On Sun, 21 Mar 2004 22:43:17 +0000, Paul Burridge
posted this:

On Sun, 21 Mar 2004 19:17:38 GMT, James Meyer
wrote:

On Fri, 19 Mar 2004 19:40:01 +0000, Paul Burridge
posted this:

Can I infer from this experience that SMD inductors of over a few uH
are a waste of time?

ANY part used to perform a function which it is not suited for is a
waste of time. It would be interesting to know which SMD inductors you used
that seemed to eat up the 40 MHz so effectively.

Eh? I've *never* used SMD inductors!

Sorry. When you said "this experience" I thought you meant "my
experience".

Carry on.

Jim

On Sun, 21 Mar 2004 20:58:07 -0500, "Tam/WB2TT"
wrote:

Paul,

I probably should have included more details. A fellow I was working with
was trying to extract a clock signal from a synchronous data stream, and was
getting nowhere. We swept the frequency back and forth to be sure he was
tuned to resonance - he was. Changed the ceramic cap to mica, and everything
worked like a charm. We never analyzed why the ceramic did not work, but I
suspect it was because of the capacitance vs. applied voltage dependence. If
the cap had 6VDC on it, and he had a few mv of RF, I expect it would have
worked. Instead, he had 0 bias, and a couple of Volts p-p signal.

Yes, ceramics are *hopeless* for tuned circuits; I wouldn't trust the
black tipped ones, either. You can't beat silver mica but they're a
bit hard to find and expensive.


BTW, somebody mentioned powdered iron toroids. Sounds like a good idea.

Indeed. I'm looking into it.
--

The BBC: Licensed at public expense to spread lies.

On Sun, 21 Mar 2004 20:58:07 -0500, "Tam/WB2TT"
wrote:

Paul,

I probably should have included more details. A fellow I was working with
was trying to extract a clock signal from a synchronous data stream, and was
getting nowhere. We swept the frequency back and forth to be sure he was
tuned to resonance - he was. Changed the ceramic cap to mica, and everything
worked like a charm. We never analyzed why the ceramic did not work, but I
suspect it was because of the capacitance vs. applied voltage dependence. If
the cap had 6VDC on it, and he had a few mv of RF, I expect it would have
worked. Instead, he had 0 bias, and a couple of Volts p-p signal.

Yes, ceramics are *hopeless* for tuned circuits; I wouldn't trust the
black tipped ones, either. You can't beat silver mica but they're a
bit hard to find and expensive.


BTW, somebody mentioned powdered iron toroids. Sounds like a good idea.

Indeed. I'm looking into it.
--

The BBC: Licensed at public expense to spread lies.

I tried to "reply", but your inbox was full!

....[snip]....
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge.

Hey Doc. Should that quote be attributed to you or what?

Yes, at least mostly, 'Way back when email first started (with long
strings of !...!...! in the addresses), I had "Three boxes..." (altho
I don't recall just which three). Shortly thereafter, someone suggested
a fourth box and someone else the fifth, and I was lucky enough to be
able to condense all five boxes into the one line I've used ever since.

--Myron.
--
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
PhD EE (retired). "Barbershop" tenor. CDL(PTXS). W0PBV. (785) 539-4448
NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol)

I tried to "reply", but your inbox was full!

....[snip]....
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge.

Hey Doc. Should that quote be attributed to you or what?

Yes, at least mostly, 'Way back when email first started (with long
strings of !...!...! in the addresses), I had "Three boxes..." (altho
I don't recall just which three). Shortly thereafter, someone suggested
a fourth box and someone else the fifth, and I was lucky enough to be
able to condense all five boxes into the one line I've used ever since.

--Myron.
--
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
PhD EE (retired). "Barbershop" tenor. CDL(PTXS). W0PBV. (785) 539-4448
NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol)

On 22 Mar 2004 13:06:44 -0600, mcalhoun wrote:

I tried to "reply", but your inbox was full!

Uh, it used to be ".invalid" but until I gat this blasted new
newsreader to allow me to use that, I dunno. Maybe example.org.
Maybe a sneakemail addy I can throw away when it gets spammed to
hell so at least some people can backchannel me for the real addy if
I think they need it.

....[snip]....
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge.

Hey Doc. Should that quote be attributed to you or what?

Yes, at least mostly, 'Way back when email first started (with long
strings of !...!...! in the addresses), I had "Three boxes..." (altho
I don't recall just which three). Shortly thereafter, someone suggested
a fourth box and someone else the fifth, and I was lucky enough to be
able to condense all five boxes into the one line I've used ever since.

--Myron.

Ok. Duly noted. Maybe Myron Calhoun, et. al. ?

--
Best Regards,
Mike

On 22 Mar 2004 13:06:44 -0600, mcalhoun wrote:

I tried to "reply", but your inbox was full!

Uh, it used to be ".invalid" but until I gat this blasted new
newsreader to allow me to use that, I dunno. Maybe example.org.
Maybe a sneakemail addy I can throw away when it gets spammed to
hell so at least some people can backchannel me for the real addy if
I think they need it.

....[snip]....
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge.

Hey Doc. Should that quote be attributed to you or what?

Yes, at least mostly, 'Way back when email first started (with long
strings of !...!...! in the addresses), I had "Three boxes..." (altho
I don't recall just which three). Shortly thereafter, someone suggested
a fourth box and someone else the fifth, and I was lucky enough to be
able to condense all five boxes into the one line I've used ever since.

--Myron.

Ok. Duly noted. Maybe Myron Calhoun, et. al. ?

--
Best Regards,
Mike

Paul Burridge wrote:

Yes, ceramics are *hopeless* for tuned circuits; I wouldn't trust the
black tipped ones, either. You can't beat silver mica but they're a
bit hard to find and expensive.

I strongly disagree with this. I've successfully used ceramic capacitors
many times for both high and low Q tuned circuits from HF to UHF. Years
ago, I found that NPO ceramics were decidedly superior to silver micas
for temperature stability, so I use them exclusively for VFO tank circuits.

You might have come across some bad parts. Or perhaps you don't realize
that many different types of ceramic are used for making capacitors.
Three general classes are most common. The "general purpose" class
(something of a misnomer) is a very high-k ceramic used for capacitors
of Z5U, Y5V and similar types. Those are very good for bypassing because
of their small physical size, but terrible for nearly anything else.
They're microphonic, hygroscopic, piezoelectric, and highly temperature
and voltage dependent.

Another class is used for X7R and related types, sometimes called
"stable". These are much more stable in all respects, but are physically
larger due to the lower dielectric constant (k) of the ceramic. They're
suitable for a wider variety of uses, but still not for high Q tuned
circuits. They should be used in low Q circuits only after evaluating
the potential effects of temperature and voltage dependence, at the least.

The third common class is used for making capacitors with near-zero
temperature coefficients, such as C0G (formerly and still often called
NPO). These *are* an excellent choice for tuned circuit applications,
and are often better than silver mica (whose temperature coefficient and
Q are variable and unpredictable). They're sometimes identified with a
black dot -- on "dog bone" capacitors, it's on one end.

Many years ago I published an article describing a stable, VFO
controlled QRP transceiver which used NPO ceramic capacitors for the
oscillator tank. Scattered feedback indicated that some people had
gotten "NPO" capacitors from less-than-reliable vendors and were
experiencing an objectionable amount of frequency drift. That didn't
happen with name-brand parts. So there are some flakey capacitors out
there. If you need to depend on the quality, get name brand parts from a
reputable vendor. And you'll find that NPO ceramics are a very good
choice for tuned circuits.

Roy Lewallen, W7EL

Paul Burridge wrote:

Yes, ceramics are *hopeless* for tuned circuits; I wouldn't trust the
black tipped ones, either. You can't beat silver mica but they're a
bit hard to find and expensive.

I strongly disagree with this. I've successfully used ceramic capacitors
many times for both high and low Q tuned circuits from HF to UHF. Years
ago, I found that NPO ceramics were decidedly superior to silver micas
for temperature stability, so I use them exclusively for VFO tank circuits.

You might have come across some bad parts. Or perhaps you don't realize
that many different types of ceramic are used for making capacitors.
Three general classes are most common. The "general purpose" class
(something of a misnomer) is a very high-k ceramic used for capacitors
of Z5U, Y5V and similar types. Those are very good for bypassing because
of their small physical size, but terrible for nearly anything else.
They're microphonic, hygroscopic, piezoelectric, and highly temperature
and voltage dependent.

Another class is used for X7R and related types, sometimes called
"stable". These are much more stable in all respects, but are physically
larger due to the lower dielectric constant (k) of the ceramic. They're
suitable for a wider variety of uses, but still not for high Q tuned
circuits. They should be used in low Q circuits only after evaluating
the potential effects of temperature and voltage dependence, at the least.

The third common class is used for making capacitors with near-zero
temperature coefficients, such as C0G (formerly and still often called
NPO). These *are* an excellent choice for tuned circuit applications,
and are often better than silver mica (whose temperature coefficient and
Q are variable and unpredictable). They're sometimes identified with a
black dot -- on "dog bone" capacitors, it's on one end.

Many years ago I published an article describing a stable, VFO
controlled QRP transceiver which used NPO ceramic capacitors for the
oscillator tank. Scattered feedback indicated that some people had
gotten "NPO" capacitors from less-than-reliable vendors and were
experiencing an objectionable amount of frequency drift. That didn't
happen with name-brand parts. So there are some flakey capacitors out
there. If you need to depend on the quality, get name brand parts from a
reputable vendor. And you'll find that NPO ceramics are a very good
choice for tuned circuits.

Roy Lewallen, W7EL

Roy,

We were talking about bypass type ceramics. See the 3/20 10:13AM posting.
BTW, I think with SM you are pretty much forced into using ceramics.

Tam/WB2TT