Driver to drive?

[John Larkin]

On Tue, 16 Nov 2004 12:59:33 -0500, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

On Tue, 16 Nov 2004 08:07:01 -0800, the renowned John Larkin
jjlarkin@highlandSNIPtechTHISnologyPLEASE.com> wrote:

On Tue, 16 Nov 2004 15:55:07 +0000, Dirk Bruere at Neopax
dirk@neopax.com> wrote:


'Rights' have historically been wrested from the powerful by force. See Magna
Carta for a good example. Or maybe the US Constitution.
Our societies are balance of forces.

But the US constitution presumes axiomatic, God-given "inalienable
rights" and defines them in the Bill of Rights. They are assumed to be
absolute.

John

How can they be absolute human rights if they are not universally
applicable to all humans?

That's my question: is there a set of universal human rights that the
world could agree on, and use action as required to enforce? If there
is no such set of rights, the UN becomes a crueler joke than it is
already.

If Hutus are hacking Tutsis to death by the hundreds of thousands, is
it purely a local affair, none of our business?

John

 

[Joerg]

Hello Ban,

No Sir, this is the cleanest limiting you can get. The current sources can
be just simple resistors, if the supplies are sufficiently high. The change
of impedance on the input side can be compensated for by an antiparallel
dual diode to gnd through a 1k resistor.

o
|
/ \
( I ) 1mA
\+/
|
+----+---+
| |
V V
+/- - - +/-
400V | | 1.2V
o-----+ +-----+--o
| | |
V V .-.Input impedance
- - | |
| | | |1k2
+---+----+ '-'
| |
/-\ ===
( I ) 1mA GND
\_/
|
o
(created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de)

You can do it that way but we only used three diodes. I can't draw ASCII
schematics but it was two "anti serial" in the signal path and one to
ground from the center. Also current driven as yours. That gave use the
best linearity during the receive phase, something that is very
important in medical ultrasound and even more so in Doppler where you
don't want any slow motion (in our case blood vessel wall motion) to
modulate into signals in the area or interest. These T/R switches do not
have a limiter effect as that is undesired because it causes non-linearity.

Of course there has to be limiting before things go 'catastrophic' but
that will typically be set much higher than 1.2V. A time controlled
attenuator makes sure that the input signals stay within the dynamic
range of the system as much as possible.

Ciao, Joerg

http://www.analogconsultants.com

 

[John Larkin]

On Tue, 16 Nov 2004 18:16:19 +0000, Dirk Bruere at Neopax
<dirk@neopax.com> wrote:

John Larkin wrote:
On Tue, 16 Nov 2004 17:25:47 +0000, Dirk Bruere at Neopax
dirk@neopax.com> wrote:


John Larkin wrote:


On Tue, 16 Nov 2004 15:55:07 +0000, Dirk Bruere at Neopax
dirk@neopax.com> wrote:




'Rights' have historically been wrested from the powerful by force. See Magna
Carta for a good example. Or maybe the US Constitution.
Our societies are balance of forces.


But the US constitution presumes axiomatic, God-given "inalienable
rights" and defines them in the Bill of Rights. They are assumed to be
absolute.

The Constitution only exists because control was wrested from the British by
force of arms.


Cool. Then why would a bunch of european wimps complain because the US
has a huge military and pretty much does what it wants?

Because your poodle Blair is making us a target along with you?

Too bad; that's what happens to weak people who have no rights.

John

 

[Rich Grise]

On Tue, 16 Nov 2004 15:36:17 +0000, Kevin Aylward wrote:

Winfield Hill wrote:
In real life they're chemical.

Yes, but chemical forces are electric forces.

True, true - valence electrons and ion exchange and electrolyte

balance and all that stuff - but don't axons literally carry
an electrical signal? Or is it just a wave of ion exchange
ports along the myelin/fiber membrane or something?

Thanks,
Rich

 

[Rich Grise]

On Tue, 16 Nov 2004 04:11:20 -0800, Winfield Hill wrote:

In real life they're chemical.

Well, yabbut, at some point an electron or two will change hands,
no? (And batteries are chemical! - RTP)

And hasn't somebody had live neurons growing on some semiconductor,
actually "talking" to each other? I mean, the semi and the neuron,
not just amongst a pile of neurons like that guy's brain-in-a-petri
dish, although even they have to get signals in and out _some_ way.

Part of the reason I'm getting at this is that I've had a dream
(some time ago - not like last night or anything) where I was involved in
developing a smart prosthesis that connected to the nerve stump and spoke
nerve signals. Bidirectionally. I've also been told, by the doctor
who was sewing up my hand once, that a severed nerve will try to grow
a ne fiber, and if the sheath is tacked back together right, so the
fiber stays inside it, it grows a millimeter a week. I guess all we
need, really, is a synthetic synapse.

Thanks!
Rich

 

[JeffM]

In real life they're chemical.
Winfield Hill

While electrical signals traveling in gray matter
may not bring to mind analogies of semiconductors or gas-filled devices,
I'm sure you can think of examples
where you believe them to be traveling in a vacuum.

 

[ChrisGibboGibson]

No. Not safely. That's why the spec exists in the first place. You pillock.

Gibbo

 

[Rich The Philosophizer]

On Tue, 16 Nov 2004 14:47:51 -0800, JeffM wrote:

In real life they're chemical.
Winfield Hill

While electrical signals traveling in gray matter
may not bring to mind analogies of semiconductors or gas-filled devices,
I'm sure you can think of examples
where you believe them to be traveling in a vacuum.

Unfortunately, in some cases, the transfer function seems to be
carved in stone.

;^j
Rich

 

[Terry Given]

Rich Grise wrote:

On Mon, 15 Nov 2004 22:15:26 -0500, KILOWATT wrote:


With the four 1n4007 wired in series, i
should get a peak reverse voltage of about 4Kv isn't? For what i know, a
diode is destroyed once it's PIV is exceeded. I think i missed something
when studying the basic operation theory of a diode. ;-) TIA for any
useful reply.


Just "exceeding the PIV" doesn't automatically destroy a diode.
In fact, that's how Zener diodes are _intended_ to be operated -
in inverse breakdown.

What lets the smoke out is exceeding the power dissipation
ability of the chip. A 1N4007 with 1KV across it and 50
microamps flowing through it would have to dissipate 50
milliwatts, which it would hardly notice, especially
considering that they'll dissipate right about a watt in
the forward direction, at one amp, just in normal operation.
With a proper heat sink, or if the pulse doesn't last very
long, they can pass a surprising amount of current and live
to tell about it. ;-)

Hope This Helps!
Rich

A better way to look at it is the total energy Elost dumped into the
device, in Joules. Then if you know the die area, thickness and material
you can calculate volume and mass, then look up specific heat capacity
cp (J/kg/K). Adiabatic temperature rise = Elost/(m*cp). Voila. You can
also make a fair estimate at the thermal resistance, and calculate the
thermal time constant:

Tau = (m*cp)*Rtheta = [J/K]*[K/W] = [W*s/K]*[K/W] =

if the pulse is less than Tau then the adiabatic approximation is good -
the die absorbs pretty much all the heat. If the pulse is longer than
Tau, then some (or perhaps almost all) of the heat flows out via the
surface and the end-caps.

I read a fascinating paper a few years back on electronic one-shots -
literally! They were electronically fired single-shot guns. I forget
exactly how the circuit worked, but basically they turned a switch on
and dumped all of the energy from a cap into a short section of pcb
track sitting below a projectile. All the energy dumps into the track,
and gets converted into heat and projectile motion. They used a 1N4007
in series with a FET as the switch. IIRC the fet leakage current was
controlled/chosen to hold the 1N4007 on the cusp of avalanche breakdown,
but keep dissipation low. To fire the device, the FET was turned hard
on, and the 1N4007 broke down. The large amount of energy involved
created a ball of plasma which swept thru the diode, turning it into a
very effective short. I must dig that back out.....

Cheers
Terry

 

[Pooh Bear]

ChrisGibboGibson wrote:

No. Not safely. That's why the spec exists in the first place. You pillock.

Oh Good !

I'm glad you said that.

That's kinda what's specs are for really.

FWIW I've seen some 'iffy' - i.e different - manufacturer dependent specs on the
nice BAV20 and 21 that are effectively higher voltage versions of the ubiquitous
1N4148. It's either 200V or 250V IIRC.

Was enough to make me take a closer look and specify Fairchild IIRC.


Graham

 

[Ross Herbert]

On Tue, 16 Nov 2004 19:44:26 -0500, Norman Pirollo <npirollo@storm.ca>
wrote:

Need some advice..

I am designing a small feed system for lumber grading.
This feed system is part of a lumber grading system.

There is a motor drive feeding the individual boards along a
horizontal surface using rubber wheels or rollers.
The feed motor is started manually with a magnetic switch.

At a certain point the piece of lumber should activate a limit or
proximity switch indicating the lumber is correclty against the
horizontal surface of the grading component ( very important to
correctly grade)

If the board rises above the surface , even as little as 1/3 in., the
limit or proximity switch should shut the feed motor down using the
same magnetic switch used to start it..(severly warped board, etc..)

I wish to use one limit/proximity switch to do this.
The difficult part is that the switch is normally open while the board
is being fed through, then becomes closed, then open if there is a
problem.

The open switch then needs to shut the feed motor down...

I have been looking at metal roller ball type switches, preferably
dust-proof and rugged.

How to perform this trickery?


Norman

You will need to use an industrial limit switch such as the 9007AW
shown here
http://www.us.telemecanique.com/us/products/limit_switches.nsf/unid/254E80FD72E7937985256A1F0057EAEE/$file/HeavyDutyIndustLimits.htm

the SPDT and DPDT types have changeover contacts (single or double
contact) so that you can use the NO or NC side of the switch for your
purpose. You can obtain application information from the technical
library here
http://ecatalog.squared.com/techlib/browse.cfm?hid=0b008926800af21a

 

[Sylvan Butler]

On 10 Nov 2004 09:03:46 GMT, Daniel Haude <haude@kir.physnet.uni-hamburg.de> wrote:

On Tue, 09 Nov 2004 16:58:13 -0500,
Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> wrote
in Msg. <49f2p0pah6riaerovggnp2d6n3gbqmcern@4ax.com

Plywood is the good stuff.

There's still a difference between plywood and multiplex. Multiplex, often
called plywood in Europe, is the really good stuff, while plywood in the

There are many, many different grades of plywood.

US refers to the stuff that they make houses from, which is really crappy.

Often crappy houses (and suprisingly, very expensive houses) are made
from "wafer board", while with less voids, I don't trust as much as
plywood.

The cheap "construction" plywood might be three plys in 1/2" (12mm) with
surfaces graded C and D. Compare that to a nice "furniture grade" 7-ply
with A or better sides, and you wonder how and why both are "plywood".

sdb

 

[Chaos Master]

In article <di3jp01mmv8eidcigouvgc7n5r1nrtv787@4ax.com>,
paulcsouls@worldnet.att.net says...

I heard rumors that Orcad for DOS was now freeware.

AFAIK, not yet. Please correct me -- I'd like to know as I have an
useless DOS + Windows 3.1 machine here which would like Orcad for DOS.

Maybe you've confused with AutoTrax (now Protel?) for DOS... this one is
free.

[]s
--
Chaos MasterŽ, posting from Brazil.
"It's not what it seems, not what you think. No, I must be dreaming."

http://marreka.no-ip.com | http://tinyurl.com/46vru
http://renan182.no-ip.org | http://marreka.blogspot.com (in Portuguese)

 

[Rich The Philosophizer]

On Tue, 16 Nov 2004 18:54:07 +0000, Dirk Bruere at Neopax wrote:

John Larkin wrote:

On Tue, 16 Nov 2004 18:16:19 +0000, Dirk Bruere at Neopax
dirk@neopax.com> wrote:


John Larkin wrote:
On Tue, 16 Nov 2004 17:25:47 +0000, Dirk Bruere at Neopax

dirk@neopax.com> wrote:



John Larkin wrote:



On Tue, 16 Nov 2004 15:55:07 +0000, Dirk Bruere at Neopax
dirk@neopax.com> wrote:





'Rights' have historically been wrested from the powerful by force. See Magna
Carta for a good example. Or maybe the US Constitution.
Our societies are balance of forces.


But the US constitution presumes axiomatic, God-given "inalienable
rights" and defines them in the Bill of Rights. They are assumed to be
absolute.

The Constitution only exists because control was wrested from the British by
force of arms.


Cool. Then why would a bunch of european wimps complain because the US
has a huge military and pretty much does what it wants?

Because your poodle Blair is making us a target along with you?



Too bad; that's what happens to weak people who have no rights.

And how could you get Bush to pull the troops out of Iraq?
Ask him nicely?
Or wait a few years.

I'm just waiting for Little Fallujah Horn.

;^j
Rich

 

[Dirk Bruere at Neopax]

Rich The Philosophizer wrote:

On Tue, 16 Nov 2004 18:54:07 +0000, Dirk Bruere at Neopax wrote:


John Larkin wrote:


On Tue, 16 Nov 2004 18:16:19 +0000, Dirk Bruere at Neopax
dirk@neopax.com> wrote:



John Larkin wrote:
On Tue, 16 Nov 2004 17:25:47 +0000, Dirk Bruere at Neopax


dirk@neopax.com> wrote:




John Larkin wrote:




On Tue, 16 Nov 2004 15:55:07 +0000, Dirk Bruere at Neopax
dirk@neopax.com> wrote:






'Rights' have historically been wrested from the powerful by force. See Magna
Carta for a good example. Or maybe the US Constitution.
Our societies are balance of forces.


But the US constitution presumes axiomatic, God-given "inalienable
rights" and defines them in the Bill of Rights. They are assumed to be
absolute.

The Constitution only exists because control was wrested from the British by
force of arms.


Cool. Then why would a bunch of european wimps complain because the US
has a huge military and pretty much does what it wants?

Because your poodle Blair is making us a target along with you?



Too bad; that's what happens to weak people who have no rights.

And how could you get Bush to pull the troops out of Iraq?
Ask him nicely?
Or wait a few years.


I'm just waiting for Little Fallujah Horn.

Fallujah is about one third of a 'Hue'.
Iraq seems to be running along at about one third of a 'Vietnam' overall.
But it's early days.

--
Dirk

The Consensus:-
The political party for the new millenium
http://www.theconsensus.org

 

[Dirk Bruere at Neopax]

Rich The Philosophizer wrote:

On Tue, 16 Nov 2004 12:59:33 -0500, Spehro Pefhany wrote:


On Tue, 16 Nov 2004 08:07:01 -0800, the renowned John Larkin
jjlarkin@highlandSNIPtechTHISnologyPLEASE.com> wrote:


On Tue, 16 Nov 2004 15:55:07 +0000, Dirk Bruere at Neopax
dirk@neopax.com> wrote:



'Rights' have historically been wrested from the powerful by force. See Magna
Carta for a good example. Or maybe the US Constitution.
Our societies are balance of forces.

But the US constitution presumes axiomatic, God-given "inalienable
rights" and defines them in the Bill of Rights. They are assumed to be
absolute.

John

How can they be absolute human rights if they are not universally
applicable to all humans?



Oh, they're always, universally, _applicable_. Actual implementation,
however, and the prevention of the violation of those rights, are
another topic entirely. Usually left as an exercise for the reader.

Only people with power, either individually or as part of a collective, have Rights.

--
Dirk

The Consensus:-
The political party for the new millenium
http://www.theconsensus.org

 

[Ken Smith]

In article <cn81ug02too@drn.newsguy.com>,
Winfield Hill <hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:

Ken Smith wrote...

[...]
For the OP I'm adding a bit of extra working things out.

I've added a capacitor to the drawing called "Cbig" and labled some
resistors.

The TIP35 and TIP36 transistors are fairly cheap. I think I'd start
like this:

10 each TIP35
------------------- ---/\/\---
! \ /e R4 !
! ----- !
! TIP36 ! !
+-/\/\/-- -----------/\/\------+
! R2 e \ / R3 !
! ------ !
! ! --------- !
---+--/\/\/\/--+-----! LM317 !---------+-+--
R1 --------- !
! --- Cbig
---
!
GND

The TIP35 and TIP36 are slow. They are extra slow when their collector
voltage drops below about 2V. Along with the usual bypass an LM317 needs,
you also need some added largish capacitor to make up for the fact that it
will take the TIP35,36 stuff time to throttle up and down. The
minimum value of this capacitor I would extimate like this:

Assume that the 150A draw starts suddenly.
Assume that the voltage can droop or spike up by 0.1V.

The TIP35 and 26 have a rise and fall time of about 0.25uS (Check data
sheet to be sure)

The TIP36 has to turn on and then the TIP35 so the total time is 0.5uS.

Rather than having to integrate, we just say the TIP35 and TIP36 stuff
doesn't do anything for 0.5uS and get an over estimate of the minimum.

In 0.5uS, 150A will transfer a charge of 75uC.

The voltage change on the Cbig will be:

V = Q / C

where
Q is the charge
C is the capacitance

We solve for C


C = Q / V = 75uC / 0.1 = 750uF

Now here's the messy bit. We have assumed tha Cbig has no resistance.
All real parts have some resistance. We now need to find the data sheet
on some lets say, 1000uF capacitor with a nice low Equivelent Series
Resistance (ESR) to see how much drop will appear in the ESR. If that
plus the droop in the 1000uF is more than the specification, you need a
larger capacitor.


Finding R1:

If the circuit is lightly loaded, we want the LM317 to pass all of the
current. This means that there should be less than about 0.6V on R1 when
a "small current" is drawn. We will define a small current as 50mA os we
can say

R1 = 0.6V / 0.05A = 12 Ohms

So we make R1 about 12 Ohms.


About R2:

R2 could in most cases be zero. It lowers the gain of the TIP36 part of
things and works to reduce the risk of oscillation. I'd make this a low
inductance resistor of about 0.01 Ohms or a short length of wire.


About R3:

We want about an Amp flowing in the TIP36 before the TIP35s are brought
into things. R3 is something like 0.1 to 1.0 Ohms.


About R4:

This is actually 10 resistors, one resistor in the emitter leg of each
TIP35. When a bipolar transistor heats up, its Vbe drop decreases. If R4
wasn't there, the hottest TIP35 would end up taking on more than its share
of the load, get hotter, draw more, get hotter and etc. This could
destroy one transistor.

Thermal resistance is a lot like electrical resistance. Heat sources are
like current sources. All of the heat must flow out of one transistor
through all of the stuff it goes through to get out to the environment.
In process, one transistor will tend to warm up its brothers. To find the
minimum R4 we start with assuming a current flows in one transistor and
work out how much its temperature rises above the coolest of its brothers.
To make the math easy, just assume 1A flows.

One you have the temperature rise, assume that the individual R4 must add
at least 2.5mV of drop for every amp flowing. It is likely that this will
be such a small value that using 10 wires running from the TIP35s to the
load instead of one big oun will be enough to do it.



A note about layout:

You want Cbig to be as close to the load as practial. Ideally, there
should be 12 wires to the (+) side of the load. The LM317, the TIP36 and
all the TIP35s each have a wire. These wires should be tightly bundled
together.


A note about fuses:

They make special fuses for things like car starter motors. They look
like a thick cable with a wide section in it. Put one of these between
the car battery and the circuit. A car battery can produce nearly
infinite current for a short time.

--
--
kensmith@rahul.net forging knowledge

 

[Winfield Hill]

KILOWATT wrote...

Hi everyones thanks to read. Since a few weeks, i'm using the LightKeeper
Pro from Ulta-Lit Tree Company http://www.lightkeeper.biz/default.asp to
test and repair miniature lights sets (series-wired). I've found the Quick
Fix Trigger utility very useful. as you can see on their website, it's based
on a piezo igniter that sends a high voltage pulse through the lights set to
activate (short) the shunt inside the bulb, that didn't do so when the
bulb's filament burned out. I wanted to see how this system is built so i
opened the unit. Here's two photos plus a schematic i've drawed for the
igniter section. (Sorry, the symbol for the piezo igniter is probably
wrong...i don't know the correct one).
http://www3.sympatico.ca/kilo.watt/images/lightkeeper1.JPG
http://www3.sympatico.ca/kilo.watt/images/lightkeeper2.JPG
http://www3.sympatico.ca/kilo.watt/images/hv_pulse_gen.bmp
As i can see, the four diodes allow a peak reverse voltage of approximately
4Kv, wich is sufficient to break down the shunt's insulation inside the
burned bulb(s) and complete the series circuit. Once completed, half of an
AC cycle can flow through the four diodes, allowing the set to glow (dimly)
and show which bulbs are burned and needs replacement.
What leads me to my question (please look at the schematic) is: why the
reverse voltage doesn't seem to damages those diodes? According to the piezo
igniter's website ( http://www.yiqiang-piezo.com/english/production2.htm ),
the output voltage is at least 15Kv. With the four 1n4007 wired in series,
i should get a peak reverse voltage of about 4Kv isn't? For what i know, a
diode is destroyed once it's PIV is exceeded.

The other replies in this thread have shown you how the four diodes can
happily survive breakdown if the breakdown energy they experience is
below a critical value. Of course they will breakdown if the voltage is
high enough, and thereby limit the piezo output, which cannot be 15kV in
this instance. It's also likely that with a bulb in place the intended
breakdown processes in the bulb (the clearing of the shunt) will limit
the piezo's output voltage before the diode breakdown voltage is reached.

You can measure the actual voltage with an oscilloscope, even if you don't
have a high-voltage probe, by using a capacitive divider, if you can get
hold of a small high-voltage capacitor. Here's a 1000:1 divider circuit.

.. 1000:1 high-voltage probe
..
.. 10pF 20kV ______________ 330
.. <------||----)_____________)--+-/\/\--+----o ) scope input
.. coax cable | _|_ _|_ | Rin = 1M
.. capacitance | --- |___| | Cin = 20pF (etc)
.. 8 ft = 220pF | | | |
.. <--------------------------+--+-------+-----+------ ground
.. ground clip ~9750pF series back-to
.. select back 20V zeners

To avoid a shock hazard, be sure to connect the ground clip and plug
the probe into the scope before probing anything! And don't touch
that 10pF cap!

The probe has a high-frequency response of 10MHz, due to the 330-ohm
input-protection resistor and the ~25pF of capacitance of two 1n5250B
zener diodes in series. It also has a -3dB low-frequency rolloff of
16Hz, due to the 1M scope Zin and the 10,000pF divider capacitance.
You're measuring pulses, so the low-freq rolloff won't be an issue.
Calibrate the probe with a 10V sine wave using the 10mV scope range.


--
Thanks,
- Win

 

[Winfield Hill]

Winfield Hill wrote...

You can measure the actual voltage with an oscilloscope, even if you don't
have a high-voltage probe, by using a capacitive divider, if you can get
hold of a small high-voltage capacitor. Here's a 1000:1 divider circuit.

I should add that most of the HV meter probes one finds around a typical
workbench are *not* suitable for pulse measurements. I'm referring to
the DC probes with the 6" proboscis tip and a double banana plug on the
other end of the cable, for use with a multimeter. These employ a long
high-voltage resistor and do not have proper internal shielding, so they
will give you an erroneous (e.g., too high) result for short pulses.


--
Thanks,
- Win

 

[Leon Heller]

"Robert Baer" <robertbaer@earthlink.net> wrote in message
news:419B16E8.3A91B1C5@earthlink.net...

Reg Edwards wrote:

New program SELFRES2.exe
--------------------------------------
Input data :

Length and diameter of solenoid.
Number of turns.
Conductor diameter
Length of line in which the coil is inserted.
Testing frequency.

Output data :

Coil self-capacitance.
Coil self-resonant frequency.
Choke impedance vs frequency.
Insertion loss of choke in dB.

Performance is based on a choke wound with coaxial cable of the same type
as
the transmission transmission line in which it is inserted. Conductor
diameter is that of the coax outer. It behaves a single wire. Coax
inner
diameter is of no consequence.

Choke insertion loss is a measure of the reduction in power radiated from
the feedline. But, despite the attention it attracts, actual power
radiated
from the feedline WITH the choke will never be known because the power
radiated WITHOUT the choke is indeterminate.

SELFRES2 is 51 K-bytes. Download from website below in a few seconds. It
is
not zipped-up and will run immediately.
----
...........................................................
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
...........................................................

Incomplete.
No core specifications and/or no way to change core specs.
I dare say, that with a given totoid size, that one would see
differences uing wood, air, plastic, iron, pyrolytic graphite, between
the various ferrites (over frequency), etc.
Then change the dimensions for more fun and games (big as a pea or
small as a truck?).

A coax choke doesn't have a core! It's just coax cable wound into a coil
shape. Very convenient, as one can often just coil up the coax feeder where
it connects to the antenna.

Leon