Introduction

This article aims to explain how to properly define the signal source to be transmitted, especially when using the USB port - and its proper signaling via the PTT/transmit events.

The standard FT-991A operator definitely will not have any of these concerns that I'm describing here. However, if you are going deviate from the vanilla operation and give a try with USB port or even the analog audio port in RTTY/Data port, keep reading.

RX

During reception, the the audio is outputted simultaneously at:

1. Speaker
2. USB port
3. DATA/RTTY port.

But this is not the case when transmitting - Keep reading.

Feeding the FT-991A

Besides the obvious front Microphone port, the 991A can also be fed via the USB interface card and also, via the RTTY/Data port.

But, how to instruct the radio to use the right sound source for transmission?

TX Possibilities

The 991A provides 5 different ways to engage the radio in transmit mode. Namely:

CAT

This is done via the TX1; CAT command, via either the USB Enhanced COM port, or the CAT/GPS port, if configured to do so. The TX0; commands a stop transmission.

PTT

This is done on the front mic port, when you press the push-to-talk button. Some other external microphones, like Heil's, provides a special cable with PTT provisions to trigger the transmit mode. The PTT transmit mode engages when the front jack pin 6 is shorted to ground.

RTTY/Data

The RTTY/Data port also provides a transmit pin/function. The radio enters the transmit mode when the PTT Pin (pin 3) is shorted to ground. This port provides a good way to create a footswitch if you are working with audio fed to the radio via the USB port or RTTY/Data port.

DTR or RTS

These are accessible via the USB Standard COM port. Especially useful to command a PTT event without competing with the Enhanced USB port.

MOX

This is done in the LCD screen. When you hit the MOX function to On, the radio enters the transmit mode.

Which TX event, which port?

Now that you are familiarized with the transmission events, how do I select the right Transmission mode for each port?

Fortunately, the 991A is smart enough - so it actually makes a good guess on where to select what to tie to the transmission bus. You have learned that the FT-991A provides 5 different ways to enter the transmit mode. The below table will provide a cue:

Transmit event from:	Radio will transmit signal from:
Mic PTT / Front Mic port	Front Mic port
CAT	The port (front or rear) defined for your current mode (set in configurations 045, 070, 074 and 106)
MOX	The port (front or rear) defined for your current mode (set in configurations 045, 070, 074 and 106)
RTTY/Data PTT	Rear. Either USB port or RTTY/Data port (set in configurations 048, 072 and 109)
DTR or RTS	Rear. Either USB port or RTTY/Data port (set in configurations 048, 072 and 109)

Notice that the default FT-991A settings for Rear input is set to the RTTY/Data port. If you want to use the USB port, set USB to configurations 048, 072, 077 and 109. DATA means RTTY/Data port. It's Yaesu playing legacy overly-zealous compatibility mode.

See below a more comprehensive table for each mode and its respective Port settings:

Mode	Mic/Rear Config	Data/USB config
AM	045	048
Data	070	072
FM	074	077
SSB	106	109

Engaging Transmission

The radio also provides a fine granularity so you can select which mechanism will engage the transmission mode based on your settings. You can choose between:

• DAKY - That's shorting RTTY/Data pin 3 to ground
• RTS, from Standard USB Port
• DTR, from Standard USB Port.

All of these causes are mutually excusive, meaning; if you set the PTT select to DAKY, the radio will ignore any RTS or DTR event; or if you set to RTS it will ignore DTR and DAKY and so forth. CAT, Front Mic and MOX are not affected by this setting.

Again, there's a fine mesh allowing you to set the PTT event per mode. Namely:

Mode	Transmit event config
AM	047
CW, RTTY	060
Data	071
FM	076
SSB	108

Yup, the radio is complex. However, it provides plasticity so it can suit your operating needs ensuring an enjoyable experience.

Hope that helps - 73s de PY2RAF.

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