[Elecraft] Balun Questions

[Chuck Catledge]

At hamfests around the Southeast, surplus RG400 is often found in terminated cables (usually BNC or N) in lengths up to around 20 feet.  The price I've paid is always less than $1.00 per foot, sometimes much less.  I've used it to make dozens of RF chokes (1:1 baluns).  The small size of RG400 allows the use of a single medium to large clamp-on #31 ferrite that works effectively from 10-160M, conditioned by the number of turns.  The large snap-on ferrite will accommodate 10-12 turns; the medium snap-on will handle 5-6 turns.  Jim, K9YC's tutorials are excellent.  Consult the Fair-Rite website for additional technical data.

BTW, the Teflon dielectric allows easy soldering in PL-259s with RG-58 reducers without any fear of melting the dielectric.
---
Chuck, AE4CW

-----Original Message-----
From: Guy Olinger K2AV [mailto:k2av.guy at gmail.com] 
Sent: Sunday, February 07, 2016 01:08
To: Robert Nobis <n7rjn at nobis.net>
Cc: elecraft at mailman.qth.net; Ron D'Eau Claire <ron at cobi.biz>; Guy Olinger K2AV <k2av.guy at gmail.com>
Subject: Re: [Elecraft] Balun Questions

RG303 is not rated for the tight bends.  RG400 with its fine stranded center conductor is rated for corner bends in aircraft wiring harnesses and will not deform the dielectric within the bends. I would not wind any solid center conductor coax on a toroid.

I would only buy cut lengths of RG400 after the lengths for a project are known. Some number of such suppliers on eBay. One currently listed at 1.98 per foot:
http://www.ebay.com/itm/RG400-Coaxial-Cable-Mil-spec-by-the-ft-US-supplier-/251260159394?hash=item3a8045c5a2:g:WpAAAOxy43FRafUe

True it ain't ham cheep. The good stuff that lasts and lasts almost never is. Back in the early days of eBay I came by a 142' length of RG400 for $25. That's $0.178  a foot  I also came by bundles of miscellaneous 6 foot to 15 foot jumpers with various connectors on end for similar ridiculous low prices per foot.

The silvered copper strands stand up to migration of dampness in a way not possible with same size copper strands minus the silvering. I have
*measured* the dry RF resistance at 1.83 MHz of a 67 foot length of corroded #14 stranded plain copper at 62 ohms. When new this wire had resistance at RF of less than an ohm. I have never found the silvered copper equivalent in anything remotely approaching that degraded state.

RG400 wound on the proper core for the job will last a lifetime.

73, Guy K2AV

On Saturday, February 6, 2016, Robert Nobis <n7rjn at nobis.net> 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.
> >
>
>
>