Tuning out QRM on datamodes using the Yaesu FT-450D with DM-780 and Ham Radio Deluxe

The standard way of operating a datamode such as PSK-31 is to leave the filter width as wide as you can and tune to the operating frequency. The software, in my case Ham Radio Deluxe running the DM780 module, then uses software filters to narrow reception down to whatever audio frequency you have selected in the waterfall. This works well 99% of the time but you do get occasions in the middle of a QSO when a very strong station starts transmitting in an adjacent audio frequency. That station probably can't hear your contact so doesn't know that it is generating QRM.
This can sometimes result in swamping the signal coming from your contact.

The two useful filters on the FT-450D highlighted in yellow

The radio then comes to the rescue. From very early days it has been possible to engage IF filters, notch filters and such like on communications equipment. When somebody is tuning up close to your listening frequency engage your tunable notch filter. If somebody is transmitting on SSB a few KHz up then engage your IF Shift. The ways of getting rid of QRM are very wide ranging and easy to do.


I normally make use of the rigs own filters to tune out QRM. The FT-450 has a tunable notch filter that is easier to control with HRD than using the controls on the rig itself. It is very narrow and you are able to use it to remove a strong station transmitting a few Hz bandwidth especially PSK-31.
I also use the Width filter to remove stations from either side. You can get it to filter all audio except for a narrow band 1400 to 1700 Hz wide on the narrowest setting. This is the 300Hz datamode filter setting on the rig with IF Shift set at its centre setting.  Of course if the signal you want to concentrate on is outside of these audio frequencies then just adjust the rig operating frequency to get the station within the passband. Alternatively move the IF shift as that achieves the same thing.

DM-780 waterfall with FT-450D Width filter engaged
The audio passband can quite easily be seen by the lack of
any activity either side of around 1300Hz and 1700Hz

With the notch filter engaged I can tune out the QRM

Before

After notch filter engaged

As can be seen the strong adjacent signal has been filtered out leaving the software with a stronger audio waveform to act upon. I find the best way to do this is to turn up the audio on the rig and adjust it by ear and finally using minimal adjustments to make the waveform disappear. It works ok on PSK-63 and less so on PSK-125 (although few stations seem to use PSK-125).