High Q smd capacitors

A

amdx

Guest
Reading a forum, a member is comparing the Q of an smd capacitor to a
good air capacitor. Maybe?, I don't have a reference of the Q of a good
High Q capacitor. Range 20pf to 400pf.

For further reference is is used in a ring down Q meter.
See last post on this page.
http://theradioboard.com/rb/viewtopic.php?f=2&t=8691
The page includes a sales sheet of a 1210 smd in Chinese.

Mikek
 
On 7/24/19 2:14 PM, amdx wrote:
Reading a forum, a member is comparing the Q of an smd capacitor to a
good air capacitor. Maybe?, I don't have a reference of the Q of a good
High Q capacitor. Range 20pf to 400pf.

 For further reference is is used in a ring down Q meter.
See last post on this page.
http://theradioboard.com/rb/viewtopic.php?f=2&t=8691
 The page includes a sales sheet of a 1210 smd in Chinese.

                              Mikek

I think it would have to be a pretty shit-ass monolithic cap to not have
such a high Q at a couple MHz that the Q of the inductor under test
doesn't dominate it into irrelevance as to what it is, precisely.
Should probably be more concerned with stability wrt temp, humidity,
aging, I think
 
On Wed, 24 Jul 2019 13:14:57 -0500, amdx <nojunk@knology.net> wrote:

Reading a forum, a member is comparing the Q of an smd capacitor to a
good air capacitor. Maybe?, I don't have a reference of the Q of a good
High Q capacitor. Range 20pf to 400pf.

For further reference is is used in a ring down Q meter.
See last post on this page.
http://theradioboard.com/rb/viewtopic.php?f=2&t=8691
The page includes a sales sheet of a 1210 smd in Chinese.

Mikek

Look at (single layer) porcelain capacitors. For example:
<https://www.atceramics.com/UserFiles/slc_catalog.pdf>
See charts on Pg 8. Different dielectrics produce radically different
Q. For your operating frequency (1MHz AM BCB) such a capacitor might
be overkill. From the photos at:
<http://www.crystalradio.cn/forum.php?mod=viewthread&tid=1756224&extra=page%3D4>
the caps sorta, kinda, maybe look like porcelain. Google translate
converted the description into:
100B high Q chip capacitor 4, capacitance and test
capacitance values are: A-221=220.8pf B-121=128pf C-680=68.2pf
D-300=31.4pf,
series-parallel capacity in 21.5--448pf
100B is the ATC designation for one type of multi-layer porcelain cap:
<http://www.atceramics.com/Product/17/100_B_Series_Porcelain_Multilayer_Capacitors_(MLCs)>

What you probably want is the ESR, which is specified for most of the
other types of porcelain caps. See tables at:
<http://www.atceramics.com/Capacitors/3/Multilayer-Capacitors>
Q can easily be calculated with:
Q = Xc / ESR
"Q & ESR Explained"
<https://www.atceramics.com/UserFiles/slc_catalog.pdf>


--
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
 
On 24/07/2019 7:14 pm, amdx wrote:
Reading a forum, a member is comparing the Q of an smd capacitor to a
good air capacitor. Maybe?, I don't have a reference of the Q of a good
High Q capacitor. Range 20pf to 400pf.

 For further reference is is used in a ring down Q meter.
See last post on this page.
http://theradioboard.com/rb/viewtopic.php?f=2&t=8691
 The page includes a sales sheet of a 1210 smd in Chinese.

                              Mikek

It would have to be a bad capacitor to have a Q under 1000. The great
Wes Hayward reports SMD ceramics with Qs at least 2000 to 5000, see:

<http://w7zoi.net/twofaces.pdf>

piglet
 
On 7/24/2019 2:12 PM, Jeff Liebermann wrote:
On Wed, 24 Jul 2019 13:14:57 -0500, amdx <nojunk@knology.net> wrote:

Reading a forum, a member is comparing the Q of an smd capacitor to a
good air capacitor. Maybe?, I don't have a reference of the Q of a good
High Q capacitor. Range 20pf to 400pf.

For further reference is is used in a ring down Q meter.
See last post on this page.
http://theradioboard.com/rb/viewtopic.php?f=2&t=8691
The page includes a sales sheet of a 1210 smd in Chinese.

Mikek

Look at (single layer) porcelain capacitors. For example:
https://www.atceramics.com/UserFiles/slc_catalog.pdf
See charts on Pg 8. Different dielectrics produce radically different
Q. For your operating frequency (1MHz AM BCB) such a capacitor might
be overkill. From the photos at:
http://www.crystalradio.cn/forum.php?mod=viewthread&tid=1756224&extra=page%3D4
the caps sorta, kinda, maybe look like porcelain. Google translate
converted the description into:
100B high Q chip capacitor 4, capacitance and test
capacitance values are: A-221=220.8pf B-121=128pf C-680=68.2pf
D-300=31.4pf,
series-parallel capacity in 21.5--448pf
100B is the ATC designation for one type of multi-layer porcelain cap:

> <http://www.atceramics.com/Product/17/100_B_Series_Porcelain_Multilayer_Capacitors_(MLCs)>

Lots of extrapolation with unknown reality from the graph for a 100pf
cap at 1MHz. The graph starts at 0.01 ohms. If I assume the 100pf is
0.01 ohm ESR at 1MHz and it is resonated at 1MHz, the reactance is 1,592
ohms, thus 1592/0.01 = 159200. I find that difficult to believe. I would
believe a vacuum variable capacitor at 15,000. (A really good one)
But, I'm here to learn, did I mess up the math? Is it over
extrapolation? Is the ESR really that good?

Mikek





What you probably want is the ESR, which is specified for most of the
other types of porcelain caps. See tables at:
http://www.atceramics.com/Capacitors/3/Multilayer-Capacitors
Q can easily be calculated with:
Q = Xc / ESR
"Q & ESR Explained"
https://www.atceramics.com/UserFiles/slc_catalog.pdf
 
On Wednesday, July 24, 2019 at 3:48:15 PM UTC-4, piglet wrote:
On 24/07/2019 7:14 pm, amdx wrote:
Reading a forum, a member is comparing the Q of an smd capacitor to a
good air capacitor. Maybe?, I don't have a reference of the Q of a good
High Q capacitor. Range 20pf to 400pf.

 For further reference is is used in a ring down Q meter.
See last post on this page.
http://theradioboard.com/rb/viewtopic.php?f=2&t=8691
 The page includes a sales sheet of a 1210 smd in Chinese.

                              Mikek

It would have to be a bad capacitor to have a Q under 1000. The great
Wes Hayward reports SMD ceramics with Qs at least 2000 to 5000, see:

http://w7zoi.net/twofaces.pdf
Cool, I do figure (#) 3. with a 50 ohm sig gen,
~1 ohm source R, and a 'scope.
For caps you want to look at the dissipation factor..
it's a resistance, but I think it's different than ESR
in polarized caps. COG ceramics are great.
I've never had the right coil to get to a Q of 1000.

George H.

> piglet
 
On 7/24/2019 2:48 PM, piglet wrote:
On 24/07/2019 7:14 pm, amdx wrote:
Reading a forum, a member is comparing the Q of an smd capacitor to a
good air capacitor. Maybe?, I don't have a reference of the Q of a
good High Q capacitor. Range 20pf to 400pf.

  For further reference is is used in a ring down Q meter.
See last post on this page.
http://theradioboard.com/rb/viewtopic.php?f=2&t=8691
  The page includes a sales sheet of a 1210 smd in Chinese.

                               Mikek

It would have to be a bad capacitor to have a Q under 1000. The great
Wes Hayward reports SMD ceramics with Qs at least 2000 to 5000, see:

http://w7zoi.net/twofaces.pdf

piglet

Yes, but they are working on a Q test instrument and I'm just
wondering if their caps are good enough so they don't know 100 or 150
off the Q number of a very good coil.
If you have coil with a Q of 1200 at 550kHz and resonate it with a
capacitor having a Q of 13,000, it will be reduced to Q=1100.
If your measuring Qs of 100 or 150, I agree the cap is insignificant,
but for measuring high Q coils, they should have a good tuning
capacitor. Mostly mental masturbation on my part, but I'm curious.
This is mostly crystal radio related.


Here's another W7zoi paper to add to your collection.
> http://sp-hm.pl/attachment.php?aid=6049

Mikek
 
On 7/24/2019 7:43 PM, George Herold wrote:
On Wednesday, July 24, 2019 at 3:48:15 PM UTC-4, piglet wrote:
On 24/07/2019 7:14 pm, amdx wrote:
Reading a forum, a member is comparing the Q of an smd capacitor to a
good air capacitor. Maybe?, I don't have a reference of the Q of a good
High Q capacitor. Range 20pf to 400pf.

 For further reference is is used in a ring down Q meter.
See last post on this page.
http://theradioboard.com/rb/viewtopic.php?f=2&t=8691
 The page includes a sales sheet of a 1210 smd in Chinese.

                              Mikek

It would have to be a bad capacitor to have a Q under 1000. The great
Wes Hayward reports SMD ceramics with Qs at least 2000 to 5000, see:

http://w7zoi.net/twofaces.pdf
Cool, I do figure (#) 3. with a 50 ohm sig gen,
~1 ohm source R, and a 'scope.
For caps you want to look at the dissipation factor..
it's a resistance, but I think it's different than ESR
in polarized caps. COG ceramics are great.
I've never had the right coil to get to a Q of 1000.

George H.

piglet

I made a group of coils on 6" styrene pipe couplers with turns from 9
turn per inch to 15 turns per inch. Just to see if one was better than
the rest. In my experiment 11 TPI was over all the best, starting at
Q=1263 at 500kHz peaking at Q=1476 at 800kHz and dropping to Q=948 at
1600kHz. 13 turns had the highest peak Q=1504, but it dropped off more
at the high end.
The styrene forms were had a tiny groove cut on a lathe to get the
proper spacing on the forms. I used litz wire 660/46.
I used a Boonton 260 to measure the Qs. When you are measuring Qs in
this range, it is a bit of a guessing game as to the accuracy, I'm
comfortable about the coils Qs relative to each other, but the accuracy
of the actual Q, I don't know.
There have been reports of Q=2000 using bigger litz or two strands of
660/46 litz.
This all AM broadcast Band frequencies.

Mikek
 
On Wed, 24 Jul 2019 19:35:05 -0500, amdx <nojunk@knology.net> wrote:

On 7/24/2019 2:12 PM, Jeff Liebermann wrote:
On Wed, 24 Jul 2019 13:14:57 -0500, amdx <nojunk@knology.net> wrote:

Reading a forum, a member is comparing the Q of an smd capacitor to a
good air capacitor. Maybe?, I don't have a reference of the Q of a good
High Q capacitor. Range 20pf to 400pf.

For further reference is is used in a ring down Q meter.
See last post on this page.
http://theradioboard.com/rb/viewtopic.php?f=2&t=8691
The page includes a sales sheet of a 1210 smd in Chinese.

Mikek

Look at (single layer) porcelain capacitors. For example:
https://www.atceramics.com/UserFiles/slc_catalog.pdf
See charts on Pg 8. Different dielectrics produce radically different
Q. For your operating frequency (1MHz AM BCB) such a capacitor might
be overkill. From the photos at:
http://www.crystalradio.cn/forum.php?mod=viewthread&tid=1756224&extra=page%3D4
the caps sorta, kinda, maybe look like porcelain. Google translate
converted the description into:
100B high Q chip capacitor 4, capacitance and test
capacitance values are: A-221=220.8pf B-121=128pf C-680=68.2pf
D-300=31.4pf,
series-parallel capacity in 21.5--448pf
100B is the ATC designation for one type of multi-layer porcelain cap:


http://www.atceramics.com/Product/17/100_B_Series_Porcelain_Multilayer_Capacitors_(MLCs)

Lots of extrapolation with unknown reality from the graph for a 100pf
cap at 1MHz. The graph starts at 0.01 ohms.

I presume you are referring to the RF Perfomance graphs at:
<http://www.atceramics.com/product_specifications.aspx?id=17#rfperformance>
The lowest frequency line is 150MHz, which is quite far from 1MHz.
Methinks we would do better using the dissipation factor or loss
tangent, which are usually specified at lower frequencies:
<https://www.electronics-notes.com/articles/basic_concepts/capacitance/esr-dissipation-factor-loss-tangent-q.php>
The porcelain caps are made for low loss high power RF and microwave
applications, so I doubt there would be a specification supplied.

If I assume the 100pf is
0.01 ohm ESR at 1MHz and it is resonated at 1MHz, the reactance is 1,592
ohms, thus 1592/0.01 = 159200. I find that difficult to believe. I would
believe a vacuum variable capacitor at 15,000. (A really good one)

Interpolating from the graph, my guess(tm) is much lower than 0.01
ohms ESR at 1Mhz. That's roughly the resistance of a PCB trace that's
20mm long which suggests you might have some problems taking advantage
of such a low ESR.

But, I'm here to learn, did I mess up the math? Is it over
extrapolation? Is the ESR really that good?

With my track record of sloppy arithmetic, you're asking me? Surely
you jest. Anyway, the calculations look right but don't make a
difference. When you resonate such a capacitor with a typical
inductor at 1MHz, the losses in the inductor determine the final Q of
the LC combination. You could have a perfect capacitor, but when you
put it across a crappy inductor, the combined Q will suck.

The ESR of a cap is much like the series resistance of the inductor.
For example, a 100pf and a 2.5mH air wound inductor to resonate at
1MHz.
<https://coil32.net/online-calculators/one-layer-coil-calculator.html>
Plugging in 32awg wire, 2.5mH inductance, and 100mm diameter coil,
yields 137 turns. Each turn circumference is:
Pi * D = 3.14 * 100mm = 314mm
Multiply that by the number of turns and the wire length is:
314mm/turn * 137 turns = 43,000mm = 43 meters
Looking up the resistance of 43 meters of 32awg copper wire:
<https://www.powerstream.com/Wire_Size.htm>
the resistance is:
43meters * 538ohsm/km / 1000 meters/km = 23 ohms
<https://www.everythingrf.com/rf-calculators/inductor-quality-factor-calculator>
Assuming no other losses, the best Q you can produce with such a loop
is 683. If you combine that with the 100pf resonating capacitor with
the sky high Q, the result will be:
Q = 1 / (1/Q1 * 1/Q2) = 1 / (1/159200 * 1/683) = 682
In other words, increasing the Q of the capacitor beyond about an
order of magnitude better than the coil (about 6820) is a wasted
effort.

What you probably want is the ESR, which is specified for most of the
other types of porcelain caps. See tables at:
http://www.atceramics.com/Capacitors/3/Multilayer-Capacitors
Q can easily be calculated with:
Q = Xc / ESR
"Q & ESR Explained"
https://www.atceramics.com/UserFiles/slc_catalog.pdf

--
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
 
On Thu, 25 Jul 2019 09:22:32 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

On Wed, 24 Jul 2019 19:35:05 -0500, amdx <nojunk@knology.net> wrote:

On 7/24/2019 2:12 PM, Jeff Liebermann wrote:
On Wed, 24 Jul 2019 13:14:57 -0500, amdx <nojunk@knology.net> wrote:

Reading a forum, a member is comparing the Q of an smd capacitor to a
good air capacitor. Maybe?, I don't have a reference of the Q of a good
High Q capacitor. Range 20pf to 400pf.

For further reference is is used in a ring down Q meter.
See last post on this page.
http://theradioboard.com/rb/viewtopic.php?f=2&t=8691
The page includes a sales sheet of a 1210 smd in Chinese.

Mikek

Look at (single layer) porcelain capacitors. For example:
https://www.atceramics.com/UserFiles/slc_catalog.pdf
See charts on Pg 8. Different dielectrics produce radically different
Q. For your operating frequency (1MHz AM BCB) such a capacitor might
be overkill. From the photos at:
http://www.crystalradio.cn/forum.php?mod=viewthread&tid=1756224&extra=page%3D4
the caps sorta, kinda, maybe look like porcelain. Google translate
converted the description into:
100B high Q chip capacitor 4, capacitance and test
capacitance values are: A-221=220.8pf B-121=128pf C-680=68.2pf
D-300=31.4pf,
series-parallel capacity in 21.5--448pf
100B is the ATC designation for one type of multi-layer porcelain cap:


http://www.atceramics.com/Product/17/100_B_Series_Porcelain_Multilayer_Capacitors_(MLCs)

Lots of extrapolation with unknown reality from the graph for a 100pf
cap at 1MHz. The graph starts at 0.01 ohms.

I presume you are referring to the RF Perfomance graphs at:
http://www.atceramics.com/product_specifications.aspx?id=17#rfperformance
The lowest frequency line is 150MHz, which is quite far from 1MHz.
Methinks we would do better using the dissipation factor or loss
tangent, which are usually specified at lower frequencies:
https://www.electronics-notes.com/articles/basic_concepts/capacitance/esr-dissipation-factor-loss-tangent-q.php
The porcelain caps are made for low loss high power RF and microwave
applications, so I doubt there would be a specification supplied.

If I assume the 100pf is
0.01 ohm ESR at 1MHz and it is resonated at 1MHz, the reactance is 1,592
ohms, thus 1592/0.01 = 159200. I find that difficult to believe. I would
believe a vacuum variable capacitor at 15,000. (A really good one)

Interpolating from the graph, my guess(tm) is much lower than 0.01
ohms ESR at 1Mhz. That's roughly the resistance of a PCB trace that's
20mm long which suggests you might have some problems taking advantage
of such a low ESR.

But, I'm here to learn, did I mess up the math? Is it over
extrapolation? Is the ESR really that good?

With my track record of sloppy arithmetic, you're asking me? Surely
you jest. Anyway, the calculations look right but don't make a
difference. When you resonate such a capacitor with a typical
inductor at 1MHz, the losses in the inductor determine the final Q of
the LC combination. You could have a perfect capacitor, but when you
put it across a crappy inductor, the combined Q will suck.

The ESR of a cap is much like the series resistance of the inductor.
For example, a 100pf and a 2.5mH air wound inductor to resonate at
1MHz.
https://coil32.net/online-calculators/one-layer-coil-calculator.html
Plugging in 32awg wire, 2.5mH inductance, and 100mm diameter coil,
yields 137 turns. Each turn circumference is:
Pi * D = 3.14 * 100mm = 314mm
Multiply that by the number of turns and the wire length is:
314mm/turn * 137 turns = 43,000mm = 43 meters
Looking up the resistance of 43 meters of 32awg copper wire:
https://www.powerstream.com/Wire_Size.htm
the resistance is:
43meters * 538ohsm/km / 1000 meters/km = 23 ohms
https://www.everythingrf.com/rf-calculators/inductor-quality-factor-calculator

Since the copper skin depth at 1 MHz is about 0.07 mm, so the total
cross section is not used and the losses are slightly larger than
that. The table lists full cross section utilization for that wire up
to 430 kHz only. A Litz wire helps of course.

Assuming no other losses, the best Q you can produce with such a loop
is 683. If you combine that with the 100pf resonating capacitor with
the sky high Q, the result will be:
Q = 1 / (1/Q1 * 1/Q2) = 1 / (1/159200 * 1/683) = 682
In other words, increasing the Q of the capacitor beyond about an
order of magnitude better than the coil (about 6820) is a wasted
effort.

What you probably want is the ESR, which is specified for most of the
other types of porcelain caps. See tables at:
http://www.atceramics.com/Capacitors/3/Multilayer-Capacitors
Q can easily be calculated with:
Q = Xc / ESR
"Q & ESR Explained"
https://www.atceramics.com/UserFiles/slc_catalog.pdf
 
On 7/25/2019 1:10 PM, amdx wrote:
On 7/25/2019 11:22 AM, Jeff Liebermann wrote:
On Wed, 24 Jul 2019 19:35:05 -0500, amdx <nojunk@knology.net> wrote:

On 7/24/2019 2:12 PM, Jeff Liebermann wrote:
On Wed, 24 Jul 2019 13:14:57 -0500, amdx <nojunk@knology.net> wrote:

Reading a forum, a member is comparing the Q of an smd capacitor to a
good air capacitor. Maybe?, I don't have a reference of the Q of a
good
High Q capacitor. Range 20pf to 400pf.

   For further reference is is used in a ring down Q meter.
See last post on this page.
http://theradioboard.com/rb/viewtopic.php?f=2&t=8691
   The page includes a sales sheet of a 1210 smd in Chinese.

                                Mikek

Look at (single layer) porcelain capacitors.  For example:
https://www.atceramics.com/UserFiles/slc_catalog.pdf
See charts on Pg 8.  Different dielectrics produce radically different
Q.  For your operating frequency (1MHz AM BCB) such a capacitor might
be overkill.  From the photos at:
http://www.crystalradio.cn/forum.php?mod=viewthread&tid=1756224&extra=page%3D4

the caps sorta, kinda, maybe look like porcelain.  Google translate
converted the description into:
     100B high Q chip capacitor 4, capacitance and test
     capacitance values are: A-221=220.8pf B-121=128pf C-680=68.2pf
     D-300=31.4pf,
     series-parallel capacity in 21.5--448pf
100B is the ATC designation for one type of multi-layer porcelain cap:


http://www.atceramics.com/Product/17/100_B_Series_Porcelain_Multilayer_Capacitors_(MLCs)


Lots of extrapolation with unknown reality from the graph for a 100pf
cap at 1MHz. The graph starts at 0.01 ohms.

I presume you are referring to the RF Perfomance graphs at:
http://www.atceramics.com/product_specifications.aspx?id=17#rfperformance

The lowest frequency line is 150MHz, which is quite far from 1MHz.
Methinks we would do better using the dissipation factor or loss
tangent, which are usually specified at lower frequencies:
https://www.electronics-notes.com/articles/basic_concepts/capacitance/esr-dissipation-factor-loss-tangent-q.php

The porcelain caps are made for low loss high power RF and microwave
applications, so I doubt there would be a specification supplied.

If I assume the 100pf is
0.01 ohm ESR at 1MHz and it is resonated at 1MHz, the reactance is 1,592
ohms, thus 1592/0.01 = 159200. I find that difficult to believe. I would
believe a vacuum variable capacitor at 15,000. (A really good one)

Interpolating from the graph, my guess(tm) is much lower than 0.01
ohms ESR at 1Mhz.  That's roughly the resistance of a PCB trace that's
20mm long which suggests you might have some problems taking advantage
of such a low ESR.

But, I'm here to learn, did I mess up the math? Is it over
extrapolation? Is the ESR really that good?

With my track record of sloppy arithmetic, you're asking me?  Surely
you jest.  Anyway, the calculations look right but don't make a
difference.  When you resonate such a capacitor with a typical
inductor at 1MHz, the losses in the inductor determine the final Q of
the LC combination.  You could have a perfect capacitor, but when you
put it across a crappy inductor, the combined Q will suck.

The ESR of a cap is much like the series resistance of the inductor.
For example, a 100pf and a 2.5mH air wound inductor to resonate at
1MHz.
https://coil32.net/online-calculators/one-layer-coil-calculator.html
Plugging in 32awg wire, 2.5mH inductance, and 100mm diameter coil,
yields 137 turns.  Each turn circumference is:
   Pi * D = 3.14 * 100mm = 314mm
Multiply that by the number of turns and the wire length is:
   314mm/turn * 137 turns = 43,000mm = 43 meters
Looking up the resistance of 43 meters of 32awg copper wire:
https://www.powerstream.com/Wire_Size.htm
the resistance is:
   43meters * 538ohsm/km / 1000 meters/km = 23 ohms
https://www.everythingrf.com/rf-calculators/inductor-quality-factor-calculator

Assuming no other losses, the best Q you can produce with such a loop
is 683.  If you combine that with the 100pf resonating capacitor with
the sky high Q, the result will be:
   Q = 1 / (1/Q1 * 1/Q2) = 1 / (1/159200 * 1/683) = 682
In other words, increasing the Q of the capacitor beyond about an
order of magnitude better than the coil (about 6820) is a wasted
effort.


 In one of my posts, I mentioned that someone is putting together a
ring down Q meter and trying to save a few bucks going with high Q smd
vs a good variable air cap. This is crystal radio stuff and Qs can get
as high as 1500. So, in order to improve accuracy I expect the best cap
at a reasonable price. But I would hope it is 10x higher Q than the highest
Q coil to be measured. Even with that, it would still measure the coil Q
down my 10%. (I didn't run the numbers, but it's close)

Sorry Jeff,
I guess I didn't read your last paragraph, you did 10x, I did 10x, but
it still gives you close 10% error. When you're doing relative
measurements to compare one coil to another that's fine, but when you
want absolute value then you want a better cap.
btw, when you measure 6" air core coils, moving yourself within a foot
will affect the Q reading.

Mikek
 
On Wednesday, July 24, 2019 at 12:48:15 PM UTC-7, piglet wrote:
On 24/07/2019 7:14 pm, amdx wrote:
Reading a forum, a member is comparing the Q of an smd capacitor to a
good air capacitor. Maybe?, I don't have a reference of the Q of a good
High Q capacitor. Range 20pf to 400pf.

 For further reference is is used in a ring down Q meter.
See last post on this page.
http://theradioboard.com/rb/viewtopic.php?f=2&t=8691
 The page includes a sales sheet of a 1210 smd in Chinese.

                              Mikek

It would have to be a bad capacitor to have a Q under 1000. The great
Wes Hayward reports SMD ceramics with Qs at least 2000 to 5000, see:

http://w7zoi.net/twofaces.pdf

Below 10-20 MHz, it is true that the coils are usually much worse than the caps. But from 100 MHz and above, the Q of the cap must be carefully considered. Assume cap Q contributes until evaluated.

In Fig. 3-13 [1] of Rhea, he shows the Q of an AVX 100 pF cap to about 100 at 200 MHz.

In Fig. 8 of Benabe, evaluating a 68 pF 1206 capacitor at about 300 MHz yields a Q of about 65.

I often read the "you can safely ignore cap Q" in texts, but work at RF and microwave frequencies has shown me that it does not apply there.

In bandpass filter work, circuit and resonator Q is usually helped by driving the inductances up and the capacitances down, ceteris paribus. As usual, such a concern is often not the most difficult issue in producing a working LC filter. There is not much wiggle room for LPF/HPF as the component values cannot be much manipulated there.


[1] Rhea, R. W., HF Filter Design and Computer Simulation, Noble Publishing, Atlanta, 1994, (pp.194-198)

[2] Benabe, Automated Characterization of Ceramic Multilayer Capacitors, UFL, RPAG-MOT
 
On 7/25/2019 11:22 AM, Jeff Liebermann wrote:
On Wed, 24 Jul 2019 19:35:05 -0500, amdx <nojunk@knology.net> wrote:

On 7/24/2019 2:12 PM, Jeff Liebermann wrote:
On Wed, 24 Jul 2019 13:14:57 -0500, amdx <nojunk@knology.net> wrote:

Reading a forum, a member is comparing the Q of an smd capacitor to a
good air capacitor. Maybe?, I don't have a reference of the Q of a good
High Q capacitor. Range 20pf to 400pf.

For further reference is is used in a ring down Q meter.
See last post on this page.
http://theradioboard.com/rb/viewtopic.php?f=2&t=8691
The page includes a sales sheet of a 1210 smd in Chinese.

Mikek

Look at (single layer) porcelain capacitors. For example:
https://www.atceramics.com/UserFiles/slc_catalog.pdf
See charts on Pg 8. Different dielectrics produce radically different
Q. For your operating frequency (1MHz AM BCB) such a capacitor might
be overkill. From the photos at:
http://www.crystalradio.cn/forum.php?mod=viewthread&tid=1756224&extra=page%3D4
the caps sorta, kinda, maybe look like porcelain. Google translate
converted the description into:
100B high Q chip capacitor 4, capacitance and test
capacitance values are: A-221=220.8pf B-121=128pf C-680=68.2pf
D-300=31.4pf,
series-parallel capacity in 21.5--448pf
100B is the ATC designation for one type of multi-layer porcelain cap:


http://www.atceramics.com/Product/17/100_B_Series_Porcelain_Multilayer_Capacitors_(MLCs)

Lots of extrapolation with unknown reality from the graph for a 100pf
cap at 1MHz. The graph starts at 0.01 ohms.

I presume you are referring to the RF Perfomance graphs at:
http://www.atceramics.com/product_specifications.aspx?id=17#rfperformance
The lowest frequency line is 150MHz, which is quite far from 1MHz.
Methinks we would do better using the dissipation factor or loss
tangent, which are usually specified at lower frequencies:
https://www.electronics-notes.com/articles/basic_concepts/capacitance/esr-dissipation-factor-loss-tangent-q.php
The porcelain caps are made for low loss high power RF and microwave
applications, so I doubt there would be a specification supplied.

If I assume the 100pf is
0.01 ohm ESR at 1MHz and it is resonated at 1MHz, the reactance is 1,592
ohms, thus 1592/0.01 = 159200. I find that difficult to believe. I would
believe a vacuum variable capacitor at 15,000. (A really good one)

Interpolating from the graph, my guess(tm) is much lower than 0.01
ohms ESR at 1Mhz. That's roughly the resistance of a PCB trace that's
20mm long which suggests you might have some problems taking advantage
of such a low ESR.

But, I'm here to learn, did I mess up the math? Is it over
extrapolation? Is the ESR really that good?

With my track record of sloppy arithmetic, you're asking me? Surely
you jest. Anyway, the calculations look right but don't make a
difference. When you resonate such a capacitor with a typical
inductor at 1MHz, the losses in the inductor determine the final Q of
the LC combination. You could have a perfect capacitor, but when you
put it across a crappy inductor, the combined Q will suck.

The ESR of a cap is much like the series resistance of the inductor.
For example, a 100pf and a 2.5mH air wound inductor to resonate at
1MHz.
https://coil32.net/online-calculators/one-layer-coil-calculator.html
Plugging in 32awg wire, 2.5mH inductance, and 100mm diameter coil,
yields 137 turns. Each turn circumference is:
Pi * D = 3.14 * 100mm = 314mm
Multiply that by the number of turns and the wire length is:
314mm/turn * 137 turns = 43,000mm = 43 meters
Looking up the resistance of 43 meters of 32awg copper wire:
https://www.powerstream.com/Wire_Size.htm
the resistance is:
43meters * 538ohsm/km / 1000 meters/km = 23 ohms
https://www.everythingrf.com/rf-calculators/inductor-quality-factor-calculator
Assuming no other losses, the best Q you can produce with such a loop
is 683. If you combine that with the 100pf resonating capacitor with
the sky high Q, the result will be:
Q = 1 / (1/Q1 * 1/Q2) = 1 / (1/159200 * 1/683) = 682
In other words, increasing the Q of the capacitor beyond about an
order of magnitude better than the coil (about 6820) is a wasted
effort.

In one of my posts, I mentioned that someone is putting together a
ring down Q meter and trying to save a few bucks going with high Q smd
vs a good variable air cap. This is crystal radio stuff and Qs can get
as high as 1500. So, in order to improve accuracy I expect the best cap
at a reasonable price. But I would hope it is 10x higher Q than the highest
Q coil to be measured. Even with that, it would still measure the coil Q
down my 10%. (I didn't run the numbers, but it's close)
 
On Thu, 25 Jul 2019 13:10:47 -0500, amdx <nojunk@knology.net> wrote:

In one of my posts, I mentioned that someone is putting together a
ring down Q meter and trying to save a few bucks going with high Q smd
vs a good variable air cap. This is crystal radio stuff and Qs can get
as high as 1500.

How does that work? The upper modulation frequency of BCB AM is
10.2KHz yielding an occupied bandwidth of about 20.4KHz. At 1MHz and
a Q=1500, the 3dB bandwidth of the LC circuit is:
1MHz / 1500 = 670 Hz
That's narrower than the AM occupied bandwidth, so the high frequency
audio will not pass. Probably great for CW or 160 meters, but nobody
does CW on the broadcast band.

The Q=1500 might be the unloaded Q as the diode detector forward
conduction resistance does present a rather low resistance in parallel
with at least part of the LC circuit. To get all the audio
frequencies through, the maximum loaded Q is:
1MHz / 20.4KHz = 49
<http://www.sengpielaudio.com/calculator-cutoffFrequencies.htm>

Incidentally, I run into the same problem with small loop antennas
also known as magnetic loop, where the antenna Q becomes sufficiently
high that only the lower audio frequencies are passed. The resulting
audio sounds "muffled". It's possible to build very high Q loop
antennas that are useless.
"Small Transmitting Loop Antennas"
<http://www.aa5tb.com/loop.html>
<http://www.aa5tb.com/aa5tb_loop_v1.22e.xlsx>

So, in order to improve accuracy I expect the best cap
at a reasonable price. But I would hope it is 10x higher Q than the highest
Q coil to be measured. Even with that, it would still measure the coil Q
down my 10%. (I didn't run the numbers, but it's close)

10 times higher Q for the capacitors in the instrument sounds about
right, but you could probably survive with less. I'm not familiar
with a ring down Q meter, so I don't know exactly what's required.

--
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
 
On Thu, 25 Jul 2019 13:10:47 -0500, amdx <nojunk@knology.net> wrote:

In one of my posts, I mentioned that someone is putting together a
ring down Q meter and trying to save a few bucks going with high Q smd
vs a good variable air cap. This is crystal radio stuff and Qs can get
as high as 1500. So, in order to improve accuracy I expect the best cap
at a reasonable price. But I would hope it is 10x higher Q than the highest
Q coil to be measured. Even with that, it would still measure the coil Q
down my 10%. (I didn't run the numbers, but it's close)

So this is for a crystal set for receiving AM broadcasts in the 0.5 -
1,5 MHz band ? For AM reception, the detector needs the carrier and at
least of one sideband. Assuming 5 kHz required bandwidth, that will
required loaded Ql at the low end of the band of 100 and 300 at the
top of the band.

On the other hand, the unloaded Qu should be a few times larger than
the loaded Ql in order to minimize passband insertion losses. The
insertion loss is given by

Loss_dB = 20 log (1/ (1-Ql/Qu) )

Assuming (unrealistically) that Qu remains at 1500 all over the band.
Thus at the low end of the band the insertion loss is 0.6 dB and at
1.5 MHz 1.9 dB. A 10 % error in the Qu measurement doesn't affect the
insertion loss very much.
 
On 25.7.19 21:52, Jeff Liebermann wrote:
On Thu, 25 Jul 2019 13:10:47 -0500, amdx <nojunk@knology.net> wrote:

In one of my posts, I mentioned that someone is putting together a
ring down Q meter and trying to save a few bucks going with high Q smd
vs a good variable air cap. This is crystal radio stuff and Qs can get
as high as 1500.

How does that work? The upper modulation frequency of BCB AM is
10.2KHz yielding an occupied bandwidth of about 20.4KHz. At 1MHz and
a Q=1500, the 3dB bandwidth of the LC circuit is:
1MHz / 1500 = 670 Hz
That's narrower than the AM occupied bandwidth, so the high frequency
audio will not pass. Probably great for CW or 160 meters, but nobody
does CW on the broadcast band.

The Q=1500 might be the unloaded Q as the diode detector forward
conduction resistance does present a rather low resistance in parallel
with at least part of the LC circuit. To get all the audio
frequencies through, the maximum loaded Q is:
1MHz / 20.4KHz = 49
http://www.sengpielaudio.com/calculator-cutoffFrequencies.htm

Incidentally, I run into the same problem with small loop antennas
also known as magnetic loop, where the antenna Q becomes sufficiently
high that only the lower audio frequencies are passed. The resulting
audio sounds "muffled". It's possible to build very high Q loop
antennas that are useless.
"Small Transmitting Loop Antennas"
http://www.aa5tb.com/loop.html
http://www.aa5tb.com/aa5tb_loop_v1.22e.xlsx

So, in order to improve accuracy I expect the best cap
at a reasonable price. But I would hope it is 10x higher Q than the highest
Q coil to be measured. Even with that, it would still measure the coil Q
down my 10%. (I didn't run the numbers, but it's close)

10 times higher Q for the capacitors in the instrument sounds about
right, but you could probably survive with less. I'm not familiar
with a ring down Q meter, so I don't know exactly what's required.

We had that kind of problem with aviation long-wave beacons (NDB).

The identification should be in amplitude-modulated Morse code
with a modulation frequency of 1050 Hz. The Q of a force-tuned
20 meter (70 ft) antennas was too high to pass the modulation sidebands,
so the identifier frequency was lowered to 400 Hz (which was the
alternate option allowed by ICAO Annex 10).

--

-TV
 
On Thu, 25 Jul 2019 11:52:42 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

On Thu, 25 Jul 2019 13:10:47 -0500, amdx <nojunk@knology.net> wrote:

In one of my posts, I mentioned that someone is putting together a
ring down Q meter and trying to save a few bucks going with high Q smd
vs a good variable air cap. This is crystal radio stuff and Qs can get
as high as 1500.

How does that work? The upper modulation frequency of BCB AM is
10.2KHz yielding an occupied bandwidth of about 20.4KHz.

A simple diode detector works quite well with a full carrier and one
sideband. Check any analog TV standard. There are a small vestigal
opposite sideband, but IIRC it was for phase accuracy of synch pulses.
For audio, the is irrelevant.

Does US AM broadcast standards really allow 10.2 MHz modulation
frequencies, when he channel spacing is 10 kHz, Apparently only every
other channel is used in a region with relatively low transmitter
powers (50 kW).

In Europe, the MW channel raster is 9 kHz and every channel is used.
Some stations are quite high power (over 1 MW). The modulation
frequency i limited to 4.5 kHz. Looking at the waterfall spectral
display, many stations utilizes fully the fC+/-4.5 kHz bandwidth.

Shortwave broadcasts are at 5 kHz raster.



At 1MHz and
a Q=1500, the 3dB bandwidth of the LC circuit is:
1MHz / 1500 = 670 Hz
That's narrower than the AM occupied bandwidth, so the high frequency
audio will not pass. Probably great for CW or 160 meters, but nobody
does CW on the broadcast band.

The Q=1500 might be the unloaded Q as the diode detector forward
conduction resistance does present a rather low resistance in parallel
with at least part of the LC circuit. To get all the audio
frequencies through, the maximum loaded Q is:
1MHz / 20.4KHz = 49

You can double loaded Q by slightly detuning and letting through the
carrier and one (either upper or lower) sideband. For speech 3.5 kHz
(telephone quality) is enough and 5 kHz would more realistic so once
again double the loaded Q.

http://www.sengpielaudio.com/calculator-cutoffFrequencies.htm

Incidentally, I run into the same problem with small loop antennas
also known as magnetic loop, where the antenna Q becomes sufficiently
high that only the lower audio frequencies are passed. The resulting
audio sounds "muffled". It's possible to build very high Q loop
antennas that are useless.
"Small Transmitting Loop Antennas"
http://www.aa5tb.com/loop.html
http://www.aa5tb.com/aa5tb_loop_v1.22e.xlsx

So, in order to improve accuracy I expect the best cap
at a reasonable price. But I would hope it is 10x higher Q than the highest
Q coil to be measured. Even with that, it would still measure the coil Q
down my 10%. (I didn't run the numbers, but it's close)

10 times higher Q for the capacitors in the instrument sounds about
right, but you could probably survive with less. I'm not familiar
with a ring down Q meter, so I don't know exactly what's required.
 
On 26/7/19 4:52 am, Jeff Liebermann wrote:
On Thu, 25 Jul 2019 13:10:47 -0500, amdx <nojunk@knology.net> wrote:

In one of my posts, I mentioned that someone is putting together a
ring down Q meter and trying to save a few bucks going with high Q smd
vs a good variable air cap. This is crystal radio stuff and Qs can get
as high as 1500.

How does that work? The upper modulation frequency of BCB AM is
10.2KHz yielding an occupied bandwidth of about 20.4KHz. At 1MHz and
a Q=1500, the 3dB bandwidth of the LC circuit is:
1MHz / 1500 = 670 Hz
That's narrower than the AM occupied bandwidth, so the high frequency
audio will not pass.

I made the same argument a previous time this came up, but as amdx
points out, the earphones provide the additional load. Because they're
after the rectifier, it does have strange effects on the received
frequencies, but who am I to tell a crystal radio purist what they
should like :)

Clifford Heath.
 
On 7/25/2019 1:52 PM, Jeff Liebermann wrote:
On Thu, 25 Jul 2019 13:10:47 -0500, amdx <nojunk@knology.net> wrote:

In one of my posts, I mentioned that someone is putting together a
ring down Q meter and trying to save a few bucks going with high Q smd
vs a good variable air cap. This is crystal radio stuff and Qs can get
as high as 1500.

How does that work? The upper modulation frequency of BCB AM is
10.2KHz yielding an occupied bandwidth of about 20.4KHz. At 1MHz and
a Q=1500, the 3dB bandwidth of the LC circuit is:
1MHz / 1500 = 670 Hz
That's narrower than the AM occupied bandwidth, so the high frequency
audio will not pass. Probably great for CW or 160 meters, but nobody
does CW on the broadcast band.

The Q=1500 might be the unloaded Q as the diode detector forward
conduction resistance does present a rather low resistance in parallel
with at least part of the LC circuit. To get all the audio
frequencies through, the maximum loaded Q is:
1MHz / 20.4KHz = 49
http://www.sengpielaudio.com/calculator-cutoffFrequencies.htm
Yep, that's just the coil, now add a cap, more loss, through in a
diode, not sure how that affects Q, then to extract maximum audio
energy, you will end up lowering the total circuit Q by 1/2.
But you only need to hear up to a little over 3kHz to understand.
People do crystal radio DXing.
To high of a Q in a crystal radio is not a problem it is very easy to
spoil the Q.


Incidentally, I run into the same problem with small loop antennas
also known as magnetic loop, where the antenna Q becomes sufficiently
high that only the lower audio frequencies are passed. The resulting
audio sounds "muffled". It's possible to build very high Q loop
antennas that are useless.
"Small Transmitting Loop Antennas"
http://www.aa5tb.com/loop.html
http://www.aa5tb.com/aa5tb_loop_v1.22e.xlsx

My next antenna build will be a BOG, Beverage on Ground.
I had one, but after the hurricane the owner of the land my BOG was on
thought they could just remove all the broken trees, tear up the stumps
and clear off the land including my antenna! Hrrrmph!
Anyway, after clearing, they made a new ditch to replace what was
there before. I still have a clear 250ft to 300ft straight shot on the
bank of my side of the ditch. I installed ferrite sleaves to lower the
velocity factor to make it seem a little longer.
It was a great antenna, very quiet, didn't pickup all the lightning
off the southern coast, (I'm in the Florida Panhandle). I pointed it at
Chicago so it heard to the North well, but very poor on the Boomer 1200
WOAI out of Texas to the West, or even a local station to the East.
Mikek
 
On 7/25/2019 2:40 PM, upsidedown@downunder.com wrote:
On Thu, 25 Jul 2019 13:10:47 -0500, amdx <nojunk@knology.net> wrote:


In one of my posts, I mentioned that someone is putting together a
ring down Q meter and trying to save a few bucks going with high Q smd
vs a good variable air cap. This is crystal radio stuff and Qs can get
as high as 1500. So, in order to improve accuracy I expect the best cap
at a reasonable price. But I would hope it is 10x higher Q than the highest
Q coil to be measured. Even with that, it would still measure the coil Q
down my 10%. (I didn't run the numbers, but it's close)

So this is for a crystal set for receiving AM broadcasts in the 0.5 -
1,5 MHz band ? For AM reception, the detector needs the carrier and at
least of one sideband. Assuming 5 kHz required bandwidth, that will
required loaded Ql at the low end of the band of 100 and 300 at the
top of the band.

I was a little surprised with the 100 and 300. But I can see the
advantage of having a high Q LC is that you can
extra more audio from the recovered signal. Thus on a DX weak signal
you can hear it because you started with high Q front end.
The DX contest winners aren't #20 wire on a cardboard tube, they go
all out to minimize losses.


On the other hand, the unloaded Qu should be a few times larger than
the loaded Ql in order to minimize passband insertion losses. The
insertion loss is given by

Loss_dB = 20 log (1/ (1-Ql/Qu) )

Assuming (unrealistically) that Qu remains at 1500 all over the band.
Thus at the low end of the band the insertion loss is 0.6 dB and at
1.5 MHz 1.9 dB. A 10 % error in the Qu measurement doesn't affect the
insertion loss very much.
 

Welcome to EDABoard.com

Sponsor

Back
Top