AVR-Chat

Hi Ken,

I have used the NRf905 IC from Nordic semiconductor many times, works
very well, SPI interface, 433MHz means a 1/4 wave antenna is only 15cm
or so. (about 10" I think) I can generally get about 800m - 1km very
reliably.

Cheers
Hein B
Auckland, NZ

--- In AVR-Chat@yahoogroups.com, kholt@... wrote:
>
> 
> I am also looking for a cheap, simple, low power RF system
> that might as well be AM.  I need to send intermittent telemetry
> over 1/2 mile of wooded hills, where there is not much RF noise
> at the low end.  I am looking for low freq because of the hills,
> but would not like to be bothered with very long antennas.
> The data at either side of the link is handled by AVR micros,
> and is mostly sensor info: water levels, temperature, etc.
> I have been experimenting with FRS radios, just because they're
> cheap and off the shelf, but they are pretty high freq.
> 
> Ken
> 
> 
> > Well, yes, but....
> >
> > That "transmitter" would have been almost as "dirty" as the
> > old spark-gap guys in the early days. Harmonics would be
> > horrendous.
> >
> > Now, you CAN do it at low frequencies using function
> > generator techniques to generate low distortion AM sine
> > waves (up to 5MHz, perhaps).
> >
> > Receivers are more difficult because you need to
> > discriminate between the signal you want and the many,
> > many, signals you do not want. Think AM broadcast stations
> > as a simple but almost ubiquitous example.
> >
> > However, if the original query is about VHF or UHF where
> > there are many fewer interfering signals (except for those
> > really strong TV and FM stations and cellphones and FMRS
> > radios and mobile 2-way radios and ....), its almost
> > interchanged.
> >
> > You CAN use a very low sensitivity receiver so that you
> > only hear relatively strong signals (such as a low power
> > transmitter) that is relatively close. The transmitter can
> > rely, to some degree, on transmission-line resonators (and
> > thus not use coils in the strictest sense).
> >
> > So, what might be done depends on so many things. The
> > original poster needs to help us with more description
> > about the requirements (range, type of information,
> > information bandwidth, etc).
> >
> > Jim Wagner
> > Another RF Engineer on the list
> >
> > On Tue, 01 May 2007 20:04:30 -0000
> >  "kernels_nz" <kernels@...> wrote:
> >> Hi Zack,
> >>
> >> Cant say I fully agree, I cant recall the exact detail,
> >> but I have
> >> built a voice-AM transmitter without any coils, I went
> >> something like:
> >>
> >> Buy a 4-pin crystal oscillator outputting square waves at
> >> the
> >> frequency of carrier your looking for, I believe mine was
> >> 1MHz, then
> >> vary the supply voltage depending on the "voice" input
> >> voltage.
> >>
> >> Cheers
> >> Hein B
> >> Auckland, NZ
> >>
> >> --- In AVR-Chat@yahoogroups.com, Zack Widup <w9sz@>
> >> wrote:
> >> >
> >> >
> >> > It can't be done. You will need a coil at least for
> >> your
> >> antenna/matching.
> >> >
> >> > How much power are you talking about?  What range do
> >> you want to cover?
> >> > For what purpose?  What frequency?  What are the laws
> >> in your country
> >> > regarding license-free transmissions on that frequency?
> >> >
> >> > Inquiring minds want to know, especially this RF
> >> engineer.
> >> >
> >> > Zack
> >> >
> >> > On Wed, 25 Apr 2007, azza eldessoky wrote:
> >> >
> >> > > please friends,can any one  send me a circuit design
> >> for AM
> >> transmitter or receiver without  any coils .
> >> > >    thanks alot
> >> > >        azza
> >> > >
> >> >
> >>
> >>
> >
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> > http://www.thinkdifferentstore.com/
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> >
>