Coax recomendations
 

Ah yes -"warranted" - my apology!

"After all Davis BuryFlex 9914 does have a warranted - 20 year service life"

Dave



Charlie wrote:

I don't recall -anyone- using the word "guarantee". Please post that
reference.....TY

--

Charlie

"Dave Holford" wrote in message
...
That's a guarantee??

Dave

Charlie wrote:

At the bottom of this page the ** footnote
1. http://www.davisrf.com/ham1/coax.htm

"note that Bury-Flex has a 20+ year abrasive resistant jacket of PE"

--

Charlie

"Dave Holford" wrote in message
...


Charlie wrote:

Wes Stewart said:
I find it curious that Andrew cable is seen so often at these events
and yet I've -never- even seen a piece of Davis cable, dispite the
claims that miles of it are in commercial use.

It might be that the BuryFlex is still in use and has not been removed
from
service as the Heliax you cite has been. After all Davis BuryFlex 9914
does
have a warranted - 20 year service life -

Is there any other coax with such a warranty?
---

Charlie

I don't seem to be able to find any mention of a warranty on their
site -
can
you point it out for me?

Dave

Coax recomendations
 

So now that has been cleared up..the question remains..
Is there any other coax available for amateur use that has a 20 years
service life warranty?

--

Charlie


"Dave Holford" wrote in message
...
Ah yes -"warranted" - my apology!

"After all Davis BuryFlex 9914 does have a warranted - 20 year service
life"

Dave



Charlie wrote:

I don't recall -anyone- using the word "guarantee". Please post that
reference.....TY

--

Charlie

"Dave Holford" wrote in message
...
That's a guarantee??

Dave

Charlie wrote:

At the bottom of this page the ** footnote
1. http://www.davisrf.com/ham1/coax.htm

"note that Bury-Flex has a 20+ year abrasive resistant jacket of PE"

--

Charlie

"Dave Holford" wrote in message
...


Charlie wrote:

Wes Stewart said:
I find it curious that Andrew cable is seen so often at these
events
and yet I've -never- even seen a piece of Davis cable, dispite the
claims that miles of it are in commercial use.

It might be that the BuryFlex is still in use and has not been
removed
from
service as the Heliax you cite has been. After all Davis BuryFlex
9914
does
have a warranted - 20 year service life -

Is there any other coax with such a warranty?
---

Charlie

I don't seem to be able to find any mention of a warranty on their
site -
can
you point it out for me?

Dave

Coax recomendations
 

On Sun, 11 Dec 2005 17:22:16 GMT, "Greg Ordy"
wrote:

Here are my personal experiences and observations with "BuryFlex".

Hi Greg,

You've made a polished report with enough data, excellent graphics,
and concise narrative to closely examine some interesting issues. It
attended those points of batch process, service, variation across
types and time. This and your follow-on VF examination from Roy's
offhand observation have that Ham spirit.

What is more important is that you revealed errors (or aberrant
results) rather than brushing them under the rug. As this thread has
proven by increasing -ahem- testimony, not all specifications prove
out and sometimes those things not specified raise interesting
questions.

73's
Richard Clark, KB7QHC

Coax recomendations
 

One thing I've learned is that a (good) short circuit is a better
termination for this kind of measurement than an open circuit. With an
open circuit you get fringing which varies with frequency and cable
diameter.

If you don't have a decent commercially made short circuit, you can do
reasonbly well with a connector and several radial wires from the shell
to the center conductor, or better yet a metal disk. Or you could put a
male connector on a short piece of coax and short circuit the end of the
cable by squeezing the braid into the center and soldering it to the
center conductor, taking its length into account for the measurement of
course. The object is to minimize the series inductance which would be
created with a single-wire or similar connection.

Wes and Ian can probably point you to more possible causes for this
measurement result -- they're the real experts on VNA measurements. I'd
be very surprised if the VF really varies with frequency -- in theory,
it can't, in an ideal coaxial cable.

Roy Lewallen, W7EL

Greg Ordy wrote:
Roy Lewallen, W7EL, wrote:


I measured 80% velocity factor, so if our respective
measurements are good, the velocity factor of your piece should be
around 72%.


Ok, my curiosity got the best of me, and I decided to
to measure the velocity factor. My VNA software has
a "distance to fault" feature, and I "worked backwards",
which is to say that I measured a length of the
BuryFlex with a tape measure (27' 2"), and adjusted
the VF on the distance to fault tool until I obtained the
same physical length. The far end of the cable was
terminated with an open circuit.

I happened to start with the measurement frequency set
to 1 MHz. Lo and behold, the VF needed to compute the
same physical length was 72%, as you suggested.

My own understanding is that VF should be constant with
respect to frequency, so I decided to vary the test frequency.
I should have left well enough alone.

I picked 1, 2, 4, 8, 16, and 32 MHz. For those frequencies,
I measured the following VFs:

1 MHz = 72%
2 MHz = 73%
4 MHz = 75%
8 MHz = 80%
16 MHz = 79%
32 MHz = 79%

I'm rounding the VF to integer values, since I don't think that any more accuracy
can be claimed in this setup.


Since that result was a little surprising, I grabbed some mini 8 (8X)
that was nearby, about 51.25 feet. The published VF is 78%, and
I measured the following, at the same test frequencies:

1 MHz = 78%
2 MHz = 78%
4 MHz = 79%
8 MHz = 79%
16 MHz = 80%
32 MHz = 80%

With this cable, the VF appeared much more constant across the
1 to 32 MHz range.

Is there an explanation that fits with my measurements?

Greg, W8WWV

Coax recomendations
 

Ian White GM3SEK wrote:
. . .
Coaxial cables with braid-over-foil shielding have a generic problem
that if they're bent too sharply, the foil will tear into separated
segments each about an inch long. The cable then relies on the braid for
overall shield continuity. It will still function, especially at low
frequencies, but there isn't much contact pressure to maintain the
continuity between the braid and the foil.
. . .

Most interesting! The cable I've been measuring has been kept in a coil
of about 3 feet diameter, but squeezing and handling it has reduced that
to probably about a foot or so at times. But I don't recall the coil
size when I received the cable, and of course I don't know anything
about how it was handled between the manufacturer and delivery to my
home. This might be an explanation for the variablility. I did hear from
someone else a while back that he'd seen variability in a foil-wrapped
cable, but I don't think it was specifically Bury-Flex. I have some
RG-58 size cable with the same general construction which doesn't show
this variability. But it looks like the stress would be worse on the
foil in a larger diameter cable. Also, there seems to be some difference
in how the foil is more-or-less bonded to the PE, and that would also
play a role in the stress.

I want to keep the piece I've measured intact for the time being, but if
I get up the time and interest to do more measurements on another piece
of cable, a post mortem might be revealing.

Roy Lewallen, W7EL

Coax recomendations
 

Where do you see a warranty?



Charlie wrote:

So now that has been cleared up..the question remains..
Is there any other coax available for amateur use that has a 20 years
service life warranty?

--

Charlie

"Dave Holford" wrote in message
...
Ah yes -"warranted" - my apology!

"After all Davis BuryFlex 9914 does have a warranted - 20 year service
life"

Dave



Charlie wrote:

I don't recall -anyone- using the word "guarantee". Please post that
reference.....TY

--

Charlie

"Dave Holford" wrote in message
...
That's a guarantee??

Dave

Charlie wrote:

At the bottom of this page the ** footnote
1. http://www.davisrf.com/ham1/coax.htm

"note that Bury-Flex has a 20+ year abrasive resistant jacket of PE"

--

Charlie

"Dave Holford" wrote in message
...


Charlie wrote:

Wes Stewart said:
I find it curious that Andrew cable is seen so often at these
events
and yet I've -never- even seen a piece of Davis cable, dispite the
claims that miles of it are in commercial use.

It might be that the BuryFlex is still in use and has not been
removed
from
service as the Heliax you cite has been. After all Davis BuryFlex
9914
does
have a warranted - 20 year service life -

Is there any other coax with such a warranty?
---

Charlie

I don't seem to be able to find any mention of a warranty on their
site -
can
you point it out for me?

Dave

Coax recomendations
 

On Sun, 11 Dec 2005 20:35:23 -0800, Roy Lewallen
wrote:


Most interesting! The cable I've been measuring has been kept in a coil
of about 3 feet diameter, but squeezing and handling it has reduced that
to probably about a foot or so at times. But I don't recall the coil
size when I received the cable, and of course I don't know anything
about how it was handled between the manufacturer and delivery to my
home. This might be an explanation for the variablility. I did hear from

Further, you may not know the manufacturers specifications for minimum
bending radius to preserve operating characteristics.

When I went to the Davis site, I found a table of losses for several
cables including BuryFlex, but it did not state the length. I assumed
that the length was 100' from the losses quoted for some other cables.
The VF (82%) was buried in text, and I found no explicit information
on Zo, mechanical properties, bending restrictions, operating
temperatures etc. Some properties may be implied by description as an
RG8 type cable, but min bending radius is likely to be larger than a
solid dielectric / no foil cable.

Perhaps there is spec sheet there somewhere, it didn't leap out at me!

Owen
--

Coax recomendations
 

Roy Lewallen wrote:

Wes and Ian can probably point you to more possible causes for this
measurement result -- they're the real experts on VNA measurements.

Not I... I'm just trying to think acurately about it...

I'd be very surprised if the VF really varies with frequency -- in
theory, it can't, in an ideal coaxial cable.

Greg had written:
adjusted
the VF on the distance to fault tool until I obtained the
same physical length. The far end of the cable was
terminated with an open circuit.
I happened to start with the measurement frequency set
to 1 MHz. Lo and behold, the VF needed to compute the
same physical length was 72%, as you suggested.
My own understanding is that VF should be constant with
respect to frequency, so I decided to vary the test frequency.
I should have left well enough alone.
I picked 1, 2, 4, 8, 16, and 32 MHz. For those frequencies,
I measured the following VFs:
1 MHz = 72%
2 MHz = 73%
4 MHz = 75%
8 MHz = 80%
16 MHz = 79%
32 MHz = 79%
I'm rounding the VF to integer values, since I don't think that any
more accuracy
can be claimed in this setup.
Since that result was a little surprising, I grabbed some mini 8
(8X)
that was nearby, about 51.25 feet. The published VF is 78%, and
I measured the following, at the same test frequencies:
1 MHz = 78%
2 MHz = 78%
4 MHz = 79%
8 MHz = 79%
16 MHz = 80%
32 MHz = 80%
With this cable, the VF appeared much more constant across the
1 to 32 MHz range.
Is there an explanation that fits with my measurements?

Since Greg's test setup measured a much more constant VF for the mini-8,
it doesn't seem that the open-circuit termination is causing much error
(note also that the largest deviation for the BF is at the lowest
frequency, where fringing C would have the least effect).

This seems to bring us back to Greg's method of computing "distance to
fault" from measurements of R and X at one end. Does that method involve
any assumptions about idealized cable behavior that could create an
*apparent* change in the computed VF?


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Coax recomendations
 

Charlie wrote:

At the bottom of this page the ** footnote
1. http://www.davisrf.com/ham1/coax.htm

"note that Bury-Flex has a 20+ year abrasive resistant jacket of PE"


Ah! If you believe that is a warranty, then I'm not
surprised at your belief in their published performance
figures.

Andy

Coax recomendations
 

Charlie wrote:
So now that has been cleared up..the question remains..
Is there any other coax available for amateur use that has a 20 years
service life warranty?

20 year jacket warranty is _not_ a 20 year service life warranty.
From what other posters are measuring, the cable has a close to
zero service life. Roy can certainly measure things properly and
if he says the piece he had was bad then I believe him. I believe
Greg too. There are just too many bad measurements showing up,
done by experienced and competent people, for it to be coincidence.
The cable is bad out of the box in at least some instances. There
is no warranty covering that AFAICS.

vy 73

Andy, M1EBV