[BC] Faraday Fence - No Foreign Signals Allowed

[PeterH]

On Feb 17, 2010, at 6:40 PM, Broadcast List USER wrote:

> Now, I don't know much about the broadcast rules in Mexico, but  
> that seems to be a very odd station.  It is XETRA 50 kW DA-2  
> licensed to Tijuana.  Then there is  However, there is also XETRA1,  
> 77 kW Day, 50 kW night, also DA-2.  The city of license is the  
> same, but the coordinates are different:
>
> XETRA, Tijuana
> 32° 25' 30.00" N Latitude
> 117° 05' 15.00" W Longitude (NAD 27)
>
> XETRA1, Tijuana
> 32°  17' 52.00" N Latitude
> 117° 01' 48.00" W Longitude (NAD 27)
>
> Finally, there is a THIRD license for XETRA with a different city  
> of license, Rosarito, but at 77 kW days like XETRA1 and those  
> coordinates.
>
> XETRA, Rosarito
> 32° 17' 52.00" N Latitude
> 117° 01' 48.00" W Longitude (NAD 27)
>
> The patterns looked slightly different when I looked at them earlier.

The first is the original Tijuana site, since replaced by residences,  
although I am advised that the tower piers still stand.

The second and third are the present Rosarito site.

The original pattern, days, was two 90 degree towers providing a  
modified clover-leaf pattern with the major axis NNW (towards L.A.)  
and SSE (towards Baja California). The suppression towards  the ENE  
and the WSW was the same as this pattern was symmetrical on two axes.

The original pattern, nights was five 90 degree towers which favored  
L.A. at the expense of Baja California, and also provided complete  
suppression towards the co-channel Class I-A in Canada and also the  
Pacific Ocean.

XETRA is not a Class I-A, it is a Class I-B.

The present pattern, days, is two 90 degree towers providing a  
significantly modified clover-leaf pattern with suppression towards  
the ENE. To compensate for the loss of day signal in L.A. with the  
new day pattern, 77 kW is used. Under "Rio" rules, which applies to  
Mexico and most Central American countries, but not to the U.S. and  
Canada, up to 100 kW could be used, but then there would be a very  
big complaint from the operators of 670 and 710 in L.A.

The present pattern, nights is five 90 degree towers which favors  
Baja California at the expense of L.A., and also provided complete  
suppression towards the co-channel and Class I-A in Canada and also  
the Pacific Ocean.

One might ask why there is 50 kHz separation between KFI and XETRA,  
640 and 690, respectively. Well, under pre-NARBA rules, it was  
expected, and required to have 50 kHz separation between same market  
stations, but if those stations were significantly separated, such as  
KFI and KPO/KNBC/KNBR, then 40 kHz or less might be possible.

Additionally, XETRA is grandfathered as to its first adjacent-channel  
interference to KPO/KNBC/KNBR largely because XETRA is a Class I  
station, in name only. Were XETRA to be a Class II station, then KPO/ 
KNBC/KNBR would have to be protected at night. The revised night  
pattern of XETRA goes to some degree to mitigate this interference to  
KPO/KNBC/KNBR, which also explains why its night pattern favors Baja  
California.

There are other examples of Class I stations which have to protect  
adjacent-channel Class I stations. When WKYC's array was rebuilt as  
four towers instead of three, the new night array reduced radiation  
towards adjacent-channel Class Is on 1520 and 1540 to the equivalent  
of its day radiation towards those same stations.