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'[PICLIST] [EE] FSK modulator'
2000\10\06@151731 by Mauro Costa Sollar

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Simple circuit FSK modulator/demulator with PIC. anywhere know?

Thanks

Mauro Sollar

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2000\10\09@135951 by Mauro Costa Sollar

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Simple circuit FSK modulator/demulator with PIC. anywhere know?

Thanks

Mauro Sollar

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2000\10\25@210800 by David Huisman

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I would prefer not to use modems with large footprints, cost and analog
signaling as I also then must convert TX signal to TTL at both transmit and
receive ends of the link.

I am wanting to create AFSK. ie. PIC micro sends serial data via UART to
FSK modulator that converts serial data to FSK tones with TTL level.This
signal controls an ASK radio transmitter. At the receive end, the RSSI
output is filtered and fed to FSK demodulator, finally TTL output of
demodulator to the receive PIC micro.

The XR-2211A demodulator looks fine for my application but I need a
generator (VCO) to suit. The XRparts (2207,2209 etc) are 8V.
I need 5V VCO that can create FSK square wave tone at 9600 Baud.

The modem IC's are normally sensitive to receive signal level (The 73M223)
"likes" a couple of hundred millivolts. The RSSI level on the receiver will
vary from 100mV to 3 or 4 Volts. The XR2211 has an input range of 10mV to
3V, which would suit the levels presented.

Alternatively, anyone know of another low cost, small footprint (<= 14 pin),
5V single supply FSK mod/dem chipset.

Regards
David Huisman

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2000\10\25@214008 by Nikolai Golovchenko

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MX604 for example at
http://www.mxcom.com

or FX604 at
http://www.cmlmicro.co.uk


Nikolai

--------------------------------------------------------------------------------
Subject: FSK modulator
From: David Huisman (spam_OUTdavid.huismanTakeThisOuTspamADVMININGTECH.COM.AU)
Date: Wed Oct 25 2000 - 19:00:37 PDT
--------------------------------------------------------------------------------

I would prefer not to use modems with large footprints, cost and analog
signaling as I also then must convert TX signal to TTL at both transmit and
receive ends of the link.

I am wanting to create AFSK. ie. PIC micro sends serial data via UART to
FSK modulator that converts serial data to FSK tones with TTL level.This
signal controls an ASK radio transmitter. At the receive end, the RSSI
output is filtered and fed to FSK demodulator, finally TTL output of
demodulator to the receive PIC micro.

The XR-2211A demodulator looks fine for my application but I need a
generator (VCO) to suit. The XRparts (2207,2209 etc) are 8V.
I need 5V VCO that can create FSK square wave tone at 9600 Baud.

The modem IC's are normally sensitive to receive signal level (The 73M223)
"likes" a couple of hundred millivolts. The RSSI level on the receiver will
vary from 100mV to 3 or 4 Volts. The XR2211 has an input range of 10mV to
3V, which would suit the levels presented.

Alternatively, anyone know of another low cost, small footprint (<= 14 pin),
5V single supply FSK mod/dem chipset.

Regards
David Huisman

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2000\10\25@220231 by Dan Michaels

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David Huisman wrote:
>
>Alternatively, anyone know of another low cost, small footprint (<= 14 pin),
>5V single supply FSK mod/dem chipset.
>

http://www.hitex.com/chipdir/f/
http://www.hitex.com/chipdir/f/osc.htm
http://www.hitex.com/chipdir/f/vco.htm
http://www.hitex.com/chipdir/f/modem.htm

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2000\10\26@013227 by Harold Hallikainen

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On Thu, 26 Oct 2000 12:00:37 +1000 David Huisman
<.....david.huismanKILLspamspam@spam@ADVMININGTECH.COM.AU> writes:
{Quote hidden}

       I did a design years ago that used the XR2211 demod and the XR2206 as
the modulator. It's great because you just put TTL level data on pin 9
and it selects between two timing resistors to generate the FSK. It also
has a sine wave output with a 600 ohm output resistance. Really nice! It
does require more than 5V (I ran it at +12V). The 2206 also has an analog
multiplier or balanced modulator in it. In one product I used it to
hetrodyne an FM subcarrier (26 to 92 kHz range) up to 455 kHz. The VCO in
the 2206 was the local oscillator. The FM baseband was put directly on
the input to the balanced modulator (I forget which pin), and the
multiplied output went to a 455 kHz ceramic filter. This then went thru a
single transistor IF amp and into a ceramic discriminator. The output of
the discriminator drove an amp to recover audio (the Bell 202 signals
generated by another 2206). There was also a low pass filter that took
the DC component of the recovered audio and fed it back to the 2206 local
oscillator to act as an AFC, keeping the whole thing locked to the
incoming subcarrier.
       All in all, the XR2206 is a pretty neat chip.  So is the XR2211. One
thing I did with the 2211 was to add a feedback resistor around the
carrier detect comparator so it had hysteresis. This got rid  of chatter
on the output due to noise.

Harold


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2000\10\26@033327 by Chris Carr

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I know you probably have good reasons for going to all this complication, I
have to ask why?. Firstly your usual ASK Tx is not exactly linear in its
modulaton characteristics, secondly FSK Tx and Rx modules are available for
not much more than ASK modules.

Regards
Chris

{Original Message removed}

2000\10\26@133448 by Dan Michaels

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Harold Hallikainen wrote:
>On Thu, 26 Oct 2000 12:00:37 +1000 David Huisman
><david.huismanspamKILLspamADVMININGTECH.COM.AU> writes:
......
>>
>> The XR-2211A demodulator looks fine for my application but I need a
>> generator (VCO) to suit. The XRparts (2207,2209 etc) are 8V.
>> I need 5V VCO that can create FSK square wave tone at 9600 Baud.
>>
.......
>        All in all, the XR2206 is a pretty neat chip.  So is the XR2211. One
>thing I did with the 2211 was to add a feedback resistor around the
>carrier detect comparator so it had hysteresis. This got rid  of chatter
>on the output due to noise.
>


Harold,

Looking over the XR2211 d/s, it appears it is only good to about
1200 baud, maybe 2400. Correct? Kinda slow by today's stds.

best regards,
- Dan Michaels
Oricom Technologies
http://www.users.uswest.net/~oricom
===================================

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2000\10\26@134740 by Barry Gershenfeld

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I've been waiting for someone else to mention this, but the
original Packet Radio hardware to come out of the ham radio
world used the two XR chips for mod and demod.  I actually
built a breadboard modem prior to buying myself one of
the real kits.   Unfortunately I haven't been able to find
anything online to reference this but I do have schematics
and stuff buried somewhere...maybe I can turn up something
on someone's website.

If the help you've gotten so far hasn't been enough...

Barry

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2000\10\26@154706 by Harold M Hallikainen

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On Thu, 26 Oct 2000 10:28:17 -0700 Barry Gershenfeld <.....barryKILLspamspam.....ZMICRO.COM>
writes:
> I've been waiting for someone else to mention this, but the
> original Packet Radio hardware to come out of the ham radio
> world used the two XR chips for mod and demod.  I actually
> built a breadboard modem prior to buying myself one of
> the real kits.   Unfortunately I haven't been able to find
> anything online to reference this but I do have schematics
> and stuff buried somewhere...maybe I can turn up something
> on someone's website.
>
> If the help you've gotten so far hasn't been enough...
>
> Barry


       Looking further back, I used the XR2206 and XR2211 to put computer data
on audio cassette according to the Kansas City standard. I bought my
first 6800 integer basic interpreter on cassette from, I think, Southwest
Technical Products.

Harold



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2000\10\26@154715 by Harold M Hallikainen

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On Thu, 26 Oct 2000 13:34:48 -0400 Dan Michaels <EraseMEoricomspam_OUTspamTakeThisOuTUSWEST.NET>
writes:
>
> Harold,
>
> Looking over the XR2211 d/s, it appears it is only good to about
> 1200 baud, maybe 2400. Correct? Kinda slow by today's stds.
>
>

       I ran it at 1200. I imagine it could run substantially higher at higher
carrier frequencies. If you are trying to run it in a voice grade
circuit, I don't think you can do much more than 1200 bps. Looking at
modem history, we had Bell 103 which was 300 pbs FSK, splitting the band
to use one frequency pair in one direction and another frequency pair in
the other. Bell 202 ran 1200 bps FSK in one direction only. This was
either used half duplex, switching directions as needed (or, in my case,
doing a multidrop network), or there was a 75 bps reverse channel using
another frequency pair. This worked well for ASCII terminals, using 1200
bps to update the screen and 75 bps for operator keystrokes.  Moving on
to Bell 212, which gave 1200 bps in each direction, we moved from FSK to
QPSK with a separate carrier for each direction. As modem speeds got
higher, I believe they went to QAM and used the same carrier frequency in
each direction, relying on echo cancellation to keep the transmit and
receive side from interfering with each other (even though they are at
the same frequency). Finally, for 56 kbps modems, we moved to pulse
amplitude modulation for the downstream side, and I don't know what for
upstream...
       So, if you're running FSK over a voicegrade circuit, I think the best
you can do is 1200 bps. Faster and you need a fancier modulation
technique.

Harold



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2000\10\26@160049 by Dan Michaels

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Harold wrote:
.......
>        So, if you're running FSK over a voicegrade circuit, I think the best
>you can do is 1200 bps. Faster and you need a fancier modulation
>technique.
>


Thanks Harold, that is about what I thought - regarding the XR2211.
As I recall, most voice grade modems run basic 2400 baud, with higher
bitrates resulting from the amplitude/phase modulation constellation.

Would be nice to find a cheap modem chip - something "not" >= 64-pin
smt - that you could easily hook to a PIC, and get to 9600 or so.
Must be something out there.

best regards,
- dan michaels
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2000\10\26@162206 by Harold M Hallikainen

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On Thu, 26 Oct 2000 16:00:49 -0400 Dan Michaels <oricomspamspam_OUTUSWEST.NET>
writes:
> Harold wrote:
> .......
> >        So, if you're running FSK over a voicegrade circuit, I
> think the best
> >you can do is 1200 bps. Faster and you need a fancier modulation
> >technique.
> >
>
>
> Thanks Harold, that is about what I thought - regarding the XR2211.
> As I recall, most voice grade modems run basic 2400 baud, with
> higher
> bitrates resulting from the amplitude/phase modulation
> constellation.
>
> Would be nice to find a cheap modem chip - something "not" >= 64-pin
> smt - that you could easily hook to a PIC, and get to 9600 or so.
> Must be something out there.
>

       Though relatively large, I always thought ISA modem boards would be easy
to interface to a PIC. Kinda nice in that they have a DAA, FCC
certification, etc. You'd use a fair number of pins on the PIC, but it'd
sure be a low cost way of getting the job done...  I just wonder how long
ISA modems will be available. I haven't tried to talk to a PCI bus device
with a PIC...

Harold


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2000\10\26@174727 by Barry King

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Dan,

I'm not clear what the overall application is- but if you want to put
data on phone line, I'd use one of the pre-built hybrid modem modules
form Cermetek or similar.

They are very easy to use with Micros, just TTL level serial I/O from
the serial port, and AT commands to do configuration, call set up and
teardown.

Look at the Cermetek CH1786 for the simplest/cheapest in their line.
They are about the same price as a PC modem card.

Regards,

The other Barry :)
------------
Barry King
NRG Systems "Measuring the Wind's Energy"
http://www.nrgsystems.com
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2000\10\26@181723 by David Huisman

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Barry,

The application is for radio. The radio module has TTL input for digital
signalling.
I want to send FSK, TTL level data over the link.
The other end is RSSI output that is fed to a data slicer and results in TTL
also.

Regards

David Huisman

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2000\10\26@183440 by Chris Carr

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I will repeat my previous question. Why are you insisting on wanting to use
AFSK by employing a ASK module which is inherently non-linear instead of a
FSK module which would make the audio modems redundant, eliminating redunant
components which would save you money, reduce board size and provide better
margins on your transmission path.

Regards
Chris

----- Original Message ----- > The application is for radio. The radio
module has TTL input for digital
> signalling.
> I want to send FSK, TTL level data over the link.
> The other end is RSSI output that is fed to a data slicer and results in
TTL
> also.
>

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2000\10\26@191707 by Plunkett, Dennis

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26/10/2000


If the radio has a TTL input, then there is no need to modulate this, just
bang in your data. The radio will then treat this as a high and low etc ,and
internally generate modulation voltage. All you need to do is frame the data
in your favourite protocol!
ie the radio will generate the FSK for you!


Dennis

> {Original Message removed}

2000\10\26@195857 by David Huisman

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Dennis.

The radio link is ASK. The reason for adding FSK to result in AFSK is to
increase sensitivity and reliability with regards to bit fading.

Regards
David Huisman

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2000\10\26@201331 by David Huisman

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Chris,

We make the ASK radio modules. We have not yet completed development on an
FM version. These modules are low cost and SAW locked so we are still doing
work on deviating the SAW far enough for wideband FM.

We do use the existing system driven directly from a UART with serial data
that is pseudo Manchester encoded at the software level and packetized with
error checking etc.
We could bit bash 2 tones from the micro and then use a software FFT
algorithm at the receiver but we don't want to use as much resource from the
micro, thus a low cost hardware solution such as XR2211 FSK demodulator and
suitable partner Modulator would be fine.
The problem is that XR2206, 2207 etc require 8V supply, we want a 5V
solution.

Regards

David Huisman

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2000\10\26@211425 by Plunkett, Dennis

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ASK, as in FM?
If this is the case then you can increase the modulation level such that
there are little problems in this manner


Dennis



> {Original Message removed}

2000\10\26@233256 by David Huisman

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Dennis,

I don't understand what you mean by "ASK, as in FM?

As explained. The radio link is ASK (a "1" is high level, a "0" is low
level - but not off).
Thus when the "0" level is being sent, there is a small amount of carrier
that helps noise immunity. This signal goes to a tracking data slicer and
results in TTL output.
Problems can occur even within a bit period where the amplitude of each bit
can vary and result in pulse width distortion of the signal. Most UARTS can
tolerate a couple of % but then you have problems.

The idea is to send AFSK (Audio Frequency Shift Keying), This comprises 2
tones, one represents "1" and the other "0".
This way the demodulator can be made very sensitive to trigger only at zero
crossing points, now the amplitude of the signal for each bit is less
important.
Many FSK demodulators can decode the signal and reliably produce the "1"
when receiving the "1" tone and a "0" when receiving the "0" tone even in
the presence of noise. Whereas it only takes a little noise in any bit of a
digital signal to ruin it.

Regards
David Huisman

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2000\10\27@004510 by Plunkett, Dennis

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26/10/2000


I have not been through all the threads on this one, but if the radio is FM
then there is always a carrier when active. The TTL input simply changes the
deviation of the radio transmitter. Max is equal to SPACE and min is equal
to MARK. Yes this does drop the sensitivity a bit, but 12dB SINAD for .35uV
is possible (120 path loss (Quite high)) What are your path losses? Are they
direct or a defraction?

As for your explanation, I suggest that you change the bit format so that a
1 (MARK) is sent by default, and tone present is a space
So I still am wondering if these radios are FM, because if they are, then
there is always carrier when the PTT is active (Not at the audio level
though, perhaps this is where the confusion starts).
If you are sending audio, then remove the preemphasis and deemphasis that is
there, and the data link will be better.


Dennis


> {Original Message removed}

2000\10\27@130852 by Dan Michaels

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Thanks Marcelo,

The chips appear pretty interesting at first look. Never
heard of MX-COM, a UK company. Anyone know about availabilty
in the US?

- dan michaels
==============

Marcelo Puhl wrote [offlist]:
{Quote hidden}

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2000\10\27@131849 by David VanHorn

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At 01:08 PM 10/27/00 -0400, you wrote:
>Thanks Marcelo,
>
>The chips appear pretty interesting at first look. Never
>heard of MX-COM, a UK company. Anyone know about availabilty
>in the US?

http://www.tapr.org, or through a few selected distys.

Also, watch the clocking, they have peculiar clock requirements.

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2000\10\27@151120 by Dan Michaels

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Dave Van Horn wrote:
>At 01:08 PM 10/27/00 -0400, you wrote:
>>Thanks Marcelo,
>>
>>The chips appear pretty interesting at first look. Never
>>heard of MX-COM, a UK company. Anyone know about availabilty
>>in the US?
>
>http://www.tapr.org, or through a few selected distys.
>
>Also, watch the clocking, they have peculiar clock requirements.
>


Thanks Dave, they have a number of interesting projects listed
on that site. Various radio/modem & PIC-controlled devices like
we've been discussing here.

Can you recommend any other good "RF sites" for those of us
to whom RF is an undiscovered planet?

best regards,
- dan michaels
==============

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2000\10\27@165007 by Graeme Zimmer

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Hi Dan,

> Can you recommend any other good "RF sites" for those of us
> to whom RF is an undiscovered planet?

For starters, get a copy of the ARRL Handbook and/or the RSGB equivalent..

(Go search ARRL and RSGB, they both have many excellent publications)

Also please ask questions on the list. Lots of ancient radio boffins here
(who mostly just lurk )!

...................... Zim ................ de VK3GJZ

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2000\10\29@185917 by David Huisman

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Dennis,

You need to look back over the thread as all the details are posted. It is
ASK system.
The required modulaton is AFSK.

Regards
David Huisman

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