-----Original Message-----
>From: Pat Barthelow <aa6eg@hotmail.com>
>Sent: Dec 31, 2007 5:57 AM
>To: Chris Pedder <chris@g3vbl.co.uk>, towertalk@contesting.com,
>aa6eg@hotmail.com
>Subject: Re: [TowerTalk] Original Hygain/Military-Commercial Products
>
>
>Folks:
>
>
>I have often wondered, if the LP design for Military/Embassies, was selected
>for broadband capabilities, which might be needed if secure HF comms
>used/needed spread spectrum modulation, back in the "olden days" of comms
>over HF.
More likely, just that there's no need for tuning, and the fact that they can
run extra power to make up for the difference in gain over a narrow band
Yagi-Uda type antenna.
HF spread spectrum systems using direct sequence spreading would typically not
use a very huge spread bandwidth, because the ionospheric channel isn't all
that wideband (i.e. if propagation only supports 7.3 to 7.6 kHz, there's not
much point in transmitting a signal that goes from 4.5 to 10.1 kHz). A spread
bandwidth of a few hundred kHz would be typical. (And would still give you a
process gain of 20dB or so)
A frequency hopper that hopped at, say, the symbol rate, would be moving too
fast for an autotuner to keep up, so a broadband antenna would be useful there,
too.
>
>Someone once told me, that, long before Spread Spectrum became familiar in
>the ham radio vernacular, that the term "Spread Spectrum" was itself
>classified, could not even be said openly, among the military/spook crowd.
Probably true, but that would have been 50s, perhaps 60s, era. R.C.Dixon
published Spread Spectrum Systems in 1976. Lots of people were thinking about
it and discussing it before then. About the time that PLL synthesizers &
microprocessors became common, it became possible to do FH fairly easily, and
there were a number of "retrofit" FH radios around.
Jim, W6RMK
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|