"Frequency Protection" definition, pls

[esco]

All:

I'd like to know what "frequency protection" means, in an IFR context. I'll deliver a great example of California brewing to a San Diego airport (OKB, RNM, MYF...) for the first who can provide a useful definition, with a reference.

From my research, my theory is that the term means the FAA has, in coordination with other spectrum users:
a) placed the navaid at such a distance that signal is not lost between stations along the same route,
AND
b) set the power of the navaid FAA nav/com signal such that it does not interfere with other coordinates uses of the same frequency,
AND
b) confirmed the frequency is protected, by distance, spectrum separation, or other means, from interference with other legitimate users of the same frequency ?


I first saw the terms in a Navigation and Communication box on the L-3/L-4 IFR low chart:
"(T) Frequency Protection - usable range 25NM at 12500 AGL" at the Camp Pendleton TACAN;
the FAA Aeronautical Chart User?s Guide, 12th Edition, October, 2013, has the same descriptive text under the "IFR Terms" tab, but no definition of the terms.

I haven't found a definition in my usual IFR sources:
Airplane Flying Handbook
Instrument Procedures Handbook
Instrument Flying Handbook
The first CFI I asked didn't know; I'm trying others as well.


Some references speak to the concept, but I haven't found a definitive, um... definition.

FAA Great Lakes Region Order, GL 6050.l2A, 11/25/77 "EXPANDED SERVICE VOLUMES FOR NAVAIDS (ESV) "
Section 4 states:
" BACKGROUND. The usable distance and altitude of NAVAIDs is determined by protection from radio frequency interference. Geographical separation of NAVAID utilized to establish frequency protection. The responsibility for providing this protection and assignment of frequencies will be provided by the Regional Frequency Engineering Office, AGL-438. NAVAIDs are frequency protected and flight checked to the normal NAVAID use limitations listed in Handbook 7110.65. "


FAA Order 6510.4A, 6/19/80, " RADIO COMMUNICATIONS REQUIREMENTS FOR AIR TRAFFIC CONTROL FACILITIES " section 4.d states:
"GENERAL.
a. Frequency protection shall be provided air/ground communications frequency assignments (except tor BUEC) which are engineered to meet the operational requirements of air traffic control facilities'.- This [demands the provision of frequency protection for co-channel and adjacent channel separation within prescribed distances, depending on the type of air traffic service involved. "

section 4.i states:
"Service Volume - The vertical and horizontal limits of airspace within which an assigned frequency is used. These limits are used to determine frequency protection Iron other frequency assignments. The service volume should represent the desired coverage area to ensure safe usage. "


FAA Order JO 7400.2H, March 10, 2011, " Procedures for Handling Airspace Matters" Section 20-4-2 states:
"NAVAID SPACING
Jet routes are normally based on ?H" class NAVAIDs spaced no farther apart than 260 NM or non-VOR/DME area navigation system performance. They may be based on more widely spaced NAVAIDs if a usable signal can be provided (e.g., GPS) and frequency protection afforded for the distance required."


FAA Order 7400.2F, 02/16/06 "PROCEDURES FOR HANDLING AIRSPACE MATTERS" section 20-3-1 states:
"NAVAID SPACING
a. VOR Federal airways are based on NAVAIDs which normally are spaced no farther apart than 80 NM. They may be based on more widely spaced NAVAIDs if a usable signal can be provided and frequency protection afforded for the distance required (see Order 9840.1, U.S. National Aviation Handbook for the VOR/DME/TACAN Systems).
b. NAVAID spacing for L/MF airways has no standard but is determined on an individual basis. "

[Doggtyred]

My non-official answer is that for a given navaid, it will be free of interference from other registered, sanctioned devices (like other navaids) within its service volume.

This is one method of ensuring that the signals received while in the navaid service volume on that frequency are the ones the pilot is intended to receive, and are presumably valid. Obviously other actions must also be taken to validate the signal and your aircraft receiver's handling of it, such as identing the code, and performing VOR/VOT checks.

I dont have a reference. Not interested in a reward. And this may fall into the FCC domain, not just FAA.

May I ask why the pointed interest in such an obscure detail?

[esco]

Good Question- Short answer, I'm curious, and I owe an apology.

When I first saw the term on a chart in IFR ground school, it looked odd. The instructor didn't have an answer, and a classmate offered a guess: "It's Mode 4."

I (think) I know enough about radar to say it has nothing to do with TACAN, so I announced across the classroom "That doesn't sound right." Given the reactions of everyone else, it came out as a bark.

In a class of high school grads and working students, thirty years younger than me, I plunged on with "I work with folks who should know; I'll check with an Engineer..."

I will apologize in class.

All that said, I'm curious now about why I can't find an answer... and still curious about the answer to the original question.

Thanks!

[aerovin]

You will probably find your answer in FAA order 6050.32B:

SPECTRUM MANAGEMENT REGULATIONS AND PROCEDURES MANUAL

that can be found here:

http://www.faa.gov/documentLibrary/m...CORPORATED.pdf

[aerovin]

Originally Posted by aerovin

You will probably find your answer in FAA order 6050.32B:

SPECTRUM MANAGEMENT REGULATIONS AND PROCEDURES MANUAL

that can be found here:

http://www.faa.gov/documentLibrary/m...CORPORATED.pdf

No specific definition, but the concept is discussed as applicable to navaids.

[Auburntsts]

Seems to me that all that note on the chart is doing is reminding pilots that standard service volume (SSV) area for a terminal "T" VOR/DME/TACAN signal is 1000agl to 12000agl at 25 NM. (ref AIM pages 1-1-5 & 1-1-6) which is much smaller that the SSV for a normal low altitiude VOR/VORTAC.

[BobTurner]

I believe the note is to indicate that the Camp Pendleton coverage is non-standard: While standard (T) class coverage is only guaranteed to 12,000' agl, at Camp Pendelton it goes to 12,500'. Pretty small difference.

[Auburntsts]

Originally Posted by BobTurner

I believe the note is to indicate that the Camp Pendleton coverage is non-standard: While standard (T) class coverage is only guaranteed to 12,000' agl, at Camp Pendelton it goes to 12,500'. Pretty small difference.

Except that's not what the note says on the L3/L4 chart. It actually says (T) = usable range at 12000 agl - 25nm. Not 12,500--I think that was a typo in the OP.

[aerovin]

The current L3/L4 shows the index note altitude (correct) as 12000' agl. For the chart index, the explanation is just for the "T" after the facility name to denote a terminal facility.