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Re: [TowerTalk] RG-58 capacitor

To: towertalk@contesting.com
Subject: Re: [TowerTalk] RG-58 capacitor
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Sun, 25 Jun 2017 21:44:05 -0700
List-post: <mailto:towertalk@contesting.com>
On Sun,6/25/2017 9:19 PM, jimlux wrote:
So, moral of the story is, check for the brand of your coax, and use the appropriate length.

And be even more specific -- although RG-numbers originally defined many specifications for cables, that has not been true for many decades. For example, there are hundreds of cables CALLED RG8, all different from each other in a variety of ways, and each carrying a different part number.

The only good place to look for cable characteristics and specs is the technical data sheet for the actual manufacturer of the specific cable type. AND -- only the major cable companies publish this data for their cables, and the data is as trustworthy as the mfr is.

As K1TTT noted, if the cable for your capacitor is a significant fraction of a wavelength, you'll have to analyze (compute) it as a stub. 1/20 wavelength (taking VF into account) is a good rule of thumb for when the calculation is more complex than pF/ft multiplied by feet.

And, of course, if the capacitor is in a circuit carrying high power, you'll need to compute things like voltage breakdown and loss. And you'll need a decent data sheet for that too. :)

73, Jim K9YC

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