parnass@ihuxz.ATT.COM (Bob Parnass, AJ9S) (01/31/88)
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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)979-5414ron@topaz.rutgers.edu (Ron Natalie) (02/01/88)
WARNING: Listening in on mobile phone conversations is now against the law. So is telling people how to do it. Better watch out for the phone cops. -Ron