High Q smd capacitors

[amdx]

On 7/31/2019 12:31 AM, upsidedown@downunder.com wrote:

On Tue, 30 Jul 2019 17:36:01 -0700 (PDT), tabbypurr@gmail.com wrote:

On Tuesday, 30 July 2019 22:26:22 UTC+1, amdx wrote:

Historically a long wire was used for crystal radios. And yes your
right that a long wire is an inverted L antenna and the "feedline" is
much of the antenna if not all and the long wire part is a top hat.

That's not hard to disprove. I had a long wire antenna with horizontal feed wire. It worked very well, thus the horizontal section does act as an antenna, not just top capacitance.

If we forget real long wire antennas such as Beverages that are
wavelengths long and assume that we are talking about horizontal wires
with one end hung high up in a tree and the receiver terminal inside
the house, the antenna is actually a sloper with a height difference
between wire end points. This absorbs the vertically polarized part of
the field. The wire doesn¨t have to perpendicular to earth to capture
any vertical component.

As far as I understand all LW/MW broadcast stations intended for local
ground wave reception has always been vertically polarized. Typically
a single mast with an elaborate grounding, such as 98 buried radials.

Especially on LW broadcast stations often two towers were used with
one or multiple horizontal wires installed between them forming a top
loading capacitance. A vertical radiator was then connected from the
transmitter to the center of the horizontal wire(s) forming a
T-antenna. Thanks to the top loading not so much loading coils and
less grounding networks were required.

In Poland they even build a 600 b high center feed half wave LW
dipole, which of course did not need a grounding network.
Unfortunately it crashed during maintenance several years ago.

I posted on a crystal radio grou[, here is a response I received.


> So, now I'd like to see the difference in the impedance of a 14ft
vertical vs 14ft vertical with a 130ft horizontal section.
Mikek

"The conductive ground shorts out (and absorbs) any Horizontally
polarised component close to the ground.
So unless the antenna is fairly high (in wavelengths) there is little
horizontal signal for it to respond to.

Plus the local AM transmitters will all be transmitting a Vertically
polarised signal.

So a short "L" shaped antenna (close to the ground) will only pick up
significant signals on its vertical section.

Adding the horizontal section adds top capacitance. Because the current
distribution must start at zero at the end of the wire, top loading
moves the current distribution upwards (in the vertical section). This
means that the Radiation Resistance of a top loaded antenna will be
higher, plus the extra Capacitance means that less Inductance will be
needed to bring it to resonance. All this results in considerably
greater efficiency, assuming a good ground.

Next would be how does the pattern change when you add the 130ft
horizontal section to the 14ft vertical.

The radiation pattern actually changes very little. The effect of the
top section is to tilt the lobe slightly away from the horizontal section.

All this only applies when the antenna is relatively small compared with
the wavelength. As the frequency rises, the radiation pattern changes
dramatically.

The exception to this is the "Non-Resonant Travelling-Wave Antenna" (eg
Beverage). A very long wire close to the the ground responds to Vertical
signals traveling along its length, because the signals induce a current
into the ground and into the antenna. But this pickup is negligible in
the horizontal section of a short "L" antenna, as it is too short to
respond to the traveling wave. However it is this "wave pickup" which
tilts the lobe slightly.

P.S. People most definitely do use short vertical Antennas with Crystal
sets. They work very well, but do require a very efficient Earth (or
ground plane) and a very efficient loading coil. This usually means a
remote antenna tuner and coax feed.
The big advantage of an efficient Vertical Antenna is greater
sensitivity to very low-angle incoming signals. eg international DX
signals."

 

[amdx]

On 7/31/2019 11:45 AM, amdx wrote:

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.

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.


 My best coil has Q=1250 at 500kHz, it peaks at Q=1500 at 800kHz, and
drops to Q=850 at 1700kHz.
 Everyone seems very concerned about Q being to high. A builder of a
high end crystal radio would be proud to have that problem, it is so
easily fixed, where building to a spec of having that problem is difficult.

                                        Mikek
Here's an analysis of an L antenna. It's over my head but may work for you.
https://nvlpubs.nist.gov/nistpubs/bulletin/14/nbsbulletinv14n4p677_A2b.pdf

Mikek

 

On Wed, 31 Jul 2019 11:45:38 -0500, amdx <nojunk@knology.net> wrote:

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.

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.


My best coil has Q=1250 at 500kHz, it peaks at Q=1500 at 800kHz, and
drops to Q=850 at 1700kHz.

That is the unloaded Qu.

> Everyone seems very concerned about Q being to high.

The loaded Ql depends of the required bandwidth BW e,g, for 5 kHz
(carrier+one sideband), Ql = f/BW, thus Ql=100, 160 resp. 340.

Calculate the Ql/Qu ratio and use the formula above or the value from
the link posted in this thread to get the insertion loss.

Clearly the coupling between the resonator and rectifier load must be
varies depending on frequency.

The worst situation is at the top of the band, i.e. Qu is lowest and
required Ql the highest.

A builder of a
high end crystal radio would be proud to have that problem, it is so
easily fixed, where building to a spec of having that problem is difficult.

Mikek

 

[John Larkin]

On Thu, 01 Aug 2019 08:33:52 +0300, upsidedown@downunder.com wrote:

On Wed, 31 Jul 2019 11:45:38 -0500, amdx <nojunk@knology.net> wrote:

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.

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.


My best coil has Q=1250 at 500kHz, it peaks at Q=1500 at 800kHz, and
drops to Q=850 at 1700kHz.

That is the unloaded Qu.

Right. It has to drive headphones.

Everyone seems very concerned about Q being to high.

The loaded Ql depends of the required bandwidth BW e,g, for 5 kHz
(carrier+one sideband), Ql = f/BW, thus Ql=100, 160 resp. 340.

Wouldn't you want the power from both sidebands?

The ideal crystal radio would use a matched-impedance-both-ends
bandpass filter.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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

 

[amdx]

On 8/1/2019 12:42 PM, John Larkin wrote:

On Thu, 01 Aug 2019 08:33:52 +0300, upsidedown@downunder.com wrote:

On Wed, 31 Jul 2019 11:45:38 -0500, amdx <nojunk@knology.net> wrote:

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.

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.


My best coil has Q=1250 at 500kHz, it peaks at Q=1500 at 800kHz, and
drops to Q=850 at 1700kHz.

That is the unloaded Qu.

I don't know if it is not understood, when I say the Q of my coil and
cap or LC if XXXX that is means just the coil and cap or LC, Yes, that
is Qu now doubt about it. Qu, Qu! .

Right. It has to drive headphones.

Everyone seems very concerned about Q being to high.

The loaded Ql depends of the required bandwidth BW e,g, for 5 kHz
(carrier+one sideband), Ql = f/BW, thus Ql=100, 160 resp. 340.

Wouldn't you want the power from both sidebands?

The ideal crystal radio would use a matched-impedance-both-ends
bandpass filter.

You will need to give me more info, maybe one of your hand drawn schematics.

I ask on a crystal group, "Have you built a radio with Q so high it
limits Bandwidth?"

So far two responses,

"It's hard to imagine a practical LC combination with that much Q. And
tunable, too.
The idea of clipping the audio of much of what's on the AMBC band these
days does sound appealing, though."

And,

"I have been hearing that "anti high-Q" / "clipping" crap for years on
forums.
Mostly from so called "experts" and angry old hams who want to dispute
the advantages of litz wire in crystal radios (having never used it).
If it was the case, then nobody would listen to regen rceivers,
specially at MW.
(The same people are happy to exhort the virtues of regens.)"

Mikek

 

[amdx]

On 7/25/2019 7:37 PM, Clifford Heath wrote:

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.

Here's a video showing audio reducing as the frequency increases.
He says Q=1190, but I don't know if that was loaded Q. I suspect yes,
but then how did he do that? It may have been a different test, it did
come from a crystal radio forum

> https://www.youtube.com/watch?v=8vwqNI9QeEo

Mikek

 

[Rick C]

On Wednesday, July 24, 2019 at 2:14:57 PM UTC-4, 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.

I've never heard of liquid filled capacitors. When it comes to variable capacitors the two choices for high Q are air and vacuum. I thought you could add a solid dielectric to increase the voltage and capacitance of an air variable cap, but the air gap, no matter how small it is, ends up with the lion's share of the voltage which would result in corona discharge at the surface of the dielectric. Not good.

I found some good liquid dielectrics, but the mechanics of a liquid variable cap are too complex to make practical.

But then you likely aren't talking about variable caps. But this is for a resonant circuit, right? Are you planning to adjust the coil?

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

 

[amdx]

On 8/27/2019 9:46 AM, Rick C wrote:

On Wednesday, July 24, 2019 at 2:14:57 PM UTC-4, 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.

I've never heard of liquid filled capacitors. When it comes to variable capacitors the two choices for high Q are air and vacuum. I thought you could add a solid dielectric to increase the voltage and capacitance of an air variable cap, but the air gap, no matter how small it is, ends up with the lion's share of the voltage which would result in corona discharge at the surface of the dielectric. Not good.

I found some good liquid dielectrics, but the mechanics of a liquid variable cap are too complex to make practical.

But then you likely aren't talking about variable caps. But this is for a resonant circuit, right? Are you planning to adjust the coil?

The cap is being used to resonate the coil. Then the tool counts how
many cycles it takes to ring down to a certain voltage.
The author used a fixed capacitor to do this.
This was to avoid the cost of a Variable air cap.
What I wanted to know was, is the Q of the cap high enough,
compared to an air cap, so as to have little effect on measured Q.
I didn't have a Q of the capacitor, I do have numbers on how good or
how bad an air cap can be.
Mikek

 

[Rick C]

On Tuesday, August 27, 2019 at 1:00:20 PM UTC-4, amdx wrote:

On 8/27/2019 9:46 AM, Rick C wrote:
On Wednesday, July 24, 2019 at 2:14:57 PM UTC-4, 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.

I've never heard of liquid filled capacitors. When it comes to variable capacitors the two choices for high Q are air and vacuum. I thought you could add a solid dielectric to increase the voltage and capacitance of an air variable cap, but the air gap, no matter how small it is, ends up with the lion's share of the voltage which would result in corona discharge at the surface of the dielectric. Not good.

I found some good liquid dielectrics, but the mechanics of a liquid variable cap are too complex to make practical.

But then you likely aren't talking about variable caps. But this is for a resonant circuit, right? Are you planning to adjust the coil?


The cap is being used to resonate the coil. Then the tool counts how
many cycles it takes to ring down to a certain voltage.
The author used a fixed capacitor to do this.
This was to avoid the cost of a Variable air cap.
What I wanted to know was, is the Q of the cap high enough,
compared to an air cap, so as to have little effect on measured Q.
I didn't have a Q of the capacitor, I do have numbers on how good or
how bad an air cap can be.
Mikek

Ok, so you don't need a variable cap. That doesn't mean you can't use an air cap with a very, very high Q so you don't even need to consider it. What value cap do you need? An air cap is just a couple of plates separated by air. Their value can be calculated easily even with the fringe effects.

I would say the Q of the cap needs to be on the order of 10x the coil to measure it without a significant influence. Of course if you know the cap Q and it is stable you can factor that in, but unless it is very well known and stable it still needs to be higher than the coil to get a good measurement.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

 

[amdx]

On 8/27/2019 6:35 PM, Rick C wrote:

On Tuesday, August 27, 2019 at 1:00:20 PM UTC-4, amdx wrote:
On 8/27/2019 9:46 AM, Rick C wrote:
On Wednesday, July 24, 2019 at 2:14:57 PM UTC-4, 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.

I've never heard of liquid filled capacitors. When it comes to variable capacitors the two choices for high Q are air and vacuum. I thought you could add a solid dielectric to increase the voltage and capacitance of an air variable cap, but the air gap, no matter how small it is, ends up with the lion's share of the voltage which would result in corona discharge at the surface of the dielectric. Not good.

I found some good liquid dielectrics, but the mechanics of a liquid variable cap are too complex to make practical.

But then you likely aren't talking about variable caps. But this is for a resonant circuit, right? Are you planning to adjust the coil?


The cap is being used to resonate the coil. Then the tool counts how
many cycles it takes to ring down to a certain voltage.
The author used a fixed capacitor to do this.
This was to avoid the cost of a Variable air cap.
What I wanted to know was, is the Q of the cap high enough,
compared to an air cap, so as to have little effect on measured Q.
I didn't have a Q of the capacitor, I do have numbers on how good or
how bad an air cap can be.
Mikek

Ok, so you don't need a variable cap. That doesn't mean you can't use an air cap with a very, very high Q so you don't even need to consider it. What value cap do you need? An air cap is just a couple of plates separated by air. Their value can be calculated easily even with the fringe effects.

I would say the Q of the cap needs to be on the order of 10x the coil to measure it without a significant influence. Of course if you know the cap Q and it is stable you can factor that in, but unless it is very well known and stable it still needs to be higher than the coil to get a good measurement.

If I was build his circuit I would put in a air variable, I have 6
good high Q caps and a many other plain old air variable caps.
The author chose to use an smd cap to reduce cost. My inquire regarded
whether he degraded the machine by using that smd cap. The cap I was
questioning was the smd on the sales sheet listed in this thread.
> http://theradioboard.com/rb/viewtopic.php?f=2&t=8691

So the question boils down to this,
What is the Q of the cap in that sales sheet?
Probably can't find that info, so, what is the Q of a high Q cap in
values between 21pf and 448pf smd capacitor?

Reading the 9th post in that thread the author says the smd caps have
higher Q than the air variable. I'm skeptical but now curious.

Mikek

 

[Rick C]

On Tuesday, August 27, 2019 at 9:02:25 PM UTC-4, amdx wrote:

On 8/27/2019 6:35 PM, Rick C wrote:
On Tuesday, August 27, 2019 at 1:00:20 PM UTC-4, amdx wrote:
On 8/27/2019 9:46 AM, Rick C wrote:
On Wednesday, July 24, 2019 at 2:14:57 PM UTC-4, 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.

I've never heard of liquid filled capacitors. When it comes to variable capacitors the two choices for high Q are air and vacuum. I thought you could add a solid dielectric to increase the voltage and capacitance of an air variable cap, but the air gap, no matter how small it is, ends up with the lion's share of the voltage which would result in corona discharge at the surface of the dielectric. Not good.

I found some good liquid dielectrics, but the mechanics of a liquid variable cap are too complex to make practical.

But then you likely aren't talking about variable caps. But this is for a resonant circuit, right? Are you planning to adjust the coil?


The cap is being used to resonate the coil. Then the tool counts how
many cycles it takes to ring down to a certain voltage.
The author used a fixed capacitor to do this.
This was to avoid the cost of a Variable air cap.
What I wanted to know was, is the Q of the cap high enough,
compared to an air cap, so as to have little effect on measured Q.
I didn't have a Q of the capacitor, I do have numbers on how good or
how bad an air cap can be.
Mikek

Ok, so you don't need a variable cap. That doesn't mean you can't use an air cap with a very, very high Q so you don't even need to consider it. What value cap do you need? An air cap is just a couple of plates separated by air. Their value can be calculated easily even with the fringe effects.

I would say the Q of the cap needs to be on the order of 10x the coil to measure it without a significant influence. Of course if you know the cap Q and it is stable you can factor that in, but unless it is very well known and stable it still needs to be higher than the coil to get a good measurement.


If I was build his circuit I would put in a air variable, I have 6
good high Q caps and a many other plain old air variable caps.
The author chose to use an smd cap to reduce cost. My inquire regarded
whether he degraded the machine by using that smd cap. The cap I was
questioning was the smd on the sales sheet listed in this thread.
http://theradioboard.com/rb/viewtopic.php?f=2&t=8691

So the question boils down to this,
What is the Q of the cap in that sales sheet?
Probably can't find that info, so, what is the Q of a high Q cap in
values between 21pf and 448pf smd capacitor?

Reading the 9th post in that thread the author says the smd caps have
higher Q than the air variable. I'm skeptical but now curious.

Until you know exactly what caps the guy used you can't say if his measurements were degraded.

BTW, it was the 7th post. I finally found you in the 8th post.

You can't know what that guy's cap was, so why not focus on your own caps? An air cap (btw, I don't know what they mean by VC, variable cap or vacuum cap?) almost certainly will have better Q than any solid dielectric cap. Q is reduced by energy losses. Air caps have exceedingly small energy losses. Most likely they are dominated by the AC resistance of the conductors.. The dielectric material can dissipate energy from the AC voltage realigning the polar moments within the dielectric.

Anything is possible, but it is very hard for me to imagine an air cap will have worse Q than virtually any solid dielectric cap. However a good non-air cap might be pretty close. Alumina and Silica can have very low dissipation factors. I'm just not sure that conveys to the material used in caps.. I did find mica caps which provide very low loss over a wide frequency range.

http://www.cde.com/resources/catalogs/MC.pdf

Digikey seems to have some for a couple/three bucks each.

The Q of a cap may not be given in a data sheet since that is not the way they are typically listed. Instead look for the other ways of describing the same thing.

"a capacitor's loss tangent is sometimes stated as its dissipation factor, or the reciprocal of its quality factor Q, as follows

tan ⁥δ = DF = 1/Q
"

Sometimes they list the dissipation factor other times I find dissipation factor angle. One is the angle, the other is the tangent of the angle, smaller is better obviously. In radians, the two values are pretty much equal for small values which is what you are looking for. For small enough angles, the angle, the sin and the tan are all equal.

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209

 

[Tauno Voipio]

On 28.8.19 02:35, Rick C wrote:

On Tuesday, August 27, 2019 at 1:00:20 PM UTC-4, amdx wrote:
On 8/27/2019 9:46 AM, Rick C wrote:
On Wednesday, July 24, 2019 at 2:14:57 PM UTC-4, 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.

I've never heard of liquid filled capacitors. When it comes to variable capacitors the two choices for high Q are air and vacuum. I thought you could add a solid dielectric to increase the voltage and capacitance of an air variable cap, but the air gap, no matter how small it is, ends up with the lion's share of the voltage which would result in corona discharge at the surface of the dielectric. Not good.

I found some good liquid dielectrics, but the mechanics of a liquid variable cap are too complex to make practical.

But then you likely aren't talking about variable caps. But this is for a resonant circuit, right? Are you planning to adjust the coil?


The cap is being used to resonate the coil. Then the tool counts how
many cycles it takes to ring down to a certain voltage.
The author used a fixed capacitor to do this.
This was to avoid the cost of a Variable air cap.
What I wanted to know was, is the Q of the cap high enough,
compared to an air cap, so as to have little effect on measured Q.
I didn't have a Q of the capacitor, I do have numbers on how good or
how bad an air cap can be.
Mikek

Ok, so you don't need a variable cap. That doesn't mean you can't use an air cap with a very, very high Q so you don't even need to consider it. What value cap do you need? An air cap is just a couple of plates separated by air. Their value can be calculated easily even with the fringe effects.

I would say the Q of the cap needs to be on the order of 10x the coil to measure it without a significant influence. Of course if you know the cap Q and it is stable you can factor that in, but unless it is very well known and stable it still needs to be higher than the coil to get a good measurement.

It is a different thing from the electronics or radio technology we
are used to - in a way similar to audiophiles...

--

-TV

 

[amdx]

On 8/28/2019 1:24 PM, Tauno Voipio wrote:

On 28.8.19 02:35, Rick C wrote:
On Tuesday, August 27, 2019 at 1:00:20 PM UTC-4, amdx wrote:
On 8/27/2019 9:46 AM, Rick C wrote:
On Wednesday, July 24, 2019 at 2:14:57 PM UTC-4, 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.

I've never heard of liquid filled capacitors.  When it comes to
variable capacitors the two choices for high Q are air and vacuum.
I thought you could add a solid dielectric to increase the voltage
and capacitance of an air variable cap, but the air gap, no matter
how small it is, ends up with the lion's share of the voltage which
would result in corona discharge at the surface of the dielectric.
Not good.

I found some good liquid dielectrics, but the mechanics of a liquid
variable cap are too complex to make practical.

But then you likely aren't talking about variable caps.  But this is
for a resonant circuit, right?  Are you planning to adjust the coil?


   The cap is being used to resonate the coil. Then the tool counts how
many cycles it takes to ring down to a certain voltage.
   The author used a fixed capacitor to do this.
This was to avoid the cost of a Variable air cap.
   What I wanted to know was, is the Q of the cap high enough,
compared to an air cap, so as to have little effect on measured Q.
   I didn't have a Q of the capacitor, I do have numbers on how good or
how bad an air cap can be.
                                          Mikek

Ok, so you don't need a variable cap.  That doesn't mean you can't use
an air cap with a very, very high Q so you don't even need to consider
it.  What value cap do you need?  An air cap is just a couple of
plates separated by air.  Their value can be calculated easily even
with the fringe effects.

I would say the Q of the cap needs to be on the order of 10x the coil
to measure it without a significant influence.  Of course if you know
the cap Q and it is stable you can factor that in, but unless it is
very well known and stable it still needs to be higher than the coil
to get a good measurement.



It is a different thing from the electronics or radio technology we
are used to - in a way similar to audiophiles...

Not at all! If you build a piece of equipment to measure the Q of an
inductor and then use a capacitor that has the same Q as your inductor
your tool is automatically going measure 50% low. So the Q of the
resonating cap is important.
Now where is my 2 gauge oxygen free litz speaker wire and my pyramid
shaped floor supports for the wire?
Mikek

lossy capacitor

 

[Rick C]

On Wednesday, August 28, 2019 at 4:35:38 PM UTC-4, amdx wrote:

Not at all! If you build a piece of equipment to measure the Q of an
inductor and then use a capacitor that has the same Q as your inductor
your tool is automatically going measure 50% low. So the Q of the
resonating cap is important.
Now where is my 2 gauge oxygen free litz speaker wire and my pyramid
shaped floor supports for the wire?
Mikek

The part I don't get is the contribution (or detraction) to Q from the ultimate load of the resonator circuit. In this circuit, how do you measure the ring down without sucking energy out and impacting your measurement? So there are three factors in the equation.

The in the application circuit a high Q gives a high sensitivity and selectivity. But again, how do you pull signal from the antenna into the receiver without lowering the Q?

It's a similar problem to measuring the Q of the coil with a low Q capacitor. If the power draw of the receiver input is not significantly lower than the power in the antenna or resonator circuit the Q will be impacted. At some point a higher Q will accomplish nothing measurable.

--

Rick C.

-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209

 

[Phil Hobbs]

On 8/28/19 4:35 PM, amdx wrote:

On 8/28/2019 1:24 PM, Tauno Voipio wrote:
On 28.8.19 02:35, Rick C wrote:
On Tuesday, August 27, 2019 at 1:00:20 PM UTC-4, amdx wrote:
On 8/27/2019 9:46 AM, Rick C wrote:
On Wednesday, July 24, 2019 at 2:14:57 PM UTC-4, 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.

I've never heard of liquid filled capacitors.  When it comes to
variable capacitors the two choices for high Q are air and vacuum.
I thought you could add a solid dielectric to increase the voltage
and capacitance of an air variable cap, but the air gap, no matter
how small it is, ends up with the lion's share of the voltage which
would result in corona discharge at the surface of the dielectric.
Not good.

I found some good liquid dielectrics, but the mechanics of a liquid
variable cap are too complex to make practical.

But then you likely aren't talking about variable caps.  But this
is for a resonant circuit, right?  Are you planning to adjust the
coil?


   The cap is being used to resonate the coil. Then the tool counts how
many cycles it takes to ring down to a certain voltage.
   The author used a fixed capacitor to do this.
This was to avoid the cost of a Variable air cap.
   What I wanted to know was, is the Q of the cap high enough,
compared to an air cap, so as to have little effect on measured Q.
   I didn't have a Q of the capacitor, I do have numbers on how good or
how bad an air cap can be.
                                          Mikek

Ok, so you don't need a variable cap.  That doesn't mean you can't
use an air cap with a very, very high Q so you don't even need to
consider it.  What value cap do you need?  An air cap is just a
couple of plates separated by air.  Their value can be calculated
easily even with the fringe effects.

I would say the Q of the cap needs to be on the order of 10x the coil
to measure it without a significant influence.  Of course if you know
the cap Q and it is stable you can factor that in, but unless it is
very well known and stable it still needs to be higher than the coil
to get a good measurement.



It is a different thing from the electronics or radio technology we
are used to - in a way similar to audiophiles...


 Not at all! If you build a piece of equipment to measure the Q of an
inductor and then use a capacitor that has the same Q as your inductor
your tool is automatically going measure 50% low. So the Q of the
resonating cap is important.

Only if there's no self-calibration.

Cheers

Phil Hobbs


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

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

 

[amdx]

On 8/28/2019 11:53 PM, Phil Hobbs wrote:

On 8/28/19 4:35 PM, amdx wrote:
On 8/28/2019 1:24 PM, Tauno Voipio wrote:
On 28.8.19 02:35, Rick C wrote:
On Tuesday, August 27, 2019 at 1:00:20 PM UTC-4, amdx wrote:
On 8/27/2019 9:46 AM, Rick C wrote:
On Wednesday, July 24, 2019 at 2:14:57 PM UTC-4, 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.

I've never heard of liquid filled capacitors.  When it comes to
variable capacitors the two choices for high Q are air and vacuum.
I thought you could add a solid dielectric to increase the voltage
and capacitance of an air variable cap, but the air gap, no matter
how small it is, ends up with the lion's share of the voltage
which would result in corona discharge at the surface of the
dielectric. Not good.

I found some good liquid dielectrics, but the mechanics of a
liquid variable cap are too complex to make practical.

But then you likely aren't talking about variable caps.  But this
is for a resonant circuit, right?  Are you planning to adjust the
coil?


   The cap is being used to resonate the coil. Then the tool counts
how
many cycles it takes to ring down to a certain voltage.
   The author used a fixed capacitor to do this.
This was to avoid the cost of a Variable air cap.
   What I wanted to know was, is the Q of the cap high enough,
compared to an air cap, so as to have little effect on measured Q.
   I didn't have a Q of the capacitor, I do have numbers on how
good or
how bad an air cap can be.
                                          Mikek

Ok, so you don't need a variable cap.  That doesn't mean you can't
use an air cap with a very, very high Q so you don't even need to
consider it.  What value cap do you need?  An air cap is just a
couple of plates separated by air.  Their value can be calculated
easily even with the fringe effects.

I would say the Q of the cap needs to be on the order of 10x the
coil to measure it without a significant influence.  Of course if
you know the cap Q and it is stable you can factor that in, but
unless it is very well known and stable it still needs to be higher
than the coil to get a good measurement.



It is a different thing from the electronics or radio technology we
are used to - in a way similar to audiophiles...


  Not at all! If you build a piece of equipment to measure the Q of an
inductor and then use a capacitor that has the same Q as your inductor
your tool is automatically going measure 50% low. So the Q of the
resonating cap is important.

Only if there's no self-calibration.

Cheers

Phil Hobbs


Guru!

Mikek

 

[amdx]

On 8/28/2019 10:41 PM, Rick C wrote:

On Wednesday, August 28, 2019 at 4:35:38 PM UTC-4, amdx wrote:

Not at all! If you build a piece of equipment to measure the Q of an
inductor and then use a capacitor that has the same Q as your inductor
your tool is automatically going measure 50% low. So the Q of the
resonating cap is important.
Now where is my 2 gauge oxygen free litz speaker wire and my pyramid
shaped floor supports for the wire?
Mikek

The part I don't get is the contribution (or detraction) to Q from the ultimate load of the resonator circuit. In this circuit, how do you measure the ring down without sucking energy out and impacting your measurement? So there are three factors in the equation.

I'm sure it does, usually you see a high input impedance FET front end
to limit loading. This circuit has a series 3pf cap to a FET gate, the
bias, basically has two 5.6 Meg resistors to ground as the load. Not to
bad, the gurus here would have some bootstrapped circuit that was
500 times high impedance, but OK.

The in the application circuit a high Q gives a high sensitivity and selectivity. But again, how do you pull signal from the antenna into the receiver without lowering the Q?

You don't, to get audio you must extract some power to get the audio,
thus it lowers Q. Since you have no amplification, you want to limit all
losses as much as possible, so the starting point is a high Q inductor
ans a high Q capacitor.

It's a similar problem to measuring the Q of the coil with a low Q capacitor. If the power draw of the receiver input is not significantly lower than the power in the antenna or resonator circuit the Q will be impacted. At some point a higher Q will accomplish nothing measurable.

That's why I ask, but it seems the caps have are pretty high Q.

Mikek