IUBio

Hear radar waves

wdr at world.std.com wdr at world.std.com
Fri Nov 6 15:12:18 EST 1998


Harry,

Good point that FSK requires a BFO or equivalent for easy aural monitoring.
A classic oatmeal-box-and-diode crystal-set receiver
might receive FSK via slope-detection, but as baseband binary, no tones.
Most ham AFSK uses are too low a duty-cycle to resemble the symptoms
cited, unless the patient were in direct line of a high-speed directlional 
link of a packet network backbone or near a key node of a DX-Cluster
net.  Either would fade if the patient tried taking the subway to
the far side of town.

One of Moto's competitors in police mobile data terminals is a direct
spinoff of ham packet. They likely are using AFSK for that, which would
create one local, high power source of AFSK in communities using
PacketCluster brand MDT's -- unless they changed it to true FSK.    
I don't know what modulation Moto brand MDTs use, nor what the cellphone
or trunking radio control channels use.

POCSAG Pagers may not be AFSK (are they? I find references saying  it's
NRZ FSK), but they sure sound tone-like when demodulated with an FM
discriminator.   Even if POCSAG isn't itself AFSK, the framing
preamble of 576 alternating 0's and 1's would be an audio tone (at half
baud rate) and probably be slope-detectable by a natural detector
(filling, crystal radio)?  Pager transmitters are high power; they
attempt to blanket the urban area with enough power for tiny antennas
to receive the data even indoors.

(Note I'm playing devils advocate in setting aside the likely
conclusion of tinititus and exploring the possibility of an EM source
of Anna's perceived signal.  I have allergic reacionts to conspiracy
theories, dismissing new theories because they don't fit the old
theories, and dismissing old theories simply because they aren't
politically current.  That ATA now has objective tests for tinititus
suggests differential diagnosis using tests for each.  I'd lay odds
the patient has tinititus, but I'll consider the alternative as an
engineering problem.)

Cheers or 73,

-- 
Bill Ricker  N1VUX  wdr at world.std.com  "The freedom of the press belongs 
http://world.std.com/~wdr               to those who own one."--A.J.Liebling



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