Decoding

Decoding Digital Data from the
airwaves has never been easier!

Hey, this is nothing new, but I am surprised at the
number of hobbyists who haven't yet taken a shot at
decoding digital data from the airwaves. Not only
is this not new; but it's easier and cheaper than ever!

The hell of it is, there is getting to be less and less to
hear out there on the airwaves, but at the same time
there is more and more to decode! Instead of having
to give up radio and take up knitting or crocheting
there is every reason to dig deeper into radio.

More and more 2-way radio users are seeing the
economics and reliability of cellular and PCS
communications. There is no reason anymore for Joe's
Pizza Shoppe in Nowheresville, USA, to have to rely
on expensive and unreliable 2-way voice radio systems,
and costly monthly repeater fees and maintenance.

The coming years will give us less and less to hear, but
more and more communications are going digital data.
Contrary to popular opinion, most data signals are not
encrypted; rather, they're some variant of a plain ASCII
format that's easily read and processed by an ordinary
computer......the kind you're reading this with, no less!

Cutting to the chase, it is well within the casual hobbyist's
grasp to decode the following types of non-voice signals:

Trunk System Control    Mobile Display Terminals (MDT)
Mobitex Systems            Fax
Packet (ham)                   Morse Code (CW)
Pagers <illegal?>            RTTY

All you need to explore decoding digital data from the
airwaves are the following items:

Any 800 MHz Scanner (cellular not required) *
Computer, 386DX/33 or better
Free or low cost software (a lot is free)
A simple 2-Level FSK Data Decoder Interface <see below>

* The scanner must have a simple modification commonly
known as the "NFM Discriminator Mod" or the "baseband
audio mod". Don't freak out - it's easy and relatively
non-invasive. Click here for how to do that mod.

If you are into scanning at all, you already have the
scanner. You're reading this, so you already have the
computer. The software is freely available around the
Internet, much of it free for the downloading. The only
thing you probably don't have is the 2-Level FSK Data
Decoder Interface. But guess what?

This 2L-FSK Data Decoder Interface is cheap and easy to
build, even if you're not a technologist. And if rounding up
all the parts and/or "rolling your own" isn't your cup of tea,
there are a couple of other attractive options for you!

First, for those who can build their own, I wrote a detailed
plain text file (with ASCII drawings) that tells it all in great
detail. Furthermore, this file is absolutely and militantly free!

Heck, click here to see for yourself!

There is another type of interface called a 4-Level FSK
Data Decoder Interface, that's required for certain kinds
of signals (FLEX, ReFLEX, etc.) but it is somewhat more
complicated and not needed as a general rule. Click here
for more information on the 4LFSKDDI, if you're interested.
The rest of this article is on the simpler 2LFSKDDI.

Okay, okay, okay, if you don't "roll your own", or if you need
hard-printed instructions, photos, etc, here are three options:

There isn't much of a technical obstacle to "rolling
your own 2-Level Data Decoder Interface, but if lack
of time, tools, or access to the parts is an obstacle,
then you can acquire one in any of these ways:

1. Laser-printed    Instructions:   $5, ppd/USA; add $2.00 S&H, foreign

Includes:
Eight pages of detailed step-by-step instructions, including
hi-res photos, drawings, tables, charts, and parts list using
Radio Shack catalog numbers. This is an Instruction Set only;
you acquire the parts and materials on your own and assemble
the 2-Level FSK Data Decoder Interface on your own.

-=OR=-

2. Kit of essential parts (you build it):   $15 + $8 S&H, USA

Includes:
3 ea Capacitor; tantalum; 10-uF/16v:
1 ea D-sub Plastic Hood/shell; DB25
1 ea DB25 connector; female; solder pin
2 ea Resistor; 100-k; 1/4-watt
1 ea Resistor; 3.3-k; 1/4-watt
4 ea Diode; silicon; 1N4148
1 ea Op-amp; LM741CN; 8-pin DIP
1 ea Perfboard; pre-cut, notched, trimmed to size
1 ea Shielded cable; 3-ft; w/RCA plug
1 ea Detailed printed instruction set, complete with
      graphics, photos, tables, and "what if's"...
1 ea 3.5" floppy disk w/shareware & freeware decoder
      programs and utilities.

Optional upgrade or add-on items:

* A. Shielded cable; 6-ft; w/RCA plug      + $2.00
* B. Shielded cable; 12-ft; w/RCA plug     + $4.00
C. Port Adapter; DB25 male-to-DB9 female + $7.50
      (adapts the 25-pin Interface to a 9-pin comport)

* Instead of the standard 3-ft cable w/RCA plug

-=OR=-

3. Assembled/tested Decoder Interface:   $40 + $8 S&H, USA

Includes:
1 ea Data Decoder Interface built into a DB25 shell
      with standard 3-ft shielded cable w/RCA plug.
1 ea Detailed printed instruction set, complete with
      graphics, photos, tables, and "what if's"...
1 ea 3.5" floppy disk w/shareware & freeware decoder
      programs and utilities.

Optional upgrade or add-on items:

* A. Built with 6-ft shielded cable and RCA plug + $2.00
* B. Built with 12-ft shielded cable and RCA plug + $4.00
C. Port Adapter; DB25 male-to-DB9 female        + $7.50
    (adapts the 25-pin Interface to a 9-pin comport)
D. Custom enhancements/designs per your specs   +$10/up

* Instead of the standard 3-ft cable w/RCA plug

TO ORDER: Use e-mail, fax, or postal mail per the
           information in my signature box below.
           MC/VISA or M.O. preferred ($10 minimum order).
           Personal and company checks okay, but shipment
           delayed until bank clearance. No COD's and no
          shipments to PO Boxes or mail drops. Alaska,
           Hawaii and foreign shipping extra.

TERMS: All sales are final; no returns-no refunds.
        30-day Performance Warranty on the Assembled/
        Tested Decoder Interface is strictly limited to
        Motorola SmartNet trunked data signals using
        TRUNKER.EXE despite that it will work on many
        other kinds of data, too. We just can't support
        it all. Repair or replacement at our option
        during that 30-day period. No warranty on Kits
        and/or Instruction Sets.

        Not responsible/liable for illegal use of this
        information and/or these products; nor for any
        consequences thereof. You must determine lawfulness
        of these products for your applications and region
        and not use them, if illegal.

Use of this information and/or these products is
100% exclusively at your own risk.

        You must determine suitability and fitness of purpose
        of these products to your needs. I will not accept
        responsibility or liability for any damage or loss that
        results from use of these products, nor for damage or
        loss that results from connecting these devices to a
        scanner and/or a computer. You must determine all risks
        and accept all consequences of any damage to hardware
        and/or data stored in the computer.

============================================
Bill Cheek - President/CEO/Publisher
COMMtronics Engineering/World Scanner Report
Box 262478 ~ San Diego ~ CA ~ 92196-2478
Voice: 619-578-9247 (1:30-5:30pm, PST, M-F)
Fax: 619-578-9247 (any time, day/night)
E-mail: bcheek@comtronics.net
Web: http://www.comtronics.net
============================================