Does it take two sound cards to use CWSkimmer and MMTTY (or whatever
you're using for RTTY)?
73 de Terry KK6T
On 7/26/2011 9:14 AM, Kok Chen wrote:
> On Jul 26, 2011, at 5:04 AM, Bill wrote:
>
>> For each rtty signal, there 'appears' to be two traces. Separated slightly.
>> I'm assuming Mark and space.
> Yep. That is the Mark-Space shift.
>
> For most people, the separation is 170 Hz. It could be 200 Hz for many who
> still insist on using an AFSK TNC, and the shift can pretty much be anything
> for an off-calibrated older generation Direct FSK rig like the Omni V or Omni
> VI (I have seen an Omni V put out 80 Hz shift on FSK :-).
>
>> The upper (higher freq) is always longer.
> It depends by what you mean by "upper." It all depends on what the software
> author did, and also whether you are using an USB or LSB receiver. It could
> as well be left and right, or some 3D plot where frequency is in the "depth"
> dimension of the plot.
>
> By convention, Mark is the one that is the higher of the two FSK frequencies
> on the RF spectrum.
>
> The Mark is the "resting" state of FSK. For FSK transmitters, Mark is the
> "unkeyed" state.
>
> Since the Stop bit, being the bit that places the FSK signal into "rest"
> state is a Mark, stations that transmit with 1.5 or 2 stop bits will transmit
> a tad more often in Mark than in Space, if all Baudot characters are random .
> You can often find a "reversed" station by just watching signals in the
> waterfall.
>
> See Figure 16.1 in Chapter 16 of the 2010 and 2011 ARRL Handbook. I have
> found that figure to be so absolutely invaluable, I had taken it lock stock
> and barrel from the older Handbooks when I rewrote the RTTY section of
> chapter 16 of the handbook. The same figure appears as a Fig 9.10 in chapter
> 9 of the 2009 Handbook.
>
>> The upper trace starts first and ends last.
> Many modems often begin with an undiddled Mark tone (could last 100ms or so)
> to allow a receiver to tune the signal (Mark tone is by convention, also
> where you spot an RTTY signal). Another reason is to let the transmitter
> settle after issuing a PTT, before keying it.
>
> Since an RTTY transmission ends with a stop bit, you will also naturally see
> the transmission end with a Mark. The Mark signal can is also slightly
> extended at the end -- i.e., the diddle is turned off a little before the PTT
> is unkeyed.
>
> In your case, "upper" on CW Skimmer is most likely the higher frequency in
> the RF spectrum :-).
>
> 73
> Chen, W7AY
>
>
>
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