Intelligence Update (fwd)

[Steve Schear]

>At 11:11 PM 1/30/97 -0800, you wrote:
>>>Note: According to a recently obtained DOJ surveillance training manual:
>>>"The typical range for the 28 ghz devices is six miles, the typical
>>>range of the 2.4 ghz is thirty miles, and the typical range for the
>>>1.7ghz  is 44 miles."
>
>How sure are you about the quality of your sources here?
>I'd expect 1.7ghz and above equipment to require line of sight,
>and even a range of six miles seems really high for a very low power
>device - getting that as "typical" seems pretty unlikely.
>Could all of these figures have been 6, 30, and 44 _meters_ instead? :-)

While these claims may be for links under near ideal conditions, Hams
routinely make very long distace links at 900, 2400 and 5700 MHz during
contests using less than 1 Watt.  Also, our deep space probes operate many
links to earth in this spectral region using low power transmitters.  Of
course they have 200 ft. antennas (e.g., Goldstone) at the receiveing end
with cryogenic reciever front-ends.

Links do become increasingly line-of-sight above 1 GHz this is radio not
visual (i.e., shots through trees. etc.) and there is increasingly the
ability to utilize reflection ("billboard" shots) advantageously.

As frequency increases path loss also increases.  Fortunately, as
frequencies increase antenna gain also increases.  In fact, by holding
antenna dimensions constant (for an arbitrary antenna design, e.g.,
parabolic) gain increases with frequency in direct proportion to increasing
path loss, thus cancelling it out.

There are other factors, such as required S/N or bit error rate for the
particular application, reciever sensitivity and noise floor, and
background noise levels, which directly affect link margins (transmit power
- path loss - reciever sensitivity; all in dB) and thus viability of a
link.  Above 1 GHz terrestrial noise, including that produced by man,
declines rapidly at the moment.  However, as more UHF communication devices
and microprocessors operating at 100s of MHz proliferate that noise floor
is sure to rise.

--Steve