IBOC interference to aviation radio beacons?

[JasonW]

Hello All,

The AM IBOC interference problems made me think of a possible related problem.

Aircraft (and to a lesser extent, ships at sea) use Non-Directional Beacons (NDBs) for navigation. They operate both as "stand alone" beacons and as DGPS (Differential Global Positioning System) beacons that re-broadcast the GPS satellite signals on the Long Wave and Medium Wave bands. These NDBs operate between 190 kHz and 530 kHz.

Could the "digital hash" from AM IBOC radio stations at or near the bottom of the AM band interfere with NDB signals at the top of their band? -- Jason

 

[sbe]

I doubt IBOC would cause any interference to anything on Longwave bands including aviation beacons. IBOC May interfere with navigation signals in the 108 Mhz nav band from FM stations on 107.9, since the adjacent channel digital is in the aviation nav band. Your lower power VOR's and ILS localizer freq's are in this area of spectrum. On the other end of the FM band you have TV 6 audio at 87.75 Mhz. However, I doubt there will be much interference because they normally do not allow an FM on 88.1 in an area with a TV 6, unless the two transmitter sites are co located.



> Hello All,
>
> The AM IBOC interference problems made me think of a
> possible related problem.
>
> Aircraft (and to a lesser extent, ships at sea) use
> Non-Directional Beacons (NDBs) for navigation. They operate
> both as "stand alone" beacons and as DGPS (Differential
> Global Positioning System) beacons that re-broadcast the GPS
> satellite signals on the Long Wave and Medium Wave bands.
> These NDBs operate between 190 kHz and 530 kHz.
>
> Could the "digital hash" from AM IBOC radio stations at or
> near the bottom of the AM band interfere with NDB signals at
> the top of their band? -- Jason
>

 

[JasonW]

> I doubt IBOC would cause any interference to anything on
> Longwave bands including aviation beacons. IBOC May
> interfere with navigation signals in the 108 Mhz nav band
> from FM stations on 107.9, since the adjacent channel
> digital is in the aviation nav band. Your lower power VOR's
> and ILS localizer freq's are in this area of spectrum. On
> the other end of the FM band you have TV 6 audio at 87.75
> Mhz. However, I doubt there will be much interference
> because they normally do not allow an FM on 88.1 in an area
> with a TV 6, unless the two transmitter sites are co
> located.

Some NDBs operate on 530 kHz, just 10 kHz below the 540 kHz "bottom channel" of the AM broadcast band. That's awfully close.

Yes, FM IBOC could indeed be a problem for the aviation voice radio frequencies that start at 108 MHz. If I recall correctly, the aviation voice band is AM mode (so that stronger signals don't blot out weaker ones--they want all pilots to be audible in emergency situations), and FM IBOC sidebands would sound interesting on an aviation radio, to say the least. -- Jason

 

[sbe]

There wont be any interference to Aviation voice frequencies, as they do not start until 118 Mhz. 108 to 118 is for aviation navigation only. Terminal VOR, Hi Power Vors, and ILS localizer. I dont believe there is any aviation beacons above about 400 Khz. 530 is an AM broadcast freq in most of the world including Canada. There is a massive AM signal in the Turks and Caicos islands on 530, and at least one in Toronto or Montreal Canada, I dont remember which.


> > I doubt IBOC would cause any interference to anything on
> > Longwave bands including aviation beacons. IBOC May
> > interfere with navigation signals in the 108 Mhz nav band
> > from FM stations on 107.9, since the adjacent channel
> > digital is in the aviation nav band. Your lower power
> VOR's
> > and ILS localizer freq's are in this area of spectrum. On
>
> > the other end of the FM band you have TV 6 audio at 87.75
> > Mhz. However, I doubt there will be much interference
> > because they normally do not allow an FM on 88.1 in an
> area
> > with a TV 6, unless the two transmitter sites are co
> > located.
>
> Some NDBs operate on 530 kHz, just 10 kHz below the 540 kHz
> "bottom channel" of the AM broadcast band. That's awfully
> close.
>
> Yes, FM IBOC could indeed be a problem for the aviation
> voice radio frequencies that start at 108 MHz. If I recall
> correctly, the aviation voice band is AM mode (so that
> stronger signals don't blot out weaker ones--they want all
> pilots to be audible in emergency situations), and FM IBOC
> sidebands would sound interesting on an aviation radio, to
> say the least. -- Jason
>

 

[JasonW]

> There wont be any interference to Aviation voice
> frequencies, as they do not start until 118 Mhz. 108 to 118
> is for aviation navigation only. Terminal VOR, Hi Power
> Vors, and ILS localizer. I dont believe there is any
> aviation beacons above about 400 Khz. 530 is an AM broadcast
> freq in most of the world including Canada. There is a
> massive AM signal in the Turks and Caicos islands on 530,
> and at least one in Toronto or Montreal Canada, I dont
> remember which.

There are quite a few NDBs between 400 kHz and 530 kHz (they're listed on www.airnav.com ).

Near me (47 miles), ICW 525 (ICE POOL) is on 525 kHz, and FA 510 (co-located with the Locator Outer Marker for Fairbanks International Airport) is just 5 miles away. ICW 525 got me interested in NDBs, when I kept hearing this funny morse code string day and night on my AM radios.

You're right about the aviation voice frequencies--it's been years since I messed around with aircraft monitoring. I'm more drawn to Long Wave. -- Jason

 

[CW]

However, I doubt there will be much interference because they normally do not allow an FM on 88.1 in an area with a TV 6, unless the two transmitter sites are co located.

Wanna bet?? Check Beaumont, TX; KFDM TV 6 + there is an 88.1 NCE going up west of but licensed to Beaumont....vertical pol only but about 15-20 miles WEST of KFDM's tower site...and still within their main service contour...Yes they do allow FMs on 88.x in a Channel 6 area....there are certain restrictions in Part 73 that pertain to this but they do not have to share the same tower.