Wanted: Pro-2003 scanner mods, Bearcat/Uniden scanner

Wanted: Pro-2003 scanner mods, Bearcat/Uniden scanner

Post by Peter Stok » Wed, 15 Jan 1992 04:04:48

I'm looking for mod details for a Realistic PRO-2003 scanner,
specifically, a circuit for removing "PL tones" betweeen
voice on certain channels.     Some scanners have a "CTCSS
accessory" that does this.

In this case, the tones are repeated ~1500 Hz bursts several
times per second from the base station whenever there is no
voice.   These tones were introduced when a certain enforcement
agency in the province of Ontario switched to a new radio system :-(      
I've had limited success with a circuit in the Bart Veerman scanner
book but need either a new circuit or help with this one.
It's basically an LM567 tone detector connected to the audio of
the IF chip (MC3359, or MC3357P or 10420) which is supposed to
somehow shunt the scan control signal of the same chip
to ground when the offending tone is present.   It works except its
not fast enough in that the tone is briefly heard every time the
channel is scanned.     Any comments or help appreciated...

I'd also be interested in books/sources for other Pro-2003
mods including quiet audio detect and 800 Mhz capability.

Secondly:   Anyone have a Bearcat/Uniden 590 or 760 for sale
for a resonable dollar amount?

Listenin'

 
 
 

Wanted: Pro-2003 scanner mods, Bearcat/Uniden scanner

Post by Jacob DeGlopp » Sat, 18 Jan 1992 08:02:25



>I'm looking for mod details for a Realistic PRO-2003 scanner,
>specifically, a circuit for removing "PL tones" betweeen
>voice on certain channels.     Some scanners have a "CTCSS
>accessory" that does this.

>In this case, the tones are repeated ~1500 Hz bursts several
>times per second from the base station whenever there is no
>voice.   These tones were introduced when a certain enforcement
>agency in the province of Ontario switched to a new radio system :-(      

K
Just to correct a little:  This isn't CTCSS (aka Motorola PL).  CTCSS
stands for Continuous Tone Coded Squelch System, and is used on many
if not most professional radio systems involving repeaters.  It works
by transmitting an audio frequency whenever the radio is keyed.  The voice
is transmitted on top of the CTCSS tone, and the tone is filtered out
on the other end.  I'm not sure of the details, but it's not something
you can hear with your ears.  Obviously the repeater controllers and the
CTCSS boards for the Bearcat mobiles don't have a problem hearing the
tones.  These tones range from 67 to 205 Hz.  

I'm not sure what you're hearing, but it sounds vaguely similar to
what an IMPS (Improved Mobile Phone Service) base sends on its next
clear channel.  IMPS predates cellular, operates on VHF and UHF, and
uses standard radios with different control heads and conventional
transmissions.

(Sorry for the theory on .swap...)

--

 
 
 

Wanted: Pro-2003 scanner mods, Bearcat/Uniden scanner

Post by Peter Stok » Sun, 19 Jan 1992 00:19:03



>>I'm looking for mod details for a Realistic PRO-2003 scanner,
>>specifically, a circuit for removing "PL tones" betweeen
>>voice on certain channels.     Some scanners have a "CTCSS
>>accessory" that does this.

>>In this case, the tones are repeated ~1500 Hz bursts several
>>times per second from the base station whenever there is no
>>voice.   These tones were introduced when a certain enforcement
>>agency in the province of Ontario switched to a new radio system :-(      
>K
>Just to correct a little:  This isn't CTCSS (aka Motorola PL).  CTCSS
>stands for Continuous Tone Coded Squelch System, and is used on many
>if not most professional radio systems involving repeaters.  It works
>by transmitting an audio frequency whenever the radio is keyed.  The voice
>is transmitted on top of the CTCSS tone, and the tone is filtered out
>on the other end.  I'm not sure of the details, but it's not something
>you can hear with your ears.  Obviously the repeater controllers and the
>CTCSS boards for the Bearcat mobiles don't have a problem hearing the
>tones.  These tones range from 67 to 205 Hz.  

>I'm not sure what you're hearing, but it sounds vaguely similar to
>what an IMPS (Improved Mobile Phone Service) base sends on its next
>clear channel.  IMPS predates cellular, operates on VHF and UHF, and
>uses standard radios with different control heads and conventional
>transmissions.

I'm confused.  If I tune in the channel, I hear 1500Hz tone bursts,
about three times a second, irritating!   This causes my scanner to
stop on the channel.   The tones continue until the base station
dispatcher decides to speak, at which point the voice is loud and
clear.   A friend of mine bought the Bearcat 760XLT with an optional
CTCSS tone board which allows one to key in the correct PL tone (in
this case the number is 107.2, corresponding to EIA standard "1B"),
eliminating the problem.  I don't know how the value 107.2 relates to
anything.   I would really like to mod my PRO-2003 though, so I can
listen to the cops again.    Help!
 
 
 

Wanted: Pro-2003 scanner mods, Bearcat/Uniden scanner

Post by Steve K » Sun, 19 Jan 1992 02:28:54


>I'm confused.  If I tune in the channel, I hear 1500Hz tone bursts,
>about three times a second, irritating!   This causes my scanner to
>stop on the channel.   The tones continue until the base station
>dispatcher decides to speak, at which point the voice is loud and
>clear.   A friend of mine bought the Bearcat 760XLT with an optional
>CTCSS tone board which allows one to key in the correct PL tone (in
>this case the number is 107.2, corresponding to EIA standard "1B"),
>eliminating the problem.  I don't know how the value 107.2 relates to
>anything.   I would really like to mod my PRO-2003 though, so I can
>listen to the cops again.    Help!

The 1500Hz tone burst is nothing more than an audio tone at 1500Hz, which
will cause the scanner to lock on that frequency.  Now your friend that has
the 760XLT also has a PL (CTCSS) decode option.  To prevent unauthorized
users to access their radio system, and to stop interference, they encode
the transmitting signal with a PL tone (you can't hear it though).  So
by adding PL decode (which tells the scanner NOT to break the squelch
until the correct PL is also received), the scanner will only recieve
stuff with the PL on it.  From the looks of it, it would seem that they
are only transimitting the PL when it is a "real" voice transmission,
thus your friend only hears "real" transmissions.  The PL tone of 107.2
is in Hz.  There are about 20 or 30 of these different tones.

As far as I know, there is no PL decode option for the Radio Shaft scanners.
The option your friend has for the 760 can be programmed for a differnt
PL tone on each frequency (which you need, since everyone uses a different
PL).  You could build an external PL decoder, but there would be no way
to assign different PLs for each channel.


 
 
 

Wanted: Pro-2003 scanner mods, Bearcat/Uniden scanner

Post by joel.peshk » Sun, 19 Jan 1992 02:58:22


>I'm confused.  If I tune in the channel, I hear 1500Hz tone bursts,
>about three times a second, irritating!   This causes my scanner to
>stop on the channel.   The tones continue until the base station
>dispatcher decides to speak, at which point the voice is loud and
>clear.   A friend of mine bought the Bearcat 760XLT with an optional
>CTCSS tone board which allows one to key in the correct PL tone (in
>this case the number is 107.2, corresponding to EIA standard "1B"),
>eliminating the problem.  I don't know how the value 107.2 relates to
>anything.   I would really like to mod my PRO-2003 though, so I can
>listen to the cops again.    Help!

Possible explanations?????

1) There is another (lower power) source of a carrier on the same frequency.
This carrier contains the annoying tone bursts. When the cops key up
they overpower the noise source and you hear them instead.

2) The cops have their repeater generating the tones (w/o PL) so that
scanner enthusiasts will not listen to them. When they key up to really
communicate, they use a PL tone so that their own units can tell the 2 apart.

If the latter is the case,  I am not sure if it is legal or not. Often,
effective emergency communications  in one area is dependent on
a break in radio chatter in an adjacent area using differrent PL tones.
I work with ambulances in several fringe areas. If I found a department
in another area using this method on one of the  frequencies I use,
I would strive to see that it stopped. BTW, often ambulances in one
area will use the same freq as cops in another and school busses in a 3rd.
Many a time, I have dropped my PL tones during an emergency to find that
Timmy Higgens won't be on the bus today or that Officer whoever wants
onions on his pizza. My patient was going downhill fast meanwhile.

 
 
 

Wanted: Pro-2003 scanner mods, Bearcat/Uniden scanner

Post by Peter Stok » Sun, 19 Jan 1992 04:02:36



>>I'm confused.  If I tune in the channel, I hear 1500Hz tone bursts,
>>about three times a second, irritating!   This causes my scanner to
>>stop on the channel.   The tones continue until the base station
>>dispatcher decides to speak, at which point the voice is loud and
>>clear.   A friend of mine bought the Bearcat 760XLT with an optional
>>CTCSS tone board which allows one to key in the correct PL tone (in
>>this case the number is 107.2, corresponding to EIA standard "1B"),
>>eliminating the problem.  I don't know how the value 107.2 relates to
>>anything.   I would really like to mod my PRO-2003 though, so I can
>>listen to the cops again.    Help!

>The 1500Hz tone burst is nothing more than an audio tone at 1500Hz, which
>will cause the scanner to lock on that frequency.  Now your friend that has
>the 760XLT also has a PL (CTCSS) decode option.  To prevent unauthorized
>users to access their radio system, and to stop interference, they encode
>the transmitting signal with a PL tone (you can't hear it though).  So
>by adding PL decode (which tells the scanner NOT to break the squelch
>until the correct PL is also received), the scanner will only recieve
>stuff with the PL on it.  From the looks of it, it would seem that they
>are only transimitting the PL when it is a "real" voice transmission,
>thus your friend only hears "real" transmissions.  The PL tone of 107.2
>is in Hz.  There are about 20 or 30 of these different tones.

>As far as I know, there is no PL decode option for the Radio Shaft scanners.
>The option your friend has for the 760 can be programmed for a differnt
>PL tone on each frequency (which you need, since everyone uses a different
>PL).  You could build an external PL decoder, but there would be no way
>to assign different PLs for each channel.



I'm beginning to understand... I've been trying to get a circuit
working that I saw in a book that supposedly modifies a Radio Shack or
Uniden/Bearcat scanner (basically any that uses the MC3357, MC3359 or
10420 IF chip)  to solve this problem.   It wasn't working and it's
possible because I was tuning it to 1500Hz to detect 1500Hz and tell
the scanner to keep scanning whereas it looks like it's supposed to
detect the 107.2Hz tone and tell the scanner to _stop_ scanning.
Back to the ba***t lab bench.

There is probably a large market for this PL circuit for Radio
Shack scanners, especially around here cause the cops use a PL
tone system.   If someone wants to give it a try , I can
fax the circuit diagram or post it on the newsgroup.  Maybe
you'll be better at getting it to work.  Let me know.

listenin' and learning,
Peter

 
 
 

Wanted: Pro-2003 scanner mods, Bearcat/Uniden scanner

Post by Mike Ard » Sun, 19 Jan 1992 04:03:27

-I'm confused.  If I tune in the channel, I hear 1500Hz tone bursts,
-about three times a second, irritating!   This causes my scanner to
-stop on the channel.   The tones continue until the base station
-dispatcher decides to speak, at which point the voice is loud and
-clear.   A friend of mine bought the Bearcat 760XLT with an optional
-CTCSS tone board which allows one to key in the correct PL tone (in
-this case the number is 107.2, corresponding to EIA standard "1B"),
-eliminating the problem.  I don't know how the value 107.2 relates to
-anything.   I would really like to mod my PRO-2003 though, so I can
-listen to the cops again.    Help!

107.2 is the frequency (in hertz) of the subaudiable (PL (tm. Motorola)) tone
that they are using.  It appears that they transmit that tone while talking
on the radio, and your friend's radio is set up to only open the squelch
while that tone is being transmitted.  The 1500 Hz tone could be either
an 'ID' tone to signal a certain radio (like a pager) or perhaps some
sort of data transmission.  They obviously wouldn't transmit the PL tone
during this tone burst.

/mike
--
\|/  Michael L. Ardai  N1IST   Teradyne EDA East
--- -------------------------------------------------------------------------

 
 
 

Wanted: Pro-2003 scanner mods, Bearcat/Uniden scanner

Post by Craig Lem » Mon, 20 Jan 1992 18:36:14



>>I'm confused.  If I tune in the channel, I hear 1500Hz tone bursts,
>>about three times a second, irritating!   This causes my scanner to
>>stop on the channel.   The tones continue until the base station
>>dispatcher decides to speak, at which point the voice is loud and
>>clear.   A friend of mine bought the Bearcat 760XLT with an optional
>>CTCSS tone board which allows one to key in the correct PL tone (in
>>this case the number is 107.2, corresponding to EIA standard "1B"),
>>eliminating the problem.  I don't know how the value 107.2 relates to
>>anything.   I would really like to mod my PRO-2003 though, so I can
>>listen to the cops again.    Help!

>Possible explanations?????

>1) There is another (lower power) source of a carrier on the same frequency.
>This carrier contains the annoying tone bursts. When the cops key up
>they overpower the noise source and you hear them instead.

>2) The cops have their repeater generating the tones (w/o PL) so that
>scanner enthusiasts will not listen to them. When they key up to really
>communicate, they use a PL tone so that their own units can tell the 2 apart.

        I know the signal that the originator is speaking of and have heard
it many times.  This "law enforcement acengy" is province-wide (Ontario's
pretty big for those that do not know) and they have upgraded to a new
super-coverage system.  These tones are present on all frequencies in use
by this agency (it seems that anywhere you go in the province you can
search out a "beacon" tower emitting this signal.  Most likely before and
after you in the network.) and I would guess is used for syncing different
receivers and towers and/or mobile computer equipment (as well as keeping
scanner buffs from listening).  The way I understand it, the mobile radios
handle channel changes automatically (aka Trunking) and any mobile unit can
"punch up" any location in the province to talk to.  I don't have any
connections in this agency to know for sure but this is the way I
understand it.  BTW, these frequencies lie around 141, 171 and 179 MHz I
believe (Yes, several bands).

--
 Craig Lemon - Kitchener, Ontario. Amiga B2000  OS 2.04  UUCPv1.15D.


 ..!uunet!watmath!xenitec!lemsys!clemon         |       -- Raul, _UHF_
*** "Hi! I'm a signature virus.  Copy me into your .sig to join in!" ***

 
 
 

Wanted: Pro-2003 scanner mods, Bearcat/Uniden scanner

Post by Skip Sande » Tue, 21 Jan 1992 04:27:58

There is another (and more likely) reason for the tones on channel in between
dispatches... many duplex systems use tones to indicate to the mobiles that
there is a mobile talking to the dispatcher, so they won't "talk over" another
unit, since they can't hear other mobile units.  The LA Sherriff's Office
did this on their low-band system.
 
 
 

Wanted: Pro-2003 scanner mods, Bearcat/Uniden scanner

Post by Peter Stok » Wed, 22 Jan 1992 01:04:55

Craig Lemon - Kitchener, Ontario. Amiga B2000  OS 2.04  UUCPv1.15D. writes:

Quote:>       I believe this tone has more prupose than this because it is more
>than 1500 Hz tones as the originator describes.  They actually seem to be
>data bursts (ie. digital tower identification, see my other post on this
>agency's networking radio system)  While it serves the "scanner lock up"
>purpose I believe that there is more to it than that.

This topic has been churning through my head all weekend and I've
figured it out thus far:   In between voice transmissions, the base
station channels (there are many base stations all over Ontario)
broadcast some kind of data burst three times a second.  It seems two
of the 24 base station frequencies are very strong in my area (Kingston
Ontario) and usually only the second channel broadcasts the databursts
when the first is in use.  Thus police car radios in my area probably
use this to determine which channel is free to use.    The data in the
databurst might contain additional related info.   Mobiles do not seem
to transmit databursts.    During voice conversations, the databursts
stop and a PL tone (Private Line tone?) of 107.2 Hz is summed with the
voice signal.  This tone is inaudible and is known as CTCSS
(I forget what that stands for).

Short of buying a Bearcat 760XLT with CTCSS option card for
CDN$750.00 :-( two options exist for modifying my Pro-2003
scanner:

1.  continue scanning on detection of the databurst
2.  stop scanning on detection of the PL tone

The databurst fundamental is a 1500Hz tone and I've succesfully
implemented option 1 above using an LM567 tone decoder, a 555 timer and
a PNP transistor.  The only problem is that it takes approx 20ms of
databurst noise for the circuit to react, causing an annoying 20ms
"blip" out of the scanner speaker every time the police channel is
scanned.  My circuit interfaces to the IF chip (MC3357P) in the
scanner.

I'm contemplating solutions for option 2 although one serious
drawback is that it will prevent reception of any other
normal broadcast... unless I can make the mod to be channel
sensitive (e.g. watch for PL tones only on scanner channels
1 through 10).

I'm not close to an acceptable solution and welcome further
discussion on the topic.  

Peter

 
 
 

Wanted: Pro-2003 scanner mods, Bearcat/Uniden scanner

Post by Mr. Lyn R. Kenne » Mon, 20 Jan 1992 00:51:57



> -I'm confused.  If I tune in the channel, I hear 1500Hz tone bursts,
> -about three times a second, irritating!   This causes my scanner to
> -stop on the channel.   The tones continue until the base station
> -dispatcher decides to speak, at which point the voice is loud and
> -clear.   A friend of mine bought the Bearcat 760XLT with an optional
> -CTCSS tone board which allows one to key in the correct PL tone (in
> -this case the number is 107.2, corresponding to EIA standard "1B"),
> -eliminating the problem.  I don't know how the value 107.2 relates to
> -anything.   I would really like to mod my PRO-2003 though, so I can
> -listen to the cops again.    Help!

> 107.2 is the frequency (in hertz) of the subaudiable (PL (tm. Motorola)) tone
> that they are using.  It appears that they transmit that tone while talking
> on the radio, and your friend's radio is set up to only open the squelch
> while that tone is being transmitted.  The 1500 Hz tone could be either
> an 'ID' tone to signal a certain radio (like a pager) or perhaps some
> sort of data transmission.  They obviously wouldn't transmit the PL tone
> during this tone burst.

The 463 MHz medical channels here were installed with a similar system
which used a signal to indicate there was a mobile unit transmitting
even though it was not being repeated. The sound was closer to a busy
signal used on the telephones and I doubt the PL tone was dropped since
the normal users did not monitor anyway. Fortunately, enough boss types
did, and the system was converted to a normal repeater.

It's unlikely to be data. It may well be intended to annoy you. Wonder
if Canadian rules prohibit transmitting non-information? Be interesting
to know if it's really legal.

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