[TowerTalk] Paintg Traps-Coax issues-Respon fr DAVIS RF Co.

Joe Subich, W4TV w4tv at subich.com
Sun Jul 20 15:36:57 EDT 2008


Steve, 

> I think that at this point of the various opinions, 
> 4" PVC is not a good route, unless the source of this 
> design (?) has done it with properly tested results.  
> That maybe is the next place to look before condemning 
> this, but I will have to leave it at that.

The "BC Trapper" design using RG-213 coax traps on the 2" 
PVC is attributed to K1ZM and has been duplicated many 
times by others for many years.  

I will not get into the debate over the quality of coax 
traps - I refer those interested to www.w8ji.com for test 
data.  However, as I understand it, this is not a matter 
of "repeated" bending - the trap is wound one time and 
left in place.  The length/number of turns should insure 
a reasonably reliable trap frequency if assembled with 
care.  Any subsequent tuning can be accomplished by 
adjusting the three antenna segments for 40/80/160 to 
accommodate any slight deviation in trap frequency.

73, 

   ... Joe, W4TV 
     




> -----Original Message-----
> From: towertalk-bounces at contesting.com 
> [mailto:towertalk-bounces at contesting.com] On Behalf Of Steve 
> Davis -Davis RF Co.
> Sent: Sunday, July 20, 2008 2:59 PM
> To: wa5zup
> Cc: towertalk at contesting.com; jackbrindle at earthlink.net
> Subject: Re: [TowerTalk] Paintg Traps-Coax issues-Respon fr 
> DAVIS RF Co.
> 
> 
>     This also reflects on Jack Brindle's astute comment
> 
> Hi John,    The min bend radius of Bury-Flex Tm is 2 inches.  
> I have sent 
> you a copy of the full spec via separate email.   Just to 
> avoid any possible 
> confusion by readers coming in at this point, the trap with  
> coax winding 
> question had to do with RG-213. .  Well made RG-213's also 
> have a 2 " bend 
> radius; however,
> an often missed point, albeit not often a consideration, is 
> the "repeat bend 
> radius" spec.  In the case of this trap winding, now that I 
> was reminded by 
> Jack Brindle that this is a 4" OD Sched 40, the repeat aspect 
> of  this trap 
> winding could be an issue.  I think the safest way to 
> approach this is to 
> contact the mfr. or distributor of the particular RG-213 
> involved (not 
> mentioned in this matter) and find out the repeat bend 
> radius, and at what 
> number of
> repeats does the issue start an adverse indication.  In my 
> first response I 
> somewhat qualified my remarks based on not having seen the actual 
> configuration of this trap, so I really can't opine much further than 
> already, thus leaving some of this subject to further 
> specifics of the 
> application.
>   If the spec'd repeat wind radius is marginal, wind the trap 
> and test it to 
> be sure.  My experience  tells me though that characteristics 
> of an RG-213 
> build will be somewhere in the 3-4 times the min. bend radius 
> to come up 
> with the prox. repeat bend radius, thus that would be 6-8" 
> min repeat bend 
> radius, unacceptable for a 4" OD winding core.
>    Also Jack's comment about internal heat:  yes, ties to 
> temp. rise of coax 
> line: related to freqcy, power, ambient temp  and attenuation.
>   Bottom line, objectively it is hard to quickly surmise; 
> however, I think that at this point of the various opinions, 
> 4" PVC is not a good route, 
> unless the source of this design (?) has done it with properly tested 
> results.  That maybe is the next place to look before 
> condemning this, but I 
> will have to leave it at that.  And, given that lightning is 
> now approaching 
> here.  HI      Cheers, Steve
> 
> ----- Original Message ----- 
> From: "wa5zup" <wa5zup at msn.com>
> To: "'Steve Davis -Davis RF Co.'" <sdavis at davisrf.com>
> Cc: <towertalk at contesting.com>
> Sent: Sunday, July 20, 2008 2:00 PM
> Subject: RE: [TowerTalk] Paintg Traps-Coax issues-Respon fr 
> DAVIS RF Co.
> 
> 
> > "I do not expect the heating
> > factor to be involved if the proper cable materials are utilized,
> > inherent
> > in a quality cable, and if the rated min. bend radius is 
> adhered to."
> >
> > What is the bending radius spec for BURY-FLEX cable?
> >
> > I looked on the web site, but did not find it, maybe I missed it.
> >
> > Thanks
> > John
> > Wa5zup
> >
> > -----Original Message-----
> > From: towertalk-bounces at contesting.com 
> > [mailto:towertalk-bounces at contesting.com] On Behalf Of Steve Davis 
> > -Davis RF Co.
> > Sent: Sunday, July 20, 2008 9:12 AM
> > To: Jack Brindle
> > Cc: towertalk at contesting.com
> > Subject: Re: [TowerTalk] Paintg Traps-Coax issues-Respon fr 
> DAVIS RF Co.
> >
> >
> > Hi Jack,  Your discussion is not over technical as your points are 
> > well
> > put
> > and fundamentally germane to the basics of coaxial design 
> and function. 
> > The
> >
> > only catch is that it appears that you are skeptical that all cable 
> > jacket PVC's, and their PE dielectrics (both ref. RG-213 and many 
> > other similars) will not hold up to heating by the sun and 
> resulting 
> > ambient  transferred through the shield to the dielectric.  
> There are 
> > many compounds of PVC jacket and PE dielectric used in cable 
> > extrusion.  Choosing the proper types
> >
> > as I noted (or relying on the mfr.; distributor; or design 
> engr),   will
> > hold up very well in any sunlight scenario for many years.  PVC 
> > compounds certified at 60 deg. C., and UV resistant,  are my 
> > requirement for outdoor applications of our RG-213 and 
> similar cable. 
> > Your concerns are not uncommon and have been  noticed in 
> some of our 
> > commercial inquiries where they have spec'd Teflon outer 
> jackets when 
> > the ambient would never reach in excess of 60  C, thus 
> we've been able 
> > to save them a lot of money by using the correct grade of 
> PVC. I agree 
> > completely with you ref. the electrical degradation due to  center 
> > cond. concentricity misalignment, IF there is enough ambient heat 
> > combined with spiral exertion to cause this...however I do 
> not expect 
> > the heating factor to be involved if the proper cable materials are 
> > utilized, inherent in a quality cable, and if the rated min. bend 
> > radius is adhered to.
> > 73,   Steve ,  K1PEK,
> >
> > DAVIS RF Co.
> >
> > Wire, Cable, RF Connectors and wire aerial parts.   LMR, 
> Heliax, Eupen
> >
> > Commercial / Military / & Custom Cable Design
> >
> > tel:  978-369-1738     Fax:  978-369-3484
> > www.davisRF.com
> >
> >
> >
> >
> >
> >
> > 
> 
> 
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> 
> 
> 
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