"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?

But even if we just limit ourselves to HF and above, there's a
problem: most "solid poly" cable I've encountered has small gas
bubbles in the dielectric, and the v.f. does not measure exactly
0.665. Most of the time, the difference doesn't matter, but sometimes
it does, and then it's not safe to assume it's 0.665. And of course a
lot of cable these days uses foam dielectric, which can be noticably
different from batch to batch.

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

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?

Your para. 2. If there are little bubbles in it, it is not solid. If it
is foamed, it is not solid.

Just to add a little more useless information, did you know the stuff also
varies with pressure and temperature as at the bottoms of the oceans? Also,
under pressure, water disassociates and hydrogen slowly diffuses through it.
Rodents seem to take a fancy to it.

Velocity factor = (Permittivity)^(- 1/2). Permittivity of polyethylene =
2.26 but it does vary slighty from one book to the next.
----
Reg.

"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,

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.

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.

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.

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.

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.

"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.