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 _______________________________________________ IRCA mailing list [email protected] http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: [email protected]
