Owen with all due respect there is no "question" why 9914 has not replaced
Heliax and that is due to loss factors. BTW 9914 is impervious to water in
and of itself..so evidently you have not done much homework on this
particular coaxial cable. Davis 9914 is recommended for rotator loops. Your
supposed quandary about "9914 replacing Heliax" is contrived in my opinion
to murk up the waters of this issue and maybe steer focus away from what
obviously, at least to me, is an unfortunate one-time testing experience by
Roy.

Yes I suppose we should always be "suspicious" of manufacturer's claims but
do you exercise that philosophy across the board? How about the tires on
your car? How about the prescription medicines you may take and also over
the counter meds? How about those fast food burgers? How about your
drinking water? Are you as equally "suspicious" of these products or is this
philosophy of yours only revealed to others when you want to discredit
someone else's data. I think the later and not the former sir.

Owen....I give you a salute for being an obvious "spin doctor" for Roy's one
time, one sample, one conclusion, years ago test cycle.
A job well done on the surface..however the underlying facts remain. Davis
BuryFlex has been sold for well over 10 years in the "real world" and these
same real people, government agencies, municipalities, and service agencies
have used thousands of miles of it with no apparent issues. Cite similar
tests to Roy's and I'll reconsider.

As for me I'll go with the Davis data, once it arrives, and do a calibration
standards trace on their test station. Was Roy's test bench's
calibration traceable? It is preposterous you would continually cast
aspersions towards a company that has been in the wire and cable business
for over 25 years and promote and crusade for a one time shot-in-the-dark
independent so-called "test".

You do not fool me sir....best regards.....

-ps How many times do you think Davis has tested their 9914 in the past 10+
years?
More than the one single time Roy has perhaps?



--

Charlie


"Owen Duffy" wrote in message
...
On Sat, 10 Dec 2005 19:46:15 -0600, "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.

We should be a little suspicious of manufacturers claims. Davis' can
be expected to support their product.

Roy's single poor experience is concerning, indicating either a
quality control issue, or more general non-compliance with spec (both
are issues for Davis). An independent test of stock cable and possibly
Roy's sample would be most interesting.

I know I have made measurements and adjustments at times and in
searching for possible explanations, the cable quality is on the
radar. In one of those cases, a mobile installation could not be
trimmed properly, and the Taiwanese RG58 centre conductor was so far
off centre, it was nearly touching the braid.

We have all cut cables up and found inconsistent braid weave, open
braid weave, voids in the dielectric, faulty stranding of inner
conductor, off centre centre conductors. It is those kind of issues
that downgrade a suppliers reputation, not their ability to select a
good cable sample for laboratory measurement.

Perhaps if you're a whiz, you should perform some measurements so you
can report first hand your experience.

We don't see the Davis stuff on this side of the world. The concept
seems a good one, PE sheath, braid+foil outer, foam dielectric,
stranded inner, but you have to ask yourself why they haven't
displaced Heliax and its copies. I suspect the reasons include IM and
noise issues associated with the braid+foil, mechanical issues with
the foam, and resistance to water. Experience with noise and IM
problems with braid+foil coax in fixed installations makes me wonder
how it stands up in a rigorous test of flexing for a rotator loop, not
anecdotal evidence, but a structured test.

Owen
--

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

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

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
--