While trying to log mediumwave stations this year, I have encountered a new problem. The mediumwave band now contains harmful interference where once it contained AM stations. The introduction of HD radio on the AM broadcast band may be to blame.
I expect the occasional instance of adjacent channel interference. I may hear a strong signal on 1400 kHz, then hear remnants of that same signal when tuned to 1410 kHz. Compensating for this problem usually involves enabling the narrow filter on a radio, tuning further away from the interference source (such as going to 1412 kHz for example), or a combination of the two. With the noise that I'm now hearing surrounding some HD broadcasts, these methods are ineffective as the noise is overwhelming.
Here are the stations that I have logged, which have harmful noise on both adjacent channels (plus and minus 10 kHz). I'll also list stations that I logged back in 2006, but will likely no longer hear as a result of adjacent channel interference. Listening tests to confirm the presence of noise on the adjacent frequencies were performed with my Eton E5 on 02 March 2008.
• 740 KCBS: Sometime in 2008, KCBS began identifying itself as "KCBS and KCBS HD". An email exchange with the station reveals that their HD broadcast is running 24/7. 730 kHz and 750 kHz are now so noisy that no stations can be identified on these frequencies. So this eliminates 730 CHMJ (Vancouver, BC, Canada), 750 KHWG (Fallon, NV), 750 KOAL (Price, UT), and 750 KXL (Portland, OR).
• 910 KNEW: Their website says "Broadcasting in HD radio." This eliminates 900 CKMO (Victoria, BC, Canada), 900 KBIF (Fresno, CA), 920 KIHM (Reno, NV), 920 KVIN (Ceres, CA), and 920 KXLY (Spokane, WA).
• 960 KKGN: This station used to be KQKE until August 2007. Their website includes an "HD radio" logo. This will eliminate 950 KAHI (Sacramento, CA), and 970 KCMD (Portland, OR).
• 1050 KNBR: This is an odd one. KNBR is the callsign here for both 680 and 1050. The 680 frequency does not have adjacent channel interference on 670 and 690. I don't know why only 1050 would use HD. The only confirmation I have for my suspicion of an HD broadcast on 1050 is Wikipedia. Fortunately, I have not previously logged any stations on 1040 or 1060.
• 1310 KMKY: Oh great, Radio Disney with its numerous stations will use HD radio too? I could not find evidence of the HD broadcast on the Radio Disney website, but I found it on the iBiquity station list for California. This eliminates 1300 KCMY (Carson City, NV) and 1320 KCTC (Sacramento, CA).