Re: [IRCA] IBOC deterioration

[Milspec390@xxxxxxx]

Stations which participate in State Sponsored Jamming are exempt  from 
adherence to tolerances.
 
                  As  it is spoken, so decreed.
 
 
                                                                              
             z
 
"Innocent until investigated? Has a nice ring to it, 
 sort of like the law being written down as it's spoken."
                               - Bob Barnes, "Syriana"
                                c.  2005
 
pv zecchino
manwhattacynic key, fl
 
 
 
 
In a message dated 11/27/2008 10:48:46 A.M. Eastern Standard Time,  
bubba@xxxxxxxxxxxxxxxxxxxx writes:

One of  the advantages of the SDR type radios is seeing the spectrum.   It
really helps when trying to null a pest or see if there are TA/TP  carriers.
Great for seeing if LSB or USB will give the best audio.   And, it shows in
good detail the IBOC sidebands.

AM stations have  slight seasonal parameter changes in their antenna systems
due to water  around the ground system.  IBOC requires a very tightly
controlled set  of parameters.  When these drift, things change and not
usually for  the better.  Unless a station is frequently monitoring these
changes,  it can put things out of tolerance.  This usually shows as  added
interference.

One of the crucial tuning tests is a set of  spurious sidebands around +/-
27KHz on either side of the main  carrier.  It needs to be -65db from that
carrier level.  When all  is good, it shows on the SDR as a very slight fuzz
on either side.   When it is pretty obvious, then it's probably out of range.
When setting up  WDDZ-550 for day IBOC, I was able to match what the
consultant's spectrum  analyzer showed against what the SDR displayed.  I got
a pretty good  idea what is good and what is not.

Installation of IBOC is usually done  by an out of town consultant who's
there only for that task.  Then the  station has no spectrum analyzer and is
blind to changes.  DXers have  better eyes and ears than most engineering
staffs.  In Providence,  there is another station with day-only IBOC and I've
noticed a significant  jump in their +/- 27KHz sidebands.  I'll chat with
their engineer next  time I see him, though I don't think there's anything he
can do without the  proper equipment.

I have to wonder if the IBOC stations have budgeted  for frequent enough
checks to keep their stations in compliance with the  FCC Rules and
Regulations.  My guess is no.

So, if a local is  trashing stations beyond the first adjacent, they may have
a  problem.

I really wish that the SDR-14 Spectravue software had a way to  store perhaps
a hundred readings and display the maximums.  That would  bring it pretty
close to the multi-thousand dollar consultant's  equipment.

Craig Healy
Providence,  RI


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