DIGU Offset

Geoff AB6BT

OK, I have successfull made hundreds of Wsjt-X contacts. I have never changed the default offset.

Can someone explain what the offset does?

I read the section in the user guide but I guess I don't understand what it means.

Thanks!

KD0RC

Hi Geoff, it centers the chosen frequency in the filter passband. As you narrow the passband, it stays centered on the selected frequency. I don't run FT-8, but I do occasionally run VarAC. Using the standard 1500 Hz DIGU offset, I can set my receive filter bandwidth to 600 Hz and it always lines up exactly with the signal I am listening to, no matter which slot I move to for QSO.

Geoff AB6BT

Hi Len,

OK, here's an example…Lets say I'm in DIGU mode on 20 Meters FT8 at 14.074MHz. My RX bandwidth is 3 kHz. I'm using WSJT-x as my FT8 program. There is a station transmitting at 500Hz and I call him at 1250Hz.

What effect does the 1500 Hz offset have?

Mike-VA3MW

For a FlexRadio there really is no requirement to use the offset for FT-8.

When in DIGU or DIGL modes, the TX and RX bandwidths are flat all the way from the HPF setting to the LPF settings. This means that you will get the same RX and TX performance anywhere in between.

On SuperHet radios, the software may move the transmitter to optimize the sweet spot in mechanical filters of around 1500hz. Again, not needed on a FlexRadio.

You may want to use it if you are tightening up filtering for some specific reason.

Geoff AB6BT

Hi Mike,

Thanks for the clarification. I forgot to mention that I am currently using my 6400, waiting on an 8600.

Is there a visual way that I can see the operation of the offset? That would help me understand how I might use it.

Mike-VA3MW

Not that I am aware of. To be honest, it is an option that I have never found a reason to use. Others might have.

Geoff AB6BT

Fair enough. I have never used it either, but then I'm not sure how it actually works…