[time-nuts] The Demise of LORAN (was Re: Reference oscillator accuracy)

[Lux, Jim (337C)]

A *much* more effective and cheap strategy is a repeater jammer.. Receive
the signal and retransmit it: two antennas and an amplifier. The victim sees
the delayed retransmitted signal at a higher level than the direct one. It's
sort of like creating fake multipath interference. No need for PN
generators, oscillators, etc.

Granted, a smart receiver that *understands* the relationship between SV to
user geometry and doppler can beat it (because the carrier phase and PN
phase of the repeated signal won't be consistent with the geometry), but the
run of the mill PN tracking loop probably won't.

Most inexpensive receivers use a single bit sampler, so a suitable CW tone
could also probably jam it effectively, but might require some knowledge of
the victim receiver to pick an appropriate frequency (i.e. You'd need to
know the sampling rate.)


On 11/15/09 4:39 PM, "Magnus Danielson" <magnus at rubidium.dyndns.org> wrote:

> Chuck Harris wrote:
>> Magnus Danielson wrote:
>>> Chuck,
>>> 
>>> Chuck Harris wrote:
>>>> What makes you think it needs to be CW, and cannot be pulsed and
>>>> chirped?
>>> 
>>> May I roll in a noise jammer into the debate?
>> 
>> Absolutely!  They can be extremely power efficient.  Raise the noise
>> floor in the vicinity of the receiver, and it is all done.
>> 
>> Probably the easiest solution would be to take a PN source and use it
>> to drive a pulser that pulses a chirp oscillator.  If you are feeling
>> really polite, you could put a bandpass filter on the thing to protect
>> other services.
> 
> The schematic out there is a PN source feeding an OCXO and then
> amplified. Crystal loop to keep fairly centered. More or less the same
> as personalized phone jammers do. Very simple design.
>