Hardware:Data Slicers

From Trunker

Data slicers are the hardware which is needed to make the various TRUNKER programs operate.

They come in two (2) versions, a two (2) level and a four (4) level data slicer.

The 2 level or original slicer is can handle Motorola and EDACS formats with no problems. Can also be used for paging protocols like Golay and POCSAG (http://en.wikipedia.org/wiki/POCSAG).

The 4 level slicer is useful for other protocols like Flex (http://en.wikipedia.org/wiki/FLEX_%28protocol%29) paging.

Schematics for various slicers:

On 11 Apr 1997 16:30:43 GMT,
in the newsgroup rec.radio.scanner,
bich@scd.hp.com (Bich Tran) 
from Hewlett Packard thoughtfully posted:

> Boy, I received so many email regarding my future mdt-hacked program.
> Some reported failure to make circuit work. Here are some of the pitfalls
> you should watch out when building the MDT ckt, ( this is my experience only):
> 1. The +/-12V generator subckt is marginal. If the opamp is drawing too
> much current, the -12V line will be overloaded and drops to almost 0 volt!
> Enough to stop the ckt from working.

The LM741 draws about 1.5mA, and the serial port should be able
to source at least 10mA. Some laptop serial ports may not be able
to source much current. Use as large of supply filter capacitors
as possible to prevent "sagging". 

Make sure you are using 1N4001/2/3/4, 1N914 or 1N4148 diodes.

The circuit, as given in the original documentation, *will* work.
However, some have reported difficulties. Excluding wiring
errors, I think this may be a signal level/discriminator loading
problem. If you are having problems, please post which circuit
you are using and the type of radio used. I bet we will find some
correlations!

> SOLUTION: use a small dual DC/DC converter, such as the BurrBorwn PWR1205
> to convert a 5V to +/-12V. Of course a drawback of this approach is an
> external 5V power supply.

If you have access to these, why not just use a low-supply
current part? Like an OP-21? LF441? (Careful, some micropower
parts are only good up to +/-8V).

> 2. If you are using a cable extender to connect your ckt to your computer, like
> my does), beware of the object/mirror phenomenon. So pin 5 (ground) should
> be pin 1 on the mating connector, etc... The pin number listed on the
> schematic is only the pin on computer side, so to be on the safe side use
> a continuity checker to trace the signal line before soldering the connection.

True. And also watch long cable lengths. Some op-amps cannot
drive high capacitive loads, and will self-oscillate. If you find
yours is oscillating, place a 100 ohm resistor between the output
and the cable.

> 3. Any dual power opamp will work: I both successfully use a TL072, and a
> comparator LM393.

I recommend the use of JFET input type op-amps
(TL071,TL081,LF411,LF351,etc). The input impedance is 10X higher,
and the input bias current 10x lower than the 741. With the
higher input impedance, you can increase the size of the
resistors 10 times (ie:10K=100K, 100K=1Meg, etc), thus reducing
the loading of the discriminator circuitry.

For various reasons, an isolation resistor and the input
capacitor should be mounted *inside* the radio. Bringing the
discriminator output directly to the outside is not recommended
(RFI, danger of shorting, etc). I recommend you connect a
isolation resistor and cap in this fashion:

		      C1     connecting wire
Tap point--10Kohm----0.1uF-------------------rear panel jack<

If you use a shielded connecting wire, ground the shield at the
panel. C1 is the input cap of the "interface".

NOT ALL DISCRIMINATOR OUTPUTS ARE ALIKE! What works with one
radio, may not work on another. A minimum of 20-50mV p-p is
required for a good "copy".

Recommended Circuit: The "Schmidt Trigger circuit"
--------------------------------------------------

This is the circuit for *JFET* type op-amps!!! NOT 741's!!

  C1(mount inside radio)
  0.01 uF                    |\ +12v
---||----O------------------|- \|
AF IN    |                  |LF \	 R4 (opt)
----     |                  |411/-O---/\/\/\------ Data Out
    |    \  R1        ------|+ /|  |     100       CTS (pin 5/8)
    |    / 1Mohm      |     |/-12v |
    |    \            |     R2     |    GND ------ GND (pin 7/5)
   GND   /            O---/\/\/\---- 
         |            |    1Meg 
	 |	      |
         |            \        N.B. Pin Numbers for com port are
        GND           /  R3    given as x/y, where x is for a 25
                      \  10K                  way, y for a 9 way.
                      /
                      |  Op amp is a TL071,TL081,LF411,LF351,etc
                     GND      

R3 determines the hysteresis level (determined by ratio of
R2/R3). R4 is optional, use if driving long cables. Note that C1
is smaller, too.

Simpler circuit:
---------------

  C1
  0.01 uF                    |\ +12v
---||----x------------------|- \|
AF IN    |                  |LF  \	R2 (opt)
----     |                  |411 /-x---/\/\/\------ Data Out
    |    \  R1        ------|+ /|        100       CTS (pin 5/8)
    |    / 1Mohm      |     |/-12v  
    |    \            |                 GND ------ GND (pin 7/5)
   GND   /            x
         |            |    
         |            |       N.B. Pin Numbers for com port are
        GND           |        given as x/y, where x is for a 25
                      |                       way, y for a 9 way.
                      |
                      |  Op amp is a TL071,TL081,LF411,LM351,etc
                     GND  

This circuit is more sensitive to noise, and should only be used
on strong signals.    

An oscilloscope is invaluable in troubleshooting these circuits.
If you have access to one, use it!

> Please advice me how to post the binary file, since I don't want to offend
> those sensitive souls who dislike seeing binary files posted in the newsgroup

Don't! You will probably be contacted by folks willing to place
it on a FTP site for you.

Good Luck!

Cheers,
Paul Grohe
--------------------------------------------------------------
 Paul Grohe                     National Semiconductor Corp.
 Sr. Electronics Technician     2900 Semiconductor Drive
 Standard Products Apps Group 	Mail Stop C2693
 grohe@galaxy.nsc.com           Santa Clara, CA. 95052-8090 USA
 (408) 721-7389 Tel             (408) 721-2513 Fax 
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