[TowerTalk] Original Hygain/Military-Commercial Products
jimlux at earthlink.net
Mon Dec 31 09:26:44 EST 2007
>From: Pat Barthelow <aa6eg at hotmail.com>
>Sent: Dec 31, 2007 5:57 AM
>To: Chris Pedder <chris at g3vbl.co.uk>, towertalk at contesting.com, aa6eg at hotmail.com
>Subject: Re: [TowerTalk] Original Hygain/Military-Commercial Products
>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.
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