ARTCC discrete frequencies

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iscanvnc2

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What makes a discrete freq discrete vs the non-discrete freqs? I've read several articles but am still not clear.
 

powahayeagle

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Basically a discrete freq is one that is not published and only used when necessary for a specific purpose. A non-discrete freq is one that is published by the FAA and is used in normal operations.

I am not sure what the purpose they serve at ARTCC. However, an airport might have one to do PAR approach (Controller basically guides the pilot on the glide slope giving azimuth and elevation information all the way down) or one where an emergency aircraft can talk to the airport fire department directly without clogging up one of the main freqs.
 

AirScan

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I've been wondering that for years and have never heard a definitive answer. In the past it appeared to be related to whether a frequency was published on the enroute charts. Were "discrete" frequencies were shown on the maps while "non-discrete" were not. This seems to be the general case although I can find a few exceptions. Although the exceptions might be related to the FAA not keeping their data up to date ? My guess anyway. From an operational perspective I've never been able to distinguish any difference ?
 
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Discrete refers to segregating an operation from the the normal traffic being worked. Example, I'm working a sector that has an MOA (miltary Operating Area). The military guys come into my sector on the normal frequency that is always on. Once I clear them to operate in the MOA, I change them to the discrete freq which I have, but do not transmit on unless I need to specifically contact those in the MOA. This leaves those in the MOA free to operate and talk to each other without hearing my routine transmissions, yet if needed, I can still contact them.
 

AirScan

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Discrete refers to segregating an operation from the the normal traffic being worked.

The problem is I can find a lot of examples where this is not the case. Here's one.

AFF3ZBW SHELTON RCAG 128.1 LOW
AFF3ZBW SHELTON RCAG 134.0 LOW DISCRETE

There is no obvious operational difference between the two sectors. 134.0 is shown on the charts while 128.10 is not.
 

drdispatch

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From an air show perspective, when a multi-aircraft act takes off, their lead is talking to the Air Boss (who is acting as the tower). Once they are airborne, the Air Boss clears them to "switch to discreet", which is the frequency the team uses to talk to each other.
 

iscanvnc2

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Wow! Looks like I really started something. Thanks for all the informative replies. The 28 Day NASR Subscription referenced by AirScan is especially interesting; tons of data.
 
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The problem is I can find a lot of examples where this is not the case. Here's one.

AFF3ZBW SHELTON RCAG 128.1 LOW
AFF3ZBW SHELTON RCAG 134.0 LOW DISCRETE

There is no obvious operational difference between the two sectors. 134.0 is shown on the charts while 128.10 is not.

Welcome to the FAA way. Their way of naming and identifying things doesn't even make sense to employees sometimes. I recall someone from RR trying to publish where all of the RADAR sites are. He was using FAA data, and had left out sites that existed and were active, but not listed in even the FAA data. I told him of this, and even explained that some he said didn't exist were alive and well on my RADAR display at work.
A thing to keep in mind is, a lot of data available on the web isn't put there by the agency for the convenience of the general public, but for specific inquiries someone made, or incidentally published. Maybe "Discrete" had some other meaning abck in the CAA days and has carried over.
 

ATCTech

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How about the "answer" from a 1970, yes 1970, IEEE document on the subject of ATC frequency congestion. Emphasis added by me, spelling errors are part of the original document.


"Summary form only given. Today's air-ground communication system normally requires the assignment of a discrete very-high frequency, and, where appropriate, an ultra-high frequency for every function associated with air traffic control. This requires that each function of a control tower, such as approach control, local control, ground control, etc., and each function of the air route traffic control centers (ARTCC), such as high and low altitude sectors, be assigned at least one discrete frequency and in many cases two or more. When a channel for a particular function becomes saturated or when new facilities or functions are added to the system, more channels are required. Recent FAA studies have indicated there is presently a requirement for more than 100 channels over and above the number now available. As aviation grows, the problem will become more severe. Solutions available within the framework of today's system and current equipment will not produce acceptable long-term results. Therefore, it appears necessary to consider and evaluate new methods of air traffic control communication techniques. One method currently under consideration by the FAA is the discrete aircraft frequency concept. This concept differs from the present system in that a single frequency would be assigned to an aircraft. The ground system would semi-automatically change to the aircraft's frequency when communication is desired, as opposed to the aircraft changing frequency for every control boundary and function in today's system. One of the advantages would be better frequency utilization, by balancing communication loading over all communication channels. In this system, assignment of the frequencies to aircraft would be done so that at any given time and place the total number of aircraft will generally be uniformly distributed among the available frequencies."

Makes me wonder if the use of the word has been a decades-long carry-over. I asked a newly-retired FAA contact about it's current meaning today and they could offer no information.

Cheers!
 

AirScan

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I still think it just has to do with whether or not a frequency is published on the charts. Looking at the AFF data over the last few years I've noticed some Centers have stopped using the "DISCRETE" label altogether. Denver (ZDV) is an example of this as now none of their frequencies are labeled as such. Now instead you will notice a "Y" or "N" for each frequency listing. Here's an example for Denver Center from the AFF listings.

AFF listing from 2015

AFF3ZDV CHEYENNE RCAG 133.175 HIGH DISCRETE
AFF3ZDV CHEYENNE RCAG 134.575 HIGH

AFF listing Now

AFF3ZDV CHEYENNE RCAG 133.175 HIGH Y
AFF3ZDV CHEYENNE RCAG 134.575 HIGH N

Again as far as I can tell there is no obvious operational difference between the two frequencies or sectors. And again 133.175 the "DISCRETE" or "Y" frequency is published on the charts while 134.575 is not.

SkyVector: Flight Planning / Aeronautical Charts

ATCTech,

Interesting concept, although I don't think they envisioned thousands of aircraft airborne at the same time over the US back in 1970. I can't see how that idea would make any sense ? They have a hard time keeping up with transponder codes and there are 4096 of those available.
 

ATCTech

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ATCTech,

Interesting concept, although I don't think they envisioned thousands of aircraft airborne at the same time over the US back in 1970. I can't see how that idea would make any sense ? They have a hard time keeping up with transponder codes and there are 4096 of those available.

Me either! When I read it, then read it again and again, the words "no way" came to mind! But then it was 50 years ago and by 2000 we weren't going to need subsonic aircraft anyway. ;)
 

spanky15805

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To expand on what profiledescent commented about radar locations. Almost all the RCAG/RCO/RTR/VOR locations I've researched on RR are off by 3-5 miles. Now if you know what your looking for while blazing across the country side, it's pretty easy. ADS-B can be 3-10 miles from an airport.
 

Sector46

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I was a controller for 33 years , towers, centers and apch/dep controls . A discrete frequency which was the original question , usually UHF ( when military / I did both civil also ) )was used when a special operation was underway , like the SR71 flying over at speeds you wouldnt believe. ...this was only one use they had . Strange I worked 3 or 4 presidential aircraft durring my career , they'd use the reg freqs , but that was 1970-- 2013 ...a longgg time ago ...including Trump in and out of PBI 100s of times long before these days ...
 

alcahuete

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I was a controller for 33 years , towers, centers and apch/dep controls . A discrete frequency which was the original question , usually UHF ( when military / I did both civil also ) )was used when a special operation was underway , like the SR71 flying over at speeds you wouldnt believe. ...this was only one use they had . Strange I worked 3 or 4 presidential aircraft durring my career , they'd use the reg freqs , but that was 1970-- 2013 ...a longgg time ago ...including Trump in and out of PBI 100s of times long before these days ...


What you're referring to is the Tactical Frequency, so the folks flying certain missions (i.e. U2, SR-71) don't have to change frequencies, and don't have to listen to constant ATC chatter, because the transmit is turned off on that frequency until it is needed to communicate with that aircraft. Some places might use different terminology, but that is not the discreet that is being referred to in this thread.
 

alcahuete

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In 2 of the 5 ARTCCs I worked in, they called it "discrete" as well.

And that's fine. A lot of people call it different things: Discreet, Tactical, Special Use. But what that is referring to is the single UHF frequency that all centers have. It is one frequency that is used for the things I mentioned above.

If you look at what the OP posted and the example a few posts down, that is not what he is referring to.
 
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