> So you could take that 8.25cm wire and wrap it into a coil and it would be
> just about as effective as leaving it straight?

No, this is not true.  Coiling up an antenna will have a significant effect
on the resonant frequency and impedance of the antenna.  The same goes for
having any conductive objects in the near field vicinity of the antenna,
especially if they resonate close to the operating frequency of the antenna.
To use a 1/4 wave antenna efficiently, it needs a ground plane.  A long wire
(>1 wavelength) does not need this, but will need some type of impedance
matching to your rf equipment, it will also be directional.

> Can I use just normal stranded ~24AWG hookup wire for the antenna?  Does
> the insulation around the wire matter?

Yes you can leave it on.  The insulation really makes very little difference
in your case.  Strictly speaking, the insulation does have an effect on the
velocity factor of the the wire used as the radiator.  It does not resist
the rf from being able to leave the wire.   Suffice it to say that much
experimentation is in order here.  You will find things that work fine for
you (regardless of what the "experts" say), and you will most assuredly find
that your real-world measurements will never exactly match your calculated
expectations.  Antenna theory and design is black magic.  ;-)

All that other stuff aside, for your application (low power/short range) a
piece of 24 ga. insulated wire approximately 1/4 wavelength long will, in
all probability, work just fine.  ;-)

> Thanks,
>
> Gary
>
> At 09:25 AM 5/14/2002 -0700, you wrote:
> >Antennas are a whole subject in itself. They come in all sizes, shapes,
and
> >colors. Simply put, a monopole is a simple antenna which is a single
piece
> >of wire, usually called a whip in most forms. Antennas should be tailored
to
> >the frequency being used. Moreover, they need to be tuned to listen in
for a
> >specfic frequency's wavelength or a function of it.  Depending on the
> >frequency and type of usage, there are different antennas for different
> >applications. Higher frequencies tend to be more directional as you go up
in
> >freq which creates the need for antennas that can transmit or listen in
all
> >or specified directions.
> >
> >A 1/4 wave antenna works fine for most applications. Use this relation to
> >figure this out required length:  C= lamda x V, where c= 3 x 10^8, V =
> >frequency, and lambda = wavelength.
> >
> >For example, a 900MHz device would need:
> >
> >3 x 10^8 / 900 x 10^6 = .333 meter wavelength. Dividing this by 4, only a
> >8.25 cm long antenna is needed. This can be a loop, coil, etc.
> >
> >Linx technologies has a good primer on antennas.
> >http://www.linxtechnologies.com/ldocs/pdfs/AN00500.pdf
> >
> >Also, they have an antenna site.
> >http://www.antennafactor.com/adocs/f_prod.html
> >
> >Hope this helps,
> >Michael
> >
> > > [Original Message]
> > > From: Gary Neal <gln103@PSU.EDU>
> > > To: <PICLIST@MITVMA.MIT.EDU>
> >  > Date: 5/14/02 8:57:12 AM
> > > Subject: Re: [EE]: RF modules
> > >
> > > Guys,
> > >
> > >          Recent discussion has peaked my interest especially since the
> > > relatively cheap Laipac modules were introduced.  I'm looking at using
the
> > > TLP434 modules outside in an open field.  I'd like to get the most
range
> > > that I can.  At least 150' but would be nice to get to ~600'.
> > >          Anyway, I have no experience with RF, specifically the
> > > antenna.  Can someone shed some light on this?  How do you know how
long a
> > > wire to use?  Do you just use a piece of wire?  What gauge?  Can it
still
> > > have the insulation on it?  What is "loop", "whip" style that I see
listed
> > > on the Laipac page?  Is the antenna different for the transmitter and
> >receiver?
> > >          As you can see, I'm a novice at this antenna stuff.  I don't
> > > really want a whole bunch of analytical antenna design mumbo jumbo.
Be
> > > nice if someone would say something like "Ya, just connect a piece of
> >24AWG
> > > wire to the antenna that's about 3" long and that'll give you pretty
good
> > > reception".  Something like that.
> > >
> > > Thanks,
> > >
> > > Gary
>
> Gary Neal
> Research Assistant - Drivetrain Technology Center
> Applied Research Laboratory - Penn State University
> PO Box 30
> Research Building West
> North Atherton Street
> State College, PA 16801
> 814-863-5468 (phone)
> 814-863-6185 (fax)
>
> --
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>

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