Station short-spacing

[#905]

There are many tech experts on Radio Info and I am seeking an explanation of short-spacing. When an application for a new station is filed and its engineering report shows it is short spaced with licensed stations, are the existing stations advised of the situation and does the FCC automatically award a Construction Permit for the new station?

 

[Goat Rodeo Cowboy]

I believe "short spacing" is a condition that only happens in the FM band. (Other rules and terminology in AM) I read some FCC notifications the other day where some applications were not accepted for filing by the FCC and returned to applicant because of short spacing.

 

[jonbruce]

I think this post would best be served on the engineering board. There are many grand fathered short spaced FM's around mostly in major markets from decades ago New application short spacings rely on contour protection to get grants. Stations elsewhere that are short on mileage from the proposal can file objections.

 

[w9wi]

There are many tech experts on Radio Info and I am seeking an explanation of short-spacing. When an application for a new station is filed and its engineering report shows it is short spaced with licensed stations, are the existing stations advised of the situation and does the FCC automatically award a Construction Permit for the new station?

Existing stations are not directly notified, but applications do appear in the Public Notices.

The CP will be awarded if the station complies with FCC regulations.

New commercial FM stations must be separated from existing stations on the same and nearby frequencies by a minimum distance that depends on the classes of the stations involved. The table appears in FCC Regulation 73.207. For example, two Class A stations in the U.S. on the same frequency must be at least 115km apart.

However, Regulation 73.215 allows for short-spacing.

Existing stations are protected from interference based on their predicted signal strength. You're predicted to cause interference to an existing protected station if the ratio of your signal to theirs is too high at a point where the existing station is predicted to provide service. There is also a table of minimum short-spacings that will be allowed - for two U.S. Class A stations, 92km is the minimum, even if the new station wouldn't be in violation of the protection ratios.

A station wishing to use 73.215 "contour protection" to get a short-spaced site approved must specify that in their application. (so you can see it if you read their application online)

A second limitation on short-spacing is the table of allotments. A commercial FM station can only be authorized on a frequency "allotted" to the proposed city-of-license. A frequency cannot be allotted unless it can be shown that a site exists that is *not* short-spaced and from which a station could provide a "city-grade" signal across its city of license. A station using that frequency doesn't have to *use* that properly-spaced site, but such a site must *exist*.

The rules are different for non-commercial stations. There is no table of allotments. Regulation 73.509 establishes a table of contour protections. For example, a new station on the same frequency as an existing station may not deliver a signal stronger than 40dBu at any point where the existing station delivers 60dBu. (these are essentially the same ratios as are in 73.215 for commercial stations)

 

[TomT]

It's a 20 dbu ratio (co-channel), but remember that the protected contours for Class B stations is the 54 dbu, and for B-1 stations, the 57 dbu. So the "New" would have to protect an existing Class B station's 54 dbu contour against it's 50/10 34 dbu contour, while the protection in another direction towards an existing co-channel A would be no overlap of the"New's" 50/10 40 dbu with the A's 50/50 60 dbu.

Nor can the "new" station accept interference to it's protected contour above these limits, except for specially negotiated agreements between the stations, usually only allowed between two co-channel Class A's, or sometimes across international borders.

Stations short-spaced prior to the creation of the table of assignments back in the 60's have a different set of rules.

 

[Play Freebird]

The contour protection rule for short-spaced stations, 73.215, requires that the predicted contours of other stations that haven't invoked this rule must be based on standard class facilities (for example 50 kW at 150 meters for Class B) regardless of actual licensed facilities. This leads to some strange results in mountainous "ridge and valley" terrain.

Some stations in upstate PA are assumed to have antenna radiation centers 100 meters or deeper underground, when in reality they transmit from moderately tall towers atop a mountain. This causes their contours to be pinched in along the ridge but pushed out further in other directions.

Before the mid-80s, many short-spaced stations in the northeast US were given the OK to operate with no contour protection whatsoever by mutual agreement. In other words, "I'll let you interfere with me if I can interfere (to the same extent) with you." This is how WBEB 101.1 in Philadelphia is allowed to operate on the same frequency as WCBS-FM New York and WWDC in Washington (both less than the required 150 miles of co-channel separation) and still use a non-directional antenna. Five more stations are also short-spaced to WBEB, yet the station pulls great numbers in spite of widespread predicted interference.

 

[ChiefEngineer]

There are noncommercial "allotments" that exist in the non reserved band. WGNR Anderson Indiana is an example. Areas currently without non com coverage can receive a non com allotment in the non reserved band. That said, these allotments are not spaced at 73.215 contour protection rules.

The earlier poster was correct that 73.215 is only viable if all stations in the allocation look are 73.215 allocations. If you have a good site to move to under 73.215 then check and a Class B that keeps the new location from working by 2 km wasn't allocated or sited using 73.215 then you are out of luck.

An existing allocation may continue to interfere to the limits it already interferes with a grandfathered short spaced station but may not increase the interference.

The FCC database has many faulty coordinates and haat profiles. Staff has decided not to make changes unless the station makes a change. You can't correct someone's coordiantes even if they are significantly off. At this point Staff will consider P2D on upgrades or changes.