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
to my own post... sorry....
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 circuit.
Bulk, smoothing, response? Other?
instance, in audio applications, folks congregate around
Elna SILMIC II series electrolytics for
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:
is the Introduction to the Mod Alert:
Elecraft • www.elecraft.com •
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
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