[Elecraft] Balun Questions

[Robert Nobis]

I have used RG303/U for chokes.  A bit smaller diameter than RG400 (0.170 versus 0.195 inches). RG303/U has a solid copper center conductor that is silver plated.  The shield for RG303 is also silver plated copper. The jacket is Class 9 Teflon. Also the dielectric material is teflon.

73,


Bob Nobis - N7RJN
n7rjn at nobis.net


> On Feb 6, 2016, at 17:49, Guy Olinger K2AV <k2av.guy at gmail.com> wrote:
> 
> If one wants a small 50 ohm coax that will take QRO with a very large
> margin and was *designed* for bending and use in aircraft wiring harnesses
> then use RG400 to wind around your core. RG400 uses a fine stranded
> silvered copper center conductor that is more flexible than its Teflon
> dielectric. It has a double shield made from silvered copper strands.
> 
> That's silvered strands whose silver sulphide patina or tarnish is
> conductive as opposed to the green copper sulphate that separates copper
> strands that have been water soaked.
> 
> Wind the coil form with RG59 to get the length and buy just what RG400 you
> need. You can buy brand new RG400 by the foot.  With the Teflon dielectric
> you can solder the RG400 without worrying about melting it.
> 
> Do it with the good stuff to start with and put it in your will.
> 
> 73, Guy K2AV
> 
> On Saturday, February 6, 2016, Ron D'Eau Claire <ron at cobi.biz> wrote:
> 
>> Bob makes an excellent point. I've seen cases where even "solid" dielectric
>> did that over time because, after all, it is not really solid. The
>> dielectric is plastic so the coax can be bent.
>> 
>> All coax has a minimum bending radius specification. Specific data is
>> available on line but, in general, RG58 size cable usually has a minimum
>> radius of 1 to 1.5 inches (2.5 to 3.8 cm) and RG8 size cable has a minimum
>> radius of at least 2 inches (5 cm). Note that is radius. If you curl the
>> cable into a circle the minimum diameter of that circle should be at least
>> twice that or 3 to 4 inches (7.5 to 10 cm).
>> 
>> It's not something I've found especially critical in HF applications at
>> least around my shack, but tighter bends, which may not actually cause a
>> short (yet), alter the impedance as the center conductor migrates toward
>> one
>> side so it is no longer equally spaced within the shield. This can be a
>> serious issue in microwave and even UHF installations.
>> 
>> 73, Ron AC7AC
>> 
>> 
>> 
>> -----Original Message-----
>> I would have concern that long term usage of RG-8X, being foam core
>> dielectric material and bent in a tight radius, may allow the center
>> conductor to migrate to the inside radius of the bend.  The Minimum Bend
>> Radius for RG-8X is 2.50".     Thus the tight bend will allow the center
>> conductor to short to the shield.  A solid core dielectric coax such as
>> RG-303  is much preferred.
>> 
>> 73
>> Bob, K4TAX
>> 
>> 
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