WSJT-X Operating Tips

Dean Jacobsen

Hi All,

New FlexRadio user here, a brand new 6400M. Great radio.

I have the radio operating in the FT8 mode. I am now experimenting with the AGC and AGC-T settings and I am wondering about what the experts here may recommend as far as using AGC for digital modes in general and for FT8 in particular and also where I should have the AGC threshold for the same modes.

Right now I have AGC turned off and I have the AGC-T set to 50 which puts the audio input level meter on the left side of the WSJT-X window at about 60 dB. I also have the Slice A RX Gain set to 45.

Comments are appreciated.

73

Dean Jacobsen W6DBJ

David Decoons, wo2x

I have AGC on medium and AGC-T set to where background noise is dropped very low. I set DAX RX1 level at 34 which when not receiving keeps WSJT-X about 50.

I have no problem decoding down to -24 and over 50 decodes per cycle on 20 meters during the day or 40 meters at night.

Dave wo2x

Dean Jacobsen

Thank you Dave.

During my experimenting I can see the interplay between the RX gain level and the AGC-T level and how they affect the WSJT-X audio input level.

What advantage does having the AGC on give me when operating in a digital mode like FT8, whether it be low, medium or high, versus just leaving it off?

73

Dean Jacobsen W6DBJ

Alan

Dean

AGC off, you are attenuating all signals, as per the slider setting.

AGC on, you are attenuating the stronger signals, so as to not prevent the nearby weak signals from being heard. The proportional attenuation of the strong signals is set per the slider setting.

Alan. WA9WUD

Dean Jacobsen

Thanks Alan. How do I know whether to choose fast, medium or slow AGC with a digital mode such as FT8? Does it just depend on band conditions and experimentation or is there a reason for choosing one flavor over another in this particular situation?
73
Dean Jacobsen W6DBJ

Alan

AGC timing requires some experimentation. The AGC speed sets the rate that the attenuation comes and goes.

FT8 level variances would be handled with "slow".

Storm noise, lighting, would be handled with "fast"

Alan

Dean Jacobsen

Thanks Alan.

> @"David Decoons, wo2x" said:
> I have AGC on medium and AGC-T set to where background noise is dropped very low. I set DAX RX1 level at 34 which when not receiving keeps WSJT-X about 50.
> I have no problem decoding down to -24 and over 50 decodes per cycle on 20 meters during the day or 40 meters at night.
> Dave wo2x

What about RF gain? How does RF gain fit into the equation?
When keeping my Slice RX gain constant, I can raise the WXJT-X audio level to something like 50 by either:
1. increasing RF gain,
2, increasing AGC-T, or
3. turning on AGC

What are the pros or cons of increasing RF Gain to increase teh WSJT-X audio to "good" levels?

David Decoons, wo2x

AGC-T is like RF Gain but it is not the same as traditional superheat receivers. Do not think of it as an RF Gain control.

Now preamp is another story. Use preamp on higher bands as needed.

Dave wo2x

Dean Jacobsen

Thanks for the reply Dave.

So, are you saying that I should be using RF gain to boost the WSJT-X audio level [specifically thinking about the 20m and 30m bands] if it is low?

Dean Jacobsen

... and as a follow-up...

Are you also saying that I should not be using AGC-T to boost the WSJT-X audio level?

Sorry for all of the questions but still trying to get my head around optimizing the new radio.

David Decoons, wo2x

I set DAX RX1 at 34. DAX TX at 48. Power slider in WSJT-X all the way up.

AGC on medium.

Adjust AGC-T to knee of compression. In other words I adjust AGC-T until background noise drops but still audible. I use slice volume at 65.

I tested earlier today varying AGC between slow and fast - no difference in decode levels. I then varied AGC-T on 17 meters between 35 and 70. No difference in decodes.

I’ve worked thousands of FT8 contacts like this and no issues. Consistent decodes down to -24 and when band is open I can see 60 decodes in a 15 second decode period.

Don’t overthink it.

Dave wo2x

Dean Jacobsen

Thanks Dave.
Here's the real world scenario that I am looking at now on the 30m band.
- DAX Rx gain at 34
- WSJT-X Pwr slider all the way up
- AGC on medium
- AGC-T set to 0
The WSJT-X audio level reads 0.
If I increase the DAX Rx gain to 50, which seems to be a reasonable level, then the WSJT-X audio level increases to 9 dB.
So, if I want to get the WSJT-X level higher than 9 dB [or 0 dB if I return the DAX Rx gain to 37], then what is the best approach?
73
Dean W6DBJ

KD0RC

Hi Dean, there is a section in the SmartSDR manual on setting RF gain and AGC-T. I would set those per the directions, then follow Dave's advice on setting the audio levels.

The AGC-T settings are all about controlling signal levels without unnecessarily amplifying noise.

The RF gain is set for maximum dynamic range. This helps when there are close-in big signals.

I am not at my computer, so I don't have the sections of the manual handy. I also think that Tim, W4TME published some separate papers on the topic that can be found in the documentation section of the web site.

Dean Jacobsen

Hi Len,
Yes, I was just reading about AGC-T in the manual.
From the manual: "Automatic Gain Control (AGC) is a feature which automatically adjusts the Slice Receiver’s audio gain (volume) based on the strength of signals in the receiver’s passband filter. The goal of AGC is to amplify weak signals and attenuate strong signals so that they all lie within a comfortable listening range."
Keeping all of the other initial settings I described above the same, I am able to increase the WSJT-X audio level to 50 dB by increasing the AGC-T level to 34 with the current band conditions.
As for RF gain, I am also able to increase the WSJT-X audio level by increasing the RF gain. However, the radio manual says "For typical HF operation below 12m, the 0 dB preamplifier gain setting provides the highest dynamic range and is recommended for most locations. Even in quiet rural locations, gain is not needed or desired unless a low gain/low noise antenna is utilized."
I am using a hand tuned 30m dipole for this band. It doesn't seem like increasing the RF gain is the best approach.
I am not an EE, so I am just trying to get a better understanding of the theory behind AGC, AGC-T and RF gain so I can make good choices.
73
Dean W6DBJ

KD0RC

Hi Dean, Yep, I sure understand - I am no engineer either.

Both the RF Gain and AGC-T can be made to give more audio output, but if mis-set, can reduce dynamic range or amplify noise.

I always start with the RF Gain adjustment. If it is too high, you lose dynamic range, making you susceptible to overloads from nearby strong stations. So even though it affects the audio output, the goal of this setting is to optimize the dynamic range.

Next, I set the AGC-T so that I reduce the amount of noise that I hear with the goal of having the AGC control the audio of the signal more than it controls the noise. This also affects the audio level.

With both of these controls optimized, you are left with some level of audio. When listening to CW or SSB, you adjust the audio gain to a comfortable level. With the digital modes, you adjust the DAX level to make the software decoding program happy.

There is no "perfect" setting for anything, as band conditions are always changing. You are just trying to get near enough to the optimal values to give the radio the best chance of hearing the weak ones. The radio will decode some amazingly tiny signals if you are set up reasonably, not necessarily perfectly.

I hope that all makes sense. If not, don't hesitate to keep asking. There is a LOT to comprehend, especially if you do not have that elusive PHD in EE. :- )

Dean Jacobsen

Thanks for the response Len. I'm sure that I will have more questions but you have given me a good start and some things to explore... and some more of the manual to read. :-)
73
Dean W6DBJ

KD0RC

Glad the help Dean. Here is a link to a video by Mike, VA3MW and Tim, W4TME from Flex about how ACG and AGC-T work. You can start at 5 mins in if you don't want the intro and small talk.

https://youtu.be/OJ36HMBQS7U

This video really makes it clear what the AGC does and what the AGC-T does (and how to adjust it).

David Decoons, wo2x

I second watching the video.

AGC-T at zero under ANY conditions is a no-no. For 30 meters I run it about 35 - 40. Preamp set to zero. AGC on medium. This allows audio from weak signals as well as strong. I can decode -24 to +27 in same decode window.

Again, take away from this, the AGC-T does not operate the same as RF Gain on an old Kenwood TS2000. I find the way I set everything (including DAX RX1 @ 34) that when no signal is present, the RX level in WSJT-X is around 45 to 50.

Use AGC-T to drop background noise to point where it is not fatiguing on the ears. I usually boost the slice volume up to 65 then it allows a slightly lower AGC-T. For 80 meters I run AGC-T @ 32.

Dave wo2x

Dean Jacobsen

> @KD0RC said:
> Glad the help Dean. Here is a link to a video by Mike, VA3MW and Tim, W4TME from Flex about how ACG and AGC-T work. You can start at 5 mins in if you don't want the intro and small talk.
> This video really makes it clear what the AGC does and what the AGC-T does (and how to adjust it).
OK, so that video was super helpful. :-) Great discussion on theory and practice and how the FlexRadio SDR is different from my old radio.
They also referenced an excellent FlexRadio document:
https://helpdesk.flexradio.com/hc/en-us/articles/360029494371-How-does-the-Automatic-Gain-Control-AGC-work-in-SmartSDR
So, thanks to everyone for pointing me in the right direction.
Now, all I have to figure out is how to optimize my FT8 transmit settings... :-) Is there a video on that too?

KD0RC

One other cool thing about the Flex AGC is what Mike, VA3MW always talks about, but is otherwise not discussed much - lightning noise.

This past summer I had my K2 running next to my Flex 6400 on 80 meters so that I could switch back and forth (I was trying to compare weak signal performance). Every lightning strike took out massive time slices on the K2 and made an otherwise great little radio pretty useless.

When I switched over to the Flex, I could see a barrage of horizontal yellow lines across the waterfall, and all kinds of spikey junk sticking up in the panadapter display. I could hear the lightning as bursts of static, but still had Q5 copy on SSB or CW stations. Really weak stations did suffer, but the radio was otherwise completely usable under these conditions.

The storms that day were all out on the plains more than 50 miles away. While not posing a safety threat, they did keep me from using the K2.

John KB4DU

My technique for the AGC-T is a little different. I start with the Agc on the low side and adjust up until the background noise just starts to increase, then reduce agc to just below where the noise decreases. Just a little easier for me to find the point where the agc kicks in to affect the noise.

Dean Jacobsen

OK, thanks to the comments here and the video I think I have the AGC - AGC-T - RF Gain thing figured out for FT8 ops with the new 6400M.
Now I need to evaluate whether my FT8 transmit audio is optimal. I don't have test equipment that I can use to plug into my antenna jack and actually see what I am transmitting. I am just relying on the Level meter, and that shows about -5dB [halfway between -10 and 0] with my RF power set to 55 and the TX Stream gain set to 50.
Are there any more great videos from Mike VA3MW and Tim W4TME on this topic. :-)
This my be an "if it isn't broke, then don't fix it" situation for me. I am heard on FT8 in South Africa, Indonesia, and Antarctica with my tree-mounted dipoles with the new radio. So, I guess I really need to know if I am overdoing it on the RF power and distorting my signal.

KD0RC

Hi Dean, well, you have a very powerful diagnostic device - your 6400M! Using Full Duplex (FDX), you can look at your transmitted signal directly. You will want to use reduced power, but it will give you an idea of how well you have your audio set up.

If you search for NM9P on YouTube, Ken has some videos on how to monitor your signals using FDX.

It definitely sounds like it ain't broke! Sounds like you are really getting your money's worth out of your new radio!

Dean Jacobsen

Thanks Len, another good video. Thanks for the recommendation.

David Decoons, wo2x

Dean,

as I said several times in this thread, set DAX TX to 48 and WSJT-X power slider all the way up. Now adjust RF Power in SmartSDR or from RF Power knob on M series for desired RF output level.

watch level meter with these settings. You will see the TX level right at zero, but yellow in color. Yellow indicates near zero but not exceeding zero. Once you exceed zero you get digital “clipping”. These are the optimal TX audio setting.

Dave wo2x

Dean Jacobsen

> @KD0RC said:
> Hi Dean, well, you have a very powerful diagnostic device - your 6400M! Using Full Duplex (FDX), you can look at your transmitted signal directly. You will want to use reduced power, but it will give you an idea of how well you have your audio set up.
> If you search for NM9P on YouTube, Ken has some videos on how to monitor your signals using FDX.

Len, as you note, the video shows how to look at audio but at a very low power.
I am also interested in knowing at what point, if any, application of additional RF power starts to distort my signal.
I realize that FT8 is a weak signal mode and generally operate with the RF power set to 50, The Level meter looks good at that power level. If I raise the RF power to 80 and leave the DAX Tx gain the same, the output on the Level meter still looks "good" [doesn't exceed 0dB and the peak level is yellow]. Is it safe to assume that I am not distorting my signal at the higher level?

KD0RC

Hi Dean, I don't think that the power level will affect signal quality, as long as you keep the audio from overdriving. These rigs are really clean. Watch the waterfall when you chat over the air with another Flex - it is normally a very good, clean signal.