AVR-Chat

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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[Non-text portions of this message have been removed]

On 4/25/07, azza eldessoky <azza972008@yahoo.com> wrote:
> please friends,can any one  send me a circuit design for AM transmitter or receiver without  any coils .
>    thanks alot

Are you looking to do voice/music or data?
Frequency band?

Either way, you're likely to be better off buying a complete radio module.
For data, I can recommend the FCC approved modules from www.rfdigital.com

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 
>

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 
> >
>

> ... I believe mine was 1MHz...

Did you treat harmonics?


Tom

Hi Hein,

I guess I should have clarified "for any distance".  Yes, you can generate 
a signal with a few transistors and couple it to a small wire with a 
capacitor but you're only going to get a few hundrerd feet at most with 
it.  That's why I wondered what it's to be used for and over what 
distance.

I guess I'm thinking like a lowfer, where we're trying to get signals 
hundreds of miles on 136 kHz. That can't be done without coils somewhere. 
Either that or very large pieces of real estate that most of us don't 
have.  :-)

Zack

On Tue, 1 May 2007, kernels_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 
> > >
> >
> 
> 
>

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 
> > >
> >
> 
> 

---------------------------------------------------------------
The Think Different Store
http://www.thinkdifferentstore.com/
For All Your Mac Gear
---------------------------------------------------------------

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
> >> > >
> >> >
> >>
> >>
> >
> > ---------------------------------------------------------------
> > The Think Different Store
> > http://www.thinkdifferentstore.com/
> > For All Your Mac Gear
> > ---------------------------------------------------------------
> >
>

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
>> > >
>> >
>>
>>
>
> ---------------------------------------------------------------
> The Think Different Store
> http://www.thinkdifferentstore.com/
> For All Your Mac Gear
> ---------------------------------------------------------------
>

Half mile in hilly wooded area is a bit of a challenge with
low power at ANY frequency. Trees tend to absorb pretty
well. 

Problem with low frequencies is that there  is a lot of
interferance. Problem with medium and higher frequencies is
the terrain loss. 

AM won't gain you much. Its simple and there are lot of AM
chips and modules out there, but they are generally good
for a few hundred feet, max. FM and other modulation modes
all have disadvantages along with the advantages. 

You might try building a net of zigbee modules though I've
heard that zigbee networking may not be ready for prime
time.

Get yourself a ham license (no morse code now, exam is
pretty simple). Then you can use a 25W transmitter or more
with ax.25 packet and you will have an off-the-shelf
solution. It would handle your half mile easily. Modems are
readily available and you only need to feed ascii in and
get ascii out. For this purpose, you could even get used
radios (cheaper) because it does not take a lot to make
this work.

Jim


On Wed, 2 May 2007 14:30:59 -0700 (PDT)
 kholt@sonic.net 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@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
> >> > >
> >> >
> >>
> >>
> >
> >
>
---------------------------------------------------------------
> > The Think Different Store
> > http://www.thinkdifferentstore.com/
> > For All Your Mac Gear
> >
>
---------------------------------------------------------------
> >
> 
> 

---------------------------------------------------------------
The Think Different Store
http://www.thinkdifferentstore.com/
For All Your Mac Gear
---------------------------------------------------------------

----- Original Message ----- 

From: "Jim Wagner" <jim_d_wagner@applelinks.net>
To: <AVR-Chat@yahoogroups.com>
Sent: Wednesday, May 02, 2007 10:32 PM
Subject: Re: [AVR-Chat] Re: AM transmitter or receiver


> Half mile in hilly wooded area is a bit of a challenge with
> low power at ANY frequency. Trees tend to absorb pretty
> well.
>
> Problem with low frequencies is that there  is a lot of
> interferance. Problem with medium and higher frequencies is
> the terrain loss.
>
> AM won't gain you much. Its simple and there are lot of AM
> chips and modules out there, but they are generally good
> for a few hundred feet, max. FM and other modulation modes
> all have disadvantages along with the advantages.
>
> You might try building a net of zigbee modules though I've
> heard that zigbee networking may not be ready for prime
> time.
>
> Get yourself a ham license (no morse code now, exam is
> pretty simple). Then you can use a 25W transmitter or more
> with ax.25 packet and you will have an off-the-shelf
> solution. It would handle your half mile easily. Modems are
> readily available and you only need to feed ascii in and
> get ascii out. For this purpose, you could even get used
> radios (cheaper) because it does not take a lot to make
> this work.

I don't think that would be a legal use of amateur radio. It wouldn't be 
legal in the UK, at any rate.

Leon
--
Leon Heller
Amateur radio call-sign G1HSM
Yaesu FT-817ND and FT-857D transceivers
Suzuki SV1000S motorcycle
leon355@btinternet.com
http://www.geocities.com/leon_heller

Probably not legal per US FCC Part 19 for Ham Radio (I am a licensee).

You should be able to get that half-mile easily with a pair of 1W
902-928MHz serial port extender radios. I've used these. And a small
yagi for one or both isn't expensive if you need its gain. Maxstream
sells these - as 100mW and 1W. I don't recall what the FCC Part 15
limit is in that band; it's usually much higher with highly
directional antennas. And higher yet for freq. hopping radios as are
the Maxstream. These kind of radios are popular in in the SCADA
business - telemetry of traffic signals, water pumps, electrical
transformers and the like. 

I got 6 miles line of sight with a pair of 100mW radios and 4 ft. long
yagis, and with 2MHz bandwidth with 1+ Mbps data. The ones I mentioned
above for serial port extension (like 19.2Kbps or so) would do much
better due to the lower modulation rate and 1W. You can save some $ by
purchasing a PC board without enclosure and power supply.

steve

> 
> On Wed, 2 May 2007 14:30:59 -0700 (PDT)
>  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
> > >> > >
> > >> >
> > >>
> > >>
> > >
> > >
> >
> ---------------------------------------------------------------
> > > The Think Different Store
> > > http://www.thinkdifferentstore.com/
> > > For All Your Mac Gear
> > >
> >
> ---------------------------------------------------------------
> > >
> > 
> > 
> 
> ---------------------------------------------------------------
> The Think Different Store
> http://www.thinkdifferentstore.com/
> For All Your Mac Gear
> ---------------------------------------------------------------
>

Thanks, all, for the advice.  I probably will try the Maxstream
devices, although the freq. might be a bit high for my steep terrain.
The FRS devices are around 450Mz, and just barely work, at about 100mw.
I haven't tried a directional antenna with the FRS, but I have a yagi
that works well for our old analog cell phones (900mhz).
Ken

> Probably not legal per US FCC Part 19 for Ham Radio (I am a licensee).
>
> You should be able to get that half-mile easily with a pair of 1W
> 902-928MHz serial port extender radios. I've used these. And a small
> yagi for one or both isn't expensive if you need its gain. Maxstream
> sells these - as 100mW and 1W. I don't recall what the FCC Part 15
> limit is in that band; it's usually much higher with highly
> directional antennas. And higher yet for freq. hopping radios as are
> the Maxstream. These kind of radios are popular in in the SCADA
> business - telemetry of traffic signals, water pumps, electrical
> transformers and the like.
>
> I got 6 miles line of sight with a pair of 100mW radios and 4 ft. long
> yagis, and with 2MHz bandwidth with 1+ Mbps data. The ones I mentioned
> above for serial port extension (like 19.2Kbps or so) would do much
> better due to the lower modulation rate and 1W. You can save some $ by
> purchasing a PC board without enclosure and power supply.
>
> steve
>
>>
>> On Wed, 2 May 2007 14:30:59 -0700 (PDT)
>>  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
>> > >> > >
>> > >> >
>> > >>
>> > >>
>> > >
>> > >
>> >
>> ---------------------------------------------------------------
>> > > The Think Different Store
>> > > http://www.thinkdifferentstore.com/
>> > > For All Your Mac Gear
>> > >
>> >
>> ---------------------------------------------------------------
>> > >
>> >
>> >
>>
>> ---------------------------------------------------------------
>> The Think Different Store
>> http://www.thinkdifferentstore.com/
>> For All Your Mac Gear
>> ---------------------------------------------------------------
>>
>
>
>

The performance of an antenna depends on its relative size
compared to the operating frequency. I would not expect a
900MHz Yagi to work very well at 450MHz.

You can make a very simple antenna called a "J-pole" out of
300 ohm twin lead and some coax (to connect to the radio).
You can hang it from a tree branch or almost anything that
gets it up in the air. Here is a web site that tells how to
build one:

http://www.qsl.net/wb3gck/jpole.htm

Simply scale it inversely with frequency. This design is
nominally centered at 146MHz. FRS band center is about
467MHz. So, multiply all of the length dimensions by
146/467). 

Jim
 
On Thu, 3 May 2007 12:21:28 -0700 (PDT)
 kholt@sonic.net wrote:
> 
> Thanks, all, for the advice.  I probably will try the
> Maxstream
> devices, although the freq. might be a bit high for my
> steep terrain.
> The FRS devices are around 450Mz, and just barely work,
> at about 100mw.
> I haven't tried a directional antenna with the FRS, but I
> have a yagi
> that works well for our old analog cell phones (900mhz).
> Ken
> 
> > Probably not legal per US FCC Part 19 for Ham Radio (I
> am a licensee).
> >
> > You should be able to get that half-mile easily with a
> pair of 1W
> > 902-928MHz serial port extender radios. I've used
> these. And a small
> > yagi for one or both isn't expensive if you need its
> gain. Maxstream
> > sells these - as 100mW and 1W. I don't recall what the
> FCC Part 15
> > limit is in that band; it's usually much higher with
> highly
> > directional antennas. And higher yet for freq. hopping
> radios as are
> > the Maxstream. These kind of radios are popular in in
> the SCADA
> > business - telemetry of traffic signals, water pumps,
> electrical
> > transformers and the like.
> >
> > I got 6 miles line of sight with a pair of 100mW radios
> and 4 ft. long
> > yagis, and with 2MHz bandwidth with 1+ Mbps data. The
> ones I mentioned
> > above for serial port extension (like 19.2Kbps or so)
> would do much
> > better due to the lower modulation rate and 1W. You can
> save some $ by
> > purchasing a PC board without enclosure and power
> supply.
> >
> > steve
> >
> >>
> >> On Wed, 2 May 2007 14:30:59 -0700 (PDT)
> >>  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
> >> > >> > >
> >> > >> >
> >> > >>
> >> > >>
> >> > >
> >> > >
> >> >
> >>
>
---------------------------------------------------------------
> >> > > The Think Different Store
> >> > > http://www.thinkdifferentstore.com/
> >> > > For All Your Mac Gear
> >> > >
> >> >
> >>
>
---------------------------------------------------------------
> >> > >
> >> >
> >> >
> >>
> >>
>
---------------------------------------------------------------
> >> The Think Different Store
> >> http://www.thinkdifferentstore.com/
> >> For All Your Mac Gear
> >>
>
---------------------------------------------------------------
> >>
> >
> >
> >
> 
> 

---------------------------------------------------------------
The Think Different Store
http://www.thinkdifferentstore.com/
For All Your Mac Gear
---------------------------------------------------------------

That 450MHz antenna may work OK on 900 because 900MHz is the 2nd
harmonic and the antenna will resonate. Certainly better to use a
proper antenna. A small 4 element yagi isn't expensive for 900MHz.

----- Original Message ----- 

From: "stevech11" <stevech@san.rr.com>
To: <AVR-Chat@yahoogroups.com>
Sent: Friday, May 04, 2007 7:05 AM
Subject: [AVR-Chat] Re: AM transmitter or receiver


> That 450MHz antenna may work OK on 900 because 900MHz is the 2nd
> harmonic and the antenna will resonate. Certainly better to use a
> proper antenna. A small 4 element yagi isn't expensive for 900MHz. 

An antenna tuned for 450 MHz won't be resonant on 900 MHz!

Leon

> ... An antenna tuned for 450 MHz won't be resonant on 900 MHz...

Probably true.  But - verging on OT here - there is nothing magic about 
antenna resonance.

An antenna is an impedance-matching transformer; the secondary load is 
space.  When an antenna matches the typical 50-ohm transmission line to 
the ~400-ohm impedance of space, power is transferred and the antenna 
will radiate.  Some antenna designs will do that at multiple 
frequencies; simple dipoles (the driver element in a Yagi is usually a 
dipole or folded dipole), for example, will behave similarly on the 
fundamental tuned frequency and the _third_ harmonic - but not the 
second - I think you'll find.

The complex Yagi antenna, with multiple director and reflector elements, 
though, will probably will not work well at any frequency but the one it 
is designed and tuned to.


Tom