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

[Bruce Griffiths]

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
>
>