Technical Topics > Propagation

Propagation on the DGPS/NDB Band (200-400 kHz)

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skeezix:

--- Quote from: ChrisSmolinski on September 01, 2017, 0952 UTC ---Yes, I saw  that. Amazing. I tried yesterday morning, while Ozy Radio was coming in well on 5045, but could not get even a carrier on any of the .au MW channels. Granted I was using the sky loop down on the lower half of MW, where it is not very sensitive.

--- End quote ---

I need to make note of 5045 and try for it here.



--- Quote from: ChrisSmolinski on September 01, 2017, 0952 UTC ---I checked, and they all seem to run 50 kW like high end US MW stations. So not the MW level used by Europe and China, but still around 2 orders of magnitude more than the typical DGSP station? I checked the Southern Avionics site, and the DGPS transmitter they sell is 50-1000 watts. I thought I read that most of the US/Canadian DGPS stations are a few hundred watts? I have no idea if that is typical for stations outside the US as well. That extra power certainly gives you a few more propagation hops before your signal crashes into the noise floor. And even then, it's a rare catch. An upside to DGPS DXing is we only need two decodes in a row to declare reception of a station  ;D

--- End quote ---

Nautel sneaks up to 3kW
http://www.nautelnav.com/solutions/dgps/

However, what the stations really put out...  ???

I did find something with power levels a couple of months ago. Few hundred up to 2kW-ish. IIRC.

Not sure why this information is so hard to find, not like its national security secret since its a beacon with a well known position whose entire purpose in life is to broadcast position information continuously.

Some good general info, however, I wonder how much has been implemented seven years later.
http://www.gps.gov/cgsic/meetings/2010/hernaez.pdf

They note moving from the Southern Avionics Company to Nautel Vector-D transmitters. Nautel makes nice MW broadcast transmitters too... with C-QUAM.   ;D

ChrisSmolinski:
The question of NDB's modulation frequency (400 Hz and 1020/1030 Hz) came up in another thread. Basically, the IACO specs are:

--- Quote ---3.4.5.4 The frequency of the modulating tone used for identification shall be 1 020 Hz plus or minus 50 Hz or 400 Hz plus or minus 25 Hz.

--- End quote ---

1030 is well within the generous 1020 +/- 50 Hz tolerance. But why 1020, which seems like a dumb choice, honestly. I can't find anything regarding the history of how it was chosen. I asked a private pilot (who is also a ham), he does not know either. He did point out that the NDBs are typically only used within 10-15 miles, so interference from other beacons is unlikely. He also said:

--- Quote ---Current FAA policy is to NOT repair failed NDB's as they are being phased out in the US in favor of GPS approaches which require zero ground equipment. So as they stop working....they're gone - and the geostationary WAAS satellites are replacing the DGPS LF stations as well.
--- End quote ---

Yes. GPS for everything. I can't see any problem with that. What could possibly go wrong?

Anyway, the question came up (for me anyway) while thinking about how to automate NDB decoding, much as Amalgamated DGPS does for DGPS.  I posted the entire ICAO NDB spec here: https://www.hfunderground.com/board/index.php/topic,37057.0.html

skeezix:

--- Quote from: ChrisSmolinski on September 02, 2017, 1437 UTC ---I asked a private pilot (who is also a ham), he does not know either. He did point out that the NDBs are typically only used within 10-15 miles, so interference from other beacons is unlikely. He also said:

"Current FAA policy is to NOT repair failed NDB's as they are being phased out in the US in favor of GPS approaches which require zero ground equipment. So as they stop working....they're gone - and the geostationary WAAS satellites are replacing the DGPS LF stations as well."

Yes. GPS for everything. I can't see any problem with that. What could possibly go wrong?

--- End quote ---

They're also decommissioning around 1/3 of the VORs:
https://www.faa.gov/nextgen/update/general_aviation/approach_procedures/


Don't have thinking people that keep pulling out all of these other system and narrowing down to one system that is not all that secure.

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