[Elecraft] Balun Questions

[Dave Cole]

Hello Bob,

The coax could be exposed to heat when in service as a balun, so I
would respectfully disagree with you on this one point.

If you exceed the bending radius of your coax, you stand a higher
percentage chance of causing a shield to center connector short, (due
to center conductor migration), than if you don't exceed the bend
radius.  When running high power, you also stand a better chance of
heating up your core material, (and hence your coax), which makes it
easier for the center conductor to migrate, and if you have exceeded
the bend radius-- well--  we're pretty sure where it will migrate
too...

One has to pick one's fights so to speak, and I would not pick bending
radius as one of my fights...  

If you lose, it is never good when the center conductor shorts to the
shield at Kilowatt power levels.  Use loops large enough to stay within
the bending radius of your coax.  Now if this is QRP, you could
probably get away with it.

-- 
73's, and thanks,
Dave

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On Tue, 2016-02-09 at 09:01 -0600, Bob McGraw K4TAX wrote:
> I'm one of the other Bob's or Robert's........
> 
> Since the assembly of coax wound around a toroid doughnut style
> bobbin 
> is typically not exposed to vibration, such as might exist in an 
> airplane, boat or space vehicle, the use of a solid conductor coax
> such 
> as RG-303 would not seem to be of concern.  The more important point
> and 
> my experience and as related by others, the use of coax which has
> foam 
> dielectric in a tight radius bend has been proven or shown to be 
> problematic.    As to if the manufactures bending radius dimension
> is 
> being violated, I find to be of little concern.
> 
> After all, as a rule, hams are noted for pushing things to the limit
> and 
> then some and getting buy with it.  If hams choose to "stick to the 
> rules 100% in all aspects of their stations"............I'd say 75%
> of 
> the stuff we use and methods employed would put most of the station 
> stuff in the trash.
> 
> 73
> Bob, K4TAX
> 
> 
> 
> 
> 
> On 2/9/2016 8:45 AM, Guy Olinger K2AV wrote:
> > Hi Bob, et al,
> > 
> > Thank you all for your careful attention.
> > 
> > I read it wrong, as several have pointed out overnight. I
> > transposed that
> > to a percentage in my memory after reading it. One of the reasons
> > for
> > referring people to the original material in these cases. Someone
> > will get
> > it right.
> > 
> > That makes it two and a half hairs :>)  Doesn't appear to change
> > the
> > argument. To me anyway the method is still a crude measurement
> > instead of
> > watching a wide frequency scan while bending the cable along with
> > other
> > performance specific measurements.
> > 
> > I still would not use the solid center conductor versions
> > (RG142/303) on a
> > winding.
> > 
> > 73, Guy K2AV
> > 
> > On Tuesday, February 9, 2016, Robert Nobis <n7rjn at nobis.net> wrote:
> > 
> > > Hi Guy,
> > > 
> > > I am not sure how you arrived at the “2/1000 of an inch” figure
> > > from the
> > > ANSI spec? The spec actually says “A change in ovality from a
> > > given
> > > sample’s initial measured value of 0.010 inches or more (> 0.010)
> > > represents the point of non-acceptable bending performance.”
> > > 
> > > 
> > > 73,
> > > 
> > > 
> > > Bob Nobis - N7RJN
> > > n7rjn at nobis.net <javascript:_e(%7B%7D,'cvml','n7rjn at nobis.net');>
> > > 
> > > 
> > > On Feb 8, 2016, at 18:01, Guy Olinger K2AV <k2av.guy at gmail.com
> > > <javascript:_e(%7B%7D,'cvml','k2av.guy at gmail.com');>> wrote:
> > > 
> > > 
> > > I also suggest that everyone carefully study the ANSI standard
> > > until it is
> > > clear what they are doing mechanically and see what they are
> > > actually
> > > measuring:
> > > 
> > > http://www.scte.org/documents/pdf/standards/ANSI_SCTE%2039%202007
> > > .pdf
> > > 
> > > The method of measuring is in section 4. They are looking for a
> > > limit of
> > > 1% surface deformity when bending.
> > > 
> > > In the case of RG400 with .195 inch OD, that would be 2/1000 of
> > > an inch
> > > (yes, that's three zeros, two one thousandths of an inch) bending
> > > deformity
> > > at the surface of the teflon jacket, or half the thickness of an
> > > average
> > > human hair.
> > > 
> > > 
> > > 
> > > 
> > > 
> > > 
> 
> 
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