns) wrote in message om...
"Reg Edwards" wrote in message ...
The velocity factor of ALL solid polyethylene coax cable, regardless of
impedance, is 0.665

Even if you just ignore the fact that at low frequencies, R dominates
over omega*L and affects the velocity factor, even if you just say
VF=c/sqrt(LC), I believe there are changes with frequency. That's
because with a good dielectric like polyethylene, C doesn't change
much with frequency (AFAIK), but L decreases as the skin depth
decreases. On large line, it's unlikely to be noticable, but on a
line with an inner conductor radius only a few skin depths at the low
end of HF, the change can be perceptable. Of course, the R term does
dominate over omega*L at low frequencies. If the velocity factor were
independent of frequency, I'd expect no dispersion.

BTW, I'd be a little surprised to find an inexpensive line which did
not have polyethylene dielectric...polyethylene isn't expensive, and
it's a good dielectric except for its low softening/melting
temperature. You should be able to get a pretty good idea what it is
from carefully measured VF, if it's a solid dielectric. There are
very few inexpensive and low-loss plastics with as low a relative
dielectric constant as polyethylene.

Cheers,
Tom

Tom,

It should be obvious when somebody asks how to find VF by using an HF
antenna analiser he is interested, like every other radio amateur, in the HF
value of VF.

If you agree with the table in the other posting, which gives VF vesus
frequency, and you are aware VF decreases with frequency, then how come you
didn't realise you had taken the value of 0.665 out of its HF context.

All my figures are correct.
----
Reg

'''''''''''''''''''''''''''''''''''''''''''''''''' ''''''''''''''''''''''''''
'''''''''''''''
"Tom Bruhns" wrote in message
m...
"Reg Edwards" wrote in message
...
"Tom Bruhns" wrote "Reg Edwards"
The velocity factor of ALL solid polyethylene coax cable, regardless
of
impedance, is 0.665

================================

And this comes from someone who I could swear posted not long ago a
table that had velocity factors for solid polyethylene cable that were
significantly different from this magic number?
...
Freq Ro jXo Angle VF
------ ------ ------ ------ ------
50 Hz 967 -965 -44.95 0.034
1 kHz 220 -213 -44 0.151
10 kHz 80 -58 -36 0.41
100 kHz 56 -9.3 -9.5 0.59
1 MHz 52.4 -2.4 -2.7 0.63
10 MHz 50.7 -0.76 -0.86 0.65
100 MHz 50.2 -0.23 -0.27 0.66

Smith Chart calculations begin to be inaccurate around 2 MHz and
below. So
do SWR meters.

Tom,

It should be obvious when somebody asks how to find VF by using an HF
antenna analiser he is interested, like every other radio amateur, in the HF
value of VF.

If you agree with the table in the other posting, which gives VF vesus
frequency, and you are aware VF decreases with frequency, then how come you
didn't realise you had taken the value of 0.665 out of its HF context.

All my figures are correct.
----
Reg

'''''''''''''''''''''''''''''''''''''''''''''''''' ''''''''''''''''''''''''''
'''''''''''''''
"Tom Bruhns" wrote in message
m...
"Reg Edwards" wrote in message
...
"Tom Bruhns" wrote "Reg Edwards"
The velocity factor of ALL solid polyethylene coax cable, regardless
of
impedance, is 0.665

================================

And this comes from someone who I could swear posted not long ago a
table that had velocity factors for solid polyethylene cable that were
significantly different from this magic number?
...
Freq Ro jXo Angle VF
------ ------ ------ ------ ------
50 Hz 967 -965 -44.95 0.034
1 kHz 220 -213 -44 0.151
10 kHz 80 -58 -36 0.41
100 kHz 56 -9.3 -9.5 0.59
1 MHz 52.4 -2.4 -2.7 0.63
10 MHz 50.7 -0.76 -0.86 0.65
100 MHz 50.2 -0.23 -0.27 0.66

Smith Chart calculations begin to be inaccurate around 2 MHz and
below. So
do SWR meters.

So, Reg, I note that (1) YOUR table shows more variation in VF over
the HF ham bands (especially so if you allow it to be extended down to
the 1.8MHz ham band, which I assume the MFJ analyzer would cover) than
the three significant digits of 0.665 would allow (the table showing
only 0.65 at 10MHz, and I suppose you'd go for about 0.64 at 2MHz,
maybe even 3.5MHz), (2) your posting in this thread of 0.665 did NOT
qualify the VF as being HF only, and (3) my posting DID say something
that SHOULD have indicated to you and anyone else who read it that I
was thinking beyond the bounds of HF with respect to large VF
variation. I'd STILL say there are instances where one should not
assume 0.665 for solid polyethylene at HF. There are instances where
0.64 and 0.665 are different enough to want to get the right value.
You're welcome to get all bent out of shape over that if you wish.

Cheers,
Tom

"Reg Edwards" wrote in message ...
Tom,

It should be obvious when somebody asks how to find VF by using an HF
antenna analiser he is interested, like every other radio amateur, in the HF
value of VF.

If you agree with the table in the other posting, which gives VF vesus
frequency, and you are aware VF decreases with frequency, then how come you
didn't realise you had taken the value of 0.665 out of its HF context.

All my figures are correct.
(As we noted at the time of the original posting, the numbers in the
table are rough approximations...certainly they're correct as
approximations...)
----
Reg

'''''''''''''''''''''''''''''''''''''''''''''''''' ''''''''''''''''''''''''''
'''''''''''''''
"Tom Bruhns" wrote in message
m...
"Reg Edwards" wrote in message
...
"Tom Bruhns" wrote "Reg Edwards"
The velocity factor of ALL solid polyethylene coax cable, regardless
of
impedance, is 0.665

================================

And this comes from someone who I could swear posted not long ago a
table that had velocity factors for solid polyethylene cable that were
significantly different from this magic number?
...
Freq Ro jXo Angle VF
------ ------ ------ ------ ------
50 Hz 967 -965 -44.95 0.034
1 kHz 220 -213 -44 0.151
10 kHz 80 -58 -36 0.41
100 kHz 56 -9.3 -9.5 0.59
1 MHz 52.4 -2.4 -2.7 0.63
10 MHz 50.7 -0.76 -0.86 0.65
100 MHz 50.2 -0.23 -0.27 0.66

Smith Chart calculations begin to be inaccurate around 2 MHz and
below. So
do SWR meters.

So, Reg, I note that (1) YOUR table shows more variation in VF over
the HF ham bands (especially so if you allow it to be extended down to
the 1.8MHz ham band, which I assume the MFJ analyzer would cover) than
the three significant digits of 0.665 would allow (the table showing
only 0.65 at 10MHz, and I suppose you'd go for about 0.64 at 2MHz,
maybe even 3.5MHz), (2) your posting in this thread of 0.665 did NOT
qualify the VF as being HF only, and (3) my posting DID say something
that SHOULD have indicated to you and anyone else who read it that I
was thinking beyond the bounds of HF with respect to large VF
variation. I'd STILL say there are instances where one should not
assume 0.665 for solid polyethylene at HF. There are instances where
0.64 and 0.665 are different enough to want to get the right value.
You're welcome to get all bent out of shape over that if you wish.

Cheers,
Tom

"Reg Edwards" wrote in message ...
Tom,

It should be obvious when somebody asks how to find VF by using an HF
antenna analiser he is interested, like every other radio amateur, in the HF
value of VF.

If you agree with the table in the other posting, which gives VF vesus
frequency, and you are aware VF decreases with frequency, then how come you
didn't realise you had taken the value of 0.665 out of its HF context.

All my figures are correct.
(As we noted at the time of the original posting, the numbers in the
table are rough approximations...certainly they're correct as
approximations...)
----
Reg

'''''''''''''''''''''''''''''''''''''''''''''''''' ''''''''''''''''''''''''''
'''''''''''''''
"Tom Bruhns" wrote in message
m...
"Reg Edwards" wrote in message
...
"Tom Bruhns" wrote "Reg Edwards"
The velocity factor of ALL solid polyethylene coax cable, regardless
of
impedance, is 0.665

================================

And this comes from someone who I could swear posted not long ago a
table that had velocity factors for solid polyethylene cable that were
significantly different from this magic number?
...
Freq Ro jXo Angle VF
------ ------ ------ ------ ------
50 Hz 967 -965 -44.95 0.034
1 kHz 220 -213 -44 0.151
10 kHz 80 -58 -36 0.41
100 kHz 56 -9.3 -9.5 0.59
1 MHz 52.4 -2.4 -2.7 0.63
10 MHz 50.7 -0.76 -0.86 0.65
100 MHz 50.2 -0.23 -0.27 0.66

Smith Chart calculations begin to be inaccurate around 2 MHz and
below. So
do SWR meters.

My figures are correct to a better accuracy than can be determind by a cheap
and nasty antenna analyser.

Now go away, leave the newsgroup in peace, and stop your childish
nitpicking.