[Elecraft] Balun Questions

Sat Feb 6 20:26:37 EST 2016

Bob,

Yes, it is a bit expensive: $2.91 per foot from “The Wireman” plus shipping.  (For lengths under 100 feet.)

73,

Bob Nobis - N7RJN
n7rjn at nobis.net

> On Feb 6, 2016, at 18:21, Bob McGraw K4TAX <rmcgraw at blomand.net> wrote:
> 
> Yep, good stuff.  Be sure of your budget before buying a roll.  It is a bit pricey.  Handles legal limit HF power with a reasonable SWR.
> 
> 73
> Bob, K4TAX
> 
> 
> 
> On 2/6/2016 7:10 PM, Robert Nobis wrote:
>> 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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> 
> 
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