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

J. Forster jfor at quik.com
Mon Nov 16 00:38:14 UTC 2009


Even 10 KM is pretty useful. If the thing were solar powered with a
supercap "battery" it could easly transmit for say 2 minutes per hour w/
significant power. It'd be hard to find if the on times were generated by
a multiple fedback CMOS shift register.

-John

================


> Mike
>
> Instead of relying on the dubious claims of those marketing an extremely
> inefficient jammer it would be better to actually do some simple
> calculations.
>
> Typical commercial receivers stop tracking with a Jam to signal ratio of
> not more than 60dB or so:
> http://www.gpsworld.com/gps/jamming-gps-778
>
> The input signal level at the receiver input is around -160dBW.
>
> A 1W ERP source with an isotropic hemispheric radiation pattern will
> exceed the the required jamming signal strength for distances less than
> several tens of kilometers.
>
> This estimate is consistent with the fact that LO parasitic radiation
> from TV systems on boats have been known to jam GPS for distances of
> several kilometers.
>
> Bruce
>
> Mike Monett wrote:
>>    Chuck Harris<cfharris at erols.com>  wrote:
>>
>>    >  I guess the point you folks aren't getting is you can make  a very
>>    >  effective local GPS jammer that runs off of a 9V  transistor radio
>>    >  battery, and  will  last for several weeks. It can be  done  for a
>>    >  total cost  of  a  few bucks per jammer....  search  the  web, the
>>    >  designs are out there.
>>
>>    >  Toss the  GPS jammers indiscriminately around  the  landscape, and
>>    >  you put GPS out of business for a very low cost.
>>
>>    >-Chuck Harris
>>
>>    I'm not so sure that would be very effective. A typical  9v alkaline
>>    contains about 900 milliamp/hours at low current drain.
>>
>>    Two weeks  is  24 * 7 * 2 = 336 hrs. Assuming  100%  efficiency, the
>>    battery would  supply  0.9  / 336 =  0.00267A,  or  0.024  watt, not
>>    including the drop in voltage after the first few dozen hours.
>>
>>    There are  quite a few commercial jammers  designed  specifically to
>>    jam GPS signals. These are extremely illegal, but they do  give some
>>    idea of the range that could be expected.
>>
>>    Below is  a list of the specified range and power.  I  calculate the
>>    highest ratio to get the meters per watt.
>>
>>    GMW12 Cellular&  GPS L1 Jammer
>>
>>    Block cellular signals and GPS L1 system in the same time
>>
>>    Jamming Range : Average 40 meters radius
>>    Output Power  : Total 6.5 Watt
>>
>>    ratio : 40/6.5 = 6.15 meters/watt
>>
>>    <http://www.tayx.co.uk/gmw12-gps-mobile-jammer.html>
>>
>>    KYG0014 Fixed Jammer
>>
>>    Output Power  : 2000mw
>>    Jamming Range : 15~20 meters
>>
>>    ratio : 20/2 = 10 meters/watt
>>
>>    <http://www.alibaba.com/product-gs/204091726/Fixed_GPS_jammer.html>
>>
>>    KYG0017 Powerful GPS signal jammer
>>
>>    Output power : 25W
>>    Range        : radius 100-300meters
>>
>>    ratio : 300 / 25 = 12 meters/watt
>>
>>
>> <http://www.alibaba.com/product-gs/213377763/Powerful_GPS_signal_jammer.html>
>>
>>    KYG0013 Car GPS jammer
>>
>>    Output power : 800mW
>>    Range        : radius 10-15 meters
>>
>>    ratio : 15 / 0.8 =  8.75 meters/watt
>>
>>    <http://www.alibaba.com/product-gs/204037628/KYG0013_Car_GPS_jammer.html>
>>
>>    KYP0050 Handheld GPS/GSM signal Jammer / blocker
>>
>>    output power  : 300mw
>>    jamming range : 2~10 meters
>>
>>    ratio : 10 / 0.3 =  33.33 meters/watt
>>
>>
>> <http://www.alibaba.com/product-gs/206648711/KYP0050_Handheld_GPS_GSM_signal_Jammer_blocker.html>
>>
>>    The average ratio is:
>>
>>    (33.33 + 8.75 + 8.75 + 12 + 10 + 6.15) / 6 = 13.16 meters/watt.
>>
>>    The highest claimed performance is the KYP0050, with 33 meters/watt.
>>
>>    Assuming the  9V  battery jammer has 100%  RF  efficiency  and equal
>>    ratio, the  jamming range would be 33.33 * 0.024 =  0.799  meters or
>>    about 2.62 feet.
>>
>>    However, a  jammer  would   require   crystal   control  to  stay on
>>    frequency. There  are no crystals for L1, so a  multiplier  would be
>>    needed. The  actual power output would be much lower,  so  the range
>>    would be much less.
>>
>>    Another example,  a 1500mAh rechargable pocket jammer has a  5 meter
>>    range, and only lasts 2~3 hrs:
>>
>>    GMT04 Pocket GPS Jammer
>>
>>    Jaming Range      : Average 5 meters radius
>>    Current&  Voltage : 200mA DC12V / AC120~140V
>>    Battery           : 1,500mAh
>>
>>    battery life 2~3 hours, recharge needs 3~4 hours
>>
>>    <http://www.tayx.co.uk/gmt04-pocket-gps-jammer.html>
>>
>>    So a  9V transistor radio battery jammer doesn't seem like  it would
>>    present much of a danger.
>>
>>    Mike Monett
>>
>>
>
>
>
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