Why Los Angelenos Can Expect Overload While Listening to 1090 AM

 

 

Mark Roberts writes:

If KNX is transmitting IBOC -- and the iBiquity website indicates that it does -- then I don't think you're going to have much luck. Take a look athttp://www.nrscstandards.org/Reports%20ref%20docs/iBiquityAM%20test%20data%20report/Appendixarev02am.pdf,page 18, diagram at the top of the page. The upper primary digital sideband for KNX extends from 1080 to 1085 kHz. So you are going to be fighting noise - at just about the transmission level of the main 1070 kHz signal - originating from the first adjacent channel to 1090. A synchronous detector might help, if you can tune the station in such a way as to use only the upper (analog) sideband of the 1090 signal. But I think you would have to combine it with a very narrow IF filter, 2 or 3 kHz at most. I don't think being in Torrance makes it more challenging, particularly; I suspect any location in much of the city of Los Angeles is going to have the same challenge. You certainly might get overload from the 1070 signal, but I don't think it would show up at 1090 unless you had an equally strong signal close-by at 1050, and the FCC simply wouldn't have allocated that, because it has required a minimum separation of 30 kHz between stations in the same general area.

KDIS, Radio Disney at 1110, is likely to be a challenge for people in the Pasadena area, and it, too, utilizes IBOC, as do most Radio Disney stations.

Keep in mind also that the days of protected clear channels and protected nighttime coverage areas are increasingly over. It's just another nail in AM's already well-fastened coffin.

Comments

[Angelo]

Well, if there's a coffin for AM, I think it's probably a lot like the "KISS" coffins that Gene Simmons sells. They're fun to have at a party, but they won't be used for burying anyone anytime soon. AM still seems to be thriving in a lot of places I go.

[Mark Roberts]

First, I'm glad that Jeff can get the station.

As for AM radio generally: I surely must think that KIRO, KOMO, KCBS, KTAR, KLBJ, KMBZ, KCMO, WBBM, and WTOP, among others, have a reason for adding FM signals in their markets -- and, in a couple of cases, WTOP most notably, leaving AM altogether.

But don't let facts bother you!

[Bob C.]

XEPRS, licensed to Rosarito, BC, Mexico, generally targets the San Diego DMA - but has a lot of listeners in parts of the LA market as well. It's groundwave signal is more than capable of traveling well up the coastline during the day and it's an easy skywave catch from much of the Intermountain West at night.

That said, it is not protected once inside the LA basin. Any listeners that the station has within that area are a bonus to the station, but are not part of the San Diego market that they are targeting. Thus, you have little recourse as far as interference is concerned. Given that Torrance is the home of KNX' blowtorch of a transmitter, it's no surprise that you're hearing interference and overload on 1090. With CBS Radio's love for the evil IBOC monster, it's a wonder that even the CC Radio SW is giving you a nice clean signal. That says a lot for that radio's DXing capability.

In answer to a comment from an earlier thread, XEPRS does indeed come in better in Ventura County than it would in parts of south LA county. Why? For one, more of the signal travels a path over salt water - which is VERY helpful. Secondly, less RF interference. Both things make a surprising difference in signal quality.

[Gary]

Bob is correct. XEPRS 1090 comes in fine on my little DT-400W out in Simi Valley.