Noise on VCO voltage ramp

[Cursitor Doom]

Gentlemen,

I've got this weird problem with the network analyser I posted about
recently. The problem *seems* to be noise spikes on the DC voltage
control ramp which are causing spurious spikes in the frequency domain
on the RF output when viewed on an RF spectrum analyser. The peculiar
thing is these spikes on the RF output are not random; they come and
go according to the point the control voltage has reached as it ramps
up. Curiously, I cannot see anything amiss with the ramp signal when I
check it with a scope. I'd have expected to see at least *some* sign
of instability, but it appears rock steady. I'm just wondering if an
ordinary oscilloscope is really fast enough to pick out these
transients, though. Maybe they're there even though I can't see them.
Any suggestions as to what other instrument might be better suited to
this purpose? A DSO, maybe? Or if not, optimising the settings on the
analogue scope to have the best chance of spotting them?
thanks!
--

No deal? No problem! :-D

 

[Phil Hobbs]

On 2020-01-12 09:36, Cursitor Doom wrote:

Gentlemen,

I've got this weird problem with the network analyser I posted about
recently. The problem *seems* to be noise spikes on the DC voltage
control ramp which are causing spurious spikes in the frequency domain
on the RF output when viewed on an RF spectrum analyser. The peculiar
thing is these spikes on the RF output are not random; they come and
go according to the point the control voltage has reached as it ramps
up. Curiously, I cannot see anything amiss with the ramp signal when I
check it with a scope. I'd have expected to see at least *some* sign
of instability, but it appears rock steady. I'm just wondering if an
ordinary oscilloscope is really fast enough to pick out these
transients, though. Maybe they're there even though I can't see them.
Any suggestions as to what other instrument might be better suited to
this purpose? A DSO, maybe? Or if not, optimising the settings on the
analogue scope to have the best chance of spotting them?
thanks!

Finding an asynchronous glitch is hard on an analog scope.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Cursitor Doom]

On Sun, 12 Jan 2020 15:21:39 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>Finding an asynchronous glitch is hard on an analog scope.

It is to a major extent reproduceable, though, Phil. I can manually
override the ramp and set a voltage which will show up a glitch in the
frequency domain, which is a useful plus. You reckon it would be
better to use a DSO for this? I do have one.
--

No deal? No problem! :-D

 

[Phil Hobbs]

On 2020-01-12 16:36, Cursitor Doom wrote:

On Sun, 12 Jan 2020 15:21:39 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

Finding an asynchronous glitch is hard on an analog scope.

It is to a major extent reproduceable, though, Phil. I can manually
override the ramp and set a voltage which will show up a glitch in the
frequency domain, which is a useful plus. You reckon it would be
better to use a DSO for this? I do have one.

Frequency domain glitch? You mean a discrete spur?

A glitch is a transient time-domain animal. A DSO can save a single
instance, or (with averaging) ignore the noise and asynchronous
background and just reproduce the glitch itself.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Jeff Liebermann]

On Sun, 12 Jan 2020 14:36:27 +0000, Cursitor Doom
<curd@notformail.com> wrote:

I've got this weird problem with the network analyser I posted about
recently. The problem *seems* to be noise spikes on the DC voltage
control ramp which are causing spurious spikes in the frequency domain
on the RF output when viewed on an RF spectrum analyser.

In other words, it's picking up garbage from something in your shop
(or cave). I suggest you start by moving or removing all the
switching power supplies, wall warts, light dimmers, desk lamps, or
gizmos within a few feet that might have a switching power supply
inside. Next, cover the network analyzer with some aluminum foil to
see if the glitches are being delivered via RF. My desktop wi-fi
access point does that sometimes. If that also fails, drag your
network analyzer and scope to another part of your shop (or cave),
that's away from all the gizmos, and see if the problem persists. In
other words, determine if the garbage is internally generated,
externally radiated, or conducted via the power lines, clip leads,
cables, etc.

If you really want to see the noise, glitch, trash, garbage, or
whatever signal, set you scope so that the horizontal trigger is off
and the horizontal sweep is free running. Then, slooooooowly vary the
horizontal sweep until you see fairly stable glitches. If the noise
is periodic, you should be able to see something.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Cursitor Doom]

On Sun, 12 Jan 2020 17:17:04 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

Frequency domain glitch? You mean a discrete spur?
A glitch is a transient time-domain animal.

I could have put it better I guess. What I mean is I'm seeing thin
spikes in the RF output spectrum of the VNA at other frequencies than
the desired one. I'm guessing these spikes are the result of unwanted
transient voltage spikes present on the DC VCO control voltage which
sweeps the RF output frequency from 4Mhz through to 1.3Ghz.

A DSO can save a single
instance, or (with averaging) ignore the noise and asynchronous
background and just reproduce the glitch itself.

Well, Jeff has posted some advice for me on that aspect which I intend
to try out tomorrow using my Tek DSO which is probably much better
suited to the task than the analogue one I've hithertofore been
using..
--

No deal? No problem! :-D

 

[Cursitor Doom]

On Sun, 12 Jan 2020 14:22:35 -0800, Jeff Liebermann <jeffl@cruzio.com>
wrote:

In other words, it's picking up garbage from something in your shop
(or cave). I suggest you start by moving or removing all the
switching power supplies, wall warts, light dimmers, desk lamps, or
gizmos within a few feet that might have a switching power supply
inside. Next, cover the network analyzer with some aluminum foil to
see if the glitches are being delivered via RF.

Yeah, I did try all that and it didn't help, Jeff. Also there's no
glitches or noise when I pull the RF signal away, so at least it's not
something coming from the spectrum analyser.

My desktop wi-fi
access point does that sometimes. If that also fails, drag your
network analyzer and scope to another part of your shop (or cave),
that's away from all the gizmos, and see if the problem persists. In
other words, determine if the garbage is internally generated,
externally radiated, or conducted via the power lines, clip leads,
cables, etc.

I *suspect* noise is somehow getting onto the DC VCO ramp voltage and
manifesting as spikes in the RF output of the VNA accordingly.
Fortunately, there is a jack in the back of the VNA for the
application of an external VCO control voltage, so I plan to avail
myself of that with a big old linear bench supply and see if the
problem goes away.

If you really want to see the noise, glitch, trash, garbage, or
whatever signal, set you scope so that the horizontal trigger is off
and the horizontal sweep is free running. Then, slooooooowly vary the
horizontal sweep until you see fairly stable glitches. If the noise
is periodic, you should be able to see something.

Thanks, Jeff. Duly noted!

--

No deal? No problem! :-D

 

[Phil Hobbs]

On 2020-01-12 19:18, Cursitor Doom wrote:

On Sun, 12 Jan 2020 17:17:04 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

Frequency domain glitch? You mean a discrete spur? A glitch is a
transient time-domain animal.

I could have put it better I guess. What I mean is I'm seeing thin
spikes in the RF output spectrum of the VNA at other frequencies
than the desired one.

Which is a discrete spur. Gotcha.

I'm guessing these spikes are the result of unwanted transient
voltage spikes present on the DC VCO control voltage which sweeps the
RF output frequency from 4Mhz through to 1.3Ghz.

If there's a forest of them, spaced at equal intervals, they could be
coming from a periodic time-domain source.

A DSO can save a single instance, or (with averaging) ignore the
noise and asynchronous background and just reproduce the glitch
itself.

Well, Jeff has posted some advice for me on that aspect which I
intend to try out tomorrow using my Tek DSO which is probably much
better suited to the task than the analogue one I've hithertofore
been using..

Yeah, I'm fonder of analog scopes than JL is, but my beautiful Tek 2467
hasn't been used in quite awhile, whereas I use the 1180x, TDS 694C and
TDS 784As most days that I'm in the lab. For manual driving, the 2467
has the best triggering of the lot, but it's very hard to beat a DSO for
general use.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Cursitor Doom]

On Mon, 13 Jan 2020 00:24:38 +0000, Cursitor Doom
<curd@notformail.com> wrote:

If you really want to see the noise, glitch, trash, garbage, or
whatever signal, set you scope so that the horizontal trigger is off
and the horizontal sweep is free running. Then, slooooooowly vary the
horizontal sweep until you see fairly stable glitches. If the noise
is periodic, you should be able to see something.

Thanks, Jeff. Duly noted!

Oh, and btw, I know you like details such as this, I'll be using my
Tek 2232 DSO for this measurement. I don't really get on with digital
scopes, but seems like there's little alternative for this job.

--

No deal? No problem! :-D

 

[Cursitor Doom]

On Sun, 12 Jan 2020 19:40:23 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

I'm guessing these spikes are the result of unwanted transient
voltage spikes present on the DC VCO control voltage which sweeps the
RF output frequency from 4Mhz through to 1.3Ghz.

If there's a forest of them, spaced at equal intervals, they could be
coming from a periodic time-domain source.

There *are* equally-spaced spikes at the lower end of the spectrum, up
to about 100Mhz, but thereafter they assume a far more random
appearance - although they are NOT random as they reappear at the same
place on the spectrum and at the same amplitude with each sweep. Plus
there *is*lower-level truly random noise around 500-600Mhz - so looks
like 3 different and unrelated faults to fix!! I do love my vintage
test gear, but I often spend more time fixing it than using it!

Yeah, I'm fonder of analog scopes than JL is, but my beautiful Tek 2467
hasn't been used in quite awhile, whereas I use the 1180x, TDS 694C and
TDS 784As most days that I'm in the lab. For manual driving, the 2467
has the best triggering of the lot, but it's very hard to beat a DSO for
general use.

I only have one DSO out of 13 scopes in all: the Tek 2232. It's
nothing special; it was okay in its day I guess, but I'm sure John's
cheapo Chinese Rigol could piss all over it in a head-to-head
"test-off" lol.
--

No deal? No problem! :-D

 

[Phil Hobbs]

On 2020-01-12 20:59, Cursitor Doom wrote:

On Sun, 12 Jan 2020 19:40:23 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

I'm guessing these spikes are the result of unwanted transient
voltage spikes present on the DC VCO control voltage which sweeps the
RF output frequency from 4Mhz through to 1.3Ghz.

If there's a forest of them, spaced at equal intervals, they could be
coming from a periodic time-domain source.

There *are* equally-spaced spikes at the lower end of the spectrum, up
to about 100Mhz, but thereafter they assume a far more random
appearance - although they are NOT random as they reappear at the same
place on the spectrum and at the same amplitude with each sweep. Plus
there *is*lower-level truly random noise around 500-600Mhz - so looks
like 3 different and unrelated faults to fix!! I do love my vintage
test gear, but I often spend more time fixing it than using it!

Yeah, I'm fonder of analog scopes than JL is, but my beautiful Tek 2467
hasn't been used in quite awhile, whereas I use the 1180x, TDS 694C and
TDS 784As most days that I'm in the lab. For manual driving, the 2467
has the best triggering of the lot, but it's very hard to beat a DSO for
general use.

I only have one DSO out of 13 scopes in all: the Tek 2232. It's
nothing special; it was okay in its day I guess, but I'm sure John's
cheapo Chinese Rigol could piss all over it in a head-to-head
"test-off" lol.

I'm the other way round: 2 analogue scopes out of 9 working ones: a 475A
and a 2467. The others are TDS 784As, a TDS 694C, 11802, 11801C, HP
54something, and an Owon something-or-other.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Jeff Liebermann]

On Mon, 13 Jan 2020 01:46:08 +0000, Cursitor Doom
<curd@notformail.com> wrote:

On Mon, 13 Jan 2020 00:24:38 +0000, Cursitor Doom
curd@notformail.com> wrote:

If you really want to see the noise, glitch, trash, garbage, or
whatever signal, set you scope so that the horizontal trigger is off
and the horizontal sweep is free running. Then, slooooooowly vary the
horizontal sweep until you see fairly stable glitches. If the noise
is periodic, you should be able to see something.

Thanks, Jeff. Duly noted!

Oh, and btw, I know you like details such as this, I'll be using my
Tek 2232 DSO for this measurement. I don't really get on with digital
scopes, but seems like there's little alternative for this job.

Bad idea. The Tek 2232 has both digital and analog storage:
<https://www.tek.com/datasheet/2232-digital-and-analog-oscillscope>
I suggest you use it as a conventional analog scope for the
untriggered horizontal sweep. If the frequency of the glitch source
is stable, you should be able to "tune" it in by adjusting the
horizontal sweep (with the trigger turned off). That works much
better in analog mode than in digital. Better yet, go back to using
your analog Tek 2465A for looking at the VCO control voltage.

Incidentally, I just noticed that you screwed up in your original
posting. You provided most of the details, a few of the numbers, but
failed to describe the "weird problem with the network analyzer" and
what "spurious spikes in the frequency domain on the RF output" might
be. Is that like a spurious RF signal appearing on the SA swept
display? If so, are you picking up some junk from nearby radio or TV
stations? If you can see it, what's the frequency on the SA? I can
also imagine that your test setup or cabling may be causing these
problems. A probe on the VCO line could easily pickup RF junk from
everywhere.

All this goes back to my three commandments for getting a sane answer
to questions on Usenet:
1. What problem are you trying to solve? Just one or two lines and
leave the details for later.
2. What do you have to work with? What's your level of expertise and
what tools and test equipment do you have available?
3. Where are you stuck and what did you do to get there?


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Jeff Liebermann]

On Mon, 13 Jan 2020 00:18:13 +0000, Cursitor Doom
<curd@notformail.com> wrote:

On Sun, 12 Jan 2020 17:17:04 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

Frequency domain glitch? You mean a discrete spur?
A glitch is a transient time-domain animal.

I could have put it better I guess. What I mean is I'm seeing thin
spikes in the RF output spectrum of the VNA at other frequencies than
the desired one. I'm guessing these spikes are the result of unwanted
transient voltage spikes present on the DC VCO control voltage which
sweeps the RF output frequency from 4Mhz through to 1.3Ghz.

I would guess(tm) that they are mixer spurs produced by the two
oscillators used to produce the network analyzer RF output signal. A
clue as to their relative amplitude compared to the RF output would be
helpful.

Look at the spurious stuff coming out of the network analyzer. Now,
vary the network analyzer frequency and see how they move. You can
tell the order (harmonic number) of the spurious components by how
much they move. For example, if you change the network analyzer 1 MHz
and the spur moves 3 MHz, than you are dealing with the 3rd harmonic
of one of the two input signals to the mixer in the network analyzer.

I also suspect that you might be picking up RF from nearby radio and
TV broadcast stations. Install a small antenna into the RF IN port of
your spectrum analyzer and see if there are signals at the same
frequencies that you are seeing them on the network analyzer RF
output. If so, you might check the shielding and grounding in the
network analyzer.

A DSO can save a single
instance, or (with averaging) ignore the noise and asynchronous
background and just reproduce the glitch itself.

Well, Jeff has posted some advice for me on that aspect which I intend
to try out tomorrow using my Tek DSO which is probably much better
suited to the task than the analogue one I've hithertofore been
using..

Yep. Failure to observe my advice will result in divine retribution.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Cursitor Doom]

On Sun, 12 Jan 2020 20:21:53 -0800, Jeff Liebermann <jeffl@cruzio.com>
wrote:

>Yep. Failure to observe my advice will result in divine retribution.

I wouldn't dare, Jeff. Thanks again for the tips; they will be
followed up....
--

No deal? No problem! :-D

 

[Cursitor Doom]

On Sun, 12 Jan 2020 19:59:52 -0800, Jeff Liebermann <jeffl@cruzio.com>
wrote:

Bad idea. The Tek 2232 has both digital and analog storage:
https://www.tek.com/datasheet/2232-digital-and-analog-oscillscope
I suggest you use it as a conventional analog scope for the
untriggered horizontal sweep. If the frequency of the glitch source
is stable, you should be able to "tune" it in by adjusting the
horizontal sweep (with the trigger turned off). That works much
better in analog mode than in digital. Better yet, go back to using
your analog Tek 2465A for looking at the VCO control voltage.

I'm afraid I don't have that option at the moment. The 2465A blew up a
couple of days ago and has now joined my pile of "awaiting attention"
junk. I didn't blow it up, by the way; it managed it all by itself.

Incidentally, I just noticed that you screwed up in your original
posting. You provided most of the details, a few of the numbers, but
failed to describe the "weird problem with the network analyzer" and
what "spurious spikes in the frequency domain on the RF output" might
be. Is that like a spurious RF signal appearing on the SA swept
display?

I think you may have missed the clarification I posted. Here it is
again:

"I could have put it better I guess. What I mean is I'm seeing thin
spikes in the RF output spectrum of the VNA at other frequencies than
the desired one. I'm guessing these spikes are the result of unwanted
transient voltage spikes present on the DC VCO control voltage which
sweeps the RF output frequency from 4Mhz through to 1.3Ghz."

If so, are you picking up some junk from nearby radio or TV
stations? If you can see it, what's the frequency on the SA? I can
also imagine that your test setup or cabling may be causing these
problems. A probe on the VCO line could easily pickup RF junk from
everywhere.

I think that's a very valuable point there. One possible 'infection
vector' for noise is the method I'm using for sniffing the VNA. As you
may know, spectrum analyzers of this vintage were very intolerant of
DC on the input socket. There doesn't even seem to be a margin of
error! So any DC riding on the signal you're trying to obtain a
spectrum for and you blow up the front end. And I have a bit of a
complex when it comes to blowing up test equipment. I'm very, very
cautious these days, so I've just used a few turns of wire to couple
the signal from the VNA to the SA. This removes the DC risk, but does
mean there's no shielding around the sniffer coil. And right next to
these items there's my linear power supply powering up my Yaesu 857d.
Now the linear supply should be fine, being linear, but I'm just
wondering if the Yaesu, even in receive mode, might be generating some
stray spurious that the SA is picking up somehow. I'll switch those
items off when I try it again. My working practices are a bit slapdash
I must admit, but no worse than the average hobbyist I would imagine.

--

No deal? No problem! :-D

 

[Gerhard Hoffmann]

Am 13.01.20 um 13:09 schrieb Cursitor Doom:

I'm afraid I don't have that option at the moment. The 2465A blew up a
couple of days ago and has now joined my pile of "awaiting attention"
junk. I didn't blow it up, by the way; it managed it all by itself.

Probably that hybrid that sends all those 24xx to their heaven.
Runs too hot. Don't expect to get a replacement hybrid.

Now back to the weird spectra that my Agilent 89441A presents under
remote control.

And while I'm at it, how does that Wehnelt cylinder stuff work in an
analog scope? I have a 200 MHz Iwatsu since > 35 years that I kinda love
and that has a trace sharpness / astigmatism problem.

cheers, Gerhard

 

[Cursitor Doom]

On Mon, 13 Jan 2020 13:28:46 +0100, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:

Probably that hybrid that sends all those 24xx to their heaven.
Runs too hot. Don't expect to get a replacement hybrid.

No, it's not that chip that's gone. And those are perfectly happy to
run hot, the problem comes when people accidentally block the air
vents directly behind the chip, in which case yes, of course it will
blow.

--

No deal? No problem! :-D

 

Cursitor Doom <curd@notformail.com> wrote in
news:cfmo1ftqkv08v7jb4pml2t51uebu5oegud@4ax.com:

On Sun, 12 Jan 2020 20:21:53 -0800, Jeff Liebermann
jeffl@cruzio.com> wrote:

Yep. Failure to observe my advice will result in divine
retribution.

I wouldn't dare, Jeff. Thanks again for the tips; they will be
followed up....

Divine intervention is what happens when your design fails to impress,
and God decides to "let the smoke out" of your circuit.

 

[Fox's Mercantile]

On 1/13/20 6:09 AM, Cursitor Doom wrote:

I'm afraid I don't have that option at the moment. The 2465A blew up a
couple of days ago and has now joined my pile of "awaiting attention"
junk. I didn't blow it up, by the way; it managed it all by itself.

My 2445 lost it's trace.
I replaced the HV module. $56 from a guy in Greece.
Works fine now.


--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com

 

[Jeff Liebermann]

On Mon, 13 Jan 2020 14:40:31 +0000 (UTC),
DecadentLinuxUserNumeroUno@decadence.org wrote:

Cursitor Doom <curd@notformail.com> wrote in
news:cfmo1ftqkv08v7jb4pml2t51uebu5oegud@4ax.com:

On Sun, 12 Jan 2020 20:21:53 -0800, Jeff Liebermann
jeffl@cruzio.com> wrote:

Yep. Failure to observe my advice will result in divine
retribution.

I wouldn't dare, Jeff. Thanks again for the tips; they will be
followed up....

Divine intervention is what happens when your design fails to impress,
and God decides to "let the smoke out" of your circuit.

Divine retribution and intervention are quite different. Divine
retribution is where a lightning bolt from out of the clear blue sky
strikes the transgressor down following a chronic failure to RTFM and
follow the instructions. Divine intervention is where the
participants in some technical or political discussion are unable to
reach a suitable conclusion or compromise, and both need to be
reminded who is the boss.

Also, none of my better designs have impressed anyone. In most cases,
they attracted far more criticism than praise. Whenever I provide
something to the design review committee for target practice, I
consider it a very good sign if they take the time to tear it apart
and offer their collective misjudgment. However, if the committee is
passive and offers little criticism, I'm certain that I've done
something fundamentally wrong.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558