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Out of curiosity, how are you connecting the probe's ground?

Even at a low frequency like 1.8MHz, more than 1 inch of probe
grounding wire will make a signal ring like that.

-Chuck Harris, WA3UQV


On Mon, 05 May 2025 11:40:18 -0700 "mux_folder2001 via groups.io"
<canthony15@...> wrote:

I just hooked my scope up to the drain of one of the? PA transistors
in my QMX+ and kicked off a 160M Phase cal (O button). I am seeing
120 volt spikes during the cal.

Here is a link to a screen shot from my scope:

160PhaseCalGlitch.jpg (

)

This is going to fry some BS170s? for sure.

Tony
ADoVC

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Hi Tony,

Being unfamiliar with your Siglent scope's screen layout,
I didn't see the vertical attenuator setting, initially.

When you said "spike", I looked at the spike, which in my
lexicon is the sharp pointy thing that is on top of the
pulse... which to me looks like ground lead ringing.

When I found the attenuator setting hidden on the right
side of the screen, I realized that the "pulse" is 120V,
which I am sure is real.

Probe capacitance is probably affecting it somewhat as well.

-Chuck Harris - WA3UQV


On Tue, 6 May 2025 13:53:17 +0000 "mux_folder2001 via groups.io"
<canthony15@...> wrote:

Hi Chuck,

I did measurements with the standard scope ground but also with ?
inch leads soldered to the transistor and attached to the probe. The
probe ground causes some high speed ringing but the fat part of the
pulse is basically the same.

If it offers any reassurance, I spent my career in the high speed
logic business. Many hours looking at nanosecond edges and I am very
familiar with the effects that are produced by the scope probe ground
leads. I am convinced that the bulk of the large pulse is real. As to
its cause, it is only speculative. I did some measurements in QDX
that convinced me that the issue there was due to the inductor. But I
have not repeated those experiments with QMX. So, there could be more
here than meets the eye, or not.

73,

Tony
AD0VC


________________________________
From: [email protected] <[email protected]> on behalf of Chuck Harris
via groups.io <cfharris@...> Sent: Tuesday, May 6,
2025 6:54 AM To: [email protected] <[email protected]>
Subject: Re: [QRPLabs] Why I think QMX Calibration Kills PA

Out of curiosity, how are you connecting the probe's ground?

Even at a low frequency like 1.8MHz, more than 1 inch of probe
grounding wire will make a signal ring like that.

-Chuck Harris, WA3UQV


On Mon, 05 May 2025 11:40:18 -0700 "mux_folder2001 via groups.io"
<canthony15@...> wrote:

I just hooked my scope up to the drain of one of the PA transistors
in my QMX+ and kicked off a 160M Phase cal (O button). I am seeing
120 volt spikes during the cal.

Here is a link to a screen shot from my scope:

160PhaseCalGlitch.jpg (
<>
)

This is going to fry some BS170s for sure.

Tony
ADoVC

开云体育

Hi Hans,

Being an engineer and manufacturer, you should have learned
about parts variability by now. Manufacturers undergo process
changes on a day-to-day, and batch-to-batch basis that change
the as-built characteristics of their parts.

That little over voltage abuse that you are currently waving
away, is a really big deal when it comes to reliability.

If the manufacturer thought it was a sustainable characteristic,
they would be exploiting it in their sales literature.

You are in a sweet spot right now, your customers adore you, and
thus far are accepting responsibility for failures that are not
their fault.

In this engineer's opinion, the 12.0V vs 12V car electrical
system issue was your first warning shot about the unsuitability
of the popular BS170 transistors for this design.

It is going to be a millstone around your neck until you bite
the bullet and fix it.

-Chuck Harris, WA3UQV

On Tue, 6 May 2025 18:04:32 +0300 "Hans Summers via groups.io"
<hans.summers@...> wrote:

Hello all

Many people, myself included, have run the QMX calibration procedure
multiple times without damage to their BS170 transistors. I was
developing the QMX firmware for 9 months, including the calibration
procedure which I ran literally hundreds of times while developing
it. Some unexplained failures have indeed been reported too.

...

Hi Hans,

You can test ad nauseum every single reliability issue
with a little wedge in your software.

If you want to know whether this high voltage pulse is
harmful to your radios you have everything in hand to
find out: Set the stage in software to make the pulse at
will, then bang every single QMX in your lab until it is
either destroyed, or survives.

When you have only tried the calibration routine a few
dozens of times, you really know nothing about what your
customers are going to experience.

Put a little wedge in your firmware that runs the calibration
cycle to completion, rests, runs (and measures) full power on
each band key down for a minute, rests, and then repeats....

Again, do this on every test radio you can get your hands
on, for a week or more.

For a real answer, enlist a few of your more stalwart
group leaders, and have them do it to their radios...

Then you will know...

Tell us what you did, and then we will know too.

People expect things to go smoothly. It is only natural
for failures to bring more attention.

The internet makes sure that all failures are visible
forever.

-Chuck Harris, WA3UQV



On Wed, 7 May 2025 18:27:09 +0300 "Hans Summers via groups.io"
<hans.summers@...> wrote:

Hello Chuck

I'm not waving it away OM. I'm saying that there isn't any proof that
ties that very short over voltage spike to a BS170 failure. And I
think the occurrence of BS170 failures is low. We always tend to hear
more of failures than successes, this is the negative bias nature of
forums.

But nobody needs to "prove" it. I said, there's no need for a sharp
sudden turn on, no reason why the key-down shouldn't be properly
envelope shaped during Calibration, which will delete the spike
anyway. There's no cost and no disadvantage, and potential benefit,
and it isn't difficult to do (in fact I thought it was already done,
so the reason why people have reported no shaping needs
investigation). As I said, I'll fix it...

The issue with high supply voltage is that depending on band and
adjustments and antenna etc., it can cause high power output and/or
high current, high heat dissipation, that increases the risk of
failure. It hasn't happened to me (and many others report long
success) but again, it happens to some people, and it's preventable.
I'll add a change that prevents the PA supply voltage exceeding 12V
even if the main supply voltage does. That will dissipate more power
in the PA modulator so I'll need to test it.

In summary both these things will be solved as soon as I can, I'm not
looking away from them.

73 Hans G0UPL



On Wed, May 7, 2025, 18:13 Chuck Harris via groups.io <cfharris=
[email protected]> wrote:

Hi Hans,

Being an engineer and manufacturer, you should have learned
about parts variability by now. Manufacturers undergo process
changes on a day-to-day, and batch-to-batch basis that change
the as-built characteristics of their parts.

That little over voltage abuse that you are currently waving
away, is a really big deal when it comes to reliability.

If the manufacturer thought it was a sustainable characteristic,
they would be exploiting it in their sales literature.

You are in a sweet spot right now, your customers adore you, and
thus far are accepting responsibility for failures that are not
their fault.

In this engineer's opinion, the 12.0V vs 12V car electrical
system issue was your first warning shot about the unsuitability
of the popular BS170 transistors for this design.

It is going to be a millstone around your neck until you bite
the bullet and fix it.

-Chuck Harris, WA3UQV

On Tue, 6 May 2025 18:04:32 +0300 "Hans Summers via groups.io"
<hans.summers@...> wrote:

Hello all

Many people, myself included, have run the QMX calibration
procedure multiple times without damage to their BS170
transistors. I was developing the QMX firmware for 9 months,
including the calibration procedure which I ran literally
hundreds of times while developing it. Some unexplained failures
have indeed been reported too.

...