[Elecraft] K3 CW and RTTY tones

Mon Jan 3 17:20:21 EST 2011

Good grief!

--- On Mon, 1/3/11, Guy Olinger K2AV <olinger at bellsouth.net> wrote:

> From: Guy Olinger K2AV <olinger at bellsouth.net>
> Subject: Re: [Elecraft] K3 CW and RTTY tones
> To: "Wes Stewart" <n7ws at yahoo.com>
> Cc: "Elecraft reflector" <elecraft at mailman.qth.net>, goldtr8 at charter.net
> Date: Monday, January 3, 2011, 2:02 PM
> > Now this is a long-winded
> explanation of more-or-less how the K3 handles tone
> offsets.
> 
> Not exactly.  Have to lean pretty far on the less...
> 
> What was wrong with the prior is that "audio" is not used
> in the
> ordinary sense, the last or "lowest" analog stage in a K3
> is a 15 kHz
> IF for both transmit and receive.  The only audio is
> on the headphone,
> microphone, speaker, line in/out leads to/from amplifiers,
> which are
> all independent digtal to/from audio points for individual
> lines.
> 
> In particular, there is no balanced modulator in the
> K3.  The 15 kHz
> IF SINGLE sideband signal, without a carrier, is directly
> generated
> from a number stream in a digital to analog
> converter.  The number
> stream was generated in firmware related to any audio input
> in use at
> the time.  The audio input was converted to digital
> from mic/line in
> inputs, and ALL processing done in firmware.
> 
> Data input from RS232, or DC states on input leads are also
> used to
> generate number streams.  In particular, the DC wave
> shape of keyed CW
> does not generate the transmitted wave. It interprets the
> DC CW wave
> state to determine the events Key Down and Key Up.  A
> firmware routine
> uses these to create a digital number stream representation
> of a
> pristine waveshape from formula and memory.  This
> number stream comes
> out clean as a whistle into the 15 kHz transmit IF and
> depends on the
> linearity of the analog TX stream from that point forward
> as does
> every other transmitted K3 signal.
> 
> In the sense that this scheme, from number stream at TX DAC
> to 15 kHz
> TX IF forward is used for ALL modulation types, your notion
> is
> correct.  To the extent that you couch it in
> non-existent (in the K3)
> analog circuit methods, the K3 ain't your daddy's analog
> radio and
> it's time for all around here to get all brains on DIGITAL
> standard
> time, and out of the analog ages.
> 
> There is no balanced modulator in a K3.  What is
> actually done in the
> digital number stream by the firmware is quite more simple
> than an
> analog phasing or filter SSB generator.  Once firmware
> writers are
> freed from the tyranny of emulating analog circuits in
> numeric
> methods, modern digital methods are surprisingly more
> simple in the
> numbers for a given end than in analog circuitry. Many
> digital methods
> have no known analog equivalents.  We only keep using
> analog in our
> head because that's all we have as a reference, and no
> other words to
> use.   Therefore, to the question posted
> earlier:
> 
> > When operating CW or Rtty there is a split tone that
> you
> > have to know
> > about.  I have been reading on the HRD forums to
> > figure this out to get
> > the software set up correctly.  I know it has
> > something to do with
> > carrier supression, but it just does not make sense to
> me.
> 
> The answer is that the K3 does not use a balanced modulator
> to create
> it's signals, therefore there is no carrier suppression to
> worry
> about. The prior poster is correct if you ignore his
> analog
> terminology and concentrate on what he is saying about
> frequency
> offsets.   The K3 can be thought of as
> having a virtual carrier
> reference frequency that shows up real only when you use
> AM.  While
> most analog circuits can't do this, just consider that the
> virtual
> carrier frequency is what would happen if your audio signal
> had a DC
> voltage added to it, and DC was always converted by the
> digital radio
> to the carrier frequency that a misaligned balanced
> modulator would
> produce in an analog radio.
> 
> 73, Guy.
> 
> On Mon, Jan 3, 2011 at 3:06 PM, Wes Stewart <n7ws at yahoo.com>
> wrote:
> > Don,
> >
> > Stripped of a lot of stuff, the essence of it is
> this:
> >
> > When we transmit using a SSB transmitter (and except
> for true FSK, all modern radios use SSB for all modes,
> including CW and digital) all that is really happening is
> the up-conversion of an audio frequency to a radio
> frequency.  When we receive, we do the opposite, convert a
> radio frequency to an audio frequency.
> >
> > Although there are (usually) intermediate steps, the
> process can actually be done directly and with some
> switching, the same hardware can be used to do both.
> >
> > For example if there is a CW signal on 7100 KHz and we
> would like to hear it in our headphones with an audio tone
> of 1000 Hz, we can use a frequency mixer in which we combine
> the 7100 KHz signal with another one which we generate on
> 7101 KHz.  When we subtract the first from the second, we
> get the tone that we desire.
> >
> > Now if we put enough "smarts" in the radio, we can say
> to the radio, "When I listen to CW, the "pitch" of the tone
> that I prefer is 1000 Hz."  The radio then knows that when
> you (or it) tune the signal so the pitch is 1000 Hz, the
> actual frequency of the incoming signal is offset by that
> amount from the locally generated conversion frequency.
> >
> > In the case of a synthesized radio like the K3, it
> already knows the frequency of the conversion oscillator
> (the "LO") so it just does the math and in this case,
> subtracts 1000 Hz from that number and presents it on the
> display as 7.100.000
> >
> > To transmit, we do the reverse: subtract 1000 from
> 7101 KHz and get 7100 KHz. But here it's not so simple, the
> mixer also adds the two signals and we get 7102 KHz too. 
> Plus, the 7101 KHz LO also appears in the mixer output.  So
> we have a mess, 7100, 7101 and 7102 KHz.  The 7101 LO is
> also called the "carrier" since it is the vehicle that
> "carries" the audio signal to the radio frequency
> spectrum.  The other two signals, 7100 and 7102 are called
> the "sidebands" since they reside equally spaced around the
> carrier.  The FCC (and our soon to be enemy ham friends)
> would really frown on us transmitting this signal in the
> 40-meter CW band.  So we have to do some more work.
> >
> > When was hams say, "SSB", what we really are
> indicating is, "Suppressed-Carrier-Single-Sideband."  So
> with our messy signal we can use a special kind of mixer
> called a balanced-modulator that does the suppression of the
> carrier, that's the 7101 KHz signal in this case. Now we are
> left with the two sidebands, when we want only one.
> >
> > We can deal with this several ways, the most common
> are to either use phasing techniques to cancel one sideband
> while enhancing the other, or to use a narrow filter to
> remove the unwanted sideband.
> >
> > The phasing technique can be performed over a band of
> frequencies, however, the narrow filter we would need has to
> be done using crystals, hence we would be stuck on 7100 KHz.
>  So another frequency conversion is usually used with
> filter radios so that a single filter at an intermediate
> frequency can be utilized.  This frequency conversion
> operates just as before, with the same math used and the
> same, or more, problems associated with unwanted
> frequencies.
> >
> > Now this is a long-winded explanation of more-or-less
> how the K3 handles tone offsets.  I have tried and rejected
> HRD so I can't begin to explain how it accounts for this.
>  But maybe this fundamental explanation will help you sort
> it out or at least formulate more specific questions.
> >
> > Good luck,
> >
> > Wes  N7WS
> >
> > --- On Sun, 1/2/11, goldtr8 at charter.net
> <goldtr8 at charter.net>
> wrote:
> >
> >> Dear All,
> >>
> >> When operating CW or Rtty there is a split tone
> that you
> >> have to know
> >> about.  I have been reading on the HRD forums to
> >> figure this out to get
> >> the software set up correctly.  I know it has
> >> something to do with
> >> carrier supression, but it just does not make
> sense to me.
> >>
> >> So the more I read there the more confused I
> become.
> >> I have also tried
> >> google searches but I still have not figured it
> out yet.
> >>
> >> So if someone can direct me to some reading
> sources to help
> >> me
> >> understand this I would really appreciate it.
> >>
> >> Thanks
> >> Don
> >> KD8NNU
> >
> >
> >
> >
> >
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