[Elecraft] K3 Harmonic Distortion
Joe Subich, W4TV
lists at microham-usa.com
Tue Sep 2 17:10:20 EDT 2008
The issue isn't the LINE OUT level, it is the voltage level. If
you leave the AGC on and AGC SLP > 11 the voltage with an S9 (-73
dBm) signal will not exceed 1V peak (.77 V RMS) and you will not
see distortion products through the transformer. If you set
turn of the AGC an/or set AGC SLP < 10, the transformers (or audio
amplifier) can be easily overdriven and the distortion products
will rise significantly - even to the point that harmonics through
the 10th or higher are down less than 10 dB.
With the line out the entire issue is keeping LINE OUT below 1V
Peak. There are other sues with the headphone and speaker output
and I'll address them elsewhere.
73,
... Joe, W4TV
> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Stewart Baker
> Sent: Tuesday, September 02, 2008 12:59 PM
> To: Jack Smith; Brendan Minish
> Cc: Elecraft
> Subject: Re: [Elecraft] K3 Harmonic Distortion
>
>
> I find virtually the same results here using 50uV RF from an
> Elecraft signal source, and measuring using Wave Spectra.
> An offset of 43 to 45dB, and below LIN OUT = 5 the harmonics drop
> rapidly.
>
> 73
> Stewart G3RXQ
> On Tue, 02 Sep 2008 12:28:02 -0400, Jack Smith wrote:
> > Brendan:
> >
> > You might wish to look at the measurements I made, with LIN OUT
> settings
> > from 2 to 100. There's an animated GIF that steps through the
> LIN OUT
> > settings so you can see the effect. The data was taken at 600
> Hz.
> > http://www.cliftonlaboratories.com/elecraft_k3_receive_audio.htm
> about
> > half way down the page
> >
> > Like you, I see a relatively constant 45 dB or so offset between
> the
> > fundamental and 3rd harmonic for LIN OUT values of 10 and over.
> >
> > However, setting the LIN OUT at 2 results in quite a bit better
> odd
> > order harmonic suppression, on the order of nearly 70 dB. By the
> time
> > LIN OUT is set to 5, however, the odd order suppression is
> reduced to a
> > bit more than 60 dB. At LIN OUT = 10, it's 45 dB or so where it
> stays at
> > all values of LIN OUT tested between 10 and 100.
> >
> > (For some reason, the 2nd harmonic pops up at certain settings,
> but not
> > others higher or lower, but that's not of immediate concern.)
> >
> > There's a related issue with the AGC. The audio output is
> proportional
> > to RF signal level, as the AGC has a slope to it. Hence, even
> though the
> > LIN OUT might be set to, say, 2, the actual audio level and
> hence the
> > distortion, will vary as the RF signal level changes. The degree
> of
> > audio level variation with RF input changes depends on how the
> user has
> > set the K3's AGC slope and intercept parameters.
> >
> > I'll make the measurements on a couple of TTC-108 parts when
> they
> > arrive as a matter of trying to understand where the harmonic
> distortion
> > arises. To duplicate the K3's audio chain, I'll drive the
> TTC-108s from
> > an op-amp so that it will be hit with a low Z source, instead of
> the
> > standard audio generators available to me, with 50 or 600 ohm
> output Z.
> >
> > Jack
> >
> >
> > Brendan Minish wrote:
> >> Jack
> >>
> >> I have seen postings on the main reflector recommending
> settings as low
> >> as 3 to avoid distortion products that are being attributed to
> >> transformer distortion. This did not really make sense to me,
> especially
> >> at such low levels where consumer sound cards tend to get
> non-linear and
> >> nasty.
> >>
> >> I took a look at the specifications for the TTC-108 audio
> transformer
> >> used in the line out of the K3
> >>
> >> Nominally it's specified as having an operating level of -45dBm
> to
> >> +7dBm
> >> THD is specified at 0.5% @0dBm 300Hz to 3.5 Khz @ 0dBm
> >> this would make the transformer related harmonics worst case at
> -46dB
> >> relative to the fundamental
> >>
> >> I did some measurements with an s9 CW signal zero beat at
> various pitch
> >> settings
> >> I used an old copy of SMAART pro that I have from my Sound
> engineering
> >> days. the sound card is a delta44
> >>
> >> Lin = 100 Pitch 300 pitch 550 pitch 800
> >> DR3 47.3dB 51.4dB 54dB
> >>
> >> Lin = 50 Pitch 300 Pitch 550 Pitch 800
> >> DR3 43.1dB 47.6dB 50.6dB
> >>
> >> Lin = 10 Pitch 300 Pitch 550 Pitch 800
> >> DR3 35dB 39.7dB 43.1dB
> >>
> >> Lin = 5 Pitch 300 Pitch 550 Pitch 800
> >> DR3 31.9dB 37.7dB 42.7dB
> >>
> >> Lin = 3 Pitch 300 Pitch 550 Pitch 800
> >> DR3 31dB 40.3db 47.6dB
> >>
> >> DR3 is the Dynamic range between the fundamental and the 3rd
> harmonic
> >> (the most dominant harmonic by a wide margin)
> >>
> >> I did a quick look at 5th and 7th orders too, again the best
> performance
> >> here was found with LIN = 100
> >>
> >> LIN = 100 is an output level of approximately 700mv for an S9
> CW sig on
> >> my K3
> >>
> >> The Harmonic distortion does not increase with higher line out
> levels,
> >> it actually improves. This does not appear to be a transformer
> >> saturation issue
> >>
> >> With lin = 100 users will see a ghost on the waterfall and may
> risk
> >> over-driving some consumer sound cards. lowering LIN may get
> rid of the
> >> visible ghost by reducing the 3rd Harmonic to below the
> waterfall
> >> threshold (& perhaps the sound card input noise floor ) but
> also reduces
> >> the overall usable dynamic range
> >>
> >>
> >> 73
> >> Brendan EI6IZ
> >>
> >>
> > _______________________________________________
> > Elecraft mailing list
> > Post to: Elecraft at 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 at 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
>
More information about the Elecraft
mailing list