parnass@ihu1h.UUCP (Bob Parnass, AJ9S) (02/24/85)
x
Update: Eavesdropping on SCA Transmissions
A few weeks ago, I posed a question about listening to
SCA transmissions on the FM commercial broadcast band.
An article in _M_o_n_i_t_o_r_i_n_g__T_i_m_e_s claimed that connecting
a vlf receiver to an FM broadcast receiver would permit
SCA detection.
Necessity being the mother of invention, a way was
found to confuse the ICOM R71A into tuning below 100
kHz1, and after receiving substantial inspiration from
Will Martin, Phil Karn, and others I now can report
success!
With the R71A in the FM mode, tuned to 67 kHz, I con-
nected the ICOM's vlf antenna input through a 0.1 ufd
capacitor2 to the earphone jack of a $16 General Elec-
tric AM/FM portable radio, and can now listen in on the
world of SCA!
In the first few minutes of tuning around, I've heard
the Physicians' Network, Muzak, commodity reports, and
several data transmissions.
Thanks again for the help!
__________
1. Parnass, Bob, "Trick the ICOM R71A below 100 kHz", to be
published in _M_o_n_i_t_o_r_i_n_g__T_i_m_e_s_.
2. The capacitor is needed with the GE radio I used to
block DC.
--
===============================================================================
Bob Parnass, Bell Telephone Laboratories - ihnp4!ihu1h!parnass - (312)979-5414 ERWINVL.DLOS@XEROX.ARPA (02/26/85)
BOB,
SOUNDS LIKE A LOT OF TROUBLE JUST TO LISTEN TO SCA. I HAVE BEEN
LISTENING TO SCA FOR AROUND 8 YRS NOW. LOOK AT ONE OF THE OLDER
SIGNETICS APPLICATIONS BOOKS AND THERE IS A SLICK LITTLE CIRCUIT THAT
WILL ALLOW YOU TO DO IT WITH A 565 PHASE LOCK LOOP CHIP. THE 565 DOES
THE DETECTION AT 67 KHZ WHICH MEANS THAT YOU DON'T NEED TWO RECEIVERS!!.
JUST TUNE THE FM RECEIVER AND THE PLL DOES ITS THING!!
REGARDS,
VAL L. ERWIN
W5PUTparnass@ihu1h.UUCP (Bob Parnass, AJ9S) (03/07/85)
> SOUNDS LIKE A LOT OF TROUBLE JUST TO LISTEN TO SCA. I HAVE BEEN > LISTENING TO SCA FOR AROUND 8 YRS NOW. LOOK AT ONE OF THE OLDER > SIGNETICS APPLICATIONS BOOKS AND THERE IS A SLICK LITTLE CIRCUIT THAT > WILL ALLOW YOU TO DO IT WITH A 565 PHASE LOCK LOOP CHIP. THE 565 DOES > THE DETECTION AT 67 KHZ WHICH MEANS THAT YOU DON'T NEED TWO RECEIVERS!!. > JUST TUNE THE FM RECEIVER AND THE PLL DOES ITS THING!! > > REGARDS, > > VAL L. ERWIN > W5PUT Thanks for the advice, Val. I built the Signetics 565 circuit in my lab, but alas, it doesn't work! The detector output of the average AM/FM radio is not high enough to drive the 565. An additional stage of amplification is needed. I spoke with the proprietor of FM Atlas, who had the same results with the 565 circuit. Please post details of the simple circuit you've been using to detect SCA for 8 years. I might experiment with the XR2211 next, but it's a $6 chip. The 565 was on sale at Radio Shack for $1.19. -- =============================================================================== Bob Parnass, Bell Telephone Laboratories - ihnp4!ihu1h!parnass - (312)979-5414