[RFI] Alarm Systems and EMI/EMC

[Jim Brown]

On Sat, 09 May 2009 22:24:11 -0700, Michael Tope wrote:

>Yes, the keyless entry on my wife's camaro gets blocked up on Mt. Wilson 
>above
>Los Angeles where the big antenna farm  is located (all manner of 
>repeaters, paging
>transmitter, TV transmitters, FM radio transmitters, etc). If you don't 
>have a physical
>key, you are SOL to get back into the car. The keyless entry just didn't 
>work at all.

No surprise there -- the RF up there is in the same spectrum as the control 
systems. OTOH, I don't recall anything comparable in downtown Chicago, where 
all the broadcasters are on two buildings only 1,500 ft above the street. Two 
important differences -- broadcasters out west have at least 10dB more power 
than those in Chicago, and virtually all Chicago UHF broadcasters are using 
lots of vertical antenna gain that shoots out at a nearly horizontal 
elevation. I also suspect that since the antennas on Mt. Wilson are on shorter 
towers. 

73,

Jim K9YC