Hi Ed, It's not just just "cheap and nasy" regens that cause this problem. Some aircraft navigation and communication receivers where found to have enough local oscillator harmonic leakage at 1575 MHz through the antenna port to jam GPS then tuned to specific frequences. The cure was a tuned stub filter on the Nav or Comm. see http://www.aircraftspruce.com/catalog/avpages/tednotch.php for an example. Robert G8RPI.
________________________________ From: ed breya <[email protected]> To: [email protected] Sent: Thursday, 5 July 2012, 22:03 Subject: Re: [time-nuts] gps jamming source found The wireless data links in those R/C sensor type things don't operate near GPS carriers, but their harmonics can land there. The transmitted power allowed should be too small to interfere with anyone's receiver farther away - yours is probably pretty close. I believe that the remote senders do not wait for any polling signals - if so, they would have to be receiving on a regular basis, taking precious battery life. It makes more sense for them to just burst transmit at regular intervals, while the line-powered (or bigger-battery-powered) base station is always listening, or listens at various intervals to see if any remotes are calling. That's why it takes a while to get the initial temperature data when the system starts up. The base station receivers used for simple, cheap VHF data are typically super-regenerative type for high sensitivity, so when they're fired up it may appear that they're transmitting, but actually are only receiving, with lots of crap kicking out of the super-regen circuit. A common carrier used for VHF remotes is around 315 MHz - the fifth harmonic of that one is especially bad, landing almost right on top of GPS. When you add in the loose frequency stability and modulation, and the regen signals, the transmitters and receivers can cause quite a spectral mess. Ed _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
