[Elecraft] [K2] NB2 heard a "spark gap" like signal 8k lower than the RX frequency

[Don Wilhelm]

Wayne,

The KNB2 can introduce IMD in the receive path, especially when using 
the low threshold and the wider blanking pulse (NB2).  I believe that is 
what you were hearing.
If you had the preamp on, the effect would be increased.  Normally there 
is no need to turn the preamp on for 40 meters unless you are using a 
low efficiency antenna.

73,
Don W3FPR

On 8/9/2011 11:01 AM, Wayne Conrad wrote:
> On my K2, in CW mode, and when I crank up the noise blanker by selecting
> NB2 (and the default noise-blanker threshold, "Hi"), I sometimes hear a
> strong signal some distance away from my receive frequency.  The signal
> I hear, when this happens, is not a tone.  It's more like a spark-gap
> buzz.  Today, when the receive frequency was 7.034, I heard a CQ on
> 7.026.  The signal on 7.026 was quite strong but otherwise sounded
> normal.  FL1 (1.50) was selected.  AF2 is installed but was off.  If I
> turned the noise blanker off, or select NB1, the interference goes
> away.  It doesn't happen often, and is seldom strong enough to be a
> problem, but it does make me wonder if something is out of whack, or if
> I'm operating the radio improperly.  Is it just the nature of the
> noise-blanker?
>
> 73, Wayne Conrad KF7QGA
>