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K-3: RTTY Dual Passband Question

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RLVZ

K-3: RTTY Dual Passband Question

Hi Rob,

Thank You for your replies to my K-3 RTTY question. I am relatively new
to both RTTY and to the K-3.... so I have alot to learn!

You mentioned: "Your problem stems from your settings on whatever decoder
you were using." I agree that settings need to be correct but I believe I
had an issue with the K-3: this being that my SHIFT control was NOT
centered. Would you agree that if the SHIFT control is not centered then I would
be off frequency when operating RTTY? In changing the SHIFT setting I
notice the received frequency does change.

What threw me for a loop was that the first time I switched the K-3 to
RTTY Mode the SHIFT control automatically jumped from center to the left side
of the display. I assumed the SHIFT jumping to the Left was a K-3 default
and left it there. With this in mind, does the SHIFT control always belong
in the center position when operating RTTY? If so, then I wish that would
be added to the K-3 Manual under RTTY operation section.

73,
Dick- K9OM

In a message dated 3/3/2010 2:49:57 PM Eastern Standard Time,
[hidden email] writes:

Dick,
Your problem has nothing to do with Dual Passband. Dual Passband affects
only reception, and just provides two sharp sided filters on the mark and
space frequencies essentially reducing stuff in between.

Your problem stems from your settings on whatever decoder you were using.
If it was MMTTY, for example, your shift should never change unless you
have AFC or ATC selected. These will try to adapt your signal to band
conditions and may change your mark frequency or shift.

You should make sure that you have no options like AFC or ATC selected.

The other common problem people have is they forget to center their RIT or
XIT control (if they are "on") so they are now listening or transmitting
offset from where they are transmitting or listening. If you used RIT to
tune someone in who was 20 or 30 Hz higher than you, and did not zero it
out, the next time you tune someone in, you'll be 20 or 30 Hz lower than
they are. For some filters, that's enough to push you out of the passband.

Using Dual Passband filtering cuts down QRM from multiple stations calling
you, assuming some are off frequency. It also makes you have to tune more
sharply when searching and pouncing. If you use the regular 400 Hz filter
instead of DP, you'll find it easier to tune, but you'll also have more
QRM and possibly need to have more repeats. Life is full of tradeoffs.

Rob K6RB

> Question: If you don't normally use Dual Passband while in RTTY Mode,
> then
> is it true that you need to be careful where the "SHIFT" control is set?
> I am new to RTTY and in last weekends NA-RTTY Test I was NOT using Dual
> Passband, and I was often off-frequency when changing bands as my SHIFT
> setting was often different for each band. I believe if I had been
using
> "Dual
> Passband" that I would have been on frequency as that disables the SHIFT
> control. Question: if your not using DUAL PASSBAND then what is the
> proper
> setting for SHIFT? Perhaps centering the SHIFT in the middle of the
> K-3's on
> screen display?
> Or is it true that if NET is On in MMTTY then it will put the
transmitter

> on the receiver frequency even if SHIFT is not centered?
>
> Thanks for your thoughts!
>
> 73,
> Dick- K9OM
>
>
> Normally I dont need the DPB. But when in RUN-CQ mode with QRM in the
> last
> NAQP I was very happy to have it.
>
> 73
> Claude Du Berger VE2FK
> _ve2fk@arrl.net_ (mailto:[hidden email])
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n7ws

Re: K-3: RTTY Dual Passband Question

I've only been on RTTY for a few months, but in that time I've settled on a mark frequency of 915 Hz. This is easier to listen to than higher frequencies and I can tune signals by ear now well enough to have MMTTY print. There is a downside to this on transmit; with the lower frequency, overdriving the audio input is more likely to generate in-band garbage that will get transmitted.

(From the sound of the bands there is a lot of this going on, either that or my K3 fails to have the ability of everyone else's to operate 10 Hz away from a megawatt station without knowing he's there.)

If you chose this frequency then you need to set your K3 for 915 Hz mark (using the pitch control) and the default 170 Hz shift. If you then normalize the DSP shift, (Push the knob in until it reads "<-NOR->" it will center itself on 1 KHz which is the center frequency between mark and space. You can then control the width to cut out QRM.

I have set M4 to recall my RTTY setup on each band. Unfortunately, the K3 doesn't memorize shift and width as part of this operation.

You could also fuss around setting up NORM1 and NORM2 but I continually get these confused with just I/II so I gave up on that. Besides it's more knob twisting.

As to the dual passband, I don't bother. MMTTY (the usual engine) already builds a dual filter around the signal. You can see this by going to the Demodulator tab in MMTTY setup and then viewing the Discriminator filter. When you cascade filters there is always some bandwidth shrinkage and this can quickly become too much of a good thing. I suppose if you were using the built-in RTTY demodulator then it would be useful.

See you on the keys.

Wes N7WS

--- On Wed, 3/3/10, [hidden email] <[hidden email]> wrote:

> Question: If you don't normally use
> Dual Passband while in RTTY Mode, then
> is it true that you need to be careful where the
> "SHIFT" control is set?
> I am new to RTTY and in last weekends NA-RTTY Test I
> was NOT using Dual
> Passband, and I was often off-frequency when changing
> bands as my SHIFT
> setting was often different for each band. I
> believe if I had been using "Dual
> Passband" that I would have been on frequency as that
> disables the SHIFT
> control. Question: if your not using DUAL
> PASSBAND then what is the proper
> setting for SHIFT? Perhaps centering the
> SHIFT in the middle of the K-3's on
> screen display?
> Or is it true that if NET is On in MMTTY then it will put
> the transmitter
> on the receiver frequency even if SHIFT is not centered?
>
> Thanks for your thoughts!
>
> 73,
> Dick- K9OM