[Elecraft] Low Frequency Modulation of Side Tone.

[Jeff Burns]

Problem found. I added a fixed audio out port to the K2. Disconnecting the
wire to the sound card stopped the modulation.  An audio transformer in line
also eliminated the problem. 

Jeff Burns
AD9T 

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of
jeff_list at burnshome.org
Sent: Saturday, January 22, 2005 12:16 PM
To: Elecraft List
Subject: [Elecraft] Low Frequency Modulation of Side Tone.

I just noticed that on 80 and 17m the side tone in my K2 has a low frequency
modulation superimposed over the normal frequency. When I discovered this I
was trying to call a Panama station on 80m. I cranked the power up to 100w
and started my call. The rig sounded like it was going nuts. It even locked
into a repeating string of dits or das. I do not remember which. I turned
the rig off to get it to stop. I suspect the repeating transmission is
unrelated to the side tone problem because I found that my computer keying
cable was part way out of the jack. It must have been bad timing that it
came out just as I was calling. 

 

The amplitude of the modulation on the side tone increases with power
output, and is only noticeable at ~60 to 100 w. On 80m if I key down for
several seconds the modulation decreases. It sounds like a capacitor
charging. On 17m, the sound is much louder and does not decrease with time. 

 

The output signal sounds fine in another receiver.

 

I tested using a dummy load. I also turned off my power supply and computer
monitor, and used a battery to power the K2. Neither helped. 

 

I built the KPA100 this last spring, and have not noticed this before.
However, I have been running mostly QRP so I do not know when this problem
showed up. KPA100 is located in an EC2 with the KAT2. The connecting cable
is 32 inches long.

 

What should I look for to fix this?

 

Jeff Burns

AD9T

 

 

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