Datamodes on the Yaesu FT-920

Introduction

Having recently purchased a Yaesu FT-920 I have spent some time getting the radio to function as required in the dedicated data mode. I had great difficulty getting the full documented functionality of the radio and the data port to function correctly and following many Internet searches and some correspondence with Yaesu technical support in the UK I have finally managed to get the radio functioning as desired.

To save others the pain I have been through, I have taken this opportunity to document my findings.

Also documented is the PC-Radio interface I have constructed for which I make little or no claim of originality!

Radio Set up

Quite simply put, the manual that came with the radio in some areas is at best misleading, and in others actually wrong. Lets start with the basics. When the radio is in data mode there are two actual modes available. One is "DATA LSB" where both the DATA and LSB indicators are showing, and the other "DATA USB" where both the DATA and USB indicators are showing.

What the manual doesn't tell you is that "DATA LSB" is FSK RTTY only, and "DATA USB" is AFSK RTTY and also suitable for use on all sound card based digital modes. On the back of the radio is an "AFSK-FSK" switch. All this switch does is route pin one of the data port either to the audio circuitry when in "AFSK" or to the tone generator when in "FSK".

So, for most of us this switch needs to be in "AFSK" mode and the radio in "DATA USB". The actual sideband that the radio is in is controlled by menu item U-46. For typical RTTY operation, this needs to be set to "2125-L", this sets the carrier injection up for an offset of 2.125 kHz in a pseudo-LSB mode, so that the transceiver actually is operating in LSB mode even though the display still indicates "DATA USB". Conversely setting menu item U-46 to "2125-U" will put the radio in USB mode.

It would appear that many digimode operators have experienced problems trying to run the FT-920 in true Data mode. Reports I have seen include "I used the Yaesu Data port on the original design but had to disconnect the data in line and move it to the Yaesu phone patch in jack. I discovered that the data port is only functional in the data mode (not in standard modes like USB and LSB) and the data mode adds information to the data in line, which causes problems."

It is worth noting at this point that the audio in via the data port is only active when the radio is in Data mode. However, the use of the data port has a number of advantages over using the mic socket or "phone patch" connections, here are some of the best:

Radio PC Interface

I wanted to build an interface for the Radio to PC that would work on all sound card based digimodes, but it seemed a useful feature to add a keyboard CW facility via the Comm port DTR line with PTT for all modes utilising the RTS line. A search of the web located the following useful site:

http://www.qsl.net/wm2u/inter_ft.html

From here there is a link to KC7DS's web site where a suitable interface can be found:

http://www.qsl.net/kc7dh/sndcrd.htm

I originally built this design as documented, but found a few problems setting sound levels low enough on the PC to make the controls on the interface useful, and the TX monitor as built was very distorted. So the design below is based on KC7DH's interface with modifications by myself. As stated earlier the circuit included below is by no means original -- but it works just fine.

The interface has been constructed in a standard way using veroboard and a housed in a case from Maplin.

The inclusion of variable controls for the TX and RX audio levels is a very useful feature as you do not need to enter the PC sound adjustment software every time you change from one mode to another or from one software package to another. You can simply make notes as to where the controls need to be and adjust them on the bench.

SW1 was included to enable the manual switching of the TX control from the radio off. I have found that my PC seems to randomly flip the RTS and DTR lines of the Comm port during boot. This allows me to ensure that the happy Microsoft "Welcome to Windows" sound is not transmitted on 20-meters!

Interface construction

Interface as installed in my Shack

Happy soldering to all you FT-920 owners!

Mark Jones (G0MGX)