Re: K3 - FSK question

[Richard Ferch]

To key the K3 in FSK D from software like MMTTY, you need a keying
circuit (typically a transistor switch) between the TxD signal line on a
serial port and pin 1 on the K3's ACC connector. There are several
different ways to do TX/RX switching (PTT), but one of them is to use a
similar keying circuit between the RTS line on the same serial port and
pin 4 on the ACC connector. Both of these circuits are referenced to
signal ground on the serial port and pin 5 on the ACC connector.

To transmit RTTY in AFSK A, the connection to pin 1 of the ACC connector
is not used. Instead you need an audio cable between the radio's LINE IN
jack and your computer sound card's LINE OUT jack. You also need some
method of TX/RX switching (PTT), just as in FSK D.

To receive RTTY, regardless of whether you are using FSK D or AFSK A you
use an audio cable between the radio's LINE OUT jack and your computer
sound card's LINE IN jack.

Now for your question about the bandpass in various digital modes.
First, PSK D mode is not really a software mode. It is for operating PSK
when you don't have a computer available. You cannot transmit from
Digipan in PSK D. If you have a computer and you are using software like
Digipan, you use DATA A mode for PSK, not PSK D.

DATA A mode is very similar to USB. The dial reads the BFO or suppressed
carrier frequency, but the actual signals being copied are higher in
frequency. If you use the default filter settings, you will be able to
copy signals between 1300 Hz and 1700 Hz above the dial frequency, and
you should see noise between 1300 Hz and 1700 Hz on the waterfall. If
you tune the dial to 9998.500 kHz, you should be able to hear the WWV
carrier at an audio pitch of 1500 Hz, and there should be a steady trace
in the waterfall at 1500 Hz.

PSK D is different. It is still a USB mode, but the filter centre audio
frequency is 1010 Hz instead of 1500 Hz as in DATA A, so what you see on
the waterfall with default filter settings will be between 810 Hz and
1210 Hz. In PSK D the radio's dial readout is 1010 Hz above the BFO
frequency. If you tune the dial to 10000.000 kHz, you will hear the WWV
carrier at an audio pitch of 1010 Hz, and see a steady trace at 1010 Hz
in the waterfall.

The two RTTY modes, AFSK A and FSK D, are both lower sideband modes. You
can choose among four different Pitch settings, which are labelled by
the RTTY Mark frequency: 915 Hz, 1275 Hz, 1445 Hz or 2125 Hz. Whatever
Pitch setting you have chosen determines the filter centre frequency -
the centre frequency is 85 Hz higher, i.e. 1000 Hz, 1360 Hz, 1530 Hz or
2210 Hz. The dial always reads the actual Mark frequency, not the BFO
frequency. With a Pitch setting of 2125 Hz, when you tune the dial to
10000.00 kHz you will hear the WWV carrier at an audio pitch of 2125 Hz
and see a steady trace at 2125 Hz on the waterfall; similarly for the
other Pitch settings.

73,
Rich VE3KI


NR4C wrote:

> Hi, I'm new to the K3, (Aug 2010 sn 4536). I have really enjoyed it a
> lot. I have dabbled into digital modes a bit and am wondering, how do
> i connect and send/rec FSK?
>
> I have determined that I need a cable from PC serial port to the
> "accessory" connector and connect to gnd, PTT, and FSK. Do I still use
> the soundcard to rec or does the radio have a line out that would
> connect to the serial port RX pin?
>
> Another question. Last night I was messing with PSK, and noticed that
> in PSKD mode, the waterfall on Digipan showed a band of activity at
> one area of the display, while in DATA A mode, it had shifted a lot to
> the left, maybe 1khz. What gives?

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