I haven't been following this coax/tower thread to closely but it just
struck me. What do all the extra loops around the tower do to you if you're
using the tower as a tuned vertical? and if the shield is ground to both the
top and bottom of the tower....?
----- Original Message -----
From: "Stephen Davis" <email@example.com>
Sent: Saturday, February 27, 2010 1:40 PM
Subject: [TowerTalk] Best Coax for Crank Ups...Flex...& Drip Loops-DAVIS
> Hi guys,
> Bury-FLex Tm Low Loss Coax, designed by DAVIS RF has several applications
> and has been lauded here on TT, eHam.net, etc. One of its prime
> applications is ancillary to its low loss, flexibility and buryability ( a
> new word that I think Webster needs to recognize HI) .
> Bury-Flex is excellent also for loops around the outside of crank-up
> towers. The main reason it is so good is due to the mid-Shore hardness
> of its PE outer jacket. The jacket is very smooth, with no friction to
> the tower members. It has enough memory to hold it's circular flow/coil
> around the tower when raised / lowered. It will settle down to its own
> coiled configuration at ground level when tower is lowered, without the
> need for a bucket, etc. (bucket aspect addressed here on TT.) There would
> be no advantage of using expensive Nycoil (mentioned by a contributor)
> for further protection or "coilability" using Bury-Flex (we do all sorts
> of standard and custom designed cables for a Nycoil company).
> Comparing Bury-Flex to LMR-400 UF (Ultra Flex), which we also sell: LMR
> 400 UF uses a TPE outer jacket which is more viscous (or higher
> coefficient of friction) and that , in part , adds flexibility vs. a PE
> outer jacket which has a higher durometer (related to density). However ,
> TPE will have more friction to the tower member. TPE does not hold up any
> where near as long as the type of PE that we use for Bury-Flex.
> So, how do we "make up" the "difference" in the flex of the TPE jacket??
> We build Bury-Flex using a 19 strand center conductor, 9.5 AWG, vs LMR
> 400 UF ctr.. cond. , which is less flexible. Thus, there is only a slight
> difference in flexibility, which nobody who has held 3 ft. of both in
> their hand, alternately bending the other end, has said it is at all an
> appreciable difference.
> Yes , the additional stranding in Bury Flex yields higher attenuation at
> microwave freq's, but for HF thru VHF, it is virtually the same and at UHF
> just a slight difference. Lastly, 400 UF Times List price is aprox 55
> cents more than Bury-Flex, and our selling price for 400 UF is
> 12 cents/ ft below Times List.
> There was also mention here on TT as to aluminum aspects of certain
> cables being a concern for coiling. I agree, but not for Bury-Flex.
> Bury-Flex Tm is all copper, with a tinned copper braid shield as well as
> an alum foil and our min bend radius is 2". I can't imagine a coiled
> around tower application where Bury Flex, internally, would not hold up
> very well for the 20 + years that the jacket is rated for.
> Rotar drip loops: Many folks use Bury-Flex right up to the antenna, thus
> eliminating connector junctions. The rule of thumb I recommend is add 20%
> to the length of the Bury Flex loop vs. what your loop length using other
> highly flexible cable choices. As with any good installation, have
> excellent strain relief as to the connector at the antenna jack or hard
> wired, and at the tower if a connector is in the line there, i.e., avoid
> any movement of the connector due to the cable blowing in wind or while
> Bury-Flex Tm, using its PE outer jacket, has no plasticizers in the
> jacket that will migrate into the dielectric, as does many common PVC
> jackets, if not NCV rated, and NCV (Non Contaminated Vinyl, also Belden
> termed PVCNC" ) is by NO MEANS BURIABLE. This is a pet peeve of mine,
> as a cable design engineer, because a well known cable expert has been
> selling an RG -213 as buriable, which is not only an oxymoron as to the
> mil spec, it is also not possible to use a PVC outer jacket on any cable
> (coax, control,etc) and bury it and have it last too long (maybe a couple
> years, depends on soil and water) before the copper inners and/or the
> dielectric is highly compromised.
> Hope this info helps,
> 73, Steve K1PEK
> Davis RF Company
> Electronic Wire, Cable and Cable Design Engineering
> RF Coaxial Cable Connectors and Telecom Parts
> A Division of Orion Wire Company, Inc.
> Main office, NH: Tel: 1-800-DAVIS RF
> Steve Davis, Direct line, MA Branch: 1-978-369-1738 sdavis@DavisRF.com
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