audio recording on IC -help wanted

[Tim Wescott]

Paul Burridge wrote:

On Mon, 08 Nov 2004 14:54:22 -0800, Tim Wescott
tim@wescottnospamdesign.com> wrote:


It's interesting that you should cite Amidon -- to my knowledge they
just resell Fair-Rite ferrites and Micro Metals iron powder cores.


IIRC, MM's powder iron toroids are about the best thing out there to
wind RF transformers on. The lossier ferrites do enable high values of
inductance to be obtained from very few windings, though, if you can
live with that loss.

You don't lose that much to ferrite if it's a wide-bandwidth
transformer, because the main job of the core is to reject flux changes,
which it does by forcing the windings into sync. Small flux change
means there isn't much loss, even with a lossy material*.

Resonant transformers are an entirely different matter.

* At least that's how it's been explained to me. On reflection it
sounds like total BS -- I'll have to do the math sometime and see what
falls out the bottom.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[Lady Chatterly]

In article <q0eno0t5jeth00tdqq9erjchp8qj086vag@4ax.com> Paul Burridge <pb@notthisbit.osiris1.co.uk> wrote:

On 5 Nov 2004 07:25:39 -0800, Winfield Hill
whill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:

Surplus VHF TV driver modules are another option.

Interesting, where does one get these?

If it's just a tuned circuit you want the best bet may be to take a
large enough FET, a tuned circuit at the drain and drive it hard
from a digital oscillator, buffer and resonant step-up transformer.

Checking the MRF464 reminded me to look at Motorola's other newer RF
MOSFET power transistors. They still offer some high-frequency parts,
but most of their RF power MOSFET line was sold to M/A-COM. The data
sheets and app notes are unchanged from the Motorola versions.

In the case of an RF MOSFET, where the device is "on" for only a small
part of each cycle, say 30 degrees (which is 2ns at 40MHz), it's not
possible to "hard drive" the FET and turn it on and off, in the sense
we are used to. Instead the gate is presented with a sine wave wave
from a tuned matching stage (the gate's high capacitance looks like a
low RF impedance), and it's DC biased to be on for a small time at the
tip of each cycle. Of course it's not going on and off, instead its
channel conductance is just increasing and decreasing for a few ns.

From what I've seen, these power MOSFETs aren't much use for anything
beyond HF.
Check these out, though:
2SC1969
2SC1971
2SC1972

The Internet is still alive and well, though people are spend more
time talking because life is more centered on the community.

These are BJTs but some sort of arrangement of them should get you
near the mark.

Are you sure?

--
Lady Chatterly

"lady chat-a-lot obsessed with her own planned obsolecence and trying
to deny it" -- yyyiiinnnggg

 

[Tim Wescott]

Dan Major wrote:

dave.harper@gmail.com (David Harper) wrote in
news:364fd697.0411120525.25f3d961@posting.google.com:


Does anyone know how severely vibration can affect a capacitor's
ability to regulate voltage? (i.e. how much the voltage can deviate
as a function of vibration) What types of caps are better at
regulating voltage under high vibration?


Caps and resisters should not be affected by vibration. They are
monolythic (solid) devices. OK, "should not be affected..." up to a point.
If you get vibration that causes g forces great enough to cause mechanical
breakdown of the physical packaging, *then* the values will change. Other
components, however, will be affected because they are either mechanical in
function (crystals), or are such that the shape can be easily changed
(coils, etc.). I suppose if the components were surface mounted on a
circuit board that was flexible enough, and the vibrations caused the
components to bend or otherwise change shape *then* caps and resistors
could change value.


High-dielectric constant ceramics certainly pick up vibration long

before anything breaks, and no matter how much you scold them they do
not stop.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[Andy]

"David Harper" <dave.harper@gmail.com> wrote in message
news:364fd697.0411121201.50c96e28@posting.google.com...

Dan Major <nospam@this.address> wrote in message
news:<Xns959F5E9C79132soonerboomergbronlin@68.12.19.6>...
dave.harper@gmail.com (David Harper) wrote in
news:364fd697.0411120525.25f3d961@posting.google.com:

Does anyone know how severely vibration can affect a capacitor's
ability to regulate voltage? (i.e. how much the voltage can deviate
as a function of vibration) What types of caps are better at
regulating voltage under high vibration?

Caps and resisters should not be affected by vibration. They are
monolythic (solid) devices. OK, "should not be affected..." up to a
point.
If you get vibration that causes g forces great enough to cause
mechanical
breakdown of the physical packaging, *then* the values will change.
Other
components, however, will be affected because they are either mechanical
in
function (crystals), or are such that the shape can be easily changed
(coils, etc.). I suppose if the components were surface mounted on a
circuit board that was flexible enough, and the vibrations caused the
components to bend or otherwise change shape *then* caps and resistors
could change value.

Yes, they are solid state devices that "assume" the distance between
charge holders will remain constant. With vibration, if you have a
few microns displacement between charges, that could result in a small
voltage deviation, correct? The question I'm concerned with is "how
much"?

Hello Dave,

If you cross section a variety of capacitors of the various designs you'll
probably find that micron scale tolerances grossly dwarfed by the distances
between other key features (i.e. plate gaps, dielectric bulk impurities,
etc.).

Are you grappling with a voltage regulation problem during vibration?
Glitches or drift? If you're are dealing with glitches, I'd suggest you
look at your non-soldered interconnects -- Even your pins and sockets.
Especially your pins and sockets if you've made several (de)mates. Without
looking at your application, I'm a bit hard pressed to guess why you may be
seeing voltage drift during vibration although spooky ideas such as stray
coupling comes to mind.

Do we get anymore clues?

Best,
Andy

Thanks,
Dave

 

[Terry Given]

Watson A.Name - "Watt Sun, the Dark Remover" wrote:

"ddwyer" <dd@ddwyer.demon.co.uk> wrote in message
news:5KVeKiAKnnlBFwBM@ddwyer.demon.co.uk...

In coupling high gain amplifier stages beware of microphonics using
the wrong capacitor type.

Hi K ceramics are piezoelectric due to barium titanate? doping.
Hi the with a pulse and they can be heard to click.
By reciprocality they are excellent high freq microphones.
Hence use low k , electrolytic or plastic film for low noise.


The only porovblem then becomes how to tell a hi K from a Low K. Like,
they con't come labeled as to that factor.

I suppose you could put them into a high gain amp circuit and plink on
them and see if they put out something. But then that's too easy, isn't
it.

A simple way is with a capacitance meter and a heat gun - high K
dielectrics drop about 80% at 60C or so. solder a pair of wires (so you
dont melt the tester leads), hook up the cap. measure C at room temp,
then heat up. If it dont change much, its X7R or better. If it changes
dramatically, its Z5U/Y5V.

The other approach is with a series cap (100x larger) and applying DC
bias (or, if you have a fancy LCR bridge, ask it to measure C at varying
DC bias)

Cheers
Terry

 

[Watson A.Name - \"Watt Su]

"Terry Given" <my_name@ieee.org> wrote in message
news:RMCld.1490$9A.66267@news.xtra.co.nz...

Watson A.Name - "Watt Sun, the Dark Remover" wrote:

"ddwyer" <dd@ddwyer.demon.co.uk> wrote in message
news:5KVeKiAKnnlBFwBM@ddwyer.demon.co.uk...

In coupling high gain amplifier stages beware of microphonics using
the wrong capacitor type.

Hi K ceramics are piezoelectric due to barium titanate? doping.
Hi the with a pulse and they can be heard to click.
By reciprocality they are excellent high freq microphones.
Hence use low k , electrolytic or plastic film for low noise.


The only porovblem then becomes how to tell a hi K from a Low K.
Like,
they con't come labeled as to that factor.

I suppose you could put them into a high gain amp circuit and plink
on
them and see if they put out something. But then that's too easy,
isn't
it.


A simple way is with a capacitance meter and a heat gun - high K
dielectrics drop about 80% at 60C or so. solder a pair of wires (so
you
dont melt the tester leads), hook up the cap. measure C at room temp,
then heat up. If it dont change much, its X7R or better. If it changes
dramatically, its Z5U/Y5V.

The other approach is with a series cap (100x larger) and applying DC
bias (or, if you have a fancy LCR bridge, ask it to measure C at
varying
DC bias)

I found this:

http://www.kemet.com/kemet/web/homepage/kechome.nsf/vabypagename/militar
yfaq

<<
Question: Are your military ceramic capacitors subject to the
piezoelectric effect?
Answer: Certain classes of ceramic capacitors exhibit a normal
characteristic, called piezoelectricity, than can cause unexpected
effects in certain circuits. In some cases, the piezoelectric effect
may result in the appearance of electrical noise, while in other cases,
an acoustic sound may be heard, coming from the capacitor itself.
Ceramic piezo effects are well known, and were even the basis for the
ceramic phono cartridges used in the past.

Piezoelectricity is a common characteristic of many ceramic chip
capacitors and occurs in those classes of dielectric which are
classified as ferroelectric. Piezoelectric effects can result in noise
for ferroelectric ceramic chips, such as those used for military BX &
BR, as well as commercial EIA Class 2 and Class 3 dielectric, such as
X7R, X5R, X8R, Y5V, Y5U, Z5U, etc. Piezoelectricity occurs in all
ferroelectric dielectrics, regardless of manufacturer. Note that there
are essentially no piezoelectric effects in Class 1 capacitors, such as
C0G, NP0, or military BP - none of which are ferroelectric.
.....
And what i would really like to know more about is what is mentioned in
"commercial EIA Class 2 and Class 3 dielectric, such as X7R, X5R, X8R,
Y5V, Y5U, Z5U, etc." Like, what's this "EIA Class 2 and Class 3
dielectric, such as X7R, X5R, X8R, Y5V, Y5U, Z5U, etc."?? Where can I
find more detailed info? Or is ths another high-priced EIA document
that's not available online? And no one is willing to go into detail
about the subject?

Cheers
Terry

 

[ddwyer]

In article <10perd2pv63vu38@corp.supernews.com>, Watson A.Name - "Watt
Sun, the Dark Remover" <NOSPAM@dslextreme.com> writes

Or is ths another high-priced EIA document
that's not available online? And no one is willing to go into detail
about the subject?
Only cog NPO plastic and electrolytic arte free from piezo

michrophonics.
Silver mica has scintillation which is random cap variation.
The only way big values are available in small volumes is to reduce the
insulation layers= lower voltage working or doping with piezo materials
= michrophonics..
Many big value HiK (high dilectric constant caps have such poor
variation over temperature down to 20% of value hot and cold!that their
advantage is an illusion.
--
ddwyer

 

[Terry Given]

Watson A.Name - "Watt Sun, the Dark Remover" wrote:

"Terry Given" <my_name@ieee.org> wrote in message
news:6KCld.1489$9A.66267@news.xtra.co.nz...

Tim Wescott wrote:

Dan Major wrote:


dave.harper@gmail.com (David Harper) wrote in
news:364fd697.0411120525.25f3d961@posting.google.com:



Does anyone know how severely vibration can affect a capacitor's
ability to regulate voltage? (i.e. how much the voltage can

deviate

as a function of vibration) What types of caps are better at
regulating voltage under high vibration?


Caps and resisters should not be affected by vibration. They are
monolythic (solid) devices. OK, "should not be affected..." up to

a

point. If you get vibration that causes g forces great enough to
cause mechanical breakdown of the physical packaging, *then* the
values will change. Other components, however, will be affected
because they are either mechanical in function (crystals), or are

such

that the shape can be easily changed (coils, etc.). I suppose if

the

components were surface mounted on a circuit board that was

flexible

enough, and the vibrations caused the components to bend or

otherwise

change shape *then* caps and resistors could change value.


High-dielectric constant ceramics certainly pick up vibration long
before anything breaks, and no matter how much you scold them they

do

not stop.


Yet another reason to avoid the poxy things. Z5U, Y5V = shite.


Avoid, how? I come across a lot of caps tha aren't marked as such, all
they have is '104' marked on them, ferinstance. How do I know if
they're "shite"? And then there's the problem of how to avoid them, if
a replacment has other serious disadvantages, such as being much bigger?

That's why I want to know more aout the different grades of caps, and
what those designations mean. That way, I can make more intelligent
decisions on whether or not they're suitable for a certain application,
and not just make an uninformed generalization and claim they're all
"shite".

Fair comments.

http://www.avx.com/docs/Catalogs/cy5v.pdf

http://www.avx.com/docs/Catalogs/cx7r.pdf


The two interesting curves are on the first page:
1 - temperature coefficient (its not but thats what its labelled; its
actually a %C change-vs-T

2 - capacitance change vs DC bias. at 20% rated voltage, -60% C. at 40%
rated V, -80%; at 60% rated V, -90%

Z5U dielectric is similarly dreadful; a little web-browsing will show
you how dreadful.

I only design with smt parts, but IME I can get X7R parts (which are a
HUGE improvement - look at the link) in the same package.

The funny thing about Y5V/Z5U is that in most apps I have seen (esp.
smt) the DC bias reduces the actual capacitance well below what you can
get with a similar-sized X7R cap. From the avx data, an 0603 1uF 10V Y5V
cap has about 150nF actual capacitance at 5V DC bias (say as a
decoupling cap) and 20C; at -20C its 75nF; at +85C its 60nF. I can also
get a 0603 220nF 10V X7R cap, which has 220nF at 20C, 215nF at -20C and
203nF at 85C.

I first "discovered" this jabout 15 years ago, when testing an IGBT
gatedrive flyback smps (+25V) with a constant-current load - during the
on-time the output voltage dropped much, much faster than I expected
with my 220nF 50V shite cap. I used a bench psu & ammeter to verify the
load current was right, and then used I/(dV/dt) to calculate C, which
was (IIRC) around 10nF. And then went "what the...?". Out came the
databook (you'll remember them), and voila - there was the answer,
written for all to see. I double-checked the tempco with a heatgun & LCR
bridge, then played silly buggers with the DC bias to measure that too.
Sure enough, Philips were right. My circuit also had to run at 85C,
which just made things worse. I swapped the part for a 1206 220nF 50V
X7R, and got 20x more capacitance. That started my "anti-shite cap"
crusade

As for unmarked caps - test with heatgun/DC bias. If you use these shite
caps, only run them at < 10% of rated voltage.

Cheers
Terry

 

[Ross Herbert]

On 15 Nov 2004 15:40:37 -0800, dave.harper@gmail.com (David Harper)
wrote:

I have a microcontroller reading a dual-channel 12-bit ADC, one
channel reading a ADXL150 accelerometer and the other a motorola 6115
pressure sensor. It is mounted on a high powered rocket (not the
little 'C' engines kids shoot, but rather H, I, and J engines, which
can exceed 100lbs of thrust and vibrate quite a bit). During the
boost phase, I expect to see around 15g's, as well as quite a bit of
vibration especially as it approaches Mach 1.

My question is how much could variation in the 5VDC reference voltage
affect the measurement of the accelerometer during the boost phase?
The pressure sensor isn't read (nor deploys the parachute) until after
the boost phase, so I'm not concerned with that.

Dave

Now we can start to understand what your question really is about.
Thanks for the welcome info.

For a start you should determine the worst case current drain on your
5VDC reference and endeavour to select components and circuitry to
keep the drain as low as possible, buffering the supply if necessary.
You should then use capacitors with the least volume possible to do
the job. Preferably they should have solid electrolyte while being
physically small and you can parallel as many as needed of the
selected component as are required. This approach will eliminate any
tendancy towards voltage variation due to plate displacement within
the capacitors themselves. That's where I would start.

 

[Roger Hamlett]

"David Harper" <dave.harper@gmail.com> wrote in message
news:364fd697.0411120525.25f3d961@posting.google.com...

Does anyone know how severely vibration can affect a capacitor's
ability to regulate voltage? (i.e. how much the voltage can deviate
as a function of vibration) What types of caps are better at
regulating voltage under high vibration?

Thanks in advance!
Dave
Lots of comments so far about the various types of component, and the

effects. However I wonder if you could be 'ingenious', and make the
effects cancel?. If (for instance), you arranged four capacitors, in a
tight circle, each rotated 90 degrees to the next, and mechanically
coupled them together (epoxy), and electrically connected them in
parallel, then presumably (within the limits of the mechanical propogation
speed of the actual vibration), the effects would largely cancel. It might
be worth considering, if the capacitor sizes required, were larger than
available in types that have little response to vibration.

Best Wishes

 

[Ross Herbert]

On 16 Nov 2004 05:12:55 -0800, dave.harper@gmail.com (David Harper)
wrote:

Ross Herbert <rherber1@bigpond.net.au> wrote in message news:<g7hip01e744r56pud958mg1pfktjkh2q1j@4ax.com>...
On 15 Nov 2004 15:40:37 -0800, dave.harper@gmail.com (David Harper)
wrote:


I have a microcontroller reading a dual-channel 12-bit ADC, one
channel reading a ADXL150 accelerometer and the other a motorola 6115
pressure sensor. It is mounted on a high powered rocket (not the
little 'C' engines kids shoot, but rather H, I, and J engines, which
can exceed 100lbs of thrust and vibrate quite a bit). During the
boost phase, I expect to see around 15g's, as well as quite a bit of
vibration especially as it approaches Mach 1.

My question is how much could variation in the 5VDC reference voltage
affect the measurement of the accelerometer during the boost phase?
The pressure sensor isn't read (nor deploys the parachute) until after
the boost phase, so I'm not concerned with that.

Dave


Now we can start to understand what your question really is about.
Thanks for the welcome info.

For a start you should determine the worst case current drain on your
5VDC reference and endeavour to select components and circuitry to
keep the drain as low as possible, buffering the supply if necessary.
You should then use capacitors with the least volume possible to do
the job. Preferably they should have solid electrolyte while being
physically small and you can parallel as many as needed of the
selected component as are required. This approach will eliminate any
tendancy towards voltage variation due to plate displacement within
the capacitors themselves. That's where I would start.

Thanks for the advice. I assume by solid electrolyte, you mean
something like tantalum? I'll probably end up putting a couple in
parallel and see if I can dampen the board from vibe as much as
possible.

Dave

Do Google search for 'solid electrolyte capacitor' and you will see
plenty of hits.

They don't have to be tantalum but this type is common in smd. Solid
electrolyte is also used in aluminium capacitors.

http://www.vishay.com/docs/28355/123sala.pdf

 

[ddwyer]

In article <4rPmd.101$k4.32@newsfe2-gui.ntli.net>, Roger Hamlett
<rogerspamignored@ttelmah.demon.co.uk> writes

"David Harper" <dave.harper@gmail.com> wrote in message
news:364fd697.0411170939.45ebc4a5@posting.google.com...
"Roger Hamlett" <rogerspamignored@ttelmah.demon.co.uk> wrote in message
news:<hsnmd.54$Zf4.34@newsfe6-win.ntli.net>...
"David Harper" <dave.harper@gmail.com> wrote in message
news:364fd697.0411120525.25f3d961@posting.google.com...
Does anyone know how severely vibration can affect a capacitor's
ability to regulate voltage? (i.e. how much the voltage can deviate
as a function of vibration) What types of caps are better at
regulating voltage under high vibration?

Thanks in advance!
Dave
Lots of comments so far about the various types of component, and the
effects. However I wonder if you could be 'ingenious', and make the
effects cancel?. If (for instance), you arranged four capacitors, in a
tight circle, each rotated 90 degrees to the next, and mechanically
coupled them together (epoxy), and electrically connected them in
parallel, then presumably (within the limits of the mechanical
propogation
speed of the actual vibration), the effects would largely cancel. It
might
be worth considering, if the capacitor sizes required, were larger
than
available in types that have little response to vibration.

Best Wishes

I guessing that it would not work much better than 4 caps in parallel
with no specific orientation... your idea assumes that the vibration
affects capacitors arranged in different angles in opposite manners.
It may affect them identically. Secondly, the overall effects could
change significantly depending on the frequency of vibration.
Yes. It was a 'thought exercise', but with some capacitors exhibiting
piezo effects, might be worth considering.

Best Wishes


Practical experience in your application.

SM components helpful also a thin layer of flexible encapsulant to damp
board vibration.
As a low cost approach single sided sm with the other side bonded
(double sided foam?) to a structural member would be beneficial.

--
ddwyer

 

[Watson A.Name - \"Watt Su]

"Leon Heller" <leon_heller@hotmail.com> wrote in message
news:41a30ac2$0$15428$cc9e4d1f@news-text.dial.pipex.com...

"James Meyer" <jmeyer@nowhere.net> wrote in message
news:m715q01a0abrihaqas7ljcdvlvuki2uj6o@4ax.com...
On 22 Nov 2004 15:08:36 -0800, jmgong74@tom.com (Jim) wroth:

I hope to design an air-core transformer which may operate at
100-500 MHz.
However I found the loss is too high.
Can anybody give me some advices to design air-core transformer?
Thanks a million!

It can't be done. Try another solution.

RF inductors are often wound without cores, especially at VHF and UHF.

Leon

Exactly. A common practice is to wind the windings by twisting them
together, bifilar or trifilar, etc. This increases the coupling. At
several hundreds of MHz, the turns may be just a few or one turn.
Here's a tutorial on how to wind one.
http://www.electronics-tutorials.com/amplifiers/broad-band-amplifiers.ht
m

 

[Leon Heller]

"James Meyer" <jmeyer@nowhere.net> wrote in message
news:q2d6q0h2oioadcevcojn834ibntme17vi9@4ax.com...

On Tue, 23 Nov 2004 10:02:42 -0000, "Leon Heller"
leon_heller@hotmail.com
wroth:

"James Meyer" <jmeyer@nowhere.net> wrote in message
news:m715q01a0abrihaqas7ljcdvlvuki2uj6o@4ax.com...
On 22 Nov 2004 15:08:36 -0800, jmgong74@tom.com (Jim) wroth:

I hope to design an air-core transformer which may operate at 100-500
MHz.
However I found the loss is too high.
Can anybody give me some advices to design air-core transformer?
Thanks a million!

It can't be done. Try another solution.

RF inductors are often wound without cores, especially at VHF and UHF.

Leon


Low loss wideband RF transformers are almost never wound without cores.

I was thinking of a narrow-band transformer within the range the specified
range.

Leon

 

[Jim]

legg <legg@nospam.magma.ca> wrote in message news:<n076q0l32ektjtrb9fq93mkvkk2ish00oc@4ax.com>...

On 22 Nov 2004 15:08:36 -0800, jmgong74@tom.com (Jim) wrote:

I hope to design an air-core transformer which may operate at 100-500 MHz.
However I found the loss is too high.
Can anybody give me some advices to design air-core transformer?
Thanks a million!

What is your loss like WITH a core? Maybe the core is not your
problem. What application/environment?

Google 'air-core transformer', 'air cored transformer', 'coreless
transformer', 'contact-free transmission', 'contactless transmission',
'transcutaneous energy' etc.

RL
I observed two unwanted phenomenon:

1. direct capacitive coupling between primary/secondary coils. It
interferes with the mutual inductance, and makes the transmissivity of
the transformer change significantly with frequency.

2. Insertion loss is higher than 10dB.

I googled air core transformer before i posted my question. It is
weird that the concept is mentioned in many places, but I can never
find a real one which works in VHF/UFH band except transmission-line
type.

My purpose is for impediance matching, from 50 ohm cable to a 0.5 ohm
load.

To my understanding, air-core transmission-line transformers have
fixed conversion ratio, e.g. 1:1, 4:1 or 1:4, is it right? What i need
is a ratio of 10:1.

I saw some companies provide RF transformer with ferrite coil inside.
The insertion loss is only 1-2dB, however, for UHF band, the maximum
ratio is 4:1 or 6:1 only.

Thank you all again! And hope to hear from you again.

 

[Winfield Hill]

Jim wrote...

My purpose is for impediance matching, from 50 ohm cable
to a 0.5 ohm load.

You could simply put a 50-ohm resistor in series with your
o.5-ohm load, to prevent reflections and insure a fixed
known current at all operating frequencies.

As far as wideband transformers are concerned, the common
4:1 transmission-line transformers (get Sevick's books) can
be made for 50 to 12.5 ohms and then 12.5 to 3.25 ohms. The
transmission line in each stage must have an impedance that's
the geometric mean between Zin and Zout, i.e. 25 ohms and
6.5 ohms. You'll have to make the transmission line yourself.
I handmade a 16:1 wideband transformer this way, and it was
a tricky task, taking several days. But it worked well.

In theory you can do the next step from 3.25 to 0.81 ohms,
but it's nearly impossible to make 1.6-ohm transmission line.

Perhaps the spot for a resistive match is here, at the 3.25
to 0.5-ohm level. At least you will have quadrupled the
delivered current into 0.5 ohms with your 16:1 transformer.

If you want to play a narrow-band matching game, no problem,
have at it.


--
Thanks,
- Win

 

[legg]

On 23 Nov 2004 09:53:58 -0800, jmgong74@tom.com (Jim) wrote:

legg <legg@nospam.magma.ca> wrote in message news:<n076q0l32ektjtrb9fq93mkvkk2ish00oc@4ax.com>...
On 22 Nov 2004 15:08:36 -0800, jmgong74@tom.com (Jim) wrote:

I hope to design an air-core transformer which may operate at 100-500 MHz.
However I found the loss is too high.
Can anybody give me some advices to design air-core transformer?
Thanks a million!

What is your loss like WITH a core? Maybe the core is not your
problem. What application/environment?

Google 'air-core transformer', 'air cored transformer', 'coreless
transformer', 'contact-free transmission', 'contactless transmission',
'transcutaneous energy' etc.

RL
I observed two unwanted phenomenon:

1. direct capacitive coupling between primary/secondary coils. It
interferes with the mutual inductance, and makes the transmissivity of
the transformer change significantly with frequency.

2. Insertion loss is higher than 10dB.

I googled air core transformer before i posted my question. It is
weird that the concept is mentioned in many places, but I can never
find a real one which works in VHF/UFH band except transmission-line
type.

My purpose is for impediance matching, from 50 ohm cable to a 0.5 ohm
load.

To my understanding, air-core transmission-line transformers have
fixed conversion ratio, e.g. 1:1, 4:1 or 1:4, is it right? What i need
is a ratio of 10:1.

I saw some companies provide RF transformer with ferrite coil inside.
The insertion loss is only 1-2dB, however, for UHF band, the maximum
ratio is 4:1 or 6:1 only.

Thank you all again! And hope to hear from you again.

The old Motorola App Note AN1304 discusses the use of coaxial baluns
around 1GHz, to reduce Z mismatches of 100:1 to approximately 6:1.

http://www.freescale.com/files/rf_if/doc/app_note/AN1034.pdf

also

http://www.freescale.com/files/rf_if/doc/app_note/AN1670.pdf

http://www.freescale.com/files/rf_if/doc/app_note/AN1033.pdf

http://www.freescale.com/files/rf_if/doc/eng_bulletin/EB105.pdf

......don't forget to check references listed in tha articles.

Going to 50ohms in the first place, may be part of the problem, as
your active devices likely exhibit output impedances in the 10ohm
range or less, to begin with. Matching earlier may help.

If galvanic isolation is required, a simpler 1:1 or 2:1 conventional
balun transformer might be introduced additionally, in a convenient
position. because required turns are low, you might consider winding
shapes that are not normally seen in baluns - perhaps a single loop
inside an isolated screen (~output winding).

With the app data aimed at achieving 50 ohms, it may be difficult to
turn it around to make sense for low load values such as 0.5 ohms.

RL

 

[John Popelish]

budgie wrote:

On 23 Nov 2004 09:53:58 -0800, jmgong74@tom.com (Jim) wrote:
(snip)
My purpose is for impediance matching, from 50 ohm cable to a 0.5 ohm
load.

It isn't clear (to me, anyway) why you are specifically seeking an air-cored
solution. What is the problem with a ferrite core? You can get a very good
match with a 3:1 turns ratio, or if you really want to get precise then increase
the turns so you get M:N ratio closer to SQRT(10).

I agree about the ferrite, but he needs a 100:1 impedance change so a
10:1 turns ratio.

--
John Popelish

 

[legg]

On 24 Nov 2004 10:15:25 -0800, Winfield Hill
<hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:

Jim wrote...

If I simply need a narrow-band transformer, e.g. 300MHz with
bandwidth>1MHz, what is the best method? I don't need continuous
tuning, so I can make a set of such transformers to cover the
range of 100-500MHz.

Ah, that's easy. You want a tuned impedance matching network,
or perhaps a tuned transformer, or a tapped resonator, etc...
http://en.wikipedia.org/wiki/Impedance_match
http://beradio.com/departments/radio_impedance_matching/
http://emclab.concordia.ca/~trueman/elec453/MW_Lecture_13_2004.pdf

And I did find an amazing report of a modestly wideband (15%)
50-ohm to 1-ohm transformer, working from 1200 to 1400 MHz.
http://ece-www.colorado.edu/~drc/eds/previous/mccalpin_4_03.pdf

One thing, keep in mind that 0.2nH of inductance is more than
0.5 ohms at 500MHz. Watch out. Do you know what you're doing?

Note also the links to course notes, transmission line and Z-matching
SW by Trueman at Concordia and Pozar at Amherst;

http://emclab.concordia.ca/~trueman/

http://emclab.concordia.ca/~trueman/trline/index.htm

http://emclab.concordia.ca/~trueman/bounce/index.htm

RL

 

[Victor Roberts]

On 1 Dec 2004 03:51:05 -0800, boothmultipler@hotmail.com (booth
multiplier) wrote:

Dear All,
I'd like to built a driver circuitry for 8 Luxeon leds in series.
Each of them has a forward voltage at 3.5 V at 350 mA. 8 in series
makes 28V. I have applied the 28 volt works fine, but if I want to
make them flash it's not working, they simply don't flash. The ON
OFF sequence is like this: 1 sec OFF, 0.4sec ON, 0.1 sec OFF,0.4sec
ON, 0.1 sec OFF AND SO ON. Do I need a higher voltage for flashing?
Thanks

I agree with Adam that you should use a current source or at least a
current regulated power supply instead of a voltage source. However,
that does not explain why your current system will not flash.

Does it not turn off or does it not turn on? Also, how are you
flashing the LEDs? Do you drop the voltage to 0 when they are supposed
to be off? Can you describe the circuit you are using?

--
Vic Roberts
http://www.RobertsResearchInc.com
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