AVR-Chat

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@slingshot.co.nz> 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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