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On Thu, 06 Sep 2018 13:00:09 -0700
"ajparent1/KB1GMX" <kb1gmx@...> wrote:

Tim,

First anything on scope that is not time or phase related is a gross
test, as apposed to fine grained test. That said if you see flat
topping you have gone too far.

That's my whole point. It's why I say find the compression point under
CW generation and don't go past it with peak SSB loads. A scope works
fine for this.

It's far easier and cheaper to do than with a two-tone test and a
spectrum analyzer.

However there are other anomalies
that show as well like asymmetric centers where the smooth sinusoidal
valley should be top and bottom.? Also Trapezoid (bowtie) displays
are more informative as well.? If you use that tool you have to
employ it fully to extract what it can tell you.?

Trying to identify asymmetric centers is, again, difficult to do. And
trapezoid displays are more difficult to set up in a test bed.

If I see flat topping I know I'm way to far there.

That's my whole point.

For CW work using a linear amp (inside the radio) is mostly not much
sense.? So testing under those conditions for anything but spurs and
trash is meaningless.? SSB requires linear operation though out the
power range and CW can't test that.

But *CW* can identify the compression point of the amplifier chain,
assuming the radio doesn't totally redo the biasing of the elements in
the amplifier chain. That's certainly the case for the ubitx.

For radios of this caliber two tones will show more than enough pain
and grief.? Its far as possible from a 40M SDR HiFi crowd as you can
get.??

A scope and a CW signal will show when the pain and grief is most
likely to start, even in a radio of this caliber. Again, it may not
provide the last possible watt out under SSB but if you don't have the
test equipment to measure the pain and grief that last watt generates
then being a good neighbor is a good thing to be. That last watt won't
actually help you communicate better in most cases.

tim ab0wr

Allison
Worn and mostly tattered BTDT tee shirt. Used to polish truck!

Rather than hem and haw of how to test it or the ins and outs of scopes?
(you did get that I consider it the inferior instrument?).

What solutions do you have for the known problems?

Allison

Allison,

The scope is perfectly usable when used as intended and you know what
it is telling you.

The known problems?

I was the first to try adding an mmic after Q90 to
help with making output more constant if you remember. Because of
physical limitations all I could get it to do was cause an oscillation
that destroyed the IRF510.

I also replaced the predriver and driver with 5109's early on (if
you remember I consulted with you on this) and, once again, caused the
IRF510's to be fried on 80M because of increased gain and probably
oscillation again.

I put the project away back in June and moved on to other pressing
projects mostly because I had no real solution to the IMD issue.

What I have to offer as solutions to other issues is meaningless when it
comes to how to set up a transmitter to minimize IMD due to overdriving
the amplifier chain. The solution for that problem is merely to not
overdrive the amplifier chain. The oscilloscope can be used for doing
that.

tim ab0wr

On Thu, 06 Sep 2018 17:45:50 -0700
"ajparent1/KB1GMX" <kb1gmx@...> wrote:

Rather than hem and haw of how to test it or the ins and outs of
scopes (you did get that I consider it the inferior instrument?).

What solutions do you have for the known problems?

Allison

Tim,

Known problems:
Amplifier power vs frequency.
IMD extremely poor for power over 2W
Output Low pass filters.
Spurs, unwanted and unfiltered mix products that show above 20mhz.
Carrier leakage that is not related to modulator or 12mhz filter.

>>>I was the first to try adding an mmic after Q90 to
help with making output more constant if you remember. Because of
physical limitations all I could get it to do was cause an oscillation
that destroyed the IRF510.<<

Both Jerry and I tried that.... instability was rife. I used my HP current limited power
supply didn't fry things.

FYI the IMD issue is related to the first item on the list.? The amp is struggling to work
because of poor choice of transistors for most of the stages before the finals.
Put decently capable parts with reasonable bias elements and you get a
significant improvement.

Do offer what you have as its part of a total set of things that need attention.
However fixing it tends to be for the brave as things like cutting traces, rewinding coils,
are needed.

Hope that helps.

Allison

Allison,

I agree with everything you have said here.

I really don't have anything new to offer at this time. I've moved on
to other, more pressing projects. Perhaps I'll get back to the ubitx as
the weather gets colder and the yard needs less work.

tim ab0wr

On Fri, 07 Sep 2018 10:58:54 -0700
"ajparent1/KB1GMX" <kb1gmx@...> wrote:

Tim,

Known problems:
Amplifier power vs frequency.
IMD extremely poor for power over 2W
Output Low pass filters.
Spurs, unwanted and unfiltered mix products that show above 20mhz.
Carrier leakage that is not related to modulator or 12mhz filter.

I was the first to try adding an mmic after Q90 to

help with making output more constant if you remember. Because of
physical limitations all I could get it to do was cause an oscillation
that destroyed the IRF510.<<

Both Jerry and I tried that.... instability was rife. I used my HP
current limited power supply didn't fry things.

FYI the IMD issue is related to the first item on the list.? The amp
is struggling to work because of poor choice of transistors for most
of the stages before the finals. Put decently capable parts with
reasonable bias elements and you get a significant improvement.

Do offer what you have as its part of a total set of things that need
attention. However fixing it tends to be for the brave as things like
cutting traces, rewinding coils, are needed.

Hope that helps.

Allison