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Re: [TowerTalk] Best Coax for Crank Ups...Flex...& Drip Loops-DAVIS RFRe

To: "Tower and HF antenna construction topics." <>
Subject: Re: [TowerTalk] Best Coax for Crank Ups...Flex...& Drip Loops-DAVIS RFResponse
From: "Gene Fuller" <>
Reply-to: "Tower and HF antenna construction topics." <>
Date: Sat, 27 Feb 2010 14:09:24 -0500
List-post: <">>
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" <>
To: <>
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,, 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 
> rotating.
> 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
> _______________________________________________
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