[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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