Dual RTTY Interface

Please note that the Dual RTTY Interface is deprecated. It is kept around but no new functions will be added directly to it. As new demodulators are developed, the Dual RTTY Interface may not be able to use them. Please use the Wideband RTTY Interface instead.


Figure 9 shows the Dual RTTY Interface. Please familiarize yourself with the Basic RTTY Interface of cocoaModem before reading the rest of this section.

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Figure 9 - Dual RTTY Interface


Dual RTTY Receivers

Notice that there are two separate receiver sections below a spectrum display. Each of these receivers is a completely independent copy of the receiver in the basic RTTY Interface of cocoaModem and each one comes with its own configuration section in the Config Panel.

Since these are independent receivers, you will need to configure both of the receivers before using the Dual RTTY Interface. The Config Panel is opened by selecting Config under the Window menu in the Menu bar. The two receiver configurations are selected using the Main Receiver and Sub Receiver tabs in the Config Panel. Each one is identical to the single Receiver configuration that is already described in the basic RTTY discussion.

There is only a single transmitter section.

Each receiver comes with its own crossed ellipse tuning indicator on the left, and its own abbreviated control section on the right.

The abbreviated control section has a VU meter and an input attenuator. If you are using two different A/D converters for each of the two receivers, you will find that the input attenuators behave independent of one another. If the Main and Sub are connected to two separate stereo channels from the same A/D converter, you may find that the attenuators tracks one another, depending on whether the A/D converter you are using allows independent left/right attenuation. (There is only a single master control with the third generation Griffin iMic device, for example. If you are using the stereo channels from that iMic to feed the two Dual RTTY receivers, you will not be able to independently adjust the input attenuators.)

The button that is next to the Aux button controls the receive polarity (Normal or reverse) for the receiver. As seen in Figure 10, the transmit polarity selector has been moved to the Aux Panel (Figure 10 below).

There is an indicator that turns yellow if you have chosen that particular receiver’s tone pair to use as the transmit tone pair (see next section).

The abbreviated control sections of the Dual RTTY interface do not have space to hold the other RTTY settings. Less often used controls are kept in their own separate window that can be opened by clicking the Aux button of each receiver. Please note that these are also independent, so you can select one tone pair for one receiver and a different tone pair for the other receiver. You can leave these open if you have enough space on your display.

Figure 10 shows a receiver Aux control panel of the Dual RTTY interface.

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Figure 10 - Dual RTTY Aux Control Panel


The Print Control Characters is an option to print received control characters such as LTRS, FIGS, carriage return and linefeed characters. If selected, LTRS characters are printed as ltrs in between angle brackets, FIGS as figs in between angle brackets, carriage returns as cr in between angle brackets and linefeeds as lf in between angle brackets.

Dual RTTY Transmitter

Like the basic RTTY interface, the transmitter section of the Dual RTTY interface has a text view that your keyboard entries are made through. The transmit and flush buttons are on the right of the text view, together with a indicator that turns red when you are transmitting.

To the left of the text view is a pair of buttons that controls which tone pair we transmit with. Earlier, we have stated that the Main and Sub receivers can have its own tone pair. The Tx (Main, Sub) buttons allow you to choose to use the main receiver’s tone pair or the Sub receiver’s tone pair, in case they have different tone pair offsets.

Depending on whether you have chosen to transmit using the Main or the Sub receiver's tone pair, the two receive sections (including the crossed ellipse indicator) will swap places so that the receiver section that is closer to the bottom (i.e., the one that is closer to the transmit interface) will be the interface whose tones you will be using to transmit with.


Spectrum Display

The top section of the Dual RTTY interface has a spectrum analyzer that you can select to monitor either the Main or the Sub receiver as the signal source. The selection is made using the bottom most popup menu to the right of the spectrum. You can also choose to turn the spectrum display completely off (it will save some processor cycles for slower machines).

Above the receiver selection popup menu is another popup menu for choosing the dynamic range of the spectrum. There are three settings, 40 dB, 60 dB and 80 dB. In the 60 dB position, the spectrum displays a total range of approximately 60 dB -- each of the green horizontal grid lines represents a 30 dB change. In a noisy environment, the 40 dB setting is probably most appropriate. With a very high dynamic range environment (and if your transceiver and the A/D converter are capable of better than 60 dB of dynamic range), the 80 dB position is useful to dig for the very weak signals.

The top most popup menu controls the integration time of the spectrum. For tuning around, it is best to use the shortest (0.2 second) integration time. If you are tuned and listening to a single station, the longest integration time (1.5 seconds) provides the most precise tuning aid and it is also useful for assessing problems with the received signal such as an overdriven AFSK signal or a FSK transmitter that has excessive keyclicks.

The spectrum display can be also be switched into a waterfall display. Notice that the integration time popup menu has an item called WF. When WF is selected, the spectrum display will change into a waterfall spectrogram:

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Tuning the transceiver using a waterfall can be very slow, but it can also provide very precise tuning for signals that are so weak that neither the crossed ellipse nor the spectrum plot are practical as tuning indicators.


Cautionary Note

There is only one transmitted signal from the Dual RTTY interface. cocoaModem uses the left stereo channel to output its AFSK signal. If you are using one of the Dual RTTY receivers to monitor a DX station while using the second receiver to scan for the QSX, make sure you have set the proper split on the transceiver when the transceiver is keyed to transmit. For example, if the physical Main receiver is watching the DX and you are searching for his QSX using the Sub receiver of the transceiver, make sure that you set the transceiver so that the transmitted frequency is set by the Sub receiver’s VFO of the transceiver. cocoaModem has no control over which transceiver VFO it is transmitting through, your transceiver setting determines that.


Example of Split RTTY Operation

My stereo sound device is connected to my FT-1000MP's rear panel stereo jack through a stereo cable. The FT-1000MP passes its main receiver output to the left stereo channel and its sub receiver to the right stereo channel in the rear panel jack. I configure the left channel of the sound device as my Dual RTTY receiver's Main input device, and I configure the right channel of the same audio device as my Dual RTTY receiver's Sub input device.

I then set the FT-1000MP into split operation to activate both the main and sub receivers with the main receiver’s IF bandwidth set to 250 Hz and the sub receiver’s IF bandwidth set to 2.4 kHz.

Next, I tell the FT-1000MP to choose the sub VFO to transmit through (i.e., split). I then tell cocoaModem to transmit using the Sub receiver's tone pair.

I tune for the DX using the main VFO knob, initially setting the Dual RTTY spectrum to watch the Main receiver to properly tune the DX in. I then set the Dual RTTY spectrum to watch the Sub receiver and use the FT-1000MP’s sub receiver knob to tune for the the QSX, or to find a quiet spot in the spectrum to call.

When I transmit, it will be at where the transceiver’s sub VFO is set to, thus presumably the QSX of the DX station.


Using the Dual RTTY Interface for regular RTTY Operation

The Dual RTTY interface is useful even if you are not using two separate receivers. Used this way, the Dual RTTY interface has an advantage over the basic RTTY interface in that you will have an additional spectrum analyzer or waterfall display as an additional tuning aid. This is especially useful if you are using a wide IF filter.

I do not recommend using wide IF filters for copying weak signals unless there is no loud signal in the passband and you are using a transceiver with a very high dynamic range front end and you are using an A/D converter that has a better dynamic range than your transceiver -- otherwise, use narrow IF bandwidth whenever possible.


To use the Dual RTTY interface as a single receiver, simply disable the Dual RTTY’s Sub receiver in its configuration panel (set the state to inactive) , and select the Main receiver as the source for the spectrum display. Then, use the Main Receiver as you have been using the regular RTTY Mode.





Back to the Main RTTY page.

Wideband RTTY Interface page.