Re: Distorted Sine Wave

On 6/1/24 14:07, Cursitor Doom wrote:

On Fri, 31 May 2024 17:33:51 -0700, boB wrote:
 

On Fri, 31 May 2024 17:02:13 -0700, boB <boB@K7IQ.com> wrote:
>

On Fri, 31 May 2024 21:40:04 -0000 (UTC), Cursitor Doom
<cd999666@notformail.com> wrote:
>

On Fri, 31 May 2024 15:10:32 -0400, Joe Gwinn wrote:
>

On Fri, 31 May 2024 18:54:06 -0000 (UTC), Cursitor Doom
<cd999666@notformail.com> wrote:
>

On Fri, 31 May 2024 11:34:46 -0400, Joe Gwinn wrote:
>

On Thu, 30 May 2024 16:24:25 -0700, john larkin <jl@650pot.com>
wrote:
>

On Thu, 30 May 2024 18:53:29 -0400, Joe Gwinn
<joegwinn@comcast.net>
wrote:
>

On Thu, 30 May 2024 14:56:30 -0700, john larkin <jl@650pot.com>
wrote:
>

On Thu, 30 May 2024 16:06:47 -0400, Joe Gwinn
<joegwinn@comcast.net>
wrote:
>

On Thu, 30 May 2024 15:02:44 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
>

On 2024-05-29 18:59, Joe Gwinn wrote:

On Wed, 29 May 2024 22:11:47 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
>

Cursitor Doom <cd999666@notformail.com> wrote:

On Wed, 29 May 2024 13:42:13 -0700, john larkin wrote:
>

On Wed, 29 May 2024 21:43:54 +0200, Arie de Muijnck
<noreply@ademu.com>
wrote:
>

On 2024-05-29 19:07, Cursitor Doom wrote:

Gentlemen,
>
Whilst fault-finding on my HP 8566B spectrum analyzer,
I've found the 10Mhz reference oscillator is generating
an 'unsatisfactory waveform'
which may be causing the device to be unable to lock
it's main PLL. I've come across this waveshape before,
but mostly with oscillators I was building and in the
process of trying to iron out the wrinkles of and
certainly NOT a critical reference oscillator from a
respected manufacturer. Can anyone tell what's most
likely going on here?
>
https://disk.yandex.com/i/z6fYbeVfPRK7aA

>
>
Looks like reflections in the cable. Try the 50 Ohm
termination.
>
Arie

>
If the drive is a sine wave, a cable can't generate that
2nd harmonic.

>
I don't understand how a reflection can account for it
either.
THe cable's only 4' long! However, with the 50 ohm input
enabled, the 2nd harmonic disappears. It's just one of
those inexplicable mysteries that no one knows the answer
to. :)

>
That?s pretty diagnostic. There must be an LC filter on the
output?mis-terminating it will cause all sorts of
frequency-response whoopdedoos.

>
It also occurs to me that if there is a diode in series with
a resistor somewhere, the impedance presented to the feed
coax may be 50 ohms for positive input voltage, and say 10
Kohm for negative.  At the very least one could get an
inverted reflection on negative.
>
Joe Gwinn
>

Yeah, or an emitter follower.  Good point.

>
Plus some LC filter wiggles, to distort and smooth things.
>
I dug around and found a copy of the HP 8566B spectrum analyzer
service manual.  The 10 MHz ref input is an amplifier driving a
mixer,
with not hint of for instance a TTL input.  So, the problem must
be elsewhere.  Or, it's just busted.
>
.<chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://

xdevs.com/doc/HP_Agilent_Keysight/
HP%208566B%20Troubleshooting%20&%20Repair%20Vol.%201.pdf>

>
Joe Gwinn

>
334 pages! Where is the issue?

>
The pagination was unclear, so I didn't see a way to say.  How I
found it was to look at the schematics.  Look for module A22.
Don't think search works on such images, but visual search didn't
take that long.
>
Joe Gwinn

>
Too much work for free consulting.

>
I took another look.  There is a page reference on the right edge,
near the bottom, which is not marked as a page X of Y, but is.
>
Anyway, look at pages 59 and 77.  At 77, look for A22 in the lower
left region.  Just above, look for INT and EXT jacks.  The EXT jack
is where an external reference enters.
>
Joe Gwinn

>
It's just a block diagram of the reference oscillator module. There's
no detailed schematic of the oscillator itself. At least that's the
case with the PDF version of the Service Manual I have.

>
It's probably in the book that I don't have, if it was ever released.
>
Joe Gwinn

>
HP actually published at least 5 manuals of various kinds about this
analyzer, so it's possible it's in one of the others. However, the
actual service manual is where I'd expect to find it if they published
it at all.
The other titles are:
>
HP 8566B Operator's Manual HP 8566B Installation and Verification
Manual HP 8566B Test and Adjustments Manual HP 8566B Troubleshooting
and Repair Manual
>
So if the answers are not in *any* of the above, it'd be jolly rotten
luck indeed!

>
>
>
Looking at that waveform again...
>
Could it be that the wavform you are seeing there is not a harmonic but
just a partial cancelation due to reflections ?
>
If you look at one peak vs. the other, they look about the same time to
me.  About 1 scope division.  Just the amplitude looks different on
alternating cycles.   A non-linearity I would think would make an even
harmonic.

>
I thought I said the wrong thing !  I mean odd harmonic(s) from a
non-linearity.
>
>

2nd harmonic is usually due to non 1/2 wave symetry (DC
offset bascially)
>
>

Here, I meant even harmonic(s)  not just second harmonic.
>
It's rather hot today in Phoenix..

 1. Everybody makes careless mistakes.
2. I don't need high temperatures to make them!
 I've taken a shot of the waveform into the 50 ohm input. It's around 850mV
peak-peak. Hopefully the slight distortion I spoke about is visible; the
slightly more leisurely negative-going excursions WRT their positive-going
counterparts. So it's not a pure sine wave as one would expect. Does it
matter? I don't know!
 https://disk.yandex.com/i/7cuuBimDbOIBZw

The shape looks perfectly acceptable to me. This is +3dBm into 50 Ohms.
Is that what it's supposed to be? Canned reference oscillators most
often deliver +13dBm, sometimes +10dBm.
Jeroen Belleman