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Re: [Amps] Alpha Input SWR

To: amps@contesting.com
Subject: Re: [Amps] Alpha Input SWR
From: Steve Thompson <g8gsq72@gmail.com>
Date: Sat, 10 Jan 2015 09:07:36 +0000
List-post: <amps@contesting.com">mailto:amps@contesting.com>
For a fixed impedance Hardy's comment is correct. Changing the feeder length alters the phase but not the SWR (ok, there's caveats but they don't apply in an ordinary ham station). If your SWR reading changes a lot, it indicates you have lots of harmonics or the SWR meter isn't good enough.

With a GG amplifier, especially one with a broadband input circuit, think of the coax as part of the cathode circuit rather than just the link between rig and amp. There's significant harmonic current in the cathode circuit and the length of coax affects how it flows to ground. That alters the impedance seen by the rig when driving it, so changing the coax length can change the SWR the rig sees.

Steve

Hardy,I do not have Mr. Smith's chart.   All I know is what I see with my own
eyes. CHANGING THE LENGTH OF THE COAX changes the swr as measured by the
driver, the radio.  What do you recommend to do when the Smiths of this world
think they know something and then actual real-world practice shows
conclusively difference?Charly

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