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

[Stephen 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 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.
www.DavisRF.com

Main office, NH:   Tel:  1-800-DAVIS RF   
Steve Davis, Direct line, MA Branch:  1-978-369-1738    sdavis at DavisRF.com