In a message dated 98-04-10 11:49:30 EDT, you write:
<< I have a 250 ft run to make to my tower and would like to buy the rotor and
feedline cables. Any suggestions for type of coax? Should I bother w/
conduit?
>>
Hi Russ, The main considerations which I, and my learned colleague, Press
Jones, The Wireman, point out concerning coax to be buried are as follows:
(1) Do not be confused by at claims out there to have "buriable PVC RG213"
because it is "non-contaminating". RG213 as well as generic RG 8's and many
others are, by spec are a PVC jacket (and PVC's come in numerous chemical
compounds, some of which are non contaminating). NO PVC JACKET, including non
contam. is buriable. Non contaminating strictly applies to the important
aspect of a cable jacket of chemical composition such that the plasticides can
not migrate into, thus contaminating, the shield and dielectric which, if
occurs, adversely changes the electrical characteristics of the cable. (2)
you should use a high density Polyethylene ("PE) jacketed cable. NOTE: PE,
by virtue of its polymer composition, is NOT a contaminating jacket as it does
not contain plasticides (3) RF frequency of application is always a
consideration as to which cable you use, regardless of jacket type - I'm sure
you and all TT members understand that but I only mention that as it pertains
to your choices here. If you are operating HF thru UHF the best choice on the
market, not only from buriable, handling and cost is BURY-FLEX" Tm which is a
low loss cable that has attenuation characteristics as good as LMR and any
other in that freq. range and which utilizes a PE jacket. Also, you can use a
standard PL259 or N connector on BURY FLEX Tm. If you are working at UHF
through microwave there would be choices I could recommend solutions for
depending on frequency, length, power attenuation, and bend radius, etc. (4)
Conduit or not: PE jackets are very resistant to cuts and abrasion. If you
felt that your buried cable would not be interferred with by errant machine
digging in the area of the buried coax, then a conduit is not necessary. PE
will survive a long time in dirt, mud, through water and various chemicals.
If you do use a conduit, please let us know and we will suggest a way of
setting it up to avoid build-up of internal condensation and proper
irrigation. Always install a nylon or dacron "pull string" in any conduit for
future cables - thus the chances of PVC future cable is there, thus the desire
to eleviate condensation and provide drainage. (5) Another alternative is
flooded buriable PE and then the option to that is flooded with an armored
(metal) jacket. Either way, expensive. Please note that most CATV companies
and/or some electrical codes require flooded (no armor) AND a conduit. This,
again, is mainly due to the premise of avoiding errant back hoeing etc.
"BURY-FLEX" is sold at various dealers including the Wireman. The average
list price is 59 cents for lengths under 500 ft. It has been highly accepted
technically and very popular. Let me know if I can help further. There is
more on this subject and product at our web site - see below. 73, Steve
Davis, K1PEK DAVIS RF Co.
DAVIS RF Co., Commercial wire/cable, RF connectors, custom cable design.
Discounts to hams. BURY-FLEX ? low loss HF-microwave HDPE coax;
.........FLEX-WEAVE? aerial wire, registered trademarks of Davis Associates,
Inc.
LMR, Heliax, etc. Visit our web site at www.davisRF.com Take advantage of
"The Triad": DAVIS RF Co., ORION WIRE CORP and The WireMan: Three types of
expertise, three corporate buying power and customer inter-personal
relationships benefitting all.
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