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Date: Mon, 16 Dec 2002 23:26:08 -0600
To: "Wilderman" <dlrwild1 at voicenet.com>, <elecraft at mailman.qth.net>
From: Tom Hammond =?iso-8859-1?Q?N=D8SS?= <n0ss at earthlink.net>
Subject: Re: [Elecraft] K2 DC note modification

Hi Bob:

>I was told that there is a mod for the K2 that improves the DC note of the 
>CW signal. Is this true? If so, can someone send me the mod information. 
>Is it something that can easily be done be an inexperienced kit builder. I 
>bought my K2 assembled. I received a signal report from a ham the other 
>day who knew I was using a K2 before I even told him what radio I was 
>using for QRP. Was he just pulling my leg or was he on to something?

He probably wasn't pulling your leg.

A number of K2 users (myself included) have received reports of "slight 
chirp" from their K2. This generally occurs on 40M for some reason, but I 
suspect can occur on other bands we well.

The problem appears to result from excessive VCO control voltage. And the 
way to fix this problem is to readjust your VCO control voltage to the 
levels specified in the K2 manual... actually a bit lower than the upper 
level specified, if I recall.

The K2 manual specifies that the VCO control voltage should rest between 
1.5VDC and 7.5VDC. After I received my 'chirp' report, I checked my VCO 
coltage on 40M and found that it was running about 8.4VDC... or almost one 
volt higher than the maximum specified.

I consulted several folks, including Wayne and Gary, and based upon their 
suggestions, I set my VCO voltage to no more than 6.0VDC (if I recall).

Since that readjustment, I've received no more reports of chirp, and the 
station who gave me the report HAS been worked again and this time gave me 
a cleam bill of health.

that's about the only cause of bad CW signal quality I recall having read 
of. However, I HAVE found that some certain types of (AC) muffin fans, when 
set on top of the KPA100 heatsink, will induce a 120 Hz ripple in both the 
TX and RX signals... as will locating your K2 too close to transformers 
with large electromagnetic fields.

Hope this helps.

Oh yeah... the docs for setting the VCO voltage can be found under "VCO 
ALIGNMENT in your K2 manual... various pages, depending upon revision 
version of the manual, but generally probably around pages 55 thru 58, I'd 
imagine.

73,

Tom Hammond   N0SS

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