What causes the squiggly Pure Signal Amp View?

[NS8K]

On occasion, my 7000 MKIII experiences an odd looking Amp View when doing a two tone P.S. calibration. I have seen other examples of this sort of Amp View by others but always with a different twist than I am seeing. Here's my normal Amp View on 80 meters, external (or internal) coupler at 50 watts out, dummy load, no external amplifier:

80 meters 50 watts normal.png (36.15 KiB) Viewed 207 times

Here's what an abnormal Amp View looks like. All conditions are the same:

80 meters 50 watts abnormal.png (40.45 KiB) Viewed 207 times

What's really weird about this is the condition comes and goes if I power the radio off and then back on. It will start up in either of the two conditions, affects all bands and no amount of fiddling with Thetis changes it and believe me, I've fiddled. Yesterday it was squirrely and tonight it started out normal and I tested for about two hours. Everything was looking just fine and I didn't know what had happened to "fix" the problem but all seemed ok. I then shifted my attention to a slightly loud radio fan. I "turned off the radio switch" in Thetis and then flipped off the radio power. Fan noise went away so I confirmed the noise wasn't coming from a different piece of gear. Powered the radio back on, fan noise returned, turned the "power button" back on in Thetis and everything looked normal. I then did a two-tone calibration and Amp View had turned ugly. Through lots of trial and error, this scenario is very repeatable. I don't do anything in Thetis other than turn the radio "power button" off, I then switch off physical radio power, wait maybe 10 seconds, switch power back on, turn the Thetis "power button" back on and do a calibration. Sometimes, the curves return to normal if they are ugly and sometimes they turn to ugly if they were good. So far, once they are bad, I've been able to return to good although it might take 4 or 5 cycles of turning the radio off and then back on. Going from good to ugly seems to take far fewer cycles - like one!

Of course, the fan has nothing to do with the problem but it is what prompted me to cycle power on the radio and I discovered doing that may either fix or discombobulate my two-tone Amp View calibration and I assume my Pure Signal operation.

The amount of squiggle in my curves after a power cycle does vary from looking great to a little wavy to even more wavy than the screen shot shown above. When really wavy, P.S. cannot find a solution and does not correct. Oddly though, if I change even one of the tones just slightly, P.S. may start to correct.

While changing tone frequencies, I've discovered something maybe everyone else always knows but here's my "normal" curves at 700/1900:

Normal Amp View at 700&1900.png (35.07 KiB) Viewed 207 times

Notice blue and yellow traces are dotted. The "normal" plot at the beginning of this post was at 701/1900. Probably not important but still interesting. May have something to do with my computer if others do not see this same behavior. 800/1800 are also dotted but not if either tone is changed by even 1 Hz, up or down. I've settled on oddball numbers like 803/1811 or 709/1137. Always smooth plot curves.

One last set of plots. Here are the gain curves when things look normal vs squiggly:

Normal gain.png (27.85 KiB) Viewed 207 times

Squiggly gain.png (37.37 KiB) Viewed 207 times

To quote Tooter Turtle, "Help, Mr. Wizard"! Any ideas on what's wrong with my radio? Thetis is at Ver 2.10.3.11 and firmware version is 2.2.2.

Thanks,

Tom - NS8K

[NS8K]

Here's a correction to a conclusion I came to in my original post.

I concluded that the changes I see in my Amp View when doing a two-tone calibration was caused by cycling power on my radio. That is not correct. While doing additional testing, I discovered the Amp View plot changes when I cycle "power" from Thetis, without cycling the physical power button on the radio. I'm not ending and re-starting Thetis, just cycling the "power" button. Sorry for the mis-information.

My next step is to upgrade to Thetis V2.10.3.12 and initially, start anew to see if anything changes. If no change, I will try firmware 2.2.2A and 2.2.2B.

BTW, my radio is an MKIII with a Cyclone V FPGA.

Thanks,

Tom - NS8K

[K1LSB]

Can you show us some PS curves that are generated from just speaking into the mic (without ever using two-tone)?

Mark

[NS8K]

Mark,

Great idea! I was so fixated on the changing two-tone graphs. Here's 75 meters voice at 54 watts peak:

75 meters voice 54 watts peak.png (37.36 KiB) Viewed 161 times

Here's 15 meters voice 44 watts peak output with gain curve followed by two-tone test with gain curve:

15 meters voice 44 watts peak.png (36.66 KiB) Viewed 161 times

15 meters voice gain.png (27.91 KiB) Viewed 161 times

15 meters two-tone.png (38.87 KiB) Viewed 161 times

15 meters two tone gain.png (32.54 KiB) Viewed 161 times

Maybe an issue of sorts with two-tone? Voice plots look ok to me. The results are essentially the same on 160 - 10 (didn't test 6). 15 is extremely good, settling in between -60 and -61 dBc for two-tone third order IMD even with the weird squiggly plots.

Not sure what to think.

Tom- NS8K

[K1LSB]

Tom,

I asked about the voice calibration because I had read somewhere in this forum that some amps don't like some combinations of two-tone frequencies. Your 15 meter curves suggest you're using frequencies your amp doesn't like.

One nice thing about PureSignal is that it will calibrate perfectly fine to any combination of tones, so I decided early on that I'd just let PS use my voice for calibration, and consequently haven't used two-tone in years.

FWIW here are the specific two tones I was using years ago, they seemed to give my amp the least amount of heartburn. YMMV.

Mark

Capture-2.jpg (98.64 KiB) Viewed 158 times

[NS8K]

Mark,

Thanks for the reply. I have also read the comment about some amps not liking some two-tone frequency combinations. In my case though, there is no external amp involved and I've tried many different frequency combinations. If I drive an external amp (Elecraft KPA500 or Collins 30L-1) and use two-tone, the plots look pretty much the same and are still wavy on all bands, not just 15. At times though, the two-tone plots also look great both with and without an external amp although the times when that happens seem to be getting less and less frequent.

I suppose I'll take your approach and not calibrate with two-tone although that's hard for me to accept. Something sure seems wrong. One thing you can do with two-tone but not voice is measure your IMD. Some would say that's just a number, get over it but to me it's assurance that PureSignal is working and how well it is working.

WRT amps not liking certain frequency combinations, I've not experienced that but I don't doubt it. What I have experienced is running a two-tone signal through an automatic antenna tuner (Elecraft KAT500) and having the tuner's frequency counter be fooled by the two-tone signal so much so that it read a two-tone signal on 17 meters as 13.9 Mhz. That caused it to switch to a tuning solution from the very bottom of 20 meters thinking it was doing the right thing. Needless to say, red lights started flashing, alarms were set off and I was concerned the amp finals had gone poof! Fortunately, they didn't and after lots of communication, Elecraft acknowledged the KAT500 frequency counter could do that. There is a parameter in the KAT500 called Frequency Counter Distance for Retune which defaults to 10 kHz. I've disabled that function and two-tone is no longer an issue for my tuner.

Again, thanks! Still wondering if others see these squiggly two-tone Amp View plots or am I the only one?

Tom - NS8K

[K1LSB]

Tom,

There is one other possibility that I haven't mentioned before now...

I had a very similar-looking issue with the PureSignal curves on my radio 2 years ago. It wound up being a bad PA in the final.

Here's the thread in this forum on my pursuits (with lots of PS pics):

viewtopic.php?t=4777

Long story short, I sent the radio to Doug and he replaced both devices in the final (per my request, as I wanted a known balanced final). Been smooth sailing ever since.

Mark

[w-u-2-o]

The "squiggly" waveforms are generally indicative of either a hardware issue (cable, amp, etc.), or bad data, which again would be due to a hardware issue (cable, coupler, etc.).

It's very unlikely the versions of Thetis and firmware you are running have anything to do with this. Also, without having an external amplifier, we can dismiss tone selection as having any bearing on the problem. The standard 700 and 1900 Hz tone pair should be fine.

Before looking for "zebras" (something rare and unusual) try looking for "horses" (boring and mundane). VSWR is obviously not a core issue, since this problem occurs into a dummy load. But are all your cables healthy? Any loose RF connectors on the back of the 7000? What do your station's grounding and bonding provisions look like?

Finally, the dotted or dashed characteristic of the lines is not a problem and need not be addressed. It is typical of a any two-tone waveform. When two tones are combined, particularly non-harmonically related ones as is the standard for two-tone measurements, the two waveforms will combine such that there is an AM modulation imposed per the mathematical relationship as shown in the following figure below. This causes the dotted characteristic as shown on the ampview display.

Two-tone is not necessary for calibration with SSB phone. Normal voice modulation is sufficient. However, remember that the audio chain both internal and external to Thetis must cause the ALC to peak at greater than or equal to 0 dB fairly frequently or PureSignal will not kick off a measurement. Two-tone is most useful for a) formal measurements, b) performing a "single cal", which is often useful for difficult "digital" waveforms, and c) adjusting amplifier drive level.

Finally, and not really relevant, but fun to discuss, is how to modify two-tone settings so that you get the same behavior and benefits without "singing the song of our people". You will find that a tone combination of 70 and 190 Hz is useful for all of the above except formal testing and sounds quite subtle on the air compared to the standard 700 and 1900 Hz tone pair.

Capture.JPG (102.34 KiB) Viewed 82 times