Xref: utzoo rec.ham-radio:3707 sci.electronics:1941
Path: utzoo!mnetor!uunet!husc6!rutgers!ames!pasteur!ucbvax!cbosgd!ihnp4!ihuxz!parnass
From: parnass@ihuxz.ATT.COM (Bob Parnass, AJ9S)
Newsgroups: rec.ham-radio,sci.electronics
Subject: Use a VLF rcvr to decode TV's secondary audio programming
Message-ID: <2547@ihuxz.ATT.COM>
Date: 18 Jan 88 01:12:35 GMT
Distribution: na
Organization: AT&T Bell Laboratories - Naperville, Illinois
Lines: 25
Keywords: SAP, subcarrier, television, tv


x
   Television stations can transmit 2 audio  signals  simul-
   taneously.   The  alternate audio information can be car-
   ried as the Secondary Audio Program (SAP), on an FM  sub-
   carrier.

   Area TV stations had not used SAP until December 20, when
   channel  9  provided  bilingual  coverage  for  a Chicago
   Christmas parade.  English was carried on the main  chan-
   nel,  and  Spanish was transmitted on a 78 KHz FM subcar-
   rier.

   One can tune a VLF receiver to 78 KHz FM (or use  AM  and
   slope  detection),  and  connect  its antenna jack to the
   earphone jack of the television tuned to the  appropriate
   channel.

   Instead of using my TV, I just tuned my ICOM R7000 to the
   191.775  MHz channel 9 WBFM audio carrier, then connected
   my ICOM R71A receiver to the R7000's  RECord  jack.   The
   R71A was set to the NBFM mode at 78 KHz.
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Bob Parnass,  Bell Telephone Laboratories - ihnp4!ihuxz!parnass - (312)979-5414