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A DC fan, brushless or not, creates noise that gets back into the radio. For decades I sold a cooling kit for the Icom IC-781, and I had a small dropping resistor
(since the available supply voltage was 15 volts), plus a 470 uF electrolytic. This isn’t an exotic circuit for the K3 or the IC-781. In my case I ran the fan on 9 volts, and in the case of the K3 there are step-wise variable speeds. I am sure size matters,
but today a 470 uF at 16 or 25 volts is quite small compared to years ago. Rob, NC0B
From: Elecraft-K3@groups.io [mailto:Elecraft-K3@groups.io]
On Behalf Of Clay Autery
Sent: Monday, January 20, 2020 11:34 AM
Subject: Re: [Elecraft-K3] CW Noise Pedestal
Replying to my own post... sorry....
I don't think I will personally just throw any old 470uF 16V electrolytic capacitor in there. I think I will dig into the schematics a bit and try to figure out for what the cap is being introduced into the
Bulk, smoothing, response? Other?
For instance, in audio applications, folks congregate around Elna SILMIC II series electrolytics for "smoothing"purposes...
I don't pretend to know ANYTHING about this, but it is an opportunity to learn.
Clay Autery, KY5G
On 01/20/20 12:23, Clay Autery wrote:
HERE is the Introduction to the Mod Alert:
Elecraft • www.elecraft.com • 831-763-4211Elecraft KPAIO3MDKT
Revision B, August 10, 2016E740287Copyright © 2016, Elecraft, Inc.All Rights Reserved
This modification applies only to K3S transceivers equipped with the KPA3A 100 watt power amplifier, serial numbers 10732 (factory assembled), 10728 (kits) or below,
and to all K3 transceivers with the KPA3 power amplifier that have been
upgraded with KSYN3A synthesizers.Tests at Elecraft have shown that a very small amount of electrical noise associated with the fans on the KPA3 (or KPA3A) amplifier module can be detected in the transmitted signal under laboratory test conditions. This
modification suppresses that noise. The noise had always been present, but was only discovered with the addition of the new KSYN3A synthesizer, due to its extremely low phase noise close to the carrier. This modification was phased into factory assembled units
starting with serial number 10732 and kits starting with serial number 10728. This modification kit allows you to make the simple change in the field to an existing K3 or K3S. It requires removing the KPAIO3 interface board and soldering a leaded capacitor
supplied onto the board.
YOU need the mod if the "small amount of noise" present under "lab conditions" bothers you.
I am applying it because I do everything reasonable to make my transmissions cleaner. It is a matter of being a "good neighbor" on the public airways for me.
Clay Autery, KY5G
On 01/20/20 11:43, Russ Tobolic via Groups.Io wrote:
Now I am all confused! I have good old trusty K3 serial #732 with the original KPA3 and upgraded with the KSYN3A. This is the first time I have heard of this mod so do I need it? No one has told me I have a problem. I have a handful
of the 470uF caps in my junk box.