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Re: [Amps] Amp causing RFI

To: Amps Amps <>
Subject: Re: [Amps] Amp causing RFI
From: Jim Brown <>
Date: Tue, 4 Feb 2020 19:44:23 -0800
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On 2/4/2020 6:07 PM, Mark Schoonover wrote:
Straight from the ARRL:

Did you read that paragraph? AND -- part of it is wrong. It confuses the difference between a counterpoise and the earth. The earth is a big resistor -- connecting it to the return for an end fed antenna adds that resistance to the antenna, burning transmitter power.

We use radials as a counterpoise -- now, return current flows in low resistance copper rather than lossy earth. The current flowing in a radial creates a field that couples to the earth underneath it, and the loss coupled from the earth shows up as resistance in series with the radial. The power dissipated is I squared R, where I is the radial current and R is the coupled resistance.

We can reduce the power lost in the radials by using more radials; as we add radials, current divides between them. If, for example, we use 16 radials, the current in each is divided by 16, and the power lost in each radial is divided by 256 (I is squared), so the total power lost is reduced by 16. In other words, the lost power falls with the in proportion to the number of radials. The EARTH is NOT the RF ground -- the radials ARE! An excellent analysis in the ARRL Antenna Book shows that radials SHIELD the field produced by the antenna from the lossy earth.

The only case where an earth connection makes an antenna work better is for certain types of RECEIVING antennas which work BECAUSE of the lossy earth underneath it and a connection to that earth. Loss doesn't matter in receiving antennas -- they work by producing a narrow receiving pattern by several different mechanisms. They don't make the signal louder, but the hear better by rejecting noise.

RF grounds do exist. Same page that lists your PDF.

For many years, I've cringed at least once (and often more than that) while reading every issue of QST. Thankfully, it's gotten a bit better in the last year or two.

73, Jim K9YC
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