Good grief! --- On Mon, 1/3/11, Guy Olinger K2AV <[email protected]> wrote:
> From: Guy Olinger K2AV <[email protected]> > Subject: Re: [Elecraft] K3 CW and RTTY tones > To: "Wes Stewart" <[email protected]> > Cc: "Elecraft reflector" <[email protected]>, [email protected] > 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 <[email protected]> > 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, [email protected] > <[email protected]> > 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 > > > > > > > > > > > ______________________________________________________________ > > Elecraft mailing list > > Home: http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/mmfaq.htm > > Post: mailto:[email protected] > > > > This list hosted by: http://www.qsl.net > > Please help support this email list: http://www.qsl.net/donate.html > > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
