Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > sci.electronics.design > #464429 > unrolled thread

EMI problems

Back to article view | Back to sci.electronics.design

Contents

  EMI problems John Larkin <jjlarkin@highland_snip_technology.com> - 2017-06-14 16:09 -0700
    Re: EMI problems Martin Riddle <martin_ridd@verizon.net> - 2017-06-14 20:05 -0400
      Re: EMI problems John Larkin <jjlarkin@highland_snip_technology.com> - 2017-06-14 18:01 -0700
        Re: EMI problems o pere o <me@somewhere.net> - 2017-06-15 09:28 +0200
          Re: EMI problems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-06-15 10:59 -0400
            Re: EMI problems Don Kuenz <g@crcomp.net> - 2017-06-21 02:53 +0000
          Re: EMI problems John Larkin <jjlarkin@highlandtechnology.com> - 2017-06-15 07:59 -0700
            Re: EMI problems George Herold <gherold@teachspin.com> - 2017-06-15 08:07 -0700
              Re: EMI problems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-06-15 11:12 -0400
                Re: EMI problems George Herold <gherold@teachspin.com> - 2017-06-15 08:42 -0700
              Re: EMI problems John Larkin <jjlarkin@highlandtechnology.com> - 2017-06-15 09:38 -0700
            Re: EMI problems Robert Baer <robertbaer@localnet.com> - 2017-06-16 22:06 -0800
    Re: EMI problems Jon Elson <jmelson@wustl.edu> - 2017-06-15 14:14 -0500
      Re: EMI problems John Larkin <jjlarkin@highland_snip_technology.com> - 2017-06-15 13:55 -0700
        Re: EMI problems Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-06-15 14:02 -0700
        Re: EMI problems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-06-16 12:43 -0400
          Re: EMI problems John Larkin <jjlarkin@highland_snip_technology.com> - 2017-06-16 10:11 -0700
            Re: EMI problems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-06-16 13:24 -0400
        Re: EMI problems Jeff Liebermann <jeffl@cruzio.com> - 2017-06-16 10:37 -0700
        Re: EMI problems Jon Elson <jmelson@wustl.edu> - 2017-06-16 13:31 -0500
          Re: EMI problems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-06-16 14:46 -0400
            Re: EMI problems John Larkin <jjlarkin@highland_snip_technology.com> - 2017-06-16 12:25 -0700
            Re: EMI problems George Herold <gherold@teachspin.com> - 2017-06-16 13:07 -0700
          Re: EMI problems John Larkin <jjlarkin@highland_snip_technology.com> - 2017-06-16 12:22 -0700
      Re: EMI problems upsidedown@downunder.com - 2017-06-16 09:35 +0300
        Re: EMI problems John Larkin <jjlarkin@highlandtechnology.com> - 2017-06-16 06:40 -0700
    Re: EMI problems Joerg <news@analogconsultants.com> - 2017-06-15 12:27 -0700
      Re: EMI problems John Larkin <jjlarkin@highland_snip_technology.com> - 2017-06-15 12:47 -0700
        Re: EMI problems Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-06-15 12:57 -0700
          Re: EMI problems Joerg <news@analogconsultants.com> - 2017-06-15 13:12 -0700
        Re: EMI problems Joerg <news@analogconsultants.com> - 2017-06-15 13:03 -0700
      Re: EMI problems "Lund-Nielsen, Jorgen" <jorgen.lund-nielsen@xyz123desy.de> - 2017-06-16 08:58 +0200
    Re: EMI problems Jeff Liebermann <jeffl@cruzio.com> - 2017-06-16 10:03 -0700
      Re: EMI problems John Larkin <jjlarkin@highland_snip_technology.com> - 2017-06-16 11:09 -0700
        Re: EMI problems Jeff Liebermann <jeffl@cruzio.com> - 2017-06-16 12:06 -0700
          Re: EMI problems John Larkin <jjlarkin@highland_snip_technology.com> - 2017-06-16 12:34 -0700
            Re: EMI problems Jeff Liebermann <jeffl@cruzio.com> - 2017-06-17 09:22 -0700
              Re: EMI problems John Larkin <jjlarkin@highlandtechnology.com> - 2017-06-17 10:08 -0700
                Re: EMI problems John Larkin <jjlarkin@highlandtechnology.com> - 2017-06-17 11:07 -0700
                  Re: EMI problems Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2017-06-17 21:30 +0300
                  Re: EMI problems pcdhobbs@gmail.com - 2017-06-17 16:34 -0700
                  Re: EMI problems krw@notreal.com - 2017-06-17 20:44 -0400
                  Re: EMI problems George Herold <gherold@teachspin.com> - 2017-06-19 06:03 -0700
                Re: EMI problems Jeff Liebermann <jeffl@cruzio.com> - 2017-06-18 12:49 -0700
                  Re: EMI problems John Larkin <jjlarkin@highlandtechnology.com> - 2017-06-18 13:42 -0700
                    Re: EMI problems Jeff Liebermann <jeffl@cruzio.com> - 2017-06-18 15:50 -0700
                      Re: EMI problems John Larkin <jjlarkin@highlandtechnology.com> - 2017-06-18 17:15 -0700
                        Re: EMI problems upsidedown@downunder.com - 2017-06-19 09:39 +0300
                          Re: EMI problems upsidedown@downunder.com - 2017-06-19 09:48 +0300
                            Re: EMI problems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-06-19 12:45 -0400
      Re: EMI problems "John Miles, KE5FX" <jmiles@gmail.com> - 2017-06-16 15:30 -0700
        Re: EMI problems John Larkin <jjlarkin@highland_snip_technology.com> - 2017-06-16 18:10 -0700
          Re: EMI problems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-06-17 11:08 -0400
        Re: EMI problems upsidedown@downunder.com - 2017-06-17 14:25 +0300
        Re: EMI problems Jeff Liebermann <jeffl@cruzio.com> - 2017-06-17 09:35 -0700
          Re: EMI problems John Larkin <jjlarkin@highlandtechnology.com> - 2017-06-17 10:42 -0700
    Re: EMI problems upsidedown@downunder.com - 2017-06-17 14:45 +0300
      Re: EMI problems John Larkin <jjlarkin@highlandtechnology.com> - 2017-06-17 08:28 -0700

Page 2 of 3 — ← Prev page 1 [2] 3  Next page →

#464713

On 06/16/2017 02:31 PM, Jon Elson wrote:
> John Larkin wrote:
> 
> 
>> I have a cap across the amp power connector on the inside. It's from a
>> switching wall wart! The DUT power (+-6V) comes through 3.3nF feedthru
>> caps, ebay bag-o from Lithuania.
>>
> That's NOWHERE good enough!  You need a feedthrough cap there, too.  That 
> wall-wart jack is the least suppressing port on the can, so most likely the 
> primary way interference gets in.
>> It seems to work! I'm seeing 15 mV RMS reported by the scope.
>> Correcting for the X100 amp, and the 200 MHz scope bandwidth, the 100
>> MHz noise is 106 uV RMS, 10.6 nV/rtHz. The noise spectrum looks flat
>> up to the scope's 200 MHz rolloff, so the 100 MHz correction is mostly
>> honest.
>>
>> I had to bolt both boxes to the bottom of the cookie can, for good
>> grounding.
>>
>> Should we ship a Danish Butter Cookie can with each production unit?
>>
>>
>>
> Only if still filled with cookies.  Instruction booklet should indicate the 
> end user needs to eat all the cookies before installing the electronics into 
> the can.
> 
> Jon
> 

That's the upmarket version of Thor Labs' Lab Snacks.  Some people get a
lot of them: https://www.youtube.com/watch?v=zhOmwTOqsbU .  That would
have hurt more with cookie tins.

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

[toc] | [prev] | [next] | [standalone]

#464725

On Fri, 16 Jun 2017 14:46:43 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 06/16/2017 02:31 PM, Jon Elson wrote:
>> John Larkin wrote:
>> 
>> 
>>> I have a cap across the amp power connector on the inside. It's from a
>>> switching wall wart! The DUT power (+-6V) comes through 3.3nF feedthru
>>> caps, ebay bag-o from Lithuania.
>>>
>> That's NOWHERE good enough!  You need a feedthrough cap there, too.  That 
>> wall-wart jack is the least suppressing port on the can, so most likely the 
>> primary way interference gets in.
>>> It seems to work! I'm seeing 15 mV RMS reported by the scope.
>>> Correcting for the X100 amp, and the 200 MHz scope bandwidth, the 100
>>> MHz noise is 106 uV RMS, 10.6 nV/rtHz. The noise spectrum looks flat
>>> up to the scope's 200 MHz rolloff, so the 100 MHz correction is mostly
>>> honest.
>>>
>>> I had to bolt both boxes to the bottom of the cookie can, for good
>>> grounding.
>>>
>>> Should we ship a Danish Butter Cookie can with each production unit?
>>>
>>>
>>>
>> Only if still filled with cookies.  Instruction booklet should indicate the 
>> end user needs to eat all the cookies before installing the electronics into 
>> the can.
>> 
>> Jon
>> 

I sometimes buy stuff from ebay and get some sort of extra treat
inside. And sometime a Bible verse.

>
>That's the upmarket version of Thor Labs' Lab Snacks.  Some people get a
>lot of them: https://www.youtube.com/watch?v=zhOmwTOqsbU .  That would
>have hurt more with cookie tins.
>
>Cheers
>
>Phil Hobbs

That makes no sense at all. Great.


-- 

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement 

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

[toc] | [prev] | [next] | [standalone]

#464734

On Friday, June 16, 2017 at 2:46:53 PM UTC-4, Phil Hobbs wrote:
> On 06/16/2017 02:31 PM, Jon Elson wrote:
> > John Larkin wrote:
> > 
> > 
> >> I have a cap across the amp power connector on the inside. It's from a
> >> switching wall wart! The DUT power (+-6V) comes through 3.3nF feedthru
> >> caps, ebay bag-o from Lithuania.
> >>
> > That's NOWHERE good enough!  You need a feedthrough cap there, too.  That 
> > wall-wart jack is the least suppressing port on the can, so most likely the 
> > primary way interference gets in.
> >> It seems to work! I'm seeing 15 mV RMS reported by the scope.
> >> Correcting for the X100 amp, and the 200 MHz scope bandwidth, the 100
> >> MHz noise is 106 uV RMS, 10.6 nV/rtHz. The noise spectrum looks flat
> >> up to the scope's 200 MHz rolloff, so the 100 MHz correction is mostly
> >> honest.
> >>
> >> I had to bolt both boxes to the bottom of the cookie can, for good
> >> grounding.
> >>
> >> Should we ship a Danish Butter Cookie can with each production unit?
> >>
> >>
> >>
> > Only if still filled with cookies.  Instruction booklet should indicate the 
> > end user needs to eat all the cookies before installing the electronics into 
> > the can.
> > 
> > Jon
> > 
> 
> That's the upmarket version of Thor Labs' Lab Snacks.  Some people get a
> lot of them: https://www.youtube.com/watch?v=zhOmwTOqsbU .  That would
> have hurt more with cookie tins.

Grin, I only get a lousy bag of microwave popcorn from Advanced Circuits.

George H. 
(It's all about the prize inside.)

> 
> Cheers
> 
> Phil Hobbs
> 
> -- 
> Dr Philip C D Hobbs
> Principal Consultant
> ElectroOptical Innovations LLC
> Optics, Electro-optics, Photonics, Analog Electronics
> 
> 160 North State Road #203
> Briarcliff Manor NY 10510
> 
> hobbs at electrooptical dot net
> http://electrooptical.net

[toc] | [prev] | [next] | [standalone]

#464723

On Fri, 16 Jun 2017 13:31:57 -0500, Jon Elson <jmelson@wustl.edu>
wrote:

>John Larkin wrote:
>
>
>> I have a cap across the amp power connector on the inside. It's from a
>> switching wall wart! The DUT power (+-6V) comes through 3.3nF feedthru
>> caps, ebay bag-o from Lithuania.
>> 
>That's NOWHERE good enough! 


But it is good enough.


 You need a feedthrough cap there, too.  That 
>wall-wart jack is the least suppressing port on the can, so most likely the 
>primary way interference gets in.

But it doesn't. My noise floor is flat when the gear is in the can.
And I'm seeing under 9 nV/rootHz RMS noise at the amp output in a 100
MHz bandwidth. That's almost exactly what I expected from simulation.


-- 

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement 

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

[toc] | [prev] | [next] | [standalone]

#464645

On Thu, 15 Jun 2017 14:14:08 -0500, Jon Elson <jmelson@wustl.edu>
wrote:

>John Larkin wrote:
>
>> The *output* of the amp needs to be around 10 nV/rootHz.
>> 
>Yikes!
>> The DUT output is 100 ohm differential, which makes it harder. So we
>> took one of our standard products, an x100 1GHz amplifier, and hacked
>> a wideband transformer into the front end. Then I stuffed the DUT and
>> the X100 amp into a custom-machined shielded enclosure.
>> 
>> 
>https://dl.dropboxusercontent.com/u/53724080/Bypassing/E2_EMI_Encllosure.JPG
>> 
>> The DUT is the smaller extruded box. There's enough gain that I can
>> use a scope to measure RMS noise voltage directly.
>> 
>> Those are really nice shield cans, but before you can use them you
>> have to find a way to dispose of the filler materials that they come
>> with.
>> 
>> 
>OK, you might have to add another box and build a PI filter at the power 
>entry.  With those DAMN transmitting antennas so close, you need SERIOUS 
>filtering.  There's another power entry that is powering the X100 amp that 
>looks to NOT have a feedthrough cap.  That likely is the real culprit.
>
>Jon

What is the power consumption of the devices. Would an internal
battery be an option, thus no need for power entry ?

Of course a good RF contact between the cookie can and the lid is
critical. Put finger stock around the edge. Alternatively secure the
lid to the can with screws every few centimeter around the perimeter
of the lid, this should be good to a few GHz.
 

[toc] | [prev] | [next] | [standalone]

#464664

On Fri, 16 Jun 2017 09:35:58 +0300, upsidedown@downunder.com wrote:

>On Thu, 15 Jun 2017 14:14:08 -0500, Jon Elson <jmelson@wustl.edu>
>wrote:
>
>>John Larkin wrote:
>>
>>> The *output* of the amp needs to be around 10 nV/rootHz.
>>> 
>>Yikes!
>>> The DUT output is 100 ohm differential, which makes it harder. So we
>>> took one of our standard products, an x100 1GHz amplifier, and hacked
>>> a wideband transformer into the front end. Then I stuffed the DUT and
>>> the X100 amp into a custom-machined shielded enclosure.
>>> 
>>> 
>>https://dl.dropboxusercontent.com/u/53724080/Bypassing/E2_EMI_Encllosure.JPG
>>> 
>>> The DUT is the smaller extruded box. There's enough gain that I can
>>> use a scope to measure RMS noise voltage directly.
>>> 
>>> Those are really nice shield cans, but before you can use them you
>>> have to find a way to dispose of the filler materials that they come
>>> with.
>>> 
>>> 
>>OK, you might have to add another box and build a PI filter at the power 
>>entry.  With those DAMN transmitting antennas so close, you need SERIOUS 
>>filtering.  There's another power entry that is powering the X100 amp that 
>>looks to NOT have a feedthrough cap.  That likely is the real culprit.
>>
>>Jon
>
>What is the power consumption of the devices. Would an internal
>battery be an option, thus no need for power entry ?
>
>Of course a good RF contact between the cookie can and the lid is
>critical. Put finger stock around the edge. Alternatively secure the
>lid to the can with screws every few centimeter around the perimeter
>of the lid, this should be good to a few GHz.
> 

I considered batteries, but I'd need +12 and +-6 volts, which would be
a nuisance.

The DBC can seems pretty tight. I'm seeing the noise floor at what we
expected based on the simulations, or maybe even a little better. 



-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics 

[toc] | [prev] | [next] | [standalone]

#464582

On 2017-06-14 16:09, John Larkin wrote:
>
>
> I designed this little photodiode amp and I'm trying to measure its
> output noise. All we can see on a spectrum analyser is radio and TV
> stations.
>
> https://dl.dropboxusercontent.com/u/53724080/Otis/EMI/Sutro.JPG
>

Who installed those vents? Did they smoke some funny-smelling cigarettes?


> The *output* of the amp needs to be around 10 nV/rootHz.
>
> The DUT output is 100 ohm differential, which makes it harder. So we
> took one of our standard products, an x100 1GHz amplifier, and hacked
> a wideband transformer into the front end. Then I stuffed the DUT and
> the X100 amp into a custom-machined shielded enclosure.
>
> https://dl.dropboxusercontent.com/u/53724080/Bypassing/E2_EMI_Encllosure.JPG
>
> The DUT is the smaller extruded box. There's enough gain that I can
> use a scope to measure RMS noise voltage directly.
>
> Those are really nice shield cans, but before you can use them you
> have to find a way to dispose of the filler materials that they come
> with.
>

If you want a nice-looking smaller box there is also Fishermen's Friend. 
You can get cans with a more international flair:

https://en.wikipedia.org/wiki/Fisherman's_Friend#/media/File:Fisherman%27s_Friend_Tin_Taiwan.jpg

Be careful. The dad of a friend popped one and then fell asleep on the 
couch. When he woke up the cheek pointing towards the pillow had become 
numb like after a major dentist session.

-- 
Regards, Joerg

http://www.analogconsultants.com/

[toc] | [prev] | [next] | [standalone]

#464590

On Thu, 15 Jun 2017 12:27:25 -0700, Joerg <news@analogconsultants.com>
wrote:

>On 2017-06-14 16:09, John Larkin wrote:
>>
>>
>> I designed this little photodiode amp and I'm trying to measure its
>> output noise. All we can see on a spectrum analyser is radio and TV
>> stations.
>>
>> https://dl.dropboxusercontent.com/u/53724080/Otis/EMI/Sutro.JPG
>>
>
>Who installed those vents? Did they smoke some funny-smelling cigarettes?

That's the roof of the San Francisco Ballet School. Artsy types.
Sometimes I can hear them practising. One of my engineers dances
Flamenco there, conveniently next door.

>
>
>> The *output* of the amp needs to be around 10 nV/rootHz.
>>
>> The DUT output is 100 ohm differential, which makes it harder. So we
>> took one of our standard products, an x100 1GHz amplifier, and hacked
>> a wideband transformer into the front end. Then I stuffed the DUT and
>> the X100 amp into a custom-machined shielded enclosure.
>>
>> https://dl.dropboxusercontent.com/u/53724080/Bypassing/E2_EMI_Encllosure.JPG
>>
>> The DUT is the smaller extruded box. There's enough gain that I can
>> use a scope to measure RMS noise voltage directly.
>>
>> Those are really nice shield cans, but before you can use them you
>> have to find a way to dispose of the filler materials that they come
>> with.
>>
>
>If you want a nice-looking smaller box there is also Fishermen's Friend. 
>You can get cans with a more international flair:
>
>https://en.wikipedia.org/wiki/Fisherman's_Friend#/media/File:Fisherman%27s_Friend_Tin_Taiwan.jpg
>
>Be careful. The dad of a friend popped one and then fell asleep on the 
>couch. When he woke up the cheek pointing towards the pillow had become 
>numb like after a major dentist session.

Some people like the Altoids cans for small stuff.


-- 

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement 

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

[toc] | [prev] | [next] | [standalone]

#464592

Den torsdag den 15. juni 2017 kl. 21.47.56 UTC+2 skrev John Larkin:
> On Thu, 15 Jun 2017 12:27:25 -0700, Joerg <news@analogconsultants.com>
> wrote:
> 
> >On 2017-06-14 16:09, John Larkin wrote:
> >>
> >>
> >> I designed this little photodiode amp and I'm trying to measure its
> >> output noise. All we can see on a spectrum analyser is radio and TV
> >> stations.
> >>
> >> https://dl.dropboxusercontent.com/u/53724080/Otis/EMI/Sutro.JPG
> >>
> >
> >Who installed those vents? Did they smoke some funny-smelling cigarettes?
> 
> That's the roof of the San Francisco Ballet School. Artsy types.
> Sometimes I can hear them practising. One of my engineers dances
> Flamenco there, conveniently next door.
> 
> >
> >
> >> The *output* of the amp needs to be around 10 nV/rootHz.
> >>
> >> The DUT output is 100 ohm differential, which makes it harder. So we
> >> took one of our standard products, an x100 1GHz amplifier, and hacked
> >> a wideband transformer into the front end. Then I stuffed the DUT and
> >> the X100 amp into a custom-machined shielded enclosure.
> >>
> >> https://dl.dropboxusercontent.com/u/53724080/Bypassing/E2_EMI_Encllosure.JPG
> >>
> >> The DUT is the smaller extruded box. There's enough gain that I can
> >> use a scope to measure RMS noise voltage directly.
> >>
> >> Those are really nice shield cans, but before you can use them you
> >> have to find a way to dispose of the filler materials that they come
> >> with.
> >>
> >
> >If you want a nice-looking smaller box there is also Fishermen's Friend. 
> >You can get cans with a more international flair:
> >
> >https://en.wikipedia.org/wiki/Fisherman's_Friend#/media/File:Fisherman%27s_Friend_Tin_Taiwan.jpg
> >
> >Be careful. The dad of a friend popped one and then fell asleep on the 
> >couch. When he woke up the cheek pointing towards the pillow had become 
> >numb like after a major dentist session.
> 
> Some people like the Altoids cans for small stuff.
> 
 

https://www.adafruit.com/product/16

https://www.adafruit.com/product/97

[toc] | [prev] | [next] | [standalone]

#464595

On 2017-06-15 12:57, Lasse Langwadt Christensen wrote:
> Den torsdag den 15. juni 2017 kl. 21.47.56 UTC+2 skrev John Larkin:
>> On Thu, 15 Jun 2017 12:27:25 -0700, Joerg <news@analogconsultants.com>
>> wrote:
>>
>>> On 2017-06-14 16:09, John Larkin wrote:
>>>>
>>>>
>>>> I designed this little photodiode amp and I'm trying to measure its
>>>> output noise. All we can see on a spectrum analyser is radio and TV
>>>> stations.
>>>>
>>>> https://dl.dropboxusercontent.com/u/53724080/Otis/EMI/Sutro.JPG
>>>>
>>>
>>> Who installed those vents? Did they smoke some funny-smelling cigarettes?
>>
>> That's the roof of the San Francisco Ballet School. Artsy types.
>> Sometimes I can hear them practising. One of my engineers dances
>> Flamenco there, conveniently next door.
>>
>>>
>>>
>>>> The *output* of the amp needs to be around 10 nV/rootHz.
>>>>
>>>> The DUT output is 100 ohm differential, which makes it harder. So we
>>>> took one of our standard products, an x100 1GHz amplifier, and hacked
>>>> a wideband transformer into the front end. Then I stuffed the DUT and
>>>> the X100 amp into a custom-machined shielded enclosure.
>>>>
>>>> https://dl.dropboxusercontent.com/u/53724080/Bypassing/E2_EMI_Encllosure.JPG
>>>>
>>>> The DUT is the smaller extruded box. There's enough gain that I can
>>>> use a scope to measure RMS noise voltage directly.
>>>>
>>>> Those are really nice shield cans, but before you can use them you
>>>> have to find a way to dispose of the filler materials that they come
>>>> with.
>>>>
>>>
>>> If you want a nice-looking smaller box there is also Fishermen's Friend.
>>> You can get cans with a more international flair:
>>>
>>> https://en.wikipedia.org/wiki/Fisherman's_Friend#/media/File:Fisherman%27s_Friend_Tin_Taiwan.jpg
>>>
>>> Be careful. The dad of a friend popped one and then fell asleep on the
>>> couch. When he woke up the cheek pointing towards the pillow had become
>>> numb like after a major dentist session.
>>
>> Some people like the Altoids cans for small stuff.
>>
>
>
> https://www.adafruit.com/product/16
>
> https://www.adafruit.com/product/97
>

Much cheaper in regular retail packaging and then you get the mints in 
there "for free":

https://www.walmart.com/ip/Altoids-Wintergreen-Mints-1.76-oz/38253375

-- 
Regards, Joerg

http://www.analogconsultants.com/

[toc] | [prev] | [next] | [standalone]

#464594

On 2017-06-15 12:47, John Larkin wrote:
> On Thu, 15 Jun 2017 12:27:25 -0700, Joerg <news@analogconsultants.com>
> wrote:
>
>> On 2017-06-14 16:09, John Larkin wrote:
>>>
>>>
>>> I designed this little photodiode amp and I'm trying to measure its
>>> output noise. All we can see on a spectrum analyser is radio and TV
>>> stations.
>>>
>>> https://dl.dropboxusercontent.com/u/53724080/Otis/EMI/Sutro.JPG
>>>
>>
>> Who installed those vents? Did they smoke some funny-smelling cigarettes?
>
> That's the roof of the San Francisco Ballet School. Artsy types.
> Sometimes I can hear them practising. One of my engineers dances
> Flamenco there, conveniently next door.
>

I wish we had a nice dance hall here because my wife and I did ballroom 
dancing in Europe. The only one we had for a few years was in a simple 
industrial building with fluorescent lighting, linoleum floor, having 
the romantic level of a Soviet stairwell. In Europe they had wet bars, 
tables, seats, mood lighting and most of all a polished wooden dance floor.

Once in a while we go to Cafe Marcos in Lotus when they have live 
country music. There we can dance. The food is IMHO subpar but they 
always have very good beers on tap.

>>
>>
>>> The *output* of the amp needs to be around 10 nV/rootHz.
>>>
>>> The DUT output is 100 ohm differential, which makes it harder. So we
>>> took one of our standard products, an x100 1GHz amplifier, and hacked
>>> a wideband transformer into the front end. Then I stuffed the DUT and
>>> the X100 amp into a custom-machined shielded enclosure.
>>>
>>> https://dl.dropboxusercontent.com/u/53724080/Bypassing/E2_EMI_Encllosure.JPG
>>>
>>> The DUT is the smaller extruded box. There's enough gain that I can
>>> use a scope to measure RMS noise voltage directly.
>>>
>>> Those are really nice shield cans, but before you can use them you
>>> have to find a way to dispose of the filler materials that they come
>>> with.
>>>
>>
>> If you want a nice-looking smaller box there is also Fishermen's Friend.
>> You can get cans with a more international flair:
>>
>> https://en.wikipedia.org/wiki/Fisherman's_Friend#/media/File:Fisherman%27s_Friend_Tin_Taiwan.jpg
>>
>> Be careful. The dad of a friend popped one and then fell asleep on the
>> couch. When he woke up the cheek pointing towards the pillow had become
>> numb like after a major dentist session.
>
> Some people like the Altoids cans for small stuff.
>

Some folks consider those too pedestrian because too many people carry 
them :-)

-- 
Regards, Joerg

http://www.analogconsultants.com/

[toc] | [prev] | [next] | [standalone]

#464648

Am 15.06.2017 um 21:27 schrieb Joerg:

> 
> If you want a nice-looking smaller box there is also Fishermen's Friend. 
> You can get cans with a more international flair:
> 
> https://en.wikipedia.org/wiki/Fisherman's_Friend#/media/File:Fisherman%27s_Friend_Tin_Taiwan.jpg 
> 
> 
> Be careful. The dad of a friend popped one and then fell asleep on the 
> couch. When he woke up the cheek pointing towards the pillow had become 
> numb like after a major dentist session.
>

http://www.meg4.de/fun/funsub/fisherman.htm

;-)


Jorgen

[toc] | [prev] | [next] | [standalone]

#464697

On Wed, 14 Jun 2017 16:09:43 -0700, John Larkin
<jjlarkin@highland_snip_technology.com> wrote:

>I designed this little photodiode amp and I'm trying to measure its
>output noise. All we can see on a spectrum analyser is radio and TV
>stations.

Welcome to my (former) nightmares.  There are plenty of articles
online that discuss proper shielding.  The problem is that they don't
go into enough detail for dealing with strong RF fields.
(Incidentally, the Subject line should be RFI, not EMI).  Some things
that should be considered (in random order):

1.  Avoid magnetic materials and dissimilar metals.  These can create
non-linear junctions which act as mixers.  You want to be dealing with
a few strong signals, not a comb line screen full of mixer products.
The best clues can be found under PIM (Passive InterModulation) design
articles.  Plate everything with silver and use silver plated
connectors.  Don't use anything magnetic which includes nickel plated
connectors and magnetic stainless connectors.  Besides, nickel and
steel have somewhat high resistivity:
    Metal    Resistivity (lower is better)
             (nano-Ohm-meters)
    Silver:     15.9
    Copper:     16.8
    Gold:       24.4
    Aluminium:  26.2
    Zinc:       59.0
    Nickel:     69.9
    Iron:      100
    Tin:       109
    Stainless: 120
Lots of stuff for the cellular industry now comes with Low PIM
connectors:
<http://www.rfindustries.com/Product-PIM.html>

It's unlikely that you'll need low PIM hardware, unless it's expected
to be used on an RF polluted mountain top transmitter site or share a
coax cable used to transmit RF.

2.  Watch out for corrosion problems.  That shiny nickel plated steel
sheet metal enclosure you soldered together from hardware store stock
will work very well for a few months.  However, when it starts to
corrode or oxidize, the shielding characteristics can change.  RF
travels on the outside of conductors (skin effect) and an oxidized
conductor is not as good as the original unoxidized metal.  

3.  Watch out for triboelectric effects in coax cables and connectors.
Just moving the cables can produce noise.  Check the tribolectric
series tables:
<http://www.school-for-champions.com/science/static_materials.htm>
and avoid anything that might produce static electricity.

4.  Check for ground loops in your connecting cables.  It's very easy
to create a ground loop if you have lots of cables running around.
While this is usually a problem at 60 Hz, a full wave loop at FM/TV
frequencies makes a dandy antenna.  If part of the loop is the
enclosure, an unshielded wire, a wire not bypassed, or anything that
can radiate RF inside the enclosure, it will radiate RF.

You can eliminate a ground loop if you only ground one end of a
coaxial cable.  This may seem counter-intuitive.  The idea is to keep
the coax cable from acting as a one turn transformer.  The grounded
end should be the signal source end.  I had a box of coax jumpers that
had the shield broken at one end.  Over that was some insulation and a
layer of copper tape connected to the adjacent coax connector.  The
idea was to cover the gap in the shield to not expose the center
conductor.  If installing such a cable magically fixed a spur or noise
problem, I knew that I had a ground loop.

5.  Play with various ferrite beads around coax cables.  They work
very well at removing RF signals from the outside of a coax cable. For
low frequencies, a toroid core with a few turns of coax through the
donut hole.

6.  Avoid exposed center conductors on coax cables.  This is a common
problem when soldering coax cable to a bulkhead connector.  There's
one in your cookie can photo in the upper right with some small parts
hanging off it.  The long coax shield lead acts like an inductor
giving a not so good RF ground connection.

7.  Try to use differential circuits.  The common mode rejection of
anything that leaks into the box is worth the added cost and
complexity.  You'll see some of that on CATV amps, where keeping RF
from leaking into (ingress) the enclosure is critical. 

There's probably more, but I can't think of anything major.  None of
the things I mentioned are critical or vital for decent shielding.
Just keep them in mind when you build your device.

Good luck and remember, RF is magic.


-- 
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

[toc] | [prev] | [next] | [standalone]

#464705

On Fri, 16 Jun 2017 10:03:51 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

>On Wed, 14 Jun 2017 16:09:43 -0700, John Larkin
><jjlarkin@highland_snip_technology.com> wrote:
>
>>I designed this little photodiode amp and I'm trying to measure its
>>output noise. All we can see on a spectrum analyser is radio and TV
>>stations.
>
>Welcome to my (former) nightmares.  There are plenty of articles
>online that discuss proper shielding.  The problem is that they don't
>go into enough detail for dealing with strong RF fields.
>(Incidentally, the Subject line should be RFI, not EMI). 

Radio waves aren't electromagnetic? My customers seem to use "EMI"


 Some things
>that should be considered (in random order):
>
>1.  Avoid magnetic materials and dissimilar metals.  These can create
>non-linear junctions which act as mixers.  You want to be dealing with
>a few strong signals, not a comb line screen full of mixer products.
>The best clues can be found under PIM (Passive InterModulation) design
>articles.  Plate everything with silver and use silver plated
>connectors.  Don't use anything magnetic which includes nickel plated
>connectors and magnetic stainless connectors.  Besides, nickel and
>steel have somewhat high resistivity:
>    Metal    Resistivity (lower is better)
>             (nano-Ohm-meters)
>    Silver:     15.9
>    Copper:     16.8
>    Gold:       24.4
>    Aluminium:  26.2
>    Zinc:       59.0
>    Nickel:     69.9
>    Iron:      100
>    Tin:       109
>    Stainless: 120
>Lots of stuff for the cellular industry now comes with Low PIM
>connectors:
><http://www.rfindustries.com/Product-PIM.html>
>
>It's unlikely that you'll need low PIM hardware, unless it's expected
>to be used on an RF polluted mountain top transmitter site or share a
>coax cable used to transmit RF.

I don't think PIM is an issue for me now. I'm talking 120 microvolts
RMS as my test limit.

>
>2.  Watch out for corrosion problems.  That shiny nickel plated steel
>sheet metal enclosure you soldered together from hardware store stock
>will work very well for a few months.  However, when it starts to
>corrode or oxidize, the shielding characteristics can change.  RF
>travels on the outside of conductors (skin effect) and an oxidized
>conductor is not as good as the original unoxidized metal.  
>
>3.  Watch out for triboelectric effects in coax cables and connectors.
>Just moving the cables can produce noise.  Check the tribolectric
>series tables:
><http://www.school-for-champions.com/science/static_materials.htm>
>and avoid anything that might produce static electricity.
>
>4.  Check for ground loops in your connecting cables.  It's very easy
>to create a ground loop if you have lots of cables running around.
>While this is usually a problem at 60 Hz, a full wave loop at FM/TV
>frequencies makes a dandy antenna.  If part of the loop is the
>enclosure, an unshielded wire, a wire not bypassed, or anything that
>can radiate RF inside the enclosure, it will radiate RF.
>
>You can eliminate a ground loop if you only ground one end of a
>coaxial cable.  This may seem counter-intuitive.  The idea is to keep
>the coax cable from acting as a one turn transformer.  The grounded
>end should be the signal source end.  I had a box of coax jumpers that
>had the shield broken at one end.  Over that was some insulation and a
>layer of copper tape connected to the adjacent coax connector.  The
>idea was to cover the gap in the shield to not expose the center
>conductor.  If installing such a cable magically fixed a spur or noise
>problem, I knew that I had a ground loop.

Leaving one end of the shield open will make the noise on the shield
couple directly into the signal. Ground loops, if any, can be killed
by a common-mode ferrite or some such.

>
>5.  Play with various ferrite beads around coax cables.  They work
>very well at removing RF signals from the outside of a coax cable. For
>low frequencies, a toroid core with a few turns of coax through the
>donut hole.

Yes.

>
>6.  Avoid exposed center conductors on coax cables.  This is a common
>problem when soldering coax cable to a bulkhead connector.  There's
>one in your cookie can photo in the upper right with some small parts
>hanging off it.  The long coax shield lead acts like an inductor
>giving a not so good RF ground connection.

It works fine in my situation. If it didn't, I would have had to work
harder.

>
>7.  Try to use differential circuits.  The common mode rejection of
>anything that leaks into the box is worth the added cost and
>complexity.  You'll see some of that on CATV amps, where keeping RF
>from leaking into (ingress) the enclosure is critical. 
>

The DUT is differential out, so we hacked our amp box to add a
wideband transformer at the input, to convert from diff to
single-ended. Luckily, it already had two SMB connectors on the input.


>There's probably more, but I can't think of anything major.  None of
>the things I mentioned are critical or vital for decent shielding.
>Just keep them in mind when you build your device.
>
>Good luck and remember, RF is magic.

My measurement bandwidth is only 100 MHz. That's almost DC.


-- 

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement 

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

[toc] | [prev] | [next] | [standalone]

#464721

On Fri, 16 Jun 2017 11:09:27 -0700, John Larkin
<jjlarkin@highland_snip_technology.com> wrote:

>On Fri, 16 Jun 2017 10:03:51 -0700, Jeff Liebermann <jeffl@cruzio.com>
>wrote:
>>(Incidentally, the Subject line should be RFI, not EMI). 

>Radio waves aren't electromagnetic? My customers seem to use "EMI"

RFI is a subset of EMI.
<http://www.transcoil.com/Support/FAQs/KRFFAQs/KRF-EMI-RFI.htm>
I tend to use RFI as anything generated by a transmitter, while EMI is
whatever else is left.  That's wrong, but convenient.  When you
started talking about seeing the various signals from the Sutro tower,
I assumed that the major problem was RF related.  

>I don't think PIM is an issue for me now. I'm talking 120 microvolts
>RMS as my test limit.

True.  Some PIM test sets have two high power transmitters (5 to 25
watts) inside the box.  I mentioned it because it can become a problem
if whatever you are designing shares a common coax cable with multiple
high power signals.  Just a precaution.

>Leaving one end of the shield open will make the noise on the shield
>couple directly into the signal. Ground loops, if any, can be killed
>by a common-mode ferrite or some such.

The jumper with one ungrounded end is useful for identifying if you
have a ground loop problem.  I don't recommend it as a permanent
solution.  

However, I beg to differ with your approach.  If a ground loop induces
more noise (1:1 xformer effect) than the shield might couple directly,
then grounding at one end only can be beneficial.  Google search
finds:
<http://control.com/thread/1373726311>  (lots of good stuff here)

<http://www.mouser.com/pdfdocs/alphawire-Understanding-Shielded-Cable.pdf>
   5. Ground the cable at one end. This eliminates the potential
   for noise inducing ground loops. 

<https://www.google.com/#q=ethernet+only+ground+one+end>
Some references mentioning to ground only one end of an ethernet
shield.

>My measurement bandwidth is only 100 MHz. That's almost DC.

No spectrum analyzer handy?  Just think of all the EMI/RFI junk above
100MHz that you're missing.

You might want to calculate the resonant frequency of the Royal Dansk
cookie can:
<http://www.rfwireless-world.com/calculators/circular-cavity-resonator-calculator.html>
If you see a noise peak in that area, it could be something
oscillating or filtering using the can as a resonator.  

-- 
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

[toc] | [prev] | [next] | [standalone]

#464727

On Fri, 16 Jun 2017 12:06:11 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

>On Fri, 16 Jun 2017 11:09:27 -0700, John Larkin
><jjlarkin@highland_snip_technology.com> wrote:
>
>>On Fri, 16 Jun 2017 10:03:51 -0700, Jeff Liebermann <jeffl@cruzio.com>
>>wrote:
>>>(Incidentally, the Subject line should be RFI, not EMI). 
>
>>Radio waves aren't electromagnetic? My customers seem to use "EMI"
>
>RFI is a subset of EMI.
><http://www.transcoil.com/Support/FAQs/KRFFAQs/KRF-EMI-RFI.htm>
>I tend to use RFI as anything generated by a transmitter, while EMI is
>whatever else is left.  That's wrong, but convenient.  When you
>started talking about seeing the various signals from the Sutro tower,
>I assumed that the major problem was RF related.  

There's also a huge amount of lower-frequency noise here, probably
from AC-line powered things in the neighborhood.

This motor controller was making 20 volt spikes in the lab, until we
hacked it.

https://dl.dropboxusercontent.com/u/53724080/Otis/EMI/VFD.JPG

Here's the general spectrum:

https://dl.dropboxusercontent.com/u/53724080/Otis/EMI/300MHz.JPG


-28 dBm with just a Pomona lead antenna.







>
>>I don't think PIM is an issue for me now. I'm talking 120 microvolts
>>RMS as my test limit.
>
>True.  Some PIM test sets have two high power transmitters (5 to 25
>watts) inside the box.  I mentioned it because it can become a problem
>if whatever you are designing shares a common coax cable with multiple
>high power signals.  Just a precaution.
>
>>Leaving one end of the shield open will make the noise on the shield
>>couple directly into the signal. Ground loops, if any, can be killed
>>by a common-mode ferrite or some such.
>
>The jumper with one ungrounded end is useful for identifying if you
>have a ground loop problem.  I don't recommend it as a permanent
>solution.  
>
>However, I beg to differ with your approach.  If a ground loop induces
>more noise (1:1 xformer effect) than the shield might couple directly,
>then grounding at one end only can be beneficial.  Google search
>finds:
><http://control.com/thread/1373726311>  (lots of good stuff here)
>
><http://www.mouser.com/pdfdocs/alphawire-Understanding-Shielded-Cable.pdf>
>   5. Ground the cable at one end. This eliminates the potential
>   for noise inducing ground loops. 
>
><https://www.google.com/#q=ethernet+only+ground+one+end>
>Some references mentioning to ground only one end of an ethernet
>shield.
>
>>My measurement bandwidth is only 100 MHz. That's almost DC.
>
>No spectrum analyzer handy?  Just think of all the EMI/RFI junk above
>100MHz that you're missing.

We have a couple of SAs, but my requirement is net RMS noise voltage,
and a scope measures that directly.

>
>You might want to calculate the resonant frequency of the Royal Dansk
>cookie can:
><http://www.rfwireless-world.com/calculators/circular-cavity-resonator-calculator.html>
>If you see a noise peak in that area, it could be something
>oscillating or filtering using the can as a resonator.  

I'm OK at 100 MHz. It might make a resonant cavity filter or something
at some higher frequency.


-- 

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement 

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

[toc] | [prev] | [next] | [standalone]

#464839

On Fri, 16 Jun 2017 12:34:02 -0700, John Larkin
<jjlarkin@highland_snip_technology.com> wrote:

>There's also a huge amount of lower-frequency noise here, probably
>from AC-line powered things in the neighborhood.

I see the same thing even in a residential neighborhood in the middle
of nowhere.  If I unplug various AC powered gadgets around the house,
the noise level goes down a little.  I can see some of it with a scope
connected to the power line through an LISN (Line Impedance
Stabilization Network).  The really nasty stuff disappears when the
sun goes down, which suggests a grid connected solar power system. The
problem is that I live in the deep dark forest where such systems are
rare.  Nothing within a mile radius but I'll keep looking.  A line
filter usually gets rid of most such noise.  If you're located in an
industrial area, you might want to investigate what the local PV
systems are putting back into the power lines.

>This motor controller was making 20 volt spikes in the lab, until we
>hacked it.
>https://dl.dropboxusercontent.com/u/53724080/Otis/EMI/VFD.JPG

Neatly done.  No capacitors to form a low pass filter?

>Here's the general spectrum:
>https://dl.dropboxusercontent.com/u/53724080/Otis/EMI/300MHz.JPG
>-28 dBm with just a Pomona lead antenna.

30 MHz/div.  TV Ch 2 on the left.  FM broadcast band 88-108MHz seems
quite strong.  One aircraft beacon.  Starting at 150Mhz, quite a bit
of VHF commercial and public safety signals which quit at about 190MHz
with TV channel 7.  Methinks if you check the UHF TV and commercial
spectrum, the signal levels will higher.

-28dBm is 9mv rms or 25mv p-p into 50 ohms.  You should see a 25mv
"noise" level on any long wires that can act as an antenna.  If you're
working with low impedances, not a problem.  If you have bandwidth in
the FM/VHF region at high impedances, I suggest a screen room, screen
box, or differential designs.

BTW, nice Marconi/IFR/Aeroflex/Cobham 2399c spectrum analyzer.  I'm
jealous.

>>You might want to calculate the resonant frequency of the Royal Dansk
>>cookie can:
>><http://www.rfwireless-world.com/calculators/circular-cavity-resonator-calculator.html>
>>If you see a noise peak in that area, it could be something
>>oscillating or filtering using the can as a resonator.  

>I'm OK at 100 MHz. It might make a resonant cavity filter or something
>at some higher frequency.

Maybe.  I've built and seen VHF (150MHz) cavity filters in much
smaller cans.  Fruit juice cans, paint cans, beer cans, etc all can be
made to work.  
<http://vk4zxi.blogspot.com/2014/08/homebrew-cavity-resonatorduplexer-for.html>
All it takes is a center rod between the two ends with a tuning
capacitor at one end.  A length of insulated wire, soldered to one end
of the can, and leaning against the top, forming a capacitor, is all
it takes.  Small cavities have much less Q, but they still will
resonate.  I don't have any cookie cans available.  I'll get some
dimensions at the market and see what happens.  

Or, you could just frequency sweep the cookie can and see what you
get.  Just sacrifice some more Danish butter cookies to a worthy
cause.  Punch a hole in the can and solder in a BNC jack.  Make a
small wire loop across the BNC.  Connect a T-connector to the BNC
which attach to sweep (tracking) generator and spectrum analyzer.
Extra credit for using a return loss bridge.  Sweep and look for
notches on the SA.

All this is probably more of an academic exercise than anything useful
for your project.  However, it is nice to know where various
enclosures resonate in case you see a frequency dependent anomaly that
happens to coincide with the resonant frequencies.


-- 
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

[toc] | [prev] | [next] | [standalone]

#464843

On Sat, 17 Jun 2017 09:22:20 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

>On Fri, 16 Jun 2017 12:34:02 -0700, John Larkin
><jjlarkin@highland_snip_technology.com> wrote:
>
>>There's also a huge amount of lower-frequency noise here, probably
>>from AC-line powered things in the neighborhood.
>
>I see the same thing even in a residential neighborhood in the middle
>of nowhere.  If I unplug various AC powered gadgets around the house,
>the noise level goes down a little.  I can see some of it with a scope
>connected to the power line through an LISN (Line Impedance
>Stabilization Network).  The really nasty stuff disappears when the
>sun goes down, which suggests a grid connected solar power system. The
>problem is that I live in the deep dark forest where such systems are
>rare.  Nothing within a mile radius but I'll keep looking.  A line
>filter usually gets rid of most such noise.  If you're located in an
>industrial area, you might want to investigate what the local PV
>systems are putting back into the power lines.
>
>>This motor controller was making 20 volt spikes in the lab, until we
>>hacked it.
>>https://dl.dropboxusercontent.com/u/53724080/Otis/EMI/VFD.JPG
>
>Neatly done.  No capacitors to form a low pass filter?

The box on the right is a commercial filter, on the input to the
controller. That helped some. I hacked the toroids in series with the
outputs, running to the blower on the roof, and that got us down to
the local noise floor. It's all in metal boxes and conduit!


>
>>Here's the general spectrum:
>>https://dl.dropboxusercontent.com/u/53724080/Otis/EMI/300MHz.JPG
>>-28 dBm with just a Pomona lead antenna.
>
>30 MHz/div.  TV Ch 2 on the left.  FM broadcast band 88-108MHz seems
>quite strong.  One aircraft beacon.  Starting at 150Mhz, quite a bit
>of VHF commercial and public safety signals which quit at about 190MHz
>with TV channel 7.  Methinks if you check the UHF TV and commercial
>spectrum, the signal levels will higher.

I still want to light an LED from the ambient RF.

>
>-28dBm is 9mv rms or 25mv p-p into 50 ohms.  You should see a 25mv
>"noise" level on any long wires that can act as an antenna.  If you're
>working with low impedances, not a problem.  If you have bandwidth in
>the FM/VHF region at high impedances, I suggest a screen room, screen
>box, or differential designs.

We're moving soon, about the same distance from the tower, and we have
considered some sort of screen room in the basement. But the EMI does
automagically test our breadboards and products for us.

>
>BTW, nice Marconi/IFR/Aeroflex/Cobham 2399c spectrum analyzer.  I'm
>jealous.

It's horrible and buggy. It has +-120 Hz spurs, which is like finding
a roach in your salad.




>
>>>You might want to calculate the resonant frequency of the Royal Dansk
>>>cookie can:
>>><http://www.rfwireless-world.com/calculators/circular-cavity-resonator-calculator.html>
>>>If you see a noise peak in that area, it could be something
>>>oscillating or filtering using the can as a resonator.  
>
>>I'm OK at 100 MHz. It might make a resonant cavity filter or something
>>at some higher frequency.
>
>Maybe.  I've built and seen VHF (150MHz) cavity filters in much
>smaller cans.  Fruit juice cans, paint cans, beer cans, etc all can be
>made to work.  
><http://vk4zxi.blogspot.com/2014/08/homebrew-cavity-resonatorduplexer-for.html>
>All it takes is a center rod between the two ends with a tuning
>capacitor at one end.  A length of insulated wire, soldered to one end
>of the can, and leaning against the top, forming a capacitor, is all
>it takes.  Small cavities have much less Q, but they still will
>resonate.  I don't have any cookie cans available.  I'll get some
>dimensions at the market and see what happens.  
>
>Or, you could just frequency sweep the cookie can and see what you
>get.  Just sacrifice some more Danish butter cookies to a worthy
>cause.

Do I have to?

The SA has a tracking generator; that might be fun.


  Punch a hole in the can and solder in a BNC jack.  Make a
>small wire loop across the BNC.  Connect a T-connector to the BNC
>which attach to sweep (tracking) generator and spectrum analyzer.
>Extra credit for using a return loss bridge.  Sweep and look for
>notches on the SA.
>
>All this is probably more of an academic exercise than anything useful
>for your project.  However, it is nice to know where various
>enclosures resonate in case you see a frequency dependent anomaly that
>happens to coincide with the resonant frequencies.

What's the point of living if you can't waste time on fun stuff?



-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics 

[toc] | [prev] | [next] | [standalone]

#464853

On Sat, 17 Jun 2017 10:08:39 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

>On Sat, 17 Jun 2017 09:22:20 -0700, Jeff Liebermann <jeffl@cruzio.com>
>wrote:
>
>>On Fri, 16 Jun 2017 12:34:02 -0700, John Larkin
>><jjlarkin@highland_snip_technology.com> wrote:
>>
>>>There's also a huge amount of lower-frequency noise here, probably
>>>from AC-line powered things in the neighborhood.
>>
>>I see the same thing even in a residential neighborhood in the middle
>>of nowhere.  If I unplug various AC powered gadgets around the house,
>>the noise level goes down a little.  I can see some of it with a scope
>>connected to the power line through an LISN (Line Impedance
>>Stabilization Network).  The really nasty stuff disappears when the
>>sun goes down, which suggests a grid connected solar power system. The
>>problem is that I live in the deep dark forest where such systems are
>>rare.  Nothing within a mile radius but I'll keep looking.  A line
>>filter usually gets rid of most such noise.  If you're located in an
>>industrial area, you might want to investigate what the local PV
>>systems are putting back into the power lines.
>>
>>>This motor controller was making 20 volt spikes in the lab, until we
>>>hacked it.
>>>https://dl.dropboxusercontent.com/u/53724080/Otis/EMI/VFD.JPG
>>
>>Neatly done.  No capacitors to form a low pass filter?
>
>The box on the right is a commercial filter, on the input to the
>controller. That helped some. I hacked the toroids in series with the
>outputs, running to the blower on the roof, and that got us down to
>the local noise floor. It's all in metal boxes and conduit!
>
>
>>
>>>Here's the general spectrum:
>>>https://dl.dropboxusercontent.com/u/53724080/Otis/EMI/300MHz.JPG
>>>-28 dBm with just a Pomona lead antenna.
>>
>>30 MHz/div.  TV Ch 2 on the left.  FM broadcast band 88-108MHz seems
>>quite strong.  One aircraft beacon.  Starting at 150Mhz, quite a bit
>>of VHF commercial and public safety signals which quit at about 190MHz
>>with TV channel 7.  Methinks if you check the UHF TV and commercial
>>spectrum, the signal levels will higher.
>
>I still want to light an LED from the ambient RF.
>
>>
>>-28dBm is 9mv rms or 25mv p-p into 50 ohms.  You should see a 25mv
>>"noise" level on any long wires that can act as an antenna.  If you're
>>working with low impedances, not a problem.  If you have bandwidth in
>>the FM/VHF region at high impedances, I suggest a screen room, screen
>>box, or differential designs.
>
>We're moving soon, about the same distance from the tower, and we have
>considered some sort of screen room in the basement. But the EMI does
>automagically test our breadboards and products for us.
>
>>
>>BTW, nice Marconi/IFR/Aeroflex/Cobham 2399c spectrum analyzer.  I'm
>>jealous.
>
>It's horrible and buggy. It has +-120 Hz spurs, which is like finding
>a roach in your salad.
>
>
>
>
>>
>>>>You might want to calculate the resonant frequency of the Royal Dansk
>>>>cookie can:
>>>><http://www.rfwireless-world.com/calculators/circular-cavity-resonator-calculator.html>
>>>>If you see a noise peak in that area, it could be something
>>>>oscillating or filtering using the can as a resonator.  
>>
>>>I'm OK at 100 MHz. It might make a resonant cavity filter or something
>>>at some higher frequency.
>>
>>Maybe.  I've built and seen VHF (150MHz) cavity filters in much
>>smaller cans.  Fruit juice cans, paint cans, beer cans, etc all can be
>>made to work.  
>><http://vk4zxi.blogspot.com/2014/08/homebrew-cavity-resonatorduplexer-for.html>
>>All it takes is a center rod between the two ends with a tuning
>>capacitor at one end.  A length of insulated wire, soldered to one end
>>of the can, and leaning against the top, forming a capacitor, is all
>>it takes.  Small cavities have much less Q, but they still will
>>resonate.  I don't have any cookie cans available.  I'll get some
>>dimensions at the market and see what happens.  
>>
>>Or, you could just frequency sweep the cookie can and see what you
>>get.  Just sacrifice some more Danish butter cookies to a worthy
>>cause.
>
>Do I have to?
>
>The SA has a tracking generator; that might be fun.

Hmmm, how does one do a tracking generator on an FFT-based spectrum
analyzer?


-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics 

[toc] | [prev] | [next] | [standalone]

#464857

On 17.6.17 21:07, John Larkin wrote:
> On Sat, 17 Jun 2017 10:08:39 -0700, John Larkin
> <jjlarkin@highlandtechnology.com> wrote:
> 
>> On Sat, 17 Jun 2017 09:22:20 -0700, Jeff Liebermann <jeffl@cruzio.com>
>> wrote:
>>
>>> On Fri, 16 Jun 2017 12:34:02 -0700, John Larkin
>>> <jjlarkin@highland_snip_technology.com> wrote:
>>>
>>>> There's also a huge amount of lower-frequency noise here, probably
>>> >from AC-line powered things in the neighborhood.
>>>
>>> I see the same thing even in a residential neighborhood in the middle
>>> of nowhere.  If I unplug various AC powered gadgets around the house,
>>> the noise level goes down a little.  I can see some of it with a scope
>>> connected to the power line through an LISN (Line Impedance
>>> Stabilization Network).  The really nasty stuff disappears when the
>>> sun goes down, which suggests a grid connected solar power system. The
>>> problem is that I live in the deep dark forest where such systems are
>>> rare.  Nothing within a mile radius but I'll keep looking.  A line
>>> filter usually gets rid of most such noise.  If you're located in an
>>> industrial area, you might want to investigate what the local PV
>>> systems are putting back into the power lines.
>>>
>>>> This motor controller was making 20 volt spikes in the lab, until we
>>>> hacked it.
>>>> https://dl.dropboxusercontent.com/u/53724080/Otis/EMI/VFD.JPG
>>>
>>> Neatly done.  No capacitors to form a low pass filter?
>>
>> The box on the right is a commercial filter, on the input to the
>> controller. That helped some. I hacked the toroids in series with the
>> outputs, running to the blower on the roof, and that got us down to
>> the local noise floor. It's all in metal boxes and conduit!
>>
>>
>>>
>>>> Here's the general spectrum:
>>>> https://dl.dropboxusercontent.com/u/53724080/Otis/EMI/300MHz.JPG
>>>> -28 dBm with just a Pomona lead antenna.
>>>
>>> 30 MHz/div.  TV Ch 2 on the left.  FM broadcast band 88-108MHz seems
>>> quite strong.  One aircraft beacon.  Starting at 150Mhz, quite a bit
>>> of VHF commercial and public safety signals which quit at about 190MHz
>>> with TV channel 7.  Methinks if you check the UHF TV and commercial
>>> spectrum, the signal levels will higher.
>>
>> I still want to light an LED from the ambient RF.
>>
>>>
>>> -28dBm is 9mv rms or 25mv p-p into 50 ohms.  You should see a 25mv
>>> "noise" level on any long wires that can act as an antenna.  If you're
>>> working with low impedances, not a problem.  If you have bandwidth in
>>> the FM/VHF region at high impedances, I suggest a screen room, screen
>>> box, or differential designs.
>>
>> We're moving soon, about the same distance from the tower, and we have
>> considered some sort of screen room in the basement. But the EMI does
>> automagically test our breadboards and products for us.
>>
>>>
>>> BTW, nice Marconi/IFR/Aeroflex/Cobham 2399c spectrum analyzer.  I'm
>>> jealous.
>>
>> It's horrible and buggy. It has +-120 Hz spurs, which is like finding
>> a roach in your salad.
>>
>>
>>
>>
>>>
>>>>> You might want to calculate the resonant frequency of the Royal Dansk
>>>>> cookie can:
>>>>> <http://www.rfwireless-world.com/calculators/circular-cavity-resonator-calculator.html>
>>>>> If you see a noise peak in that area, it could be something
>>>>> oscillating or filtering using the can as a resonator.
>>>
>>>> I'm OK at 100 MHz. It might make a resonant cavity filter or something
>>>> at some higher frequency.
>>>
>>> Maybe.  I've built and seen VHF (150MHz) cavity filters in much
>>> smaller cans.  Fruit juice cans, paint cans, beer cans, etc all can be
>>> made to work.
>>> <http://vk4zxi.blogspot.com/2014/08/homebrew-cavity-resonatorduplexer-for.html>
>>> All it takes is a center rod between the two ends with a tuning
>>> capacitor at one end.  A length of insulated wire, soldered to one end
>>> of the can, and leaning against the top, forming a capacitor, is all
>>> it takes.  Small cavities have much less Q, but they still will
>>> resonate.  I don't have any cookie cans available.  I'll get some
>>> dimensions at the market and see what happens.
>>>
>>> Or, you could just frequency sweep the cookie can and see what you
>>> get.  Just sacrifice some more Danish butter cookies to a worthy
>>> cause.
>>
>> Do I have to?
>>
>> The SA has a tracking generator; that might be fun.
> 
> Hmmm, how does one do a tracking generator on an FFT-based spectrum
> analyzer?

Inverse FFT?

-- 

-TV

[toc] | [prev] | [next] | [standalone]

Page 2 of 3 — ← Prev page 1 [2] 3  Next page →

Back to top | Article view | sci.electronics.design

csiph-web