[Elecraft] K3 on-channel strong signal overload?

[Jim Brown]

On Sun, 3 May 2009 21:39:55 -0700 (PDT), orbarrett wrote:

>I was joined while ragchewing with some friends on 5371.5
>by two other friends locally, one operating HF mobile from the same driveway
>and another operating from a base rig in the shack (using a backyard dipole
>antenna).  When either of these two friends transmitted on the same channel
>(at 100W), I observed severe signal breakup in the K3 receive audio.
Why are you surprised by this?  This is entirely normal 

>To investigate further, I switched the portable antenna from the K3 to my
>friend's FT-817 on the same operating table, and no audio breakup was
>observed under the same conditions.  Returning the antenna to the K3, I then
>got rid of most of the signal breakup by turning on the input attenuator and
>turning down the RF gain to near minimum.

DUH!  Why are you surprised by this? You had the K3 set for maximum 
sensitivity and then hit it with a 100 watt transmitter. OF COURSE it's going 
to overload! You probably had the preamp on too, which is entirely un-
necessary on 60M.  The 817 is probably a much less sensitive radio, and may 
have a more brute force AGC. The K3 will outperform it by 40-50 dB in 
rejecting signals outside its passband. 

The K3 is doing exactly what you SET its controls to do -- pull very weak 
signals out of the mud. NO radio has infinite dynamic range. If you set it to 
perform well on weak signals (preamp on, attenuator off, RF gain all the way 
up), it's going to be badly overloaded by 100 watts ON FREQUENCY from an 
antenna 30 feet away. 

These are fundamental concepts of radio. It's too bad that they are seldom 
taught today. Most of us old farts learned them as Novices when we put our 
first rigs on the air. In those days, there were no transceivers. You had a 
transmitter and you had a receiver, and when you transmitted your receiver 
overloaded. 

73,

Jim Brown K9YC