Coax recomendations
 

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

Coax recomendations
 

Charlie wrote:

-ps How many times do you think Davis has tested their 9914 in the past
10+ years?

Before we go much further, is there an engineering data sheet on
Bury-Flex? I couldn't find one on the Davis RF site.

In particular, what is the rated minimum bending radius?

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.

If a cable had been treated in this way, it's not hard to imagine that a
precision measurement at 450MHz would reveal small jumps in the loss and
SWR when the cable is flexed.

But this is NOT something you'd ever notice in a normal amateur station
operation. Even when I was using braid-over-foil coax with 1.5kW at
432MHz, and monitoring the SWR continuously, I never noticed any major
jumps when rotating the antenna. The break-up of the foil only came to
light after the cable had failed for an unrelated reason, and was slit
open for a post-mortem.



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

Coax recomendations
 

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

Back in the 90's, I went through a period of station upgrade,
followed by a period of antenna experimentation, mainly with lower
band receiving antennas. To support all of that work I purchased a few
thousand feet of coaxial transmission line, in a wide range of types
and brands.

For my "main" lines, which needed to be buried to make it
from the house, under the lawn, to the "antenna fields", I chose
BuryFlex. I also used it for my single tower, and around the
rotator. The buried runs are approximately 150 and 175 feet long.

For other purposes, such as test antennas that I would
put up for a few weeks, to arrays of those antennas, I would use
BuryFlex, RG-213, RG-8, RG-8X, RG-58, all sort of stuff. I even
had some 75 Ohm RG-11 which was used mainly as "phasing lines"
in delta loop arrays, and series matching sections.

Before all the dust had settled, I had probably installed
well over 100 UHF coax connectors on cables of all sorts of
lengths, from 1 foot to about 250 feet.

Mechanically, I found BuryFlex to be very rugged, and
whenever I have had the opportunity to check out cables in the
field, including buried, they are in excellent condition. It
does have a high degree of flex, and a small turning radius.
Around the rotator, it worked very well, and after a few
years of turning, it showed no signs of wear at all.

As far as attaching coax connectors, I did find that the
stranded center conductor was a little too wide for a few
of the various connectors I would try to use. I tended to
pick up packs of 10 to 25 male connectors at hamfests and
from the Internet, and they probably covered the range of
name brand, strange brand, gold pins, silver pins, Teflon
insulator, and on and on.

I found that about 10% of the range of connectors
I had would not fit over the twisted BuryFlex center conductor.
Initially, I cut two of the stranded center conductors to reduce
the diameter, but as I accumulated a range of connectors,
I just learned which connectors to avoid when putting ends
on BuryFlex.


As part of my antenna experimentation, I would often
be out in the field, right at the antenna, with a typical
antenna analyzer, such as the MFJ-259, 259B, 269, AEA HF-CIA,
and the Autek RF-1. I would then come back inside
the house, where I had a computer next to the radio. I had
a serial interface for the AEA HF-CIA, so I could capture
SWR graphs on the computer, for a whole range of purposes.


At some point, I picked up a laptop computer, which
made it easy to record antenna analyzer output data right in the
field, next to the antenna, before I entered the BuryFlex
runs back to the house.

An ideal lossless 50 Ohm transmission line should repeat
the SWR found at its load end at its input. The impedance will
be transformed as a function of the length of the cable, but
the SWR should remain the same. Of course we don't have
ideal lines out in the field, we have real lines, with loss.
The impact of the loss is to reduce the SWR at the input (station side)
of the line. In many typical HF situations the reduction is
small.

I noticed that when I overlaid the SWR graphs in the
field on top of the SWR graphs made inside the house, they
did not follow the expected relationship, which is to say the same
general shape, with the inside values slightly lower due
to loss on the cable between the two points.

In some cases, the SWR would rise - I admit, it was
a small amount, but that made no sense to me.


I then performed a test which I must confess I
had not done before. I put a 50 Ohm load on the end of a
length of BuryFlex, and a typical antenna analyzer on the other
end, and swept the frequency across the HF range, perhaps
1 to 30 MHz. I expected to see a flat SWR of 1.0, since
I had a 50 Ohm load, 50 Ohm cable, and a 50 Ohm analyzer.

Well, with BuryFlex, the SWR would swing, as a
function of frequency, between 1.0 and a high of 1.3.

By this time, most of the coax I had once used out
in the field had been rolled up, and stored within
some metal cabinets in the garage. I went and grabbed an
armful of assorted cables, from high quality RG-213, to
pretty darn cheap RG-58 that I used in receiving antenna
arrays. All other 50 Ohm cable, when terminated with
a 50 Ohm load, had a flat sweep across the HF range.

So, something about that BuryFlex was different.
I found all of the lengths that I had rolled up, and
all exhibited the same behavior. I did wonder if I
got a "bad batch", but I do believe that I was measuring
across a set of cables that I had purchased over
a period of perhaps 3 years, and I assumed that meant
that I was looking at different batches and runs and
seasons.

I wasn't sure what was going on, and I wasn't going
to replace that buried BuryFlex, but I stopped using more of it,
especially if I was trying to make useful measurements.
The cable obviously "worked", since I had been pumping
1500 watts through it for year, from 160 meters to 6 meters.


As a few more years passed, and I ended up
interested in higher quality impedance measurements,
as part of understanding and building phased vertical
arrays. I accumulated even more impedance measuring
devices, including old Gen-Rad and Boonton boat anchors.
I did end up with an N2PK VNA, which I believe has
near professional/lab accuracy.

A year or so ago, I got curious about this whole
area again, and now that I had some good quality
measurement equipment, I grabbed some different cables
from the cabinet, and put on a 50 Ohm load, and swept
them from 1 to 50 MHz. Now, what I was really
measuring was the complex reflection coefficient, which
could be converted, by formula, to complex impedance,
SWR, return loss, and all sorts of useful quantities.

When I displayed the data on a Smith Chart, an
interesting pattern emerged. The other 50 Ohm cables spiraled
around the 50 Ohm load. A 75 Ohm cable (with a 50 Ohm load)
also showed a spiral, but it was centered higher up the resistance
axis. The BuryFlex, however, had a spiral which was
centered under 50 Ohms.

Now I'm no Smith Chart expert, especially when it
comes to combining data from different Zo cables, but especially
when comparing BuryFlex to other 50 Ohm cables, to 75 Ohm
RG-11, the pattern is pretty clear.

My conclusion was that the BuryFlex I had here had
a characteristic impedance lower than 50 Ohms, perhaps around 45 Ohms.



After the messages in recent days about BuryFlex,
I went out to the shop this morning, and again grabbed two
different rolls of BuryFlex, a few typical 50 Ohm cables,
and some 75 Ohm RG-11. I wanted to see if I could
duplicate the measurements. All of these cables are a few
years old, and some have been used quite a bit. In other
words, I am not trying to work with new cable right off
of a roll.

I got the same results that I had seen in the
past. I captured two Smith Charts showing BuryFlex versus
other 50 Ohm cable, and some 75 Ohm RG-11. The test
scenario is a random length of cable (more than a few
feet, less than 100), with a 50 Ohm load, and a sweep
from 1 MHz to 50 MHz with 100 KHz spacing. If I were
willing to terminate the BuryFlex with a variable noninductive
resistor, I could probably nail down the actual cable
impedance.

I put the two Smith Charts on a web page so that
they could be inspected by all interested parties.
The URL is:

http://www.seed-solutions.com/gregor...n/buryflex.htm

I certainly can be interpreting this data incorrectly,
and please feel free to correct me if you believe that
I've come to the wrong conclusion.



I do not have an opinion about the "loss" of BuryFlex.
I could make return loss measurements, but for those to
have meaning, I would need to unroll the cable, and measure the
length, and since it's 10 degrees F outside, with 18 inches
of snow, and more coming down, I'm not quite that motivated.
My VNA also stops at about 50 MHz, and the frequency first
mentioned was quite a bit higher (400 MHz). The initial report
also talked about loss as a function of coiling and bending,
which can complicate the test scenario.

For me, and my test equipment here, BuryFlex does
not have the characteristics of any other "50 Ohm" cable
I have measured. I believe that my conclusion that it is more
like 45 Ohm cable as opposed to 50 Ohm cable is correct -
again, for the samples I have here. I have found it to be
mechanically excellent and very rugged. Some coax connectors
don't quite fit over the center conductor.

I am quite suspect, however. I encourage
anybody with access to the cable and appropriate test
equipment to confirm the loss measurements, since I trust
the source of the original claim. Because I don't believe the
50 Ohm specification, I guess it's easier for me to believe that
the loss specification is incorrect too.

If you want to know if your cable is like mine - that's
easy - terminate a length with a good quality 50 Ohm resistive load,
and sweep the frequency while watching the SWR. My BuryFlex
bounces up and down.


Greg Ordy, W8WWV

Coax recomendations
 

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

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

EXCELLENT REPORT!

Thank you,

Very 73
Danny, K6MHE

Danny, K6MHE

email: k6mheatarrldotnet
http://www.k6mhe.com/

Coax recomendations
 

On Sun, 11 Dec 2005 14:56:13 GMT, Cecil Moore wrote:

Owen Duffy wrote:
LMR400: 300' at 14.2MHz with VSWR=1.5, loss~=1.5dB

Open-wire line: 300' at 14.2MHz with VSWR=1.5, loss~=0.225dB
Costs about 16 cents/ft if one rolls one's own.

.... or unrolls it as the case may be!
--

Coax recomendations
 

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

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

Very well done Greg.

Hopefully, in the fullness of time, you will roll all this information
into the web page.

I have read articles on issues with control of the foaming of
dielectric during manufacture, it seems more difficult to control than
all of the aspects of conventional solid PE dielectric line, so it
leaves one wondering if that may be the cause of the apparently low Zo
(~43 ohms) that you observed. If so, is it a batch to batch variation,
variable along the line (although your charts don't suggest that),
aging, temperature, migration of the centre conductor on the roll,
etc?

Well done OM.

Owen
--

Coax recomendations
 

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
 

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 Sat, 10 Dec 2005 17:15:44 -0800, Roy Lewallen
wrote:

Charlie wrote:
I have emailed Davis RF and asked them to send me their test results. Yes
it will be interesting.

Roy..doesn't seem a bit odd that NO ONE ELSE in over 10 years of BuryFlex
production has cited these same alarming "test results".

No. My experience is that the vast majority of amateurs don't have the
ability and/or confidence and/or interest and/or equipment to make good
measurements. And lacking the ability to measure it, very few would be
able to discern the difference in loss. If my measurements are typical,
commercial and government users (if there indeed are any for this
particular cable type) would quietly reject the stuff on incoming
inspection and order something else.

I'd ten to agree and most take cable on faith as well.

I do have a high degree of confidence that my measurements are accurate.
I took a lot of care in characterizing the cable before using it for
making remote antenna impedance measurements in the course of a
consulting job. But it's entirely possible that the particular piece of
cable I have is defective. That would just point to a quality control
problem rather than overzealous specsmanship.

There are a number of things that can or possibly happen.

When you test coax connectors and termination effects are part
of the system and need to be considered.

I bought 250ft, then tested the 50ft sections I made up for the tower.
All five tested the same at 440mhz and my confidence factor was
good. The test setup was 0.100 Watt RF source, 3DB attenuator,
RLB, cable section, termaline watmeter. All check on spec
and I was doing to verify connectors installed as well. I only tried
one section for bening effects near the end as I was interested in
how it would behave for rotor loops. I saw now ill efects until I
reduced the bend radius to under 4 inches where it developed
a definitate bump that showed on a TDR. Like most foam cored
cables you can overbend it with bad results. The damaged length
was removed (only 4ft) and the cable placed in service.

Expected 2.9db @ 400mhz. But that does not allow for connectors
or measurment setup. Half that should be 1.45db (50ft).

However my testing was at 440mhz. All loss testing I did was
at 440 because small things look bigger there.

To the limits of the attenuators and meter calibration I'd call the
losses including the connectors right where I'd expect 50ft with
PL259s on at least one end would be. I got at 440, greater
than 1.6db but less than 1.8db. The loss was determined by
removing cable and substituting a known attenuators of .2db
steps as that was as fine as I had. Calculated was 1.66db
based on measurements. Allowing for test error and
connectors the there is some range of error. The RLB was
used to verify there were no visible bumps over the 6m, 2m and
420-450mhz range of the source.

The same setup for 50ft or both RG58A/U, RG8X and RG213
gave me 7db(pl259/ug174), 4.6-4.8(pl259/ug175), 2.4-2.6(pl259).
The RG213 was a suprize as I'd expected losses to be lower.
But the results were consistant. Where I give a range in loss
it is because the lower and higher attenuateors used were
either too low or too high meaning the exact result was somewhere
in between. The loss substitution is likely more accurate than
analog meters. Also I tried to minimize the error from adaptors
and cable transitions where needed though te test method tends
to zero them out by substiution.

I did during installation notice one thing over RG213. The 2M antenna
I'd tuned with a length of RG213 showed a higher VSWR when using the
Buryflex. Further tests reveled the losses of the 213 made the SWR
look better than it was. Antenna was readjusted and all was happy.

Allison
Kb1GMX

Coax recomendations
 

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

[snip]

Good job Greg. Also thanks for the work on the N2PK VNA software.

By inspection of the loss figures for Buryflex on Davis' web site one
can note that the loss at lower frequencies is higher than other RG-8
type cables.

Importing their data into Dan's (AC6LA) "bestfit.xls" spreadsheet
shows very poor correlation with theoretical k1, k2 coefficients. I'm
observing something similar on some RG-142 that I am measuring with my
N2PK VNA. The '142 has a silver-coated, copper-plated steel center
conductor and I believe that the skin depth encompasses the steel at
lower frequencies.

Anyway, that might be a factor, assuming of course, that their data
are valid.

Coax recomendations
 

Ralph Mowery wrote:

Roy what kind of coax do you recommend along the same type ? I soon plan on
putting up several beams, tribander for the low bands, 6 meter, 2 meter and
a 432 antenna. Should be running about 125 feet or so. While I know
hardline would be best for the VHF , I don't want to (can't spend the money,
easy to install for the rotator) so I want to stay with one of the
9913/lmr400 types. I have had a piece of 9913 up for about 10 years and it
seems to be ok, no water I can tell, I still would like to go with a solid
foam type instead of the hollow core .

Just looking at the specks and advertising can sometimes be deceiving.

Sorry, I'm not the best person to ask. A lot of the other folks here
have a lot more experience than I do with applications like yours.
Ruggedness and other physical properties can easily be more important
than the technical specifications of a cable under idealized conditions,
so I'd listen to people who have used cable for an extended period of
time in similar circumstances to yours.

As far as loss goes, you're bump up against the laws of physics. Below a
few GHz, dielectric loss in common coaxial cables is negligible. The
shield has much larger surface area than the center conductor, so the
loss ends up being dictated mainly by the diameter of the center
conductor -- the larger it is for a given cable Z0, the lower the loss.
Assuming a fixed Z0, the only ways you can make the center conductor
larger are to increase the cable outer diameter, or reduce the effective
dielectric constant of the insulation between center conductor and
shield. The effective dielectric constant is reduced by using foamed
dielectric coax, or even more by using mainly air dielectric, with a
minimal amount of insulation for physical support. Consequently, for a
given Z0 and outer diameter, and otherwise similar construction, foamed
dielectric cable has less loss than solid dielectric cable, because its
center conductor is larger. Mostly-air dielectric cable has less loss
yet for the same reason. (In the microwave region, dielectric loss
becomes significant, so there's a further loss reduction when the
dielectric density is reduced.)

A stranded center conductor or braided shield increase the loss
somewhat. It's difficult to find definitive data on just how much,
probably because of the number of variables involved, like shield weave
tightness and frequency. But the amount of increased loss can be quite
significant, judging by the actual loss of typical coax vs. the loss
predicted by the assumption of a solid center conductor and perfect
shield. Ian, G3SEK just posted a possible explanation of an additional
loss mechanism for aluminum-foil shielded cable like BuryFlex -- tearing
of the foil shield due to bending too sharply.

But I think amateurs often get too hung up on small amounts of cable
loss. It's admittedly sometimes very important, but not in most cases.
Cost, convenience, ease of use, connector type, and physical ruggedness
might well be much more important criteria. And again, there are a lot
of folks here who have a lot more relevant experience than I do, so you
should listen carefully to their advice.

I do fully agree with your last statement.

Roy Lewallen, W7EL

Coax recomendations
 

On Sun, 11 Dec 2005 15:29:20 -0700, Wes Stewart
wrote:


Importing their data into Dan's (AC6LA) "bestfit.xls" spreadsheet
shows very poor correlation with theoretical k1, k2 coefficients. I'm
observing something similar on some RG-142 that I am measuring with my
N2PK VNA. The '142 has a silver-coated, copper-plated steel center
conductor and I believe that the skin depth encompasses the steel at
lower frequencies.

I noted when I imported Davis' Bury Flex data to tllce that the
regression model correlation coefficient was lower at 0.9918 than most
other data which tends to come in better than 0.997 and mostly 0.998
or better.

One of the reasons that some lines show a very good fit to the model
(eg 5 nines) is that the measurement data was fitted to a model, and
the published figures are from the model, not the original
measurements, and the error in deriving a model from the published
figures is principally caused by rounding of the published figures.

A possible explanation of Greg's observation of low Zo is that the
foam is more dense than intended, increasing C, lowering Zo, and
increasing loss at higher frequencies.

Owen
--

Coax recomendations
 

Owen Duffy wrote:

Very well done Greg.

Hopefully, in the fullness of time, you will roll all this information
into the web page.

I have read articles on issues with control of the foaming of
dielectric during manufacture, it seems more difficult to control than
all of the aspects of conventional solid PE dielectric line, so it
leaves one wondering if that may be the cause of the apparently low Zo
(~43 ohms) that you observed. If so, is it a batch to batch variation,
variable along the line (although your charts don't suggest that),
aging, temperature, migration of the centre conductor on the roll,
etc?

Well done OM.


I've measured a lot of cable over the years, and have found considerable
variation of velocity factor from batch to batch of otherwise identical
cable from the same manufacturer, as Owen's articles imply. Assuming
that the physical dimensions of the cable stay the same, Z0 will also
vary with foam density.

The piece of BuryFlex I have measures right at 80% velocity factor, and
very close to 50 ohms. I believe I'm within a percent or two on VF, and
an ohm for Z0.

Roy Lewallen, W7EL

Coax recomendations
 

Wes Stewart wrote:
. . .
Importing their data into Dan's (AC6LA) "bestfit.xls" spreadsheet
shows very poor correlation with theoretical k1, k2 coefficients. I'm
observing something similar on some RG-142 that I am measuring with my
N2PK VNA. The '142 has a silver-coated, copper-plated steel center
conductor and I believe that the skin depth encompasses the steel at
lower frequencies.
. . .

I've definitely seen this in RG-174 and some similar diameter 75 ohm
cable, at 7 MHz. The problem with those cables is that the center
conductor is made of very fine strands of Copperweld. While the fraction
of copper relative to the wire diamter is large, the actual copper
thickness is small due to the very small diameter wire, allowing current
to penetrate into the steel at lower frequencies.

I've also seen the effect in the time domain when using RG-174 type
cable but with solid silver-plated Copperweld center conductor. The
increased loss at low frequency actually improves the step response
somewhat because of the disproportionately higher loss at lower frequency.

Roy Lewallen, W7EL

Coax recomendations
 

Good work, Greg. It's refreshing to see that some people, at least, are
still willing and able to do this rather than unquestioningly accept
manufacturer's data. Even if the data turn out to be accurate, the
process is truly educational.

The varying SWR while terminated with 50 ohms is consistent with the 45
ohm Z0 you observed. My piece of BuryFlex is right at 50 ohms, but I'm
not too surprised at this amount of variation given the foamed
dielectric. I measured 80% velocity factor, so if our respective
measurements are good, the velocity factor of your piece should be
around 72%.

Roy Lewallen, W7EL

Coax recomendations
 

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
 

It is NOT brand loyalty, but the published data by GM for the past xx+ years
shows that their cars are best so I'll continue to drive GM, despite what
independent testers may say. Besides which my son-in-law sells them so they
must be best.

Dave

Charlie wrote:

Owen it is NOT brand loyalty. It is the publicly published data by RF Davis
(for the past 10+ years) vs. Roy's one-shot test setup some years ago. I'm
not out to discredit Roy...I even shook his hand once at a Hamfest.

--

Charlie

"Owen Duffy" wrote in message
...
On Sat, 10 Dec 2005 17:15:44 -0800, Roy Lewallen
wrote:

If no other reader of this newsgroup has some of this cable and the
ability to test it, I'll see if I can arrange for someone else to make
measurements and post results.

Roy, this seems a case of brand loyalty vs objective measurement and
evaluation (albeit on a single sample).

You will change your mind based on more measurement data, either
strengthening your existing opionion or changing it.

Those with brand loyalty already know all they need to know, life is
comfortable.

You are talking different languages, and the only way there will be
agreement is if you capitulate (which would be unprincipled in the
absence of evidence).

Owen

I remember the fierce debates over 9913, there were nearly as many
words written about how fabulous it was, as there were words written
on how to keep water out of it.
--

Coax recomendations
 

Got your dig Roy.....kinda sad.....

--

Charlie


"Roy Lewallen" wrote in message
...
Good work, Greg. It's refreshing to see that some people, at least, are
still willing and able to do this rather than unquestioningly accept
manufacturer's data. Even if the data turn out to be accurate, the process
is truly educational.

The varying SWR while terminated with 50 ohms is consistent with the 45
ohm Z0 you observed. My piece of BuryFlex is right at 50 ohms, but I'm not
too surprised at this amount of variation given the foamed dielectric. I
measured 80% velocity factor, so if our respective measurements are good,
the velocity factor of your piece should be around 72%.

Roy Lewallen, W7EL

Coax recomendations
 

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
 

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
 

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

Coax recomendations
 

Reg Edwards wrote:
To find ALL electrical characteristics and performance of
solid-polyethylene transmission line, use program COAXPAIR, from audio
frequencies to UHF.

Accuracy is of the same order as physical dimensions can be measured.
Use a micrometer to measure inner conductor diameter and diameter over
insulant. Or just guess at it. No need to unwind the cable off the
drum!

In a few seconds, download COAXPAIR from website below and run
immediately.

Have you compared the results to any measurements of real cables?

Roy Lewallen, W7EL

Coax recomendations
 

Reg Edwards wrote:
To find ALL electrical characteristics and performance of
solid-polyethylene transmission line, use program COAXPAIR, from
audio
frequencies to UHF.

Accuracy is of the same order as physical dimensions can be
measured.
============================================

Have you compared the results to any measurements of real cables?

Roy Lewallen, W7EL

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

Yes, Roy. Countless times.

Have you any more questions?
----
Reg, G4FGQ

Coax recomendations
 

Reg Edwards wrote:
Reg Edwards wrote:

To find ALL electrical characteristics and performance of
solid-polyethylene transmission line, use program COAXPAIR, from

audio

frequencies to UHF.

Accuracy is of the same order as physical dimensions can be

measured.
============================================


Have you compared the results to any measurements of real cables?

Roy Lewallen, W7EL


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

Yes, Roy. Countless times.

Have you any more questions?
----
Reg, G4FGQ

Yes. Where can I buy some of that RG-58 that has only 2.2 dB/100 foot
loss, or RG-213 that has only 0.89 dB loss, at 50 MHz?

Roy Lewallen, W7EL

Coax recomendations
 

On Tue, 13 Dec 2005 00:26:25 -0800, Roy Lewallen
wrote:

Have you compared the results to any measurements of real cables?

Roy Lewallen, W7EL


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

Yes, Roy. Countless times.

Have you any more questions?
----
Reg, G4FGQ

Yes. Where can I buy some of that RG-58 that has only 2.2 dB/100 foot
loss, or RG-213 that has only 0.89 dB loss, at 50 MHz?

Roy Lewallen, W7EL

The silence is deafening.

Danny, K6MHE





email: k6mheatarrldotnet
http://www.k6mhe.com/

Coax recomendations
 

Howdy:
I was wondering if, for a long run, instead of running coax for vhf or
uhf, if you could
have your radio up by the antenna, then run some large, but cheep wire to
the head unit
on say a ic-208? Would there be too much loss in D.C., or is there any other
problems
that I don't know about that would make this a really stupid idea, such as
some kind
of timing delay problem?

--

SeeYaa:) Harbin Osteen KG6URO

!sdohtem noitpyrcne devorppa-tnemnrevog troppus I

-

Coax recomendations
 

Harbin Osteen wrote:
Howdy:
I was wondering if, for a long run, instead of running coax for vhf or
uhf, if you could
have your radio up by the antenna, then run some large, but cheep wire to
the head unit
on say a ic-208? Would there be too much loss in D.C., or is there any other
problems
that I don't know about that would make this a really stupid idea, such as
some kind
of timing delay problem?

Locating an amplifier at the antenna is a fairly common
practice both for transmitting and/or receiving.
--
73, Cecil http://www.qsl.net/w5dxp

Coax recomendations
 

Remoting radios is nothing new and quite do-able. Signal line loss
problems depend on the design of the remoting. ie if line drivers are
used, not a problem. If high Z TTL lines then you might have a problem.
Power supply will be a problem. It may be smart to also remote a large
battery for current peaks. Easy to work out...

You may wish to address other issues though like lightning strikes and
weather ingress..

I use to remote a linear amp and preamp with a remote NiCd pack of D
cells. Worked well. RFO was about 70W on 144MHz.

Open wire feeder may also be an option to you.. The line loss would be
lower. You could also make some out of small dia copper pipe and spacers
you size/drill yourself.

Cheers Bob VK2YQA

Harbin Osteen wrote:
Howdy:
I was wondering if, for a long run, instead of running coax for vhf or
uhf, if you could