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