[time-nuts] gps jamming source found

Michael Blazer mblazer at satx.rr.com
Thu Jul 5 23:41:14 UTC 2012


A badly tuned/designed super-regenerative receiver can put out a lot of 
garbage. For commercial products, the receiver needs FCC approval to 
ensure this doesn't happen.

Mike

On 7/5/2012 4:03 PM, ed breya wrote:
> 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 -- time-nuts at febo.com
> To unsubscribe, go to 
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>





More information about the time-nuts mailing list