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'Low freq. Intro into CTCSS [OT] and LONG'
1999\11\02@231706 by Dennis Plunkett

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3/11/'99

CTCSS is subaudiable tones implanted onto the VF carrier. There is no need
for DSP in the general sense, but the levels you are looking for are
extreamly low (If I remember from my HT600 days it is around -20dB). These
tones where intended to only open up the sequlch and not for use during the
conversation (Although they remain present). The lock time was around
200mS, and consisted of a very narow band bandpass filter. Zero crossing
detection may not function, as the actual signal can (But not always) be in
some form of noise, but! The tone is not precedded any other modulation, so
detection is a bit easyer, and the squelch reamained open until the signal
was lost. NO!

The decay time of the CTCSS unit was long (While squelch was open, and
shorted when the squelch was closed), and the CTCSS looked for the tone
during the conversation time, remember that it is effectively out of band.

You will have to do some form of FFT to decide on what frequencies are in
the signal, and will be limited by the number of samples and the processing
time (You will only get one or two full cycles of tone), and will have some
30 odd mS to process them, or around 150000 processor cycles (This should
be more than enough).

Can be done, the ADC section will be the hardest, you simply start looking
for the tone once you get squelch detection (Sample for hte required period
and store (OPPS not enough room in the PIC for this so you will have to
process between samples, lets see, 320Hz = 640 sample rate or at 20MHz
(Just for Wagner!) = 7812 cycles (This will be more than enough, and it can
make a cup of coffee at the same time, hover the house and wash and wax the
car). However!

This is not a sound byte, just one sample, so the FFT becomes well.. and
you will have to store on chip running calculations, very messey=>
100mS of detection @ 640Hz sample = 64 bytes, not much room at all!, but
will that fit into an ity bity PIC? Ah yes, it can, but anther way is to
sample 16 bytes at a time, and then some form of interrupt is required. The
implementation mechanics are up to you, but first you will need to know a
bit about CTCSS, it is quite simple, zero crossing detection may work, but
the overall reliability may be in question, as you are hoping that the
receiver is functioning correctly and that there will be no overmodulation
be another transmitter at the end of the CTCSS users session etc. Speed of
detection is an issue, and you will find specs that have this all over the
place (Up to 500mS (Again for Wagner)), best to aim for sub 200mS, else
users will get a bit upset.


Hope that this points you in the correct direction. Good project to work on

Dennis

1999\11\02@234013 by paulb

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Dennis Plunkett wrote:

> (Up to 500mS (Again for Wagner)), best to aim for sub 200mS, else
> users will get a bit upset.

 You've got me.  Millisieverts?  Measure of radiation level, isn't it?
--
 Cheers,
       Paul B.

1999\11\02@235454 by W. Sierke

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> be another transmitter at the end of the CTCSS users session etc. Speed of
> detection is an issue, and you will find specs that have this all over the
> place (Up to 500mS (Again for Wagner)), best to aim for sub 200mS, else
> users will get a bit upset.

Uh oh! What's that formula for converting units of conductance to units of
time again?

s=S**(Pi*c)

where:

s = time (seconds)
S = conductance (Siemens)
Pi= something for you to nibble on while you read this drivel
c = constant of amazement that S gets mis-used for units of time, time and
time again!

So much humour, so little time. :)

(And there's even a Pi*c in there!)


Wayne

1999\11\02@235701 by Sean Breheny

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At 03:39 PM 11/3/99 +1100, you wrote:
>Dennis Plunkett wrote:
>
>> (Up to 500mS (Again for Wagner)), best to aim for sub 200mS, else
>> users will get a bit upset.
>
>  You've got me.  Millisieverts?  Measure of radiation level, isn't it?

Or millisiemens ;-)

>--
>  Cheers,
>        Paul B.
>
|
| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
\--------------=----------------
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
spam_OUTshb7TakeThisOuTspamcornell.edu ICQ #: 3329174

1999\11\03@004415 by Sean Breheny

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Actually,it is interesting that you mention this,because there IS a
relationship between conductance and time:

t = c/g

t = time (seconds)
c = capacitance (Farads)
g = conductance (Siemans)

This is normally written as t = RC, the RC time constant.

Sean

At 02:56 PM 11/3/99 +1000, you wrote:
{Quote hidden}

| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
\--------------=----------------
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
.....shb7KILLspamspam@spam@cornell.edu ICQ #: 3329174

1999\11\03@010450 by W. Sierke

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> At 03:39 PM 11/3/99 +1100, you wrote:
> >Dennis Plunkett wrote:
> >
> >> (Up to 500mS (Again for Wagner)), best to aim for sub 200mS, else
> >> users will get a bit upset.
> >
> >  You've got me.  Millisieverts?  Measure of radiation level, isn't it?
>
> Or millisiemens ;-)

Shouldn't that be milliSieverts and milliSiemens?

And shouldn't that also be a good reason not to begin a sentence with a unit
of radiation level? :)

1999\11\03@025137 by Russell McMahon

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Dennis Plunkett scribe -
>> (Up to 500mS (Again for Wagner)), best to aim for sub 200mS

& Paul B writ -
>  You've got me.  Millisieverts?  Measure of radiation level, isn't it?

So I sez  -

Nah - I think its milli-Siemen - measure of conductivity.
(And, shouldn't that have been milliSieverts?)



     Russell McMahon
_____________________________

>From another world - http://www.easttimor.com

What can one man* do?
Help the hungry at no cost to yourself!
at  http://www.thehungersite.com/

(* - or woman, child or internet enabled intelligent entity :-))

1999\11\03@085350 by Wagner Lipnharski

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"Paul B. Webster VK2BZC" wrote:
>
> Dennis Plunkett wrote:
>
> > (Up to 500mS (Again for Wagner)), best to aim for sub 200mS, else
> > users will get a bit upset.
>
>   You've got me.  Millisieverts?  Measure of radiation level, isn't it?
> --
>   Cheers,
>         Paul B.
Sieverts? Paul, again, you are so silly!!!
He was meaning 1.26MV, (milli Volts), lets see how:
hehe, perhaps a militarized Sentry, a battalion of 500 fully armored
men, so 500mS, but then again, it can not be Siemens, the conductance
unit, because german people don't do things less than a whole unit and
it would represent ¸ Siemens, right? oh well, the world don't need to be
complicated, so why not say everything in hours, it is easy, everyone
understand it...:)  so 500ms... errr, 500mS, would be 138.8mH... ooops,
does it sound as micro hour?... probably not, perhaps 138.8mHrs... still
wrong, now everyone will think it is micro Henries, huh?... but using
138.8µh is so difficult to entry the "µ" symbol, so nobody will use it
anyway, and lets say that "hour" is an important part of the day so it
needs to be written in capital letter (this is why the "H"), but talking
about day, anyone knows what is a day, so why not say that the above
delay is just 5.7md (micro day, not a "medical doctor"), and the use of
"m" for micro is because it is difficult to type "µ" and bla bla bla,
and everyone knows how to differentiate "m" (micro) from "m" (milli),
isn't that right? or perhaps we should use "M" for milli to avoid any
confusion? oh ho, what about M for Mega?, easy, we use "Meg" instead.
ok, now everything is clear. 500mS = 0.8mW (micro week), because if it
would be "Watt", then we would have a voltage... square of 0.0000008
Watt times 500mS (2 Ohms) = sqr(0.0000016) or 1.26mv... oops, 1.26MV,
argg, doesn't matter, anyone knows that it means 1.26 milli Volts, so
this is the easier way, so we all are set and ready for our project
documentation, that will be easy to do and *everyone* will understand.

cheer up, come on, I saw your smile..

Wagner.

1999\11\03@113846 by Lea

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Hi All, thanks for your replies

At 03:23 PM 11/3/99 +1100, you wrote:
>some form of noise, but! The tone is not precedded any other modulation, so
>detection is a bit easyer, and the squelch reamained open until the signal
>was lost. NO!
>
well It is one of my problems, that the tone is not alone, If it was the
case, will be a little easier, but no, usually there is at least 3Khz
of modulation in the frecuencies above 600 hz (voice), and the subtone
(CTCSS) modulation has only 600 hz of deviation, now, If I use a
3rd order active LPF (low pass filter) Will be it enough H.F. rejection?,
or still it will be a problem to detect the lower frecuencies without a
DSP? (too complicated to my knownledge level :-)

> You will have to do some form of FFT to decide on what frequencies are in
>the signal, and will be limited by the number of samples and the processing
>time (You will only get one or two full cycles of tone), and will have some
>30 odd mS to process them, or around 150000 processor cycles (This should
>be more than enough).
>
UUHHhh, OUCH!, AU!, FFT!?!?!?!, I'm in a big trouble here :-).
isn't aother way to do it without spectrum analisys???
I was trying to understand the FFT routines on the embebbed handbook without
sucess :-).

>implementation mechanics are up to you, but first you will need to know a
>bit about CTCSS, it is quite simple, zero crossing detection may work, but
>the overall reliability may be in question, as you are hoping that the
>receiver is functioning correctly and that there will be no overmodulation
>be another transmitter at the end of the CTCSS users session etc. Speed of
>detection is an issue, and you will find specs that have this all over the
>place (Up to 500mS (Again for Wagner)), best to aim for sub 200mS, else
>users will get a bit upset.

Can I make a real stupid question (that denotes my low level knowledge in the
area), what do you mean with zero crossing section?, is a way to count
frecuencies
checking when the value readed in a dac is 0 (the transition from + to - or vice
versa?)?.

about the speed, no problem, 2 seconds will be enough time, but the problem is
precision (2 hz error max) is important.

thank dannis!

At: dont remember when (yesterday I think) you wrote:-)

 If you have a quiet signal for a whole second such that the CTCSS is
your only modulation, you could probably count zero-crossings OK.

 Otherwise, it means using DSP techniques and for that a PIC won't do.
Interestingly, Microchip *used to* make DSP chips but has dropped these!
--
 Cheers,
       Paul B.

AAUCH!, OUCH, DSP!!! is not a bit complex???, I think that for this
proyect this is too much complicated, and also an area that I have been never
involved :) (It is well wrote?)
the subtone, unfortunately is not alone, there are always voice mixed with it,
but using a 3rd order LPF may be work (I hope so) what do you think about?.

thanks Paul B. for the reply.


  Leandro J. Laporta (LU2AOQ)
  mail: lu2aoqspamKILLspamyahoo.com
  wrk: Arg. Assoc. for Space Technology.
  ham: TCP/IP high speed group HSG

1999\11\08@054600 by Dr. Imre Bartfai

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Hi,

I guess no, as Sievert is shown as Sv. S stands for normally for Siemens,
the inverse of Ohm.

Regards,
Imre


On Wed, 3 Nov 1999, Paul B. Webster VK2BZC wrote:

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