|Dec 22, 2012, 12:14 AM|
NEXRAD radar interference info
While the number of RC flying fields that are close to a NEXRAD weather radar site are small, I know from RCG searches that there are at least several others that have suspected radar interference problems.
I just posted an article on my soaring club's RCG forum here that explores how the NEXRAD radar works and when/why RC interference might result.
January 6, 2013 Update:
Several days after my original NEXRAD post on our club forum I received a nice email from club member Jonathan Heritage offering some great feedback. In it he suggested that using the Friis Transmission Equation we might get a better idea of how closely we could fly to the NEXRAD radar ball before our 2.4gHz receivers get swamped out from the high power radar pulses. After running some quick numbers Jonathan's well-reasoned conclusion was that our planes should be safe as long as we don't get too close. Since we aren't seeing very many control issues in that quadrant of the sky he's no doubt right.
I decided that it would be helpful to build a spreadsheet that implemented the Friis equation and then apply it at various points on our flying field. The basic idea was to calculate how much NEXRAD power would be received at a plane's 2.4gHz receiver antenna terminals compared to our RC transmitter signals.
So here's the net conclusion from this analysis. At the worst possible field location point "I" (i.e. farthest from where pilots stand with their transmitters and your plane is closest to the NEXRAD ball while still being visible) the received radar signal is 90 decibels greater than the received RC transmitter signal. i.e. 1,000,000,000 times stronger. To put it another way, the NEXRAD is pumping 43 milliWatts directly to the receiver terminals which is similar to what it would be if your plane was on the ground and you had your TX antenna several feet away.
I agree with Jonathan that you should be safe if you don't get too close but if your plane is out toward the radar ball AND lower than launch height AND you are at the edge of being able to see it, good luck buddy, you're asking for it.
The spreadsheet is available on the RC Info Share website in the File Cabinet page. Note the second Excel tab is where the NEXRAD signal comparison calcs are made. The first tab is for the Friis calculator by itself.
I welcome feedback and comments.
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