"Roy Lewallen" wrote in message
...

I've got some of that which I purchased new, and did some extensive
tests on it with a network analyzer. The loss varies all over the map
depending on how you coil, bend, or flex the cable, and I never saw loss
anywhere near as low as the spec says. A typical value at 400 MHz was
more like 5 - 5.5 dB/100 ft. Glad you're happy with it.

Roy Lewallen, W7EL

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.

de KU4PT

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

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

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/

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
--

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

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.

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
--

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

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