On 11/08/11 08:03, Chuck Forsberg WA7KGX N2469R wrote:
The FCC has decided GPS is worth saving ... but not necessarily all
current GPS receivers.
http://www.aero-news.net/index.cfm?do=main.textpost&id=1c898613-45b1-48a0-9d86-a767db2b017d
Root cause for interference is significantly changed dynamics
requirements on the GPS receivers, as side-bands would become stronger.
The dynamics has allowed for simple 1-bit or 1.5 bit receivers, where
1.5 bit receivers with separate level detection for AGC steering has
better supression of CW signal than straight 1-bit. Much work went into
few-bit ADC analysis in the early days, so the use is widespread. Using
say 8-bit ADC would allow for the C/A code to de-correlate the signal
further 30 dB down rather than letting the AGC be captured. That and
filtering.
One has to realize that the relative low interference have allowed many
small and cheap designs to evolve, for the benefit of mobile phone use,
tracking devices on packages etc. etc.
Reducing civilian receivers resistance to jamming would also potentially
reduce the effect of intentional jamming. Still, modern jamming
techniques should not see much of such effect, so I don't think the
green guys worry too much.
Cheers,
Magnus
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