Topband: Updated K9YC common-mode choke PDF now available

[Jim Garland]

Guy, I agree in principle that coax with a stranded center conductor will be more flexible than coax with a solid conductor, although in applications where there is mechanical stress on the coax, coax with a solid steel core will be significantly stronger than its stranded counterpart.

However, I think you are overstating the supposed weakness of RG142b, which appears to be identical to RG400, except for having a silver plated steel inner conductor. As a test, I took an eight inch length of new RG142b and bent it in a U-shape (about a 1/4 inch diameter) back and forth sixty times, measuring the continuity between the ends. Afterwards, I cut away the shield and dielectric to expose the solid inner conductor, which showed no perceived wear or damage. Afterwards, I continued to flex the bare inner conductor with the dielectric and shields cut away and it finally broke after twenty additional flexes (70 in all). Frankly, I was surprised at how well the coax held up under this abuse. It would be interesting to conduct the same test with RG400. Note that both types of coax are specified for a 1 inch minimum bending radius, which I believe to be an excessively conservative rating.

 

My little test greatly exceeded demands placed on the coax in any normal application, such as winding a choke or toroid, or routing RF around an amplifier. I have also used RG142b jumpers in my station for many years with no problems. However, the coax is relatively stiffer than, say, RG58, so I'd guess the more flexible RG400 is better for that purpose. Because of its strength, RG142B would be desirable for long outdoor runs where the coax is self-supporting. Basically, however, both RG142B and RG400 are very rugged and excellent for almost any amateur use, and both are vastly superior to RG58 and its variants in almost any application.

73.

Jim W8ZR

 

From: Guy Olinger K2AV [mailto:k2av.guy at gmail.com] 
Sent: Sunday, February 03, 2019 07:17 AM
To: MU 4CX250B
Cc: Jim Brown; Mike Waters; topband at contesting.com
Subject: Re: Topband: Updated K9YC common-mode choke PDF now available

 

I would not repeatedly bend any coax with a solid center conductor. Which leaves RG142 for permanent routing. Jumpers to and from back of TXR and amps etc are always RG400. Windings on cores are always RG400. RG400 shield weave and center conductor made of very fine strands of silver coated copper. 

 

On K9YC’s latest cookbook he only specifies RG400. Do it right, do it once, happily keep it. 

 

RG400 can usually be had in useful lengths off EBay for half retail or better.  The stuff almost never goes bad. So these are safe buys.

 

There are a lot of jumpers listed. I can sometimes get the stuff with a needed connector already installed. 

 

73, Guy K2AV 

 

On Wed, Jan 23, 2019 at 8:07 AM MU 4CX250B <4cx250b at miamioh.edu> wrote:

Very interesting, Jim. I wasn't familiar with RG-400, but I've used
RG-142B for years. I compared the specs and found they're virtually
identical, the only significant difference being that RG-400 has a
stranded center conductor, while RG-142B has a solid steel
(silver-plated) center conductor. They both have a 1 inch minimum
bending radius (for repeated bending), but I imagine the RG-400 Is
slightly more flexible and the RG142B is slightly stronger. At GHz
frequencies, the RG142B has slightly lower loss. They both have
excellent high temperature properties. If you buy it new from a
distributor, either will cost about $5 a foot.
73,
Jim w8zr

Sent from my iPad

> On Jan 22, 2019, at 6:42 PM, Mike Waters <mikewate at gmail.com> wrote:
>
> ---------- Forwarded message ---------
> From: Jim Brown <jim at audiosystemsgroup.com>
> Date: Mon, Jan 21, 2019, 11:36 PM
> Subject: Re: Topband: Inverted L improvements - Part 3 (now with data)
> To: Mike Waters <mikewate at gmail.com>
>
> After nearly a year of work, I published a new "cookbook" last month.
> For reasons that are detailed in the accompanying text, I no longer
> recommend coax wound through multiple cores.
>
> The short answer for "why not?" is that it's simply not practical to wind
> chokes that way and get anything close to the same result every time --
> turns must go through the core in the same order, a scrambled turn cancels
> a turn, turn diameter matters a lot, and so on.
>
> The new cookbook uses RG400, 12-2 Teflon/silver pairs, or 12/2 THHN or NM
> pairs, all tightly wound around a single core.  There are recommendations
> for chokes in series to increase power handling. There is also data for the
> new 4-in o.d. supersized toroids, which are great for 160M.
> k9yc.com/2018Cookbook.pdf
>
> 73, Jim K9YC
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