FAX EAVESDROPPING TECHNICIAL DATA FOR
COUNTERMEASURES PROFESSIONALS
By: euroforce@aol.com (EuroForce)

EDITORIAL NOTE: Fax monitoring is illegal except by permission. This information is being provided as technical information for countermeasures professionals.

On the basis that I do not know your technical skill level, I will try to explain the mechanism involved in the Fax recording task. In order to replay a "fax-analogue" recording a few things
have to happen:

Firstly:
When you record a "fax-encoded" signal it is important that you use a ultra stable dual track audio recorder, which has the automatic gain control disabled.

• Step 1- Your recording equipment:
• 
  
• Use Track 1:
• As your "Fax-encoded" audio track, monitoring the audio level
• very carefully.
• 
  
• Use Track 2:
• Record a 1200 Hz(US) 1000 Hz(Europe) square wave signal
• from a crystal source.
• 
  
• 
  
• Step 2- Your replay equipment:
• 
  
• Playback your "fax-encoded" audio signal; in a phase lock loop
• circuit, comparing the 1200Hz reference signal against a stable
• 1200Hz external crystal source.
• 
  
• 
  
• Step 3- The small black box:
• 
  
• Go to your local library, or call Rockwell in the US and call their
• applications engineer for a data sheet and application note on
• their fax/modem encoder chips. Their is a mod which enables
• you to decode, without using handshaking.