18nH Inductor
 

I have been searching the catalogs for an 18nanohenry inductor to use in
conjunction with a Radiotronix RCR-433-RP Receiver and transmitter pair for
a remote control I am working on. Radiotronix has an app note that shows
this inductor used with a couple of 8.2pf caps to get good
reception/transmission for their modules.

I have been unable to find a source other than surface mount parts. Does
anyone know of a source for this size inductor, or know the formula that I
would use to wind my own?

I am posting this to rec.radio.amateur.homebrew and
rec.radio.amateur.antenna

TIA,

Joe
KB1KVI

On Thu, 30 Sep 2004 19:56:34 GMT, "Joe"
wrote:

I have been unable to find a source other than surface mount parts. Does
anyone know of a source for this size inductor, or know the formula that I
would use to wind my own?

"Wind" ?

As a rule of thumb, a thin wire has an inductance about 1 nH/mm, so a
straight wire about 18 mm long would have the required inductance. For
a thicker wire, about 25-30 mm straight wire would be required. Even a
single turn would increase the inductance quickly, so you would have
to shorten the wire considerably.

If 18 nH surface mount inductors exists, why not use them ? At least
the inductance would be much predictable.

Paul OH3LWR

On Thu, 30 Sep 2004 22:10:09 +0000 (UTC), "Reg Edwards"
wrote:

However, to find the length, diameter and number of turns to make such a
small coil you can use program SOLNOID3 which can be downloaded in a few
seconds, free of charge, and run immediately from the the website below.
Try it and see what happens.

Does it crash, Reg? ;-)
Seriously, would it not be better to use a spiral PCB trace?
--

"What is now proved was once only imagin'd." - William Blake, 1793.

"Paul Keinanen" wrote in message
...
On Thu, 30 Sep 2004 19:56:34 GMT, "Joe"
wrote:

I have been unable to find a source other than surface mount parts. Does
anyone know of a source for this size inductor, or know the formula that
I
would use to wind my own?

"Wind" ?

As a rule of thumb, a thin wire has an inductance about 1 nH/mm, so a
straight wire about 18 mm long would have the required inductance. For
a thicker wire, about 25-30 mm straight wire would be required. Even a
single turn would increase the inductance quickly, so you would have
to shorten the wire considerably.

If 18 nH surface mount inductors exists, why not use them ? At least
the inductance would be much predictable.

Paul OH3LWR


Thanks Paul,

What do you mean by a thin wire? #20 magnet wire, #26?

Sounds like I can make my own and very easily, with just a 18mm length of
(not sure what size) wire.

Joe
KB1KVI

"Reg Edwards" wrote in message
...
An 18 nano-henry inductor seems, to me, to be an impractical inductor
value.
The length of the connecting wires will form an appreciable part of the
inductance. There must be another way of acheiving the desired circuit
functions.

However, to find the length, diameter and number of turns to make such a
small coil you can use program SOLNOID3 which can be downloaded in a few
seconds, free of charge, and run immediately from the the website below.
Try it and see what happens.
---
.................................................. .........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. .........


Thanks Reg,

I will download that program. It sounded kind of small to me too. I don't
use smd because I don't know how.

The link to the schematic is:
http://www.radiotronix.com/downloads/433_pair.pdf


Joe
KB1KVI

On Fri, 01 Oct 2004 02:33:14 GMT, "John Smith"
wrote:

Or, do these transmitters require the PI network to stay within FCC limits?

Hi John,

In the old days, this question use to appear on the FCC's serious
tests - also required math too.

You already demonstrated as much with:
If you analyze the receiving network, you will see that, if the antenna is
50 Ohms, the receiver sees 50 Ohms. So the network appears to simply be a
filter.
that meets the minimum technical requirment for coupling. All that
remains is the technical in-band/out-band issues (which segue into the
legal issues).

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Fri, 01 Oct 2004 02:33:14 GMT, "John Smith"
wrote:

Or, do these transmitters require the PI network to stay within FCC
limits?

Hi John,

In the old days, this question use to appear on the FCC's serious
tests - also required math too.

You already demonstrated as much with:
If you analyze the receiving network, you will see that, if the antenna is
50 Ohms, the receiver sees 50 Ohms. So the network appears to simply be a
filter.
that meets the minimum technical requirment for coupling. All that
remains is the technical in-band/out-band issues (which segue into the
legal issues).

73's
Richard Clark, KB7QHC

I don't understand what you're driving at here, Richard. I'm saying that an
analysis of the PI network shows that it serves no "matching" purpose if the
antenna is 50 Ohms and the receiver wants to see 50 Ohms. Its only purpose
seems to be to provide a narrow bandwidth. Does the receiver need it?
Probably not, unless there are a other transmitters in near by operating on
an adjacent frequency.

As for the transmitter, perhaps it needs a filter, perhaps not. But, is a PI
sufficient to meet any regulations if it does require a filter? Does the
transmitter not meet the regulations without it? I remember hearing that
these transmitters use SAW devices. Aren't SAW devices filters? All I'm
saying is that, if you can meet the FCC rules without the PI filter, you
don't need the filter at all.

73,
John

Hi John

SAW, surface acoustic wave, filters are not transmitter pass filters.

As for the need, that is simple: OF COURSE it needs filtering. Simply
observing the manufacturer's requirements reveals that:
In most cases, the output of the transmitter may need a low-pass LC filter to reduce harmonic emissions.
As for matching:
The output of the oscillator is derived directly from the collector of the oscillator transistor. It is, therefore, very sensitive to VSWR.
This, alone, demands filtering to reduce harmonics.

As for SAW filters. It has one, and uses it in the conventional
manner (not as an output filter) for frequency determination in the
oscillator.

73's
Richard Clark, KB7QHC

On Fri, 01 Oct 2004 00:20:37 GMT, "Joe"
wrote:

Mouser sells them too, but I don't know how to work with surface mounted
parts.

Since the inductor is only a two "pin" component and assume you have
two PCB tracks at a suitable distance from each other, soldering
should not be a problem even without SMD experience. Using a toothpick
or some other device to keep the component steady, first solder one
end, let it cool for awhile and then solder the other end.

By the way, what type of capacitor are you using for that 8 pF ? If it
is a leaded component, it might have quite a few nH of wire
inductance. In addition to the SMD inductor, I would also recommend a
SMD capacitor, since these have a lower self inductance. Soldering it
close to the inductor should not be any harder.

I suggest that you buy some cheap SMD resistors or capacitors with the
same size package as the inductor or capacitor you are going to use
and solder these to a Vero 0.1" strip board to get some confidence in
SMD soldering, before installing the real components into the module.

Paul OH3LWR

For anyone interested in what an 18 nano-H inductor looks like under a
magnifying glass -

3 turns of 0.33 mm diameter wire, wound on a 2.2 mm diameter former, over a
length of 2.0 mm.

Its self-resonant frequency is 4.6 GHz and it is tuned to 1 GHz with a
capacitor of 1.3 pF. Q = 330 at 1 GHz.
----
Reg

"Reg Edwards" wrote in message
...
An 18 nano-henry inductor seems, to me, to be an impractical inductor
value.
The length of the connecting wires will form an appreciable part of the
inductance. There must be another way of acheiving the desired circuit
functions.

However, to find the length, diameter and number of turns to make such a
small coil you can use program SOLNOID3 which can be downloaded in a few
seconds, free of charge, and run immediately from the the website below.
Try it and see what happens.
---
.................................................. .........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. .........
Reg,
A 1/2 turn loop of the proper dimensions might be more practical. I recall
using one that was about .5 in high between .5 centers, made of #14 wire.
(it carried 10 amps). Don't remember the exact value, but it was probably a
little more than what he is looking for.

At any rate, as you say, it is important to add the inductance of the
circuit board traces to the inductor value. BTW, the last job I was on used
402 SM inductors down to about 10 nH, but that was at 2+ GHz.

Tam

"Joe" wrote in message link.net...
"Reg Edwards" wrote in message
...
An 18 nano-henry inductor seems, to me, to be an impractical inductor
value.

;-) You just aren't working with small enough, high enough frequency
circuits, Reg.

3 turns of 28AWG on a 4-40 (USA) screw (remove the screw, of course)
will give you about 18 nH. Unloaded Q at 440MHz will be around 200.

The link to the schematic is:
http://www.radiotronix.com/downloads/433_pair.pdf

Easy enough to use SMT components soldered to a piece of copper-clad
for a ground plane. Just put down the two caps and the shunt resistor
"tombstone" style, one end soldered to the ground plane and the other
up in the air, separated by enough distance to put the series coil and
resistor between them. You can keep the parasitic L and C very low
indeed this way. You can also use tiny squares of copper-clad glued
down to the ground plane as tie points.

It's also possible to mechanically make a simple circuit like this on
copper-clad using surface mount parts, by scribing lines with
something like an X-Acto knife and removing strips of copper. In this
case, I could see scribing four lines across the board, separated by
about 1/16 inch, and removing two copper strips, one from between the
first and second scribe, and one from between the thrid and fourth
scribe. That leaves a trace about 1/16 inch wide. Cut gaps in the
trace, about 1/16 inch long, where you want to solder down series
components. Solder shunt components across from the trace to the
copper ground plane. Bridge across the trace with a copper strap to
connect the two gound plane sides, with the bridge up in the air over
the trace. Nice to have a ground plane on the opposite side, with
some holes and wires to connect to the top-side ground planes, but not
necessary. I'm thinking 0805 parts with the sizes I mentioned...make
things slightly larger for 1206. You can make the trace be a 50 ohm
transmission line if you want, by sizing things right.

Cheers,
Tom

"Tom Bruhns" wrote in message
...
"Joe" wrote in message
link.net...
"Reg Edwards" wrote in message
...
An 18 nano-henry inductor seems, to me, to be an impractical inductor
value.

;-) You just aren't working with small enough, high enough frequency
circuits, Reg.

3 turns of 28AWG on a 4-40 (USA) screw (remove the screw, of course)
will give you about 18 nH. Unloaded Q at 440MHz will be around 200.

The link to the schematic is:
http://www.radiotronix.com/downloads/433_pair.pdf

Easy enough to use SMT components soldered to a piece of copper-clad
for a ground plane. Just put down the two caps and the shunt resistor
"tombstone" style, one end soldered to the ground plane and the other
up in the air, separated by enough distance to put the series coil and
resistor between them. You can keep the parasitic L and C very low
indeed this way. You can also use tiny squares of copper-clad glued
down to the ground plane as tie points.

It's also possible to mechanically make a simple circuit like this on
copper-clad using surface mount parts, by scribing lines with
something like an X-Acto knife and removing strips of copper. In this
case, I could see scribing four lines across the board, separated by
about 1/16 inch, and removing two copper strips, one from between the
first and second scribe, and one from between the thrid and fourth
scribe. That leaves a trace about 1/16 inch wide. Cut gaps in the
trace, about 1/16 inch long, where you want to solder down series
components. Solder shunt components across from the trace to the
copper ground plane. Bridge across the trace with a copper strap to
connect the two gound plane sides, with the bridge up in the air over
the trace. Nice to have a ground plane on the opposite side, with
some holes and wires to connect to the top-side ground planes, but not
necessary. I'm thinking 0805 parts with the sizes I mentioned...make
things slightly larger for 1206. You can make the trace be a 50 ohm
transmission line if you want, by sizing things right.

Cheers,
Tom

Hi Tom,

Being so new at this, I don't even know what you mean by 'tombstone style',
and it sounds like an awful lot of work to be scoring pcboard with an Xacto
knife to create transmission line effects.

I talked with a tech rep from radiotronix today. They called me because I
ordered a half dozen modules from mouser. He explained that the pi circuit
on the TX is so the TX sees 50 ohms, which is pretty critical. I have not
done anything with the transmitter modules yet (they are from Velleman
because they are thru hole), but I am building a receiver board on pc board
using pcbexpress and single sided copper pcboard. It will be the first
prototype. Now that I have it working on a breadboard I am going to build
one and see how it works. I am planning on using a straight piece of (20ga)
wire for the 18nH inductor and using the T network of 2 8pf caps beside it.
The tech said this is just a low pass filter, but it seems to make a
difference in receiver sensitivity. The noise on the receiver is supposed to
be there according to him. It is between 1Khz and 1.5Khz. he said some
people use the data slicer pin with a holtek ht12D decoder, which i am doing
or you can also use a micro to look for the bit pattern and decode the
signal. I am just using the TV (transmission valid) to set off the rest of
my circuit which, right now, consists of a latch and an LED.

Joe

Joe wrote:

Being so new at this, I don't even know what you mean by 'tombstone
style', and it sounds like an awful lot of work to be scoring pcboard
with an Xacto knife to create transmission line effects.

You can easily build what you need using single-sided board: a
continuous groundplane, components soldered on top, and connections made
using sticky-backed copper tape (available at craft stores for
stained-glass work).

If you cut strips 0.1in wide, these will be a good approximation to
50-ohm microstrip, for the relatively low frequencies and short lengths
that you will need. On the reverse side, use broader the copper tape to
link the groundplanes of your extension and the Radiotronix module.

Simply lay the SMD components against each other, and solder them
together... but before you do, mark where the connections through to
ground will need to be, for the two capacitors in the pi-network and
possibly other places. Then drill the board and insert links of thick
wire (14AWG) so that the ground connections will have zero length beyond
the thickness of the board - but I really do mean ZERO, or else your
network will not perform correctly. The ground links must be touching
the ends of the capacitor chips before you solder them.

Likewise, use ZERO lead lengths inside the pi-network. Butt the ends of
the two Cs and the L chips directly together, and solder. Any
"connecting leads" must be restricted to the places that can use 50-ohm
microstrip.

This construction method is very quick and simple. The SMD parts are
well-enough anchored to the board for all normal conditions of use.

I talked with a tech rep from radiotronix today. They called me
because I ordered a half dozen modules from mouser. He explained that
the pi circuit on the TX is so the TX sees 50 ohms, which is pretty
critical.

- so remember what I just said about zero lead lengths.

I have not done anything with the transmitter modules yet (they are
from Velleman because they are thru hole), but I am building a receiver
board on pc board using pcbexpress and single sided copper pcboard. It
will be the first prototype. Now that I have it working on a breadboard
I am going to build one and see how it works. I am planning on using a
straight piece of (20ga) wire for the 18nH inductor and using the T
network of 2 8pf caps beside it. The tech said this is just a low pass
filter, but it seems to make a difference in receiver sensitivity.

On the face of it, this pi-network has a 1:1 impedance transformation
(two equal capacitors) so it shouldn't make any difference. However,
there may be stray capacitances and/or inductances in the module that we
don't know about. Bottom line is, this network is what the Radiotromix
techs have found to work.

Since you don't have the design experience and the test equipment to
measure how the whole thing performs, you would be very wise to copy
EXACTLY what Radiometrix did, which includes building the whole network
using the best possible construction practice.

Also, a straight piece of wire is actually a short length of
transmission line: it does not have quite the same electrical properties
as an inductor. So use an 18nH chip inductor like Radiometrix said.

This is really part of your "contract" with the module manufacturer. It
isn't fair or reasonable to expect their tech support to second-guess
what the effects of every individual user's network might be, if they're
all slightly different. You might get away with it this time, but some
of the worst tech-support problems are caused by people who decla

"I did exactly what you said..."

[Now follows 20 minutes of intensive cross-examination over the phone]

"... oh, apart from all these things that are different."

[Deleted: strange sounds on the phone line. The tech has the curly cord
gripped in both hands. He's puling it out straight, and he has a red
glint in his eyes. Be very thankful that you're several hundred miles
away...]



--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Ian White, G3SEK wrote:
You can easily build what you need using single-sided board: a
continuous groundplane, components soldered on top, and connections
made using sticky-backed copper tape

Sorry, that wasn't quite clear (not enough coffee yet this morning).

The continuous groundplane is on the underside of the board. All the SMD
components are on the bare fibreglass side. The SMD components are held
in place by soldering them directly to each other, to the ground links,
to the striplines, and to various other fixed points.

No board etching is required, and this technique will is good to
frequencies well above 1GHz.

The 0.1in stripline width was for standard 0.064in FR-4. You can
obviously refine that calculation if you want, but there's little point
for this particular application.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

"Joe" wrote in message link.net...
"Tom Bruhns" wrote in message
...
....
Easy enough to use SMT components soldered to a piece of copper-clad
for a ground plane. Just put down the two caps and the shunt resistor
"tombstone" style, ...
Joe: "I don't even know what you mean by 'tombstone style',"

Tombstone style...just solder one end to the copper-clad board, and
the other end sticking up in the air. Looks like a micro-size
tombstone sticking up from the board.

....

Cheers,
Tom

Hi Tom,

Being so new at this, I don't even know what you mean by 'tombstone style',
and it sounds like an awful lot of work to be scoring pcboard with an Xacto
knife to create transmission line effects.

It's really not all that difficult. Just use a ruler to guide the
knife, use a sharp knife, and the strips you want to remove can
usually just be pulled up in one piece (each). Or do it as Ian
suggested, with sticky copper tape.

As Ian wrote, keep lead lengths extremely short, like "zero." He
suggested putting a piece of heavy copper wire through the board where
you want to connect to the ground plane. Another way is to simply
drill a hole through the board and drop an 0805-size surface mount
part into the hole, and solder both ends. A 1/16" hole would work,
but you'd do better to pick a size that just fits the part you want to
use. Not all 0805 parts are quite the same size, but the body lengths
are pretty accurate and work nicely in 1/16" thick board material.
Any of the methods mentioned by Ian and myself will work well, and all
are reasonably easy to implement with a bit of practice and patience.

Cheers,
Tom

Tom Bruhns wrote:
Any of the methods mentioned by Ian and myself will work well, and all
are reasonably easy to implement with a bit of practice and patience.

One method of "etching" that worked for me was using a reamer
bit on a drill press to cut through the copper and barely into
the PCB material. This has the advantage of leaving a ground
plane in between the active traces. Also great for scouring
and sizing PCBs.
--
73, Cecil, W5DXP

On Wed, 06 Oct 2004 12:20:57 -0500, Cecil Moore
wrote:

Tom Bruhns wrote:
Any of the methods mentioned by Ian and myself will work well, and all
are reasonably easy to implement with a bit of practice and patience.

One method of "etching" that worked for me was using a reamer
bit on a drill press to cut through the copper and barely into
the PCB material. This has the advantage of leaving a ground
plane in between the active traces. Also great for scouring
and sizing PCBs.

This is where those Dremmel tools come into their own!

--

"What is now proved was once only imagin'd." - William Blake, 1793.

Paul Burridge wrote:
Cecil Moore wrote:
One method of "etching" that worked for me was using a reamer
bit on a drill press to cut through the copper and barely into
the PCB material. This has the advantage of leaving a ground
plane in between the active traces. Also great for scouring
and sizing PCBs.

This is where those Dremmel tools come into their own!

As a matter of fact, when I did this stuff at home, I used a
Dremmel tool.

Thanks all for the suggestions, I have a dremel, and this might be a good
project for me to learn how to use smt stuff. I will need to get a small
lighted magnifier tho, cause my eyes ain't what they used to be, even with
my reading glasses.

Joe

"Joe" wrote in message
ink.net...
Thanks all for the suggestions, I have a dremel, and this might be a good
project for me to learn how to use smt stuff. I will need to get a small
lighted magnifier tho, cause my eyes ain't what they used to be, even with
my reading glasses.

Joe

Joe,
If you are like me, you will want to use 805 or larger SM. 402 type drive me
batty, and if you ever drop one on the floor, it is gone forever.

Tam/WB2TT

"Tam/WB2TT" wrote in message
...

"Joe" wrote in message
ink.net...
Thanks all for the suggestions, I have a dremel, and this might be a
good
project for me to learn how to use smt stuff. I will need to get a small
lighted magnifier tho, cause my eyes ain't what they used to be, even
with
my reading glasses.

Joe

Joe,
If you are like me, you will want to use 805 or larger SM. 402 type drive
me
batty, and if you ever drop one on the floor, it is gone forever.

Tam/WB2TT



Hi Tam,

Actually, the ones that looked easiest to use were the 1210 case size. I
ordered some from mouser yesterday. I hope they're big enough for me to see.

I was wondering about a post I read somewhere else a long time ago. Is there
such a thing as a paste (that comes in a tube) that can be applied to the
terminals of a surface mount device and then when it is stuck to the board,
the paste hardens into something like hardened solder? So it is mounted to
the board and soldered with this paste?

Joe
KB1KVI

Joe wrote:
. . .
I was wondering about a post I read somewhere else a long time ago. Is there
such a thing as a paste (that comes in a tube) that can be applied to the
terminals of a surface mount device and then when it is stuck to the board,
the paste hardens into something like hardened solder? So it is mounted to
the board and soldered with this paste?

One-part conductive epoxy fits that description. It's commonly used to
mount SMT parts on hybrid circuits. However, the ones I'm familiar with
require curing at an elevated temperature (e.g., 150C for an hour). I
believe there are also some UV curing conductive epoxies. Conductive
epoxy can be used for mounting parts on a PCB, too, but I don't think
it's commonly done because it's considerably more expensive than solder.
There might be two-part conductive epoxies that cure at room
temperature, but I've never used one and am not sure they exist. The
one-part epoxies I've used aren't conductive until they're cured -- the
tiny conductive (gold or silver) particles in the paste don't contact
each other until the curing process causes the epoxy to shrink and pull
them together.

Then there's solder paste, nearly universally used for mounting parts on
PCBs. This also fits your description and can by applied by hand with a
syringe, then melted by a number of means -- hot air, IR, soldering
iron. It's actually a slurry of flux and tiny spheres of solder. It's
not really sticky, but sort of gummy, so some other means (like
superglue) has to be used if the parts need to be kept in place when the
board is inverted or severely disturbed before the paste is melted.

Roy Lewallen, W7EL

"Roy Lewallen" wrote in message
...
Joe wrote:
. . .
I was wondering about a post I read somewhere else a long time ago. Is
there
such a thing as a paste (that comes in a tube) that can be applied to
the
terminals of a surface mount device and then when it is stuck to the
board,
the paste hardens into something like hardened solder? So it is mounted
to
the board and soldered with this paste?

One-part conductive epoxy fits that description. It's commonly used to
mount SMT parts on hybrid circuits. However, the ones I'm familiar with
require curing at an elevated temperature (e.g., 150C for an hour). I
believe there are also some UV curing conductive epoxies. Conductive
epoxy can be used for mounting parts on a PCB, too, but I don't think
it's commonly done because it's considerably more expensive than solder.
There might be two-part conductive epoxies that cure at room
temperature, but I've never used one and am not sure they exist. The
one-part epoxies I've used aren't conductive until they're cured -- the
tiny conductive (gold or silver) particles in the paste don't contact
each other until the curing process causes the epoxy to shrink and pull
them together.

Then there's solder paste, nearly universally used for mounting parts on
PCBs. This also fits your description and can by applied by hand with a
syringe, then melted by a number of means -- hot air, IR, soldering
iron. It's actually a slurry of flux and tiny spheres of solder. It's
not really sticky, but sort of gummy, so some other means (like
superglue) has to be used if the parts need to be kept in place when the
board is inverted or severely disturbed before the paste is melted.

Roy Lewallen, W7EL


Thanks Roy,

It sounds like the solder paste is what I heard about. Sounds easier than
trying to solder such small parts with an iron. I will see if mouser carries
it and give it a try.

Joe
KB1KVI