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[TowerTalk] Best Coax for Crank Ups...Flex...& Drip Loops-DAVIS RF Respo

Subject: [TowerTalk] Best Coax for Crank Ups...Flex...& Drip Loops-DAVIS RF Response
From: Stephen Davis <>
Reply-to: "Tower and HF antenna construction topics." <>
Date: Sat, 27 Feb 2010 13:40:08 -0500
List-post: <">>
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 

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 
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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