ATIS Transmitter - Power Ouput

[Darth_vader]

"What's the farthest an ATIS has ever been heard from its source? How far have you heard one?"

PDX (128.350 MHz, if I recall correctly) usually fades into oblivion between the Burton Road overpass and Highway 500 offramp on I205, about 2-3 miles south of Vancouver Mall -- see here: http://old.wikimapia.org/#lat=45.6494358&lon=-122.5662938&z=15&l=0&m=o. At the mall it's completely gone.

Even at my current place in the vicinity of here: http://old.wikimapia.org/#lat=45.6270514&lon=-122.549471&z=16&l=0&m=b, it's usually very difficult to copy clearly.

 

[nr2d]

Here in the states, the power output for an ATIS can vary from 2.5 to 10 watts, standalone transmitter. The power depends on the coverage requirements of Air Traffic.

That being said when I worked at Trenton - Mercer County (TTN) airport in New Jersey we had to lower our the power out of our ATIS transmitter due to user complaints. Pilots departing Philadelphia International (PHL) were complaining that the TTN ATIS was interfering with the Binghamton (BGM) airport ATIS. The pilots were about 5 - 10 miles from TTN but 150 miles or so from BGM.

 

[nr2d]

I was wondering about something, do the ATIS antennas transmit upwards or 360 all around?

360 around. As with any vertically polarized "dipole" above and below the antenna you have a null, an area of attenuated or no signal, sometimes called a cone of silence or ambiguity. I made a quick drawing of the antenna
pattern in space to so the patterns from the side and top. If this was 3D the patterns would look like a donut.

 

[Rt169Radio]

Thanks for the info nr2d, I had been wondering about that.

 

[navaidstech]

Don't forget, this is a free space pattern. The radiation patters of a ground/tower mounted vertical antennas is "slightly" different.

 

[glideslope]

There's probably not a lot of point in having coverage that extends further than the approach arc, it is, after all, Terminal information. Depending on the surrounding terrain, 5watts should give coverage out to 25nm with a good antenna, usually just a quarter wave ground plane up on the tower.

Actually, the main point is to have coverage outside of just a published approach procedure or immediate terminal area. I always like to have the current airport weather at least 70 miles outside of the airport. Think about it; 70 miles in a commuter turboprop moving 5 miles a minute is only 14 minutes away from the airport. A lot needs to happen in 14 minutes, especially in a crew environment. We need to descend, we need to load the approach fixes/waypoints, set altitudes, set frequencies, set courses, etc. We need to brief the entire approach including the missed approach if we can't actually see the airport due to weather and the landing configuration of the aircraft. There are also some challenge & response checklists that need to be accomplished. Subtract the time we're communicating with ATC, getting vectored around, repeating clearances and the time we're actually established on the approach. Once established we're glued to instruments and making call outs. Basically, 25nm outside the airport is no time to be obtaining local weather.

Now, if you're flying small, slow, piston single engine airplanes in beautiful weather - sure 25nm is no problem.

 

[nr2d]

Navaidstech - You are very correct. That is a "free space" antenna pattern.

glideslope - No the main point is to provide the ATIS within the requirement as defined by Air Traffic. Also here is quote out of the FAA AIM: "ATIS transmissions on a discrete VHF radio frequency are
engineered to be receivable to a maximum of 60 NM from the ATIS site and a maximum altitude of
25,000 feet AGL."

But with the frequency congestion here on the east coast and in all major metropolitan it is extremely difficult to engineer and assign new VHF frequencies. In fact I have had to "give up" VHF comm frequencies assigned to the FAA Tech Center in order to provide new frequencies to support Air Traffic requirements. The Tech Center uses these frequencies to perform R&D and operational testing of new comm equipment, confirm engineering lab data, and to provide real world comm testing of filter, intermod and co-site frequency assignment treating.

 

[glideslope]

Navaidstech - You are very correct. That is a "free space" antenna pattern.

glideslope - No the main point is to provide the ATIS within the requirement as defined by Air Traffic. Also here is quote out of the FAA AIM: "ATIS transmissions on a discrete VHF radio frequency are
engineered to be receivable to a maximum of 60 NM from the ATIS site and a maximum altitude of
25,000 feet AGL."

The AIM is not regulatory but, I appreciate you citing from it.

What pilot certificates do you currently hold and what aviation experience do you have?

 

[glideslope]

Navaidstech - You are very correct. That is a "free space" antenna pattern.

glideslope - No the main point is to provide the ATIS within the requirement as defined by Air Traffic. Also here is quote out of the FAA AIM: "ATIS transmissions on a discrete VHF radio frequency are
engineered to be receivable to a maximum of 60 NM from the ATIS site and a maximum altitude of
25,000 feet AGL."

But with the frequency congestion here on the east coast and in all major metropolitan it is extremely difficult to engineer and assign new VHF frequencies. In fact I have had to "give up" VHF comm frequencies assigned to the FAA Tech Center in order to provide new frequencies to support Air Traffic requirements. The Tech Center uses these frequencies to perform R&D and operational testing of new comm equipment, confirm engineering lab data, and to provide real world comm testing of filter, intermod and co-site frequency assignment treating.

Just to touch on this again, the AIM is not regulatory. It's a great guideline for operating procedures and a great way to stay violation free as a pilot but, for setting a standard/regulation for radio transmissions for that matter, it's not accurate. I know it's confusing for those of you not involved in aviation.

For example, yesterday at 22,000 feet I was able to listen to an ATIS Broadcasts about 150 nautical miles away from the aircraft. Does this fall within your requirement? No, it doesn't. I have practical knowledge and experience in aviation and am explaining to individuals on this board the practical reasons for having to obtain important weather information well outside of 25 nautical miles. Please, do not reply with non-regulatory AIM material and no practical knowledge.

 

[ATCTech]

Actually your reception report DOES fall within his "requirement" as you put it. The statement in the AIM is meant to mean the ATIS broadcast "shall be" for lack of a better phrase receivable to 60NM @ 25000'. It does NOT mean it must STOP at 60NM or 25000'. It is a baseline, and I agree not a regulation.

 

[autovon]

Let's try to not throw too many darts at one another here. I enjoy listening to both sides and learning a different perspective. The 60nm "limit" does have me laughing though. Like the RF is magically going to come to a screeching halt! Then again, the regulations are written by the same govt that put a 250km restriction on 27MHz frequencies as well.

Hearing ATIS outside of the terminal area is important for a lot of aviators.

 

[nr2d]

Just to touch on this again, the AIM is not regulatory. It's a great guideline for operating procedures and a great way to stay violation free as a pilot but, for setting a standard/regulation for radio transmissions for that matter, it's not accurate. I know it's confusing for those of you not involved in aviation.

For example, yesterday at 22,000 feet I was able to listen to an ATIS Broadcasts about 150 nautical miles away from the aircraft. Does this fall within your requirement? No, it doesn't. I have practical knowledge and experience in aviation and am explaining to individuals on this board the practical reasons for having to obtain important weather information well outside of 25 nautical miles. Please, do not reply with non-regulatory AIM material and no practical knowledge.

glideslope for your info I work for the FAA. Started as a NAVAID/COM tech at TTN then 5 years in Flight Inspection and and presently the Frequency Management Officer for the FAA Technical Center in Atlantic City, Egg Harbor Twp., NJ. I don't hold any pilot certificate. Because I quoted the AIM I was not trying infer a regulatory requirement but just to state what is normally used for reference by the user. ALL frequency assignments engineered by the FAA are accomplished to fulfill the requirements as requested by ATC. I've read my post several times an no where in the post did I say the AIM was regulatory.

You as a user may need to access the ATIS beyond 60 nm but you are now using the facility beyond it's engineered service volume. Trying to use a frequency beyond the engineered service volume will not guarantee interference free reception.

Here is a quote from the FAA Frequency Management order, FAA Order 6050.32B, "c. Service volume of an ATIS operating on a discrete VHF or UHF channel must be consistent with theTerminal Radar Approach Control (TRACON) airspace, and is normally limited to 60 nmi and 25,000 feet above ground level (AGL). The concerned service area air traffic organization must approve requirements in excess of this value."

We also engineer a frequency, any comm frequency, to insure a 14 dB desired to undesired power separation for an aircraft at the edge of the desired facility to a facility using the same frequency.

I can understand why you might need to have the ATIS info beyond the engineered service volume. You as the pilot/pilot in command are the sole individual responsible for how you use comm frequencies, ATIS facilities, NAVAIDs. We as FAA Technicians and Engineers try to the best of our ability to make sure you are able to use the service within a certain engineered service volume. Beyond that service volume you are on your own.

As someone else mentioned the radio signal doesn't just stop at the edge of the engineered service volume. You can use the ATIS 5 miles from your airport or 125 miles from your airport. You make that decision. Enjoy your flying.

 

[glideslope]

As someone else mentioned the radio signal doesn't just stop at the edge of the engineered service volume. You can use the ATIS 5 miles from your airport or 125 miles from your airport. You make that decision. Enjoy your flying.

This is the only point I was attempting to make. Thanks for the additional information.

 

[majoco]

nr2d said:

"ATIS transmissions on a discrete VHF radio frequency are engineered to be receivable to a maximum of 60 NM from the ATIS site and a maximum altitude of 25,000 feet AGL."

...a MAXIMUM of 60nm, not a minimum.