Yes indeed it would be a sorry situation if an operator can't tell the
difference between a desired signal and an audio harmonic, fortunately
my thread is not about that.
Anyway, the "noise/distortion" is still there coming out of the
headphone socket.
Berni
Joe Subich, W4TV wrote:
Jim,
Insignificant depends on the decoder, what you are decoding (PSK
or RTTY), band conditions, and the operator. If a PSK operator is
using the IF with a broadband setting and tries to work a signal
that's really a harmonic, it won't work -- he'll be transmitting
on a frequency displaced from the signal he thinks he's working
(displaced by 2X the audio frequency of the actual signal if it's
a third harmonic, 1X if it't the second harmonic). If it's a
crowded RTTY contest, there can be lots of big signals creating
that IM. Or the operator could be using a narrow roofing filter
and those other signals are not there or heavily suppressed, so
can't cause IM.
It would be a sorry situation if an operator can't tell the
difference between a desired signal and an audio harmonic down
50 dB. K3_Line_out.jpg shows the line out spectrum of my K3
at 1 KHz, Data_A, 2.8 KHz 1st IF filter and 4 KHz filter. The
third harmonic is -62 dB and the fifth harmonic is - 80 dB.
See: www.microHAM-USA.com/Downloads/K3_Line_Out.jpg.
A typical waterfall does not show the spurious signals at the
soundcard input (noise on the cables) which is well below the
"band noise" - typically around -60 dBu.
73,
... Joe, W4TV
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Jim Brown
Sent: Monday, September 01, 2008 1:33 PM
To: elecraft@mailman.qth.net
Subject: RE: [Elecraft] K3 Harmonic Distortion
On Mon, 1 Sep 2008 12:38:31 -0400, Joe Subich, W4TV wrote:
Jim is entirely correct although we will disagree a bit about
the need to keep the line out as low as he suggests. My own
measurements say the harmonic distortion is insignificant as
long as the Line Out levels stay below .5V RMS.
Insignificant depends on the decoder, what you are decoding (PSK
or RTTY), band conditions, and the operator. If a PSK operator is
using the IF with a broadband setting and tries to work a signal
that's really a harmonic, it won't work -- he'll be transmitting
on a frequency displaced from the signal he thinks he's working
(displaced by 2X the audio frequency of the actual signal if it's
a third harmonic, 1X if it't the second harmonic). If it's a
crowded RTTY contest, there can be lots of big signals creating
that IM. Or the operator could be using a narrow roofing filter
and those other signals are not there or heavily suppressed, so
can't cause IM.
The headphone outputs are exceptionally clean as long as the
audio amplifier level is kept below 2V peak (1.4V RMS) and
the output impedance is not too low. In fact, noise in the
audio amplifier (headphones) is 70 dB below the desired (CW
at 500 Hz) signal +/- 250 Hz and 80 dB below the desired
signal above that. All harmonics are down more than 60 dB
as long as the headphone level is not at levels that could
damage hearing (> 1.4V RMS).
YES! My measurements of the headphone output, taken at about 1
volt RMS, show harmonic distortion at about 0.02% and IM at less
than 0.1%. That is VERY VERY good! 1VRMS is LOUD!
The headphone output in the K3 is cleaner than any amateur
receiver I have seen and certainly better than the current
crop from Ikensu or Yaecomwood.
Yes.
73,
Jim
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