[Elecraft] Balun Questions

Tue Feb 9 10:36:20 EST 2016

If one has heating issues to that magnitude, they have other more critical issues which should be addressed. 

Bob, K4TAX

Sent from my iPhone

> On Feb 9, 2016, at 9:24 AM, Dave Cole <dave at nk7z.net> wrote:
> 
> 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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