Xref: utzoo rec.ham-radio:3763 sci.electronics:1974
Path: utzoo!utgpu!water!watmath!clyde!rutgers!uwvax!oddjob!gargoyle!ihnp4!ihuxz!parnass
From: parnass@ihuxz.ATT.COM (Bob Parnass, AJ9S)
Newsgroups: rec.ham-radio,sci.electronics
Subject: Convert your cordless telephone to 800 MHz
Message-ID: <2585@ihuxz.ATT.COM>
Date: 31 Jan 88 02:53:25 GMT
Organization: AT&T Bell Laboratories - Naperville, Illinois
Lines: 52


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          CONVERT YOUR CORDLESS TELEPHONE TO 800 MHZ?

                     by Bob Parnass, AJ9S

   Convert your cordless telephone to receive 800 MHz?  Yes,
   I'm quite serious.

   How do you convert a 47 MHz cordless phone  to  800  MHz?
   With a converter, of course!

   But you don't need a fancy $99 Hamtronics converter.  All
   you  need  is  the  UHF tuner from a spare television set
   that was manufactured when  TVs  still  covered  channels
   14-83.  I used the solid state, tuneable UHF tuner from a
   cheapie JVC television set given me a few years ago.

   This tuner seems typical of the type available in TVs for
   the  past  several  years.  It uses a variable capacitor,
   not a varicap diode,  to  tune  channels  14-83  (470-890
   MHz),  and  convert  them  to an IF of 47 MHz.  If 47 MHz
   sounds familiar, that's because it is the upper  edge  of
   the  cordless  telephone  band.   A cordless telephone is
   just a full duplex 46-47 MHz FM receiver and 49-50 MHz FM
   transmitter in the same case.

   Since I don't own a cordless  phone,  I  used  a  scanner
   tuned  to 47 MHz and connected its antenna jack to the IF
   output of the TV tuner.  My  tuner  required  a  300  ohm
   impedance  antenna,  so  I  placed  an  ordinary TV balun
   between the tuner input and my scanner antenna.

   The IF is pretty broad - at  least  10  MHz,  so  I  tune
   around  on  my  scanner,  rather than use the very coarse
   tuning control on the tuner itself.

   This tuner lacks an RF amplifier, so it's not  as  sensi-
   tive  as  a modern 800 MHz scanner, but I sure hear a lot
   of stations between 460 and about 890 MHz!

   My tuner works well when powered at 6-9 VDC, and since it
   only  draws  about  10 milliamps, I use a 9 volt alkaline
   battery.  An article in January 1988 Ham  Radio  Magazine
   describes  other TV tuners, and suggests ways to put them
   to good use.

   WARNING:  Listening in on mobile phone  conversations  is
   now against the law.
-- 
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Bob Parnass,  Bell Telephone Laboratories - ihnp4!ihuxz!parnass - (312)979-5414