Re: K3 Audio routing question

Posted by Jim Brown-10 on Jul 05, 2010; 11:25pm
URL: http://elecraft.85.s1.nabble.com/K3-Audio-routing-question-tp5257517p5258067.html

On Mon, 05 Jul 2010 15:53:39 -0700, Lyle Johnson wrote:

>Perhaps the person who wishes to hear both receivers in diversity mode
>is partially or fully deaf in one ear, so he or she needs the ability to
>listen to both receivers in the same audio transducer.

SNIP

>I don't know if there will be side effects you'd rather not hear when
>you do this, nor how often you'll have to send this string if you remain
>in DIVRSTY mode.

The problem is that there ARE SERIOUS DESTRUCTIVE SIDE EFFECTS from
mixing the audio from the two receivers in diversity mode because the two
receivers are not in phase with each other!  That is, they are listening
to antennas that are PHYSICALLY SEPARATED, and thus are receiving the
signal at different times. AND they may also be hearing a direct and
reflected signal.

BTW -- an important definition. Inverting the signal by reversing wires
changes the POLARITY, not the phase. Phase is a continuously valued
function that can have any value between -infinity degrees and +infinity
degrees. The phase difference between two signals that differ in TIME is
proportional to their time offset.

When signals are precisely in phase AND in polarity with each other, they
can be summed together in the same channel and they will add. When
signals are precisely in phase and OUT of polarity, they will cancel. And
when signals are out of phase and IN polarity with each other, they can
add or cancel each other to varying degrees depending on the phase
relationship AT EACH FREQUENCY!  The result of such a summation produces
a frequency response that looks like the teeth of a comb -- that is,
peaks and dips of addition and cancellation. In the pro audio world, it
is called comb filtering, or phasing, or flanging, depending on how the
delays are generated and used.

Bottom line -- it is a REALLY BAD IDEA to sum the output of both
receivers into the same channel!  It is a REALLY GOOD IDEA to put one RX
in one ear and the other RX in the other, allowing the brain to combine
them.

73, Jim Brown K9YC


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