Imbedded Aerial Cameras Re: Radio Scanners At Airshows SecurityRisk!?/Radio Inteference At Airshows & Potential New Services Re:[MilCom] Airshows / Scanners...

[David I. Emery]

On Thu, Apr 26, 2007 at 06:53:08PM -0400, Bill wrote:
> The encryption can be turned on or off as needed.

	There are two technologies common here - wide-band FM video
(universally used until recently for remote cameras and ENG) and much
newer MPEG2 or MPEG4 based digital systems using OFDM (DVB-T) or QPSK or
QAM digital modulation on the microwave carrier - almost always carrying
a packetized digital MPEG video transport stream.

	Encrypting analog video is possible, but the gear to do so is
expensive and somewhat finicky especially if the signal quality is
variable because the signal  fades in and out.

	Encrypting digital video is a well established and mature
technology in the satellite and cable worlds - and there are standards
for how to do so and lots of gear for doing so available - at rather
little additional cost provided one does not need military grade high
security encryption.

	Many digital microwave video systems use standards based off the
shelf technology - such as DVB-S or DVB-T modulation, MPEG 2 compression
and transport streams and other standard features.   This makes it
possible to intercept them with commercially available digital video
gear.   Other systems may use proprietary standards and protocols, but
doing this with something as complex as digital video is expensive...

	FM video - analog - is readily received with simple receivers
including many left over from the backyard BUD dish TVRO era...

	One can readily tell which mode is in use on a given system by
watching the picture when the signal starts to fade.   FM video develops
very characteristic black "sparklies" (tails) on the sharp  contrasty
edges of objects and sometimes on the body of brightly colored objects
(especially reds and oranges).   Digital video starts to develop
macroblocks (square blocks several scan lines big) or drop out suddenly
altogether or freeze the image momentarily.

	Anyone with any video experience can see this difference
immediately though digital encoding of noisy analog video often has
blocking artifacts due to the inability of the compression to handle the
all the randomness from the analog noise in the original source.   Thus
the thing to look for is the sparklies which means FM analog is in the
path somewhere... and likely the part of the path one might be able to
monitor...

-- 
   Dave Emery N1PRE,  die at dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."