[Elecraft] [K3] K3 RF speech processor > aliasing ?

[Lyle Johnson]

Hello Paul!

> Yesterday I sinned and whistled shortly into my microphone to see my watt
> meter reading. I apologize for this bad bad operator habit...
> 
> To my surprise I heard a second whistle monitoring the signal. When I
> whistled "up" the other whistle was going down in frequency, when I whistled
> "down" the byproduct was going up...
> 
> Fortunately there is no aliasing at all with the RF processor turned off.

I ran some tests here this morning regarding this.

The MON function, which allows you to hear your transmitted audio, is 
the source of the aliasing artifact you are hearing.  I deliberately 
removed most filtering from the demodulator to minimize delay.  The 
downside is lack of alias suppression.  In my radio, I only hear this if 
I whistle and have CMP set to a very high value -- 20 or more.  At 
normal CMP levels (15 or less)I don't hear it, and never hear it with 
speech.

I also confirmed that this aliasing product does not go over the air; it 
is local to the MON audio.

I'll look into adding some filtering to reduce this effect and see if 
the resulting additional delay is acceptable.

Meanwhile, your transmitted signal is clean!

73,

Lyle KK7P