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RF IC at less than 75MHz

C

ChronoFish

Jan 1, 1970
0
Hello,

I'm trying to find an RF IC transmitter that operates preferably in the 25MHz (or lower) range but would be open to anything up to
75MHz.

I don't believe RFID will work because the receiver won't be sophisticated enough to power the ID chip.

Any help would be greatly appreciated.

Thanks!
Christopher
 
J

Jim Thompson

Jan 1, 1970
0
Hello,

I'm trying to find an RF IC transmitter that operates preferably in the 25MHz (or lower) range but would be open to anything up to
75MHz.

I don't believe RFID will work because the receiver won't be sophisticated enough to power the ID chip.

Any help would be greatly appreciated.

Thanks!
Christopher

Clear as mud! WHAT are you trying to do? (There are RFID chips from
134KHz up into the GHz range.)

...Jim Thompson
 
C

ChronoFish

Jan 1, 1970
0
Jim Thompson said:
....

Clear as mud! WHAT are you trying to do? (There are RFID chips from
134KHz up into the GHz range.)


You're right. I apologize. What I'm trying to do is identify items 0-2 meters away through water. The transmitter is simply
broadcasting an ID. The receiver should be able to identify several (up to six) transmitters simultaneously. The low frequency is
requested because the medium is water.

I don't think RFID will work because I would like to keep the total cost VERY cheap (component cost < $15). While the RFID
transmitters are very cheap the readers are not.

So my question: Can you refer me to a low frequency (less than 70MHz) RF transmitter IC?

Thanks!
Christopher
 
J

James Arthur

Jan 1, 1970
0
From: "ChronoFish" [email protected]
Date: 11/14/03 10:39 AM Pacific Standard Time
Message-id: <2k9tb.707$zx.676@lakeread03>


25MHz (or lower) range but would be open to anything up
to


You're right. I apologize. What I'm trying to do is identify items 0-2
meters away through water. The transmitter is simply
broadcasting an ID. The receiver should be able to identify several (up to
six) transmitters simultaneously. The low frequency is
requested because the medium is water.

I don't think RFID will work because I would like to keep the total cost VERY
cheap (component cost < $15). While the RFID
transmitters are very cheap the readers are not.

So my question: Can you refer me to a low frequency (less than 70MHz) RF
transmitter IC?

Thanks!
Christopher


But why RF? It seems a little out of place here -- infrared's easy if the
water's clear, magnetic loops could handle your ranges, or even conduction
(place signal directly in the water). Or go acoustic ... underwater crickets!

Saltwater or fresh?

--James
"et.net" -- delete it. (incoming e-mail subject to brutal filtering)
 
C

ChronoFish

Jan 1, 1970
0
Luhan Monat said:
....
The water is still a bit muddy. What is the objective in doing this?


Are you aware of multiple RF IC transmitters in the range I am looking for? Are you aware of any? I have not had much success in
finding with the exception of some AM/FM transmitter ICs. The problem with them is that there are too many external components
needed. But if that's the way I have to go, then that's what I will do.


I understand your desire to know the intricate details of my objective. But really the only question is:

Can you refer me to a low frequency (less than 70MHz) RF transmitter IC?

Thanks!
CF
 
L

Luhan Monat

Jan 1, 1970
0
ChronoFish said:
You're right. I apologize. What I'm trying to do is identify items 0-2 meters away through water. The transmitter is simply
broadcasting an ID. The receiver should be able to identify several (up to six) transmitters simultaneously. The low frequency is
requested because the medium is water.

I don't think RFID will work because I would like to keep the total cost VERY cheap (component cost < $15). While the RFID
transmitters are very cheap the readers are not.

So my question: Can you refer me to a low frequency (less than 70MHz) RF transmitter IC?

Thanks!
Christopher
The water is still a bit muddy. What is the objective in doing this?
 
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that ChronoFish <[email protected]>
You're right. I apologize. What I'm trying to do is identify items
0-2 meters away through water. The transmitter is simply broadcasting an
ID. The receiver should be able to identify several (up to six)
transmitters simultaneously. The low frequency is requested because the
medium is water.

At that range, use magnetic induction, not radiation at all. Far lower
losses and no spectrum management issues. You could even use audio-
frequencies if your transmitter IDs use a code similar to Morse code.
 
Z

Zak

Jan 1, 1970
0
ChronoFish said:
You're right. I apologize. What I'm trying to do is identify items 0-2 meters away through water. The transmitter is simply
broadcasting an ID. The receiver should be able to identify several (up to six) transmitters simultaneously. The low frequency is
requested because the medium is water.

How many IDs do you need? You could use oscillators... say a 555 - and
poke the output in the water. Maybe two oscillators out of phase, and
use 3 contacts, to be more omnidirectional if you need.

Then use a low frequency spectrum analyser (a PC with sound card?) and
two or 3 electrodes (hey, it is stereo, you got diversity there so use
it) to do the spectrum analyis.

Can't get much cheaper I think.


Thomas
 
L

Luhan Monat

Jan 1, 1970
0
ChronoFish said:
You're right. I apologize. What I'm trying to do is identify items 0-2 meters away through water. The transmitter is simply
broadcasting an ID. The receiver should be able to identify several (up to six) transmitters simultaneously. The low frequency is
requested because the medium is water.

I don't think RFID will work because I would like to keep the total cost VERY cheap (component cost < $15). While the RFID
transmitters are very cheap the readers are not.

So my question: Can you refer me to a low frequency (less than 70MHz) RF transmitter IC?

Thanks!
Christopher
Yo,

Use a PIC12f629 with a 20 mhz xtal. Put the pic to sleep most of the
time, this kills the oscillator. Now, at some time, wake it up and go
in and out of sleep mode creating the ID code. Then go back to sleep.

Connect a short antenna to the output buffer driving the xtal.

Use any frequency you want - from 1 mhz to 20 mhz and tune it in on an
appopriate receiver.

Transmitter and ID generator in a $1 chip.
 
C

ChronoFish

Jan 1, 1970
0
Luhan Monat said:
Yo,

Use a PIC12f629 with a 20 mhz xtal. Put the pic to sleep most of the
time, this kills the oscillator. Now, at some time, wake it up and go
in and out of sleep mode creating the ID code. Then go back to sleep.

Connect a short antenna to the output buffer driving the xtal.

Use any frequency you want - from 1 mhz to 20 mhz and tune it in on an
appopriate receiver.

Transmitter and ID generator in a $1 chip.

Thanks. I'll give it a try!

-CF
 
C

ChronoFish

Jan 1, 1970
0
John Woodgate said:
I read in sci.electronics.design that ChronoFish <[email protected]>
wrote (in <2k9tb.707$zx.676@lakeread03>) about 'RF IC at less than
75MHz', on Fri, 14 Nov 2003:
At that range, use magnetic induction, not radiation at all. Far lower
losses and no spectrum management issues. You could even use audio-
frequencies if your transmitter IDs use a code similar to Morse code.
--


I confess that I had not considered magnetic induction. Will that work at 2 meters?

The audio we have considered and is still an option we may choose to go with.

Thanks!
CF
 
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that ChronoFish <[email protected]>
I confess that I had not considered magnetic induction. Will that work
at 2 meters?

Certainly. For communicating with people who use hearing aids, induction
loops can communicate over tens of metres.

If you use a bandwidth-controlled receiver, aim for a field strength of
about 100 mA/m at 2 metres. That should give you an adequate signal-to-
noise ratio.
 
F

Frank Raffaeli

Jan 1, 1970
0
John Woodgate said:
I read in sci.electronics.design that ChronoFish <[email protected]>


Certainly. For communicating with people who use hearing aids, induction
loops can communicate over tens of metres.

If you use a bandwidth-controlled receiver, aim for a field strength of
about 100 mA/m at 2 metres. That should give you an adequate signal-to-
noise ratio.

Perhaps you meant 100 uA/m ? I just completed an RFID transmitter for
125 kHz. It's got a 12-watt output ;-) ... problem is, a magnetic
"loop" antenna, is small compared to the wavelength .... and the
magnetic dipole looks like a relative tiny spec in the "field" of
things, so ... the signal falls of as 1/(d-cubed) - ignoring "ground"
effects.

A 100 mA/m field sounds like a lot (at 2 meters), since the 12-watt
unit only generates a field of 56 mA/m at 1 meter.

High frequency magnetic induction is still a fancy name for EM. The
difficulty: once immersed in water (depending upon the conductive
properties at the frequency of interest), if you short out the
electric field, and the magnetic field won't propagate either.

I like the direct conduction idea (setting up two or more dipole
probes at the transmitter and receiver). This method works well with
ground rods in earth.

Best of luck,

Frank Raffaeli
http://www.aomwireless.com/
 
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Frank Raffaeli
sting.google.com>) about 'RF IC at less than 75MHz', on Sat, 15 Nov
2003:
Perhaps you meant 100 uA/m ?

No, I meant 100 mA/m.
I just completed an RFID transmitter for
125 kHz. It's got a 12-watt output ;-) ... problem is, a magnetic "loop"
antenna, is small compared to the wavelength .... and the magnetic
dipole looks like a relative tiny spec in the "field" of things, so ...
the signal falls of as 1/(d-cubed) - ignoring "ground" effects.

A 100 mA/m field sounds like a lot (at 2 meters), since the 12-watt unit
only generates a field of 56 mA/m at 1 meter.

I haven't any idea where your 12 watts are going. I am concerned with
audio-frequency communication by induction. an amplifier with a 5 VA
capability (VA because the load is inductive) will run a 4 m square
1-turn loop and produce 400 mA/m at 1.6 m above its centre. I have
assumed that the water is not a good conductor.
 
F

Frank Raffaeli

Jan 1, 1970
0
John Woodgate said:
I read in sci.electronics.design that Frank Raffaeli
sting.google.com>) about 'RF IC at less than 75MHz', on Sat, 15 Nov
2003:


No, I meant 100 mA/m.


I haven't any idea where your 12 watts are going. I am concerned with
audio-frequency communication by induction. an amplifier with a 5 VA
capability (VA because the load is inductive) will run a 4 m square
1-turn loop and produce 400 mA/m at 1.6 m above its centre. I have
assumed that the water is not a good conductor.

I am interested in learning more about this application. Is there a
carrier? What is the dynamic range of the AGC?

In our case, we must work with a 0.5 inch diameter tx coil. That's why
we need so much power. Also, the receiver isn't very sensitive. The
larger tx coil changes the physics of the propagation. It's definitly
the way to go.

Frank Raffaeli
http://www.aomwireless.com/
 
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Frank Raffaeli
I am interested in learning more about this application. Is there a
carrier?

No, it's baseband audio, 100 Hz to 5 kHz.
What is the dynamic range of the AGC?

There doesn't necessarily need to be any AGC, although there often is.
Dynamic range depends on the application: sometimes it can be changed by
the user. What do you have in mind?
 
F

Frank Raffaeli

Jan 1, 1970
0
John Woodgate said:
I read in sci.electronics.design that Frank Raffaeli


No, it's baseband audio, 100 Hz to 5 kHz.


There doesn't necessarily need to be any AGC, although there often is.
Dynamic range depends on the application: sometimes it can be changed by
the user. What do you have in mind?

Just trying to learn. I can still squeeze new information in faster
than the old info leaks out. You mentioned this was for hearing
impaired? We have some clients who manufacture devices for the
physically handicapped. These are mostly speaking tools for
unfortunate folks who are partially paralyzed - PDA's modified to
facilitate simple conversation by pressing icons with a stylus.

Does your loop system 'power' the receiver, or is the rx active?

Frank Raffaeli
 
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John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Frank Raffaeli
sting.google.com>) about 'RF IC at less than 75MHz', on Sun, 16 Nov
2003:
Does your loop system 'power' the receiver, or is the rx active?

The receiver is the hearing aid and they have batteries. People have
made 'induction headphones' using diaphragm receivers with extended
pole-pieces. Powered induction headphones have also been offered.

If you are *really * interested in audio-frequency induction loop
systems, I can send you a 2MB zip archive on the subject.
 
W

Winfield Hill

Jan 1, 1970
0
ChronoFish said:
I'm trying to identify items 0-2 meters away through water. The
transmitter is simply broadcasting an ID. The receiver should be able
to identify several (up to six) transmitters simultaneously. The low
frequency is requested because the medium is water.

Christopher, someone should suggest an ultrasonic acoustics solution,
that's an inexpensive approach that works extremely well in water.
For example you can use low-power 40kHz, 100kHz or 200kHz, etc., with
simple transducers and get excellent range. Use a code scheme similar
to that used by infra-red TV remote controls, but add check characters
so multiple-device transmit collisions can be ignored. Each device
should broadcast its ID quickly and delay a lengthy random time before
repeating. Eventually all will have been received in the clear.
 
C

ChronoFish

Jan 1, 1970
0
John Woodgate said:
If you are *really * interested in audio-frequency induction loop
systems, I can send you a 2MB zip archive on the subject.

- I'll take one of those. Send it to audio_info at chronofish dot com.

Thanks!

CF
 
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