Obsolete artice. Maintained for historical purposes only.
REC has released a new version of myLPFM/Search, the LPFM channel search tool of the myLPFM suite of programs.
The main aspect of this release includes the use of "effective HAAT" for contour measurements. In the past, the REC tools have used the station's ERP (reduced if directional) and assumed the same height above average terrain in all directions. This was resulting in less than accurate results, esecially in areas with hilly terrain.
First, we are now using the FCC's service contour data for determining a station's 60/57/54 dBu (F50,50) service contour. This can be found in the REC Broadcast Query tool and its also used to generate the service contour maps in myLPFM when the "Check Waiver Availability" button is clicked.
We are now obtaining HAAT data from an outside source to determine effective HAAT, the height above average terrain between two specific points. This is the method that is used to determine the actual curves of the contours.
Using this new functionality, you will now notice the following changes...
Channel Search Results/Second Adjacent Waiver Channels
The presentation of second adjacent waiver channels has changed. Due to the implementation of Effective HAAT, we will no longer measure overlap zones on the main screen other than to check to see if the LPFM site is located outside the service contours of all short spaced second adjacent channel stations.
The display of channels will be divided by those channels that are short spaced under 73.807 but cause no real interference due to the LPFM interference contour not overlapping the second adjacent channel station's service contour.
All channels where there is an overlap, regardless of zone size is now placed in its own category. Each channel should be checked by using the [Check Waiver Potential] button.
This will perform a Effective HAAT search for the second adjacent channel stations and will show a map depicting the LPFM service contour in black and the second adjacent channel stations in different colors. This is similar to existing functionality except now that service contours using the FCC data set are used. These contours (as depicted on the map only) should be considered as precise as it uses actual coordinates provided by the FCC and no REC calculation is used.
Under the map, the station details have been reformatted in a columinar design similar to that used on the Interference screen. The display of effective radiated power (ERP) does now take directional antennas into consideration The ERP you see is the station power in the direction of the proposed LPFM site. The effective HAAT for the bearing from the full power station to the LPFM site is also shown.
Service Area Map
The service area map will now display the actual service contour based on the effective HAAT in 36 different directions. Stations that are on a hillside will notice that they will obtain service contours of more than 5.6km in some directions while in others, they may not achieve a far contour. This map will be first seen when a search for a specific location for the first time.
Below the service area map is a measurement of HAAT to the 36 different radians and the estimated 60dBu service contour in each direction. A overall HAAT will appear based on the normal 12 radials formula. This HAAT is based on a 10 meter (30 foot) antenna at the transmitter site. You can use the normal tower height function to adjust the size of your tower to update the map and these figures.
Interference Button
When the [Interference] button is pressed, the user will see a new layout. The new layout will also include the ERP in the direction of the LPFM station (if the other station is directional) and the effective HAAT in that direction. Like with second adjacent waivers, the interference maps have also been enhnaced to show estimated interference contours using effective HAAT and like with second adjacent waivers, the ERP and Effective HAAT columns are based on the bearing from the interfering station and the LPFM site and if the interfering station is using a directional antenna, the ERP will be reduced to show the radiation in the direction of the LPFM site.
NOTE: On the interference and second adjacent channel maps, if the precise LPFM site location has been used in the past in myLPFM or the previous Channel Search Tool where a short code (lpfm.ws) was generated for the location, the LPFM may appear on the map as just a 5.6km circle. We will work on fixing this later but for now, you can click the [Adjust] button and slightly move the antenna to generate a new short code and be presented with the maps with the predicted LPFM service contour.
At this time, these changes are in the desktop website version of myLPFM only. They will be pushed into the mobile version at a later date.
Please note that REC's calculation of service and interference contours should not be considered precision and actual field strength readings may vary by up to one kilometer. All results should be cross checked with REC's Premium Channel Search services, a qualified consulting engineer or for those who plan to "DIY" their application, the FCC's CURVES website.
