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 > > > _______________________________________________ > Elecraft mailing list > Post to: Elecraft@mailman.qth.net > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
