Toroid or molded inductor in low voltage tank?
 

In a coupling circuit such as:

C1|| C3||
IN----||----o----o----||--OUT
|| | | ||
--- C
--- C L1
C2| C
| |
'----'
|
===
GND

(see, eg, the "38 Special" NorCal 30m QRP tranceiver sch connecting
the NE602 single-ended output to an amplification stage:
http://www.amqrp.org/kits/38spcl/ )

What is the purpose maximizing the Q of L1 by using, say, a hand-
wound toroid vs a molded inductor? Rs of a 1.8uH moulded inductor
might be 1.5 ohms vs .1 ohm for 5 inches of 24ga wire. However the
expected effect in tank bandwidth doesn't seem to matter compared to
the large effect of varying C1 (very narrow for small C1, 5p in the
example).

I can see why a homebrewer would prefer to keep a bag of T37-2 and
some enamelled wire around, but in a kit such as that, wouldn't a
moulded inductor do just as well?

--
Ben Jackson AD7GD

http://www.ben.com/

Toroid or molded inductor in low voltage tank?
 

The much lower Q of the molded inductor can result in significantly
worse rejection of spurious outputs from the amplifier. I don't know
whether that's important for this particular design or not. But a toroid
also has other advantages over a solenoidal inductor. A toroid has a
much smaller external field, so it can be mounted close to other
components including other inductors with minimal mutual coupling. For
the same reason, a solenoid's Q can be degraded substantially by
proximity to other components or conductors, while a toroid is
relatively immune to this problem.

Roy Lewallen, W7EL

Ben Jackson wrote:
In a coupling circuit such as:

C1|| C3||
IN----||----o----o----||--OUT
|| | | ||
--- C
--- C L1
C2| C
| |
'----'
|
===
GND

(see, eg, the "38 Special" NorCal 30m QRP tranceiver sch connecting
the NE602 single-ended output to an amplification stage:
http://www.amqrp.org/kits/38spcl/ )

What is the purpose maximizing the Q of L1 by using, say, a hand-
wound toroid vs a molded inductor? Rs of a 1.8uH moulded inductor
might be 1.5 ohms vs .1 ohm for 5 inches of 24ga wire. However the
expected effect in tank bandwidth doesn't seem to matter compared to
the large effect of varying C1 (very narrow for small C1, 5p in the
example).

I can see why a homebrewer would prefer to keep a bag of T37-2 and
some enamelled wire around, but in a kit such as that, wouldn't a
moulded inductor do just as well?

Toroid or molded inductor in low voltage tank?
 

Ben,

Don't confuse the 'unloaded' Q of the part with the 'loaded Q' of the
circuit.

The unloaded Q of the part is a measure of internal resistance in the part
and will mainly affect the loss of the network, not the bandwidth. The
loaded Q of the network is a measure of the external network resistance that
the part is embedded in and will mainly determine the bandwidth.
The ratio of unloaded Q to loaded Q will determine the losses of the network
(higher unloaded Q is better).

In general, high unloaded component Q is 'goodness'.

Joe
W3JDR


"Ben Jackson" wrote in message
...
In a coupling circuit such as:

C1|| C3||
IN----||----o----o----||--OUT
|| | | ||
--- C
--- C L1
C2| C
| |
'----'
|
===
GND

(see, eg, the "38 Special" NorCal 30m QRP tranceiver sch connecting
the NE602 single-ended output to an amplification stage:
http://www.amqrp.org/kits/38spcl/ )

What is the purpose maximizing the Q of L1 by using, say, a hand-
wound toroid vs a molded inductor? Rs of a 1.8uH moulded inductor
might be 1.5 ohms vs .1 ohm for 5 inches of 24ga wire. However the
expected effect in tank bandwidth doesn't seem to matter compared to
the large effect of varying C1 (very narrow for small C1, 5p in the
example).

I can see why a homebrewer would prefer to keep a bag of T37-2 and
some enamelled wire around, but in a kit such as that, wouldn't a
moulded inductor do just as well?

--
Ben Jackson AD7GD

http://www.ben.com/

Toroid or molded inductor in low voltage tank?
 

For a quick graphic demonstration of what the other posters are
pointing out without having to build and measure a physical circuit,
try putting this circuit into "RFSim99" (a free program), and select
"Use physical model" in the inductor value dialog box. Then change the
unloaded Q of the inductor there to see the effects on performance,
both loss and filter sharpness (-- rejection of unwanted signals).
You'll need to connect "IN" and "OUT" to measurement ports (one of the
available components in RFSim99) that you set to appropriate
impedances.

Such a simulation doesn't address the effects that Roy mentioned of
coupling to external fields and lowering of Q by coupling to external
material. On the other hand, though toroid coils have lower coupling
to externals, their coupling isn't zero, especially when you use a
low-mu core---so be careful how you mount the toroids, too. In a
couple minutes, the simulation can give you some insights to get you
started and save a lot of time soldering, but expect to ultimately
learn even more by actually building and measuring the circuit.

Cheers,
Tom


Ben Jackson wrote:
In a coupling circuit such as:

C1|| C3||
IN----||----o----o----||--OUT
|| | | ||
--- C
--- C L1
C2| C
| |
'----'
|
===
GND

(see, eg, the "38 Special" NorCal 30m QRP tranceiver sch connecting
the NE602 single-ended output to an amplification stage:
http://www.amqrp.org/kits/38spcl/ )

What is the purpose maximizing the Q of L1 by using, say, a hand-
wound toroid vs a molded inductor? Rs of a 1.8uH moulded inductor
might be 1.5 ohms vs .1 ohm for 5 inches of 24ga wire. However the
expected effect in tank bandwidth doesn't seem to matter compared to
the large effect of varying C1 (very narrow for small C1, 5p in the
example).

I can see why a homebrewer would prefer to keep a bag of T37-2 and
some enamelled wire around, but in a kit such as that, wouldn't a
moulded inductor do just as well?

--
Ben Jackson AD7GD

http://www.ben.com/

Toroid or molded inductor in low voltage tank?
 

On 2006-07-10, K7ITM wrote:
try putting this circuit into "RFSim99" (a free program)

Thanks, I'd been looking for something like that.

unloaded Q of the inductor there to see the effects on performance,
both loss and filter sharpness (-- rejection of unwanted signals).

I see. So the reason that the Q matters so much is not that it affects
the filter shape much (in this topology), but that it has a big effect
on the amplitude of the (tiny) passband which provides additional
separation from the unwanted signals. In this case it looks like
raising from Q=50 to 250 gives about 4dB of "wanted" signal without
really affecting anything else.

couple minutes, the simulation can give you some insights to get you
started and save a lot of time soldering, but expect to ultimately
learn even more by actually building and measuring the circuit.

I actually have such a circuit built, and I took some measurements
today. I'll wind a 1.8uH inductor on a T37-2 tonight and compare.

Thanks to all for the responses.

--
Ben Jackson AD7GD

http://www.ben.com/

Toroid or molded inductor in low voltage tank?
 

On 2006-07-10, Ben Jackson wrote:

I actually have such a circuit built, and I took some measurements
today. I'll wind a 1.8uH inductor on a T37-2 tonight and compare.

Ok, I wound 20 turns of about 30ga wire on a T30-2 and compared before/
after (each with the trim cap set for peak) and it's about 2.75V p-p
vs 2.0V p-p, or ~3dB. I'll put it on the spectrum analyzer at work
again to make sure the unwanted products are still in the same place,
but it looks like a win for high Q.

Thanks to everyone who replied, it was very educational!

Anyone have any tips for securing fine-wire toroids in
Ugly/Manhattan construction? :)

--
Ben Jackson AD7GD

http://www.ben.com/

Toroid or molded inductor in low voltage tank?
 

Ben Jackson wrote:
. . .
Anyone have any tips for securing fine-wire toroids in
Ugly/Manhattan construction? :)

A dab of hot melt glue or RTV. Or a Nylon screw through the middle. Or a
couple of holes in the board and a cable tie. The only thing to avoid
is laying it down flat on a solid copper plane.

Roy Lewallen, W7EL

Toroid or molded inductor in low voltage tank?
 

On Tue, 11 Jul 2006 08:29:05 +0100, Roy Lewallen wrote:

Ben Jackson wrote:
. . .
Anyone have any tips for securing fine-wire toroids in
Ugly/Manhattan construction? :)

A dab of hot melt glue or RTV. Or a Nylon screw through the middle. Or a
couple of holes in the board and a cable tie. The only thing to avoid
is laying it down flat on a solid copper plane.

Roy Lewallen, W7EL

Roy

Excuse my ignorance, but what is the problem with laying a toroid down on
a solid copper plane? I thought the magnetic field was contained within
the toroid and thus minimised external effects. I have completed a couple
of projects recently with some of the inductors like that and didn't
notice any real problem. Mind you, I guess they might have performed
better if not mounted that way :o)

Best 73

John, G4GOY

--
Using Opera's revolutionary e-mail client: http://www.opera.com/mail/

Toroid or molded inductor in low voltage tank?
 

On Tue, 11 Jul 2006 13:02:48 +0100, "John Hague"
wrote:

On Tue, 11 Jul 2006 08:29:05 +0100, Roy Lewallen wrote:

Ben Jackson wrote:
. . .
Anyone have any tips for securing fine-wire toroids in
Ugly/Manhattan construction? :)

A dab of hot melt glue or RTV. Or a Nylon screw through the middle. Or a
couple of holes in the board and a cable tie. The only thing to avoid
is laying it down flat on a solid copper plane.

Roy Lewallen, W7EL

Roy

Excuse my ignorance, but what is the problem with laying a toroid down on
a solid copper plane? I thought the magnetic field was contained within
the toroid and thus minimised external effects. I have completed a couple
of projects recently with some of the inductors like that and didn't
notice any real problem. Mind you, I guess they might have performed
better if not mounted that way :o)

Twofold. One is added capacitance across the windings and secondary
is the proximitry of a conductor to the small field around the wire(s)
that are not in direct contact with the toroid.

Allison



Best 73

John, G4GOY

Toroid or molded inductor in low voltage tank?
 

John Hague wrote:
On Tue, 11 Jul 2006 08:29:05 +0100, Roy Lewallen wrote:

Ben Jackson wrote:
. . .
Anyone have any tips for securing fine-wire toroids in
Ugly/Manhattan construction? :)

A dab of hot melt glue or RTV. Or a Nylon screw through the middle. Or
a couple of holes in the board and a cable tie. The only thing to
avoid is laying it down flat on a solid copper plane.

Roy Lewallen, W7EL

Roy

Excuse my ignorance, but what is the problem with laying a toroid down
on a solid copper plane? I thought the magnetic field was contained
within the toroid and thus minimised external effects. I have completed
a couple of projects recently with some of the inductors like that and
didn't notice any real problem. Mind you, I guess they might have
performed better if not mounted that way :o)

Two potential problems. One is that the field isn't completely
contained. Leakage is greater with more sparsely wound toroids and ones
with lower permeability cores. The second is the "one turn effect" -
There's a net field equivalent to that of a single turn running
circumferentially around the core. A solid plane parallel to this would
act as a shorted turn. Both effects would act to lower the Q, and might
be the cause of some drift or microphonics if the inductor was in an
oscillator tank.

But to be honest, I've never run any experiments to see just how much of
a problem it might cause -- it's quite possible you could get away with
it in some or even most applications. I'll put it on my list of things
to do when time permits -- unless somebody else is willing to take on
the job.

Roy Lewallen, W7EL

Toroid or molded inductor in low voltage tank?
 

On Tue, 11 Jul 2006 15:21:51 +0100, wrote:

On Tue, 11 Jul 2006 13:02:48 +0100, "John Hague"
wrote:

On Tue, 11 Jul 2006 08:29:05 +0100, Roy Lewallen wrote:

Ben Jackson wrote:
. . .
Anyone have any tips for securing fine-wire toroids in
Ugly/Manhattan construction? :)

A dab of hot melt glue or RTV. Or a Nylon screw through the middle. Or
a
couple of holes in the board and a cable tie. The only thing to avoid
is laying it down flat on a solid copper plane.

Roy Lewallen, W7EL

Roy

Excuse my ignorance, but what is the problem with laying a toroid down
on
a solid copper plane? I thought the magnetic field was contained within
the toroid and thus minimised external effects. I have completed a
couple
of projects recently with some of the inductors like that and didn't
notice any real problem. Mind you, I guess they might have performed
better if not mounted that way :o)

Twofold. One is added capacitance across the windings and secondary
is the proximitry of a conductor to the small field around the wire(s)
that are not in direct contact with the toroid.

Allison



Best 73

John, G4GOY


Allison

Thanks for the info. I'll watch how I mount my toroids in future.

Best 73

John, G4GOY

--
Using Opera's revolutionary e-mail client: http://www.opera.com/mail/

Toroid or molded inductor in low voltage tank?
 

On Tue, 11 Jul 2006 18:35:26 -0700, Roy Lewallen
wrote:

John Hague wrote:
On Tue, 11 Jul 2006 08:29:05 +0100, Roy Lewallen wrote:

Ben Jackson wrote:
. . .
Anyone have any tips for securing fine-wire toroids in
Ugly/Manhattan construction? :)

A dab of hot melt glue or RTV. Or a Nylon screw through the middle. Or
a couple of holes in the board and a cable tie. The only thing to
avoid is laying it down flat on a solid copper plane.

Roy Lewallen, W7EL

Roy

Excuse my ignorance, but what is the problem with laying a toroid down
on a solid copper plane? I thought the magnetic field was contained
within the toroid and thus minimised external effects. I have completed
a couple of projects recently with some of the inductors like that and
didn't notice any real problem. Mind you, I guess they might have
performed better if not mounted that way :o)

Two potential problems. One is that the field isn't completely
contained. Leakage is greater with more sparsely wound toroids and ones
with lower permeability cores. The second is the "one turn effect" -
There's a net field equivalent to that of a single turn running
circumferentially around the core. A solid plane parallel to this would
act as a shorted turn. Both effects would act to lower the Q, and might
be the cause of some drift or microphonics if the inductor was in an
oscillator tank.

But to be honest, I've never run any experiments to see just how much of
a problem it might cause -- it's quite possible you could get away with
it in some or even most applications. I'll put it on my list of things
to do when time permits -- unless somebody else is willing to take on
the job.

Roy Lewallen, W7EL

I've not tested for Q degradation but the added capacitance and chance
for movement makes VFOs far more unstable. Microphonics from
movement are part of the problem but if glue is used that goes away
and the stability of the glue with temperature is then an issue.

The single turn field while small is likely related to the number of
turns and with fewer turns I'd think even a modest distance such as
0.1" it would not be a significant factor.

Allison

Toroid or molded inductor in low voltage tank?
 

Roy Lewallen wrote:

John Hague wrote:
On Tue, 11 Jul 2006 08:29:05 +0100, Roy Lewallen wrote:

Ben Jackson wrote:
. . .
Anyone have any tips for securing fine-wire toroids in
Ugly/Manhattan construction? :)

A dab of hot melt glue or RTV. Or a Nylon screw through the middle. Or
a couple of holes in the board and a cable tie. The only thing to
avoid is laying it down flat on a solid copper plane.

Roy Lewallen, W7EL

Roy

Excuse my ignorance, but what is the problem with laying a toroid down
on a solid copper plane? I thought the magnetic field was contained
within the toroid and thus minimised external effects. I have completed
a couple of projects recently with some of the inductors like that and
didn't notice any real problem. Mind you, I guess they might have
performed better if not mounted that way :o)

Two potential problems. One is that the field isn't completely
contained. Leakage is greater with more sparsely wound toroids and ones
with lower permeability cores. The second is the "one turn effect" -
There's a net field equivalent to that of a single turn running
circumferentially around the core. A solid plane parallel to this would
act as a shorted turn. Both effects would act to lower the Q, and might
be the cause of some drift or microphonics if the inductor was in an
oscillator tank.

But to be honest, I've never run any experiments to see just how much of
a problem it might cause -- it's quite possible you could get away with
it in some or even most applications. I'll put it on my list of things
to do when time permits -- unless somebody else is willing to take on
the job.

Roy Lewallen, W7EL

"One turn effect" in magnetic core computer memory?
Miniature toroids single-stitched and woven with wi
http://www.fortunecity.com/marina/reach/435/coremem.htm
What's the Amidon number of these cores?

Some electric guitar tube amps used perpendicular
point-to-point wiring in 3-dimensions between
terminal strips to minimize inductive and capactive
crosstalk. They are amazing to see.

--
LIGO: World's largest SWR meter or
the world's most expensive grid dip meter?:
http://www.nytimes.com/2006/05/02/sc...ce/02hole.html

Toroid or molded inductor in low voltage tank?
 

On Wed, 12 Jul 2006 14:45:22 -0000, Xor wrote:


"One turn effect" in magnetic core computer memory?
Miniature toroids single-stitched and woven with wi
http://www.fortunecity.com/marina/reach/435/coremem.htm
What's the Amidon number of these cores?

Different animal. Those cores have a high remnent magnetism
and a very hard BH curve. The initial ui is far higher than common
ferrites used in RF today. Some were nickel based steels in very
thin foils wound as 50-200mil toroids. The idea is you write them
with a lot of current (for a 50mil core around 2-300ma) and read them
by "writing" them with an apposing polarity pulse, the size and
timing of the pulse returned is a 0 or 1 after amplification and
slicing. The key is you always get a pulse during read but it's about
3-5x bigger and delayed in time (25 to 300ns depending on core size,
temperature and material) _if_ the core was written in with the
opposing magnetic polarity. Typical cores such as used in DEC
pdp-8E had a memory cycle time of 1.6uS (read, modify, write) as a
read is destructive and requires a write cycle to restore the data.
That was typical speed for core memory of the day (1970).

If you want to try this for yourself (1bit memory) a nail or better a
peice of hypersil (transformer core material) with a few turns of
wire, compass and a scope will demonstrate it. The test will be to
find how much DC current will magnetize it then find out how much it
takes to reverse the magnetism (compass helps here). Then you add a
few turn sense winding and watch the pulse that results when you
magnetize it with a given polarity, repeatedly. Then reverse the
power and hit it and the resulting pulse will be later in time and
bigger.

Some electric guitar tube amps used perpendicular
point-to-point wiring in 3-dimensions between
terminal strips to minimize inductive and capactive
crosstalk. They are amazing to see.

Different animal, thats called cordwood construction and its
also for space savings and affords mechanical ruggedness.
Early aerospace systems were built that way for size. Problem
is they are impossible to maintain and heat is problematic for
larger cordwood.

Neither directly relate to the concept of an tuned toroid inductor
in proxmetry to other conductors/metal cases/ inductors.


Allison

Toroid or molded inductor in low voltage tank?
 

Well, it's less of a problem than I'd have guessed. It turns out that
I was already set up to measure inductance and Q of little toroid
coils, since I'm winding some for some filters. These are on T25-6
cores. The one I measured for the results below has 22 turns of AWG28
wire on it, essentially evenly spaced around the core, with a gap of
about 45 degrees between the wire ends. That is, the wire occupies
about 7/8 of the core. I won't claim high absolute accuracy, but the Q
measurement should be well within 10%, and the relative accuracy (from
one condition to the next) should be much better than that. In
particular, I can guarantee the direction that Q moves as I add
shielding. The first measurement is with the toroid inductor standing
vertically off a copper ground plane, with the core at the gap in the
winding about a millimeter up from the plane. The second measurement
adds a piece of copper foil tape stuck to the ground plane, and bent up
at right angles to the ground plane so it's immediately adjacent to one
side of the coil. The third measurement folds the copper foil over the
top of the toroid and down the other side, so the coil is surrounded by
copper foil. These are labelled 1, 2 and 3 below.

Inductance Q
1 1.355uH 160
2 1.349uH 158
3 1.335uH 157

The actual drop in inductance is almost certainly a little more than
indicated. That's because the copper foil adds capacitance, which
would lower the resonant frequency and be seen by my measurement
technique as increased apparent inductance. I could resolve that by
making a similar measurement with lower resonating capacitance, but I'm
not set up to do that right now. Of course, the lowered inductance is
because the shield reduces the volume occupied by the magnetic field,
so there is less energy stored in it for a given current. But these
measurements tell me that even for the low-mu type 6 cores, there is
quite a low external field.

Cheers,
Tom

Roy Lewallen wrote:
John Hague wrote:
On Tue, 11 Jul 2006 08:29:05 +0100, Roy Lewallen wrote:

Ben Jackson wrote:
. . .
Anyone have any tips for securing fine-wire toroids in
Ugly/Manhattan construction? :)

A dab of hot melt glue or RTV. Or a Nylon screw through the middle. Or
a couple of holes in the board and a cable tie. The only thing to
avoid is laying it down flat on a solid copper plane.

Roy Lewallen, W7EL

Roy

Excuse my ignorance, but what is the problem with laying a toroid down
on a solid copper plane? I thought the magnetic field was contained
within the toroid and thus minimised external effects. I have completed
a couple of projects recently with some of the inductors like that and
didn't notice any real problem. Mind you, I guess they might have
performed better if not mounted that way :o)

Two potential problems. One is that the field isn't completely
contained. Leakage is greater with more sparsely wound toroids and ones
with lower permeability cores. The second is the "one turn effect" -
There's a net field equivalent to that of a single turn running
circumferentially around the core. A solid plane parallel to this would
act as a shorted turn. Both effects would act to lower the Q, and might
be the cause of some drift or microphonics if the inductor was in an
oscillator tank.

But to be honest, I've never run any experiments to see just how much of
a problem it might cause -- it's quite possible you could get away with
it in some or even most applications. I'll put it on my list of things
to do when time permits -- unless somebody else is willing to take on
the job.

Roy Lewallen, W7EL