For a long time, KBNP has had a "buzz" on their audio that sounds like harmonics of 60 or 120Hz. If one tunes to 1400 or 1420 kHz using a radio with typical bandwidth (i.e. not AMAX and not a communications receiver), a sound very similar to switching power supply interference is heard. I am curious where this "buzz" is coming from and why it seems that nothing has been done about it.

2380 (1190 2nd harmonic) minus 970 = 1410

or

2(KEX)-KCMD = KBNP

The intercarrier difference between them can vary day to day, but anything above subaudible becomes on carrier detectable interference when tuning 1410. There's a whole lotta 1190 and more 970 than 1410, so until someone suggest a better reason, I'll go with this.

I have heard that they are feeding their streaming computer with a radio from their studio site so when they are at 9 watts or so at night the stream sounds horrible.

I've heard it too and up until reading the above posts I always assumed it was ground loop buzz in their audio.

"2380 (1190 2nd harmonic) minus 970 = 1410"

I don't hear any KEX second harmonic (2380) in Hillsboro on my Icom (even in CW mode). I do hear quite a bit of power line buzz near 1410.

In the parking lot of Home Depot on 82nd I can pick up KEX at about 4 or 5 places on the dial.

2A - B interference is a notorious 3rd order intermodulation product. It can not be detected by listening or measuring for 2A by itself.

"2A - B interference is a notorious 3rd order intermodulation product. It can not be detected by listening or measuring for 2A by itself."

Interesting... So does the generation of the 2A signal and the mixing with B frequency occur within the receiver in question, or at the transmitter?

When it is a blatant market wide problem with clear interference occurring and demod audio being heard, the transmitter. Spurs often are so strong, they pop up on the dial like a station ... the audio detected not necessarily being the offending signal.

(circa early 1980's when 103.3 came on the air and created a giant spur with 106.7 audio being detected ... turned out 97.1 transmitter is where they were mixing and they had to add another notch filter on their antenna system .. where 103.3 and 106.7 were throwing out a spur up in the aviation band ... their third if memory serves ... stations hated them because of the insertion loss ... this was before Stonehenge).

There is also receiver induced third order intermod. There are a jillion white papers on tackling this issue in the cell phone bands.

In this case, it's probably just a glitch. AM is so simple to detect that almost anything can get into a receiver and cause grumblings of a noisy nature. KEX has such a monster signal, though, that I would not be surprised if their second harmonic is getting into the front end and mixing with 970 and the 2A-B difference becomes on freq material and happily glides its way through the receiver. If their carriers are off by +- 50 - 100 Hz it could cause audible hum, pops, etc.

It's just a theory. Is it just one radio receiver at one location? That's hard to pin down.

Has it been doing this ever since moving to Oaks Park? If so and if the problem didn't exist when the station was at Healy Heights, perhaps there was enough signal to cover up the interference from 970.

The buzz can be heard anywhere in the KBNP listening area, so my first guess would be a ground loop somewhere in the audio wiring, as Scott suggested. When I first noticed the problem (a long time ago), the buzz would pump up and down with the audio, almost as if it were going through a noise gate. Nowadays, the buzz is louder and more constant.

As others have said, if the buzz occurs all over town, then it most likely originates at the station.

If you can hear a buzz in one location but not another, it might originate from nearby equipment or the receiver's own power supply. See the following article. It was written for shortwave listeners but applies equally to AM broadcast reception.

http://home.computer.net/~pritch/shortwav.htm

Does KBNP share there tower with another AM station? That might explain the buzzing sound.

KBNP shares its tower with KXPD (1040). Some time ago, when 1040 was transmitting a dead carrier, I remember hearing a hint of the 1410 audio bleeding over on 1040.