6400M and WSJT-X

WØYVA · December 2021

I have noticed when operating FT8 the output power fluctuates a bit (~45-52w). You can also see this on the display (when transmitting) which 'jumps' up and down. Normal? Something misadjusted?

It doesn't seem right but I'm making plenty of FT8 QSO's.

Erik Carling EI4KF · December 2021

FT8 uses GFSK modulation which shapes the pulses and so there will be 'spaces' within the 15 second transmission which then translates to a small fluctuation in power. It is when you do not see that, something is maladjusted for example when over driving. The author of JTDX published a full explanation and there might be some similar document for WSJTx.

Mike-VA3MW · December 2021

It isn't the RF that fluctuates, it is the audio being sent to the radio that fluctuates.

73

WØYVA · December 2021

Yep, I understand that. What is curious to me is that some of time the change in RF is quite minimal - I expected that but, every so often, the change is quite large. Doesn't seem to bother anything however ...

Thanks for your comment. 73

bahillen · December 2021

Try increasing the TX audio bandwidth in the Radio pane in SmartSDR. I run 100 hz on low side and 3,900 on high end. For digiu.

73

Bill W9JJB

WØYVA · December 2021

I will give that a try - thanks! 73

scotthibbs · July 2023

I noticed my forward power bouncing during FT8 transmissions. Read online that this is a result of the tx audio cutting hi and low. Turns out I had my TX EQ on. Turned this off and Forward power is steady.

FWIW, when WSJT-X transmits the radio and you see no signal forward turn your DAX TX Stream off and on again. My working theory is that Windoze turns this service off or suspends it. I think it helps if I leave it active on the desktop.
73-KD4SIR

Mike-VA3MW · July 2023

This is interesting since the EQ software is fully bypassed when in DIGU or DIGL. So, that should not be part of the solution.

If you can recreate that (I can't) can you open a support ticket please.

bahillen · July 2023

Mike Walker

The issue is not equalization, that is not in the DAX path. It is the transmitter bandwidth, that is not the same as the audio equalization. This is the Low Cut and High Cut TX Filter in the Rig Control - Window in the Phone applet.

To solve that problem for me, beside the low and high settings that are a small part, I use the WSJT Fake It in the Settings - Radio - Split Operation option.

This shifts the carrier and audio to the center of the band pass. Solid Power output. This is important for FT8 F/H because when the software moves you down to the closer to the band edge on the DX, you want the solid power out.

With the TX in DIGU the drive is not flat below 500 hz and you see the power jump around around with the frequency shift keying.

As an aside, on 60 m digital the High Cut has to be below 3,000 to allow transmission and Fake it can not be used because it could allow you to TX out of band.

73

Bill

W9JJB

Erik Carling EI4KF · July 2023

Because of the GFSK modulation, those power fluctuations can occur if the user inadvertently has set Mode = None in the FT8 software and USB as the mode SmartSDR. Yes, turning EQ off will solve it if this is the case, not saying it is, but better is to use DIGU mode in SSDR.

6400M and WSJT-X

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