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<cfhar...@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
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
