> 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.
... Joe, W4TV
> -----Original Message-----
> From: email@example.com
> [mailto:firstname.lastname@example.org] On Behalf Of Steve
> Davis -Davis RF Co.
> Sent: Sunday, July 20, 2008 2:59 PM
> To: wa5zup
> Cc: email@example.com; firstname.lastname@example.org
> 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
> 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" <email@example.com>
> To: "'Steve Davis -Davis RF Co.'" <firstname.lastname@example.org>
> Cc: <email@example.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: firstname.lastname@example.org
> > [mailto:email@example.com] On Behalf Of Steve Davis
> > -Davis RF Co.
> > Sent: Sunday, July 20, 2008 9:12 AM
> > To: Jack Brindle
> > Cc: firstname.lastname@example.org
> > 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
> > 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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