The AM Forum

It looks like there is a bunch of digital T-rash between BC stations expecially 530-1000kHz.  What is that? How is it decoded?  Is there anything interesting in the programming?

ILA

Google IBOC (in band on channel)

It wipes out weak analogue stations on channels adjacent to the big guns that are running IBOC.  So far the FCC has not allowed it for night-time operation, but the one company that has the monopoly on the system via proprietary licensing, is lobbying hard for it to be allowed full time.

Night time operation is now allowed as of Thursday after the full commissioners meeting.

From the FCC web site on all AM stations running IBOC:
Click, "Get data":
http://svartifoss2.fcc.gov/cgi-bin/ws.exe/prod/cdbs/pubacc/prod/sta_list.pl?Service=AM&digital_status=H (http://svartifoss2.fcc.gov/cgi-bin/ws.exe/prod/cdbs/pubacc/prod/sta_list.pl?Service=AM&digital_status=H)

And all the FM stations; Click, "Get data":
http://svartifoss2.fcc.gov/cgi-bin/ws.exe/prod/cdbs/pubacc/prod/sta_list.pl?Service=FM&digital_status=H (http://svartifoss2.fcc.gov/cgi-bin/ws.exe/prod/cdbs/pubacc/prod/sta_list.pl?Service=FM&digital_status=H)

 >:( >:( >:( >:(

It looks like there are all kinds of technical papers and advertisements written by engineers who claim this is the best thing since sliced bread.  Maybe even better.  But everything is written by the engineers who work for the transmitter manufacturers.  Plenty of bits and bites and kilobit synchronization information.

But has anyone listened to a station with an consumer grade radio and gotten anything?  Is there any programming worth listening?

Maybe this should be moved under QSO. 

Tm
 

I haven't heard any AM IBOC yet. Have tuned in the three or four FM stations transmitting in the area. Fidelity was not drastically improved, maybe a little better/cleaner high end. The most noticeable things were the much improved SNR (gone is the HF hiss common on FM analog stereo signals) and better stereo separation.

Did you tune in the stations on a conventional receiver, or on an IBOC one?

The (analogue dial) FM tuner in my house stereo amplifier has a mono/stereo button you can push to kill the stereo feature.  If the station is not absolutely full quieting, there is much less hiss in the mono mode.

I have noticed the NPR station about 50 miles from here has a constant gurgling sound in the background when the receiver is in the stereo mode.  It is very distracting and sounds like a weak unstable heterodyne in the background, very similar to the sound of an AM carrier with the SBE effect.  It's not the receiver because I hear it on another receiver with digital tuning (not IBOC) as well.  In the mono mode, the background  sound disappears.

I don't hear the gurgling carrier on the car radio, and it receives in the stereo mode all the time.

Back to the topic, here are a couple of interesting websites regarding IBOC:

http://www.analogzone.com/nete0819.htm

http://www.rwonline.com/reference-room/commentary/2006.07.19-03_rw_hd_guest_barry_2.shtml

I used an IBOC capable receiver. It is easy switched between analog and IBOC. In analog, the station takes about a 20 dB (IIRC) SNR hit when transmitting in stereo. There's no way around this.

Maybe that gurgling sound on NPR is a heterodyne beat note with weaker FM carrier in the background.  I notice that it sometimes becomes a steady whistle when there is a pause in the audio.  The FM capture effect is not always 100%.  Not sure how the stereo mode affects that.  There is another station on the frequency that sometimes overrides the station and pops up when the FM antenna is oriented to a null on the desired signal.