Why do some station's on AM have more "hash", I do not know the technical term if there is one. But what I mean is when you tune to say 670 10 points down from WCNN 680, it is very loud and noticeable, then some stations don't have as much when you are not completely on the frequency, hope this makes sense.
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Hash sounds????
- Thread starter BIGSTICK
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The simplified explanation is that the "hash" (or "splatter") is mostly due to the amount of high-frequency equalization used by the station. The more high-frequency boost they use, the more splatter you'll hear. Since the majority of AM receivers have an unreasonable roll-off of high frequencies, most stations boost the mid and high bands in an exponential fashion to help overcome receiver limitations and provide better intelligibility.
The degree of splatter is also dependent upon the power level of the station - stronger signals will have stronger splatter. Along the same lines, distance has the same effect - the closer you are to the tower, the stronger the signal will be, and the more splatter you'll hear.
In the case of WCNN, they have a very strong signal, and they also apply a lot of high frequency equalization.
The more technical explanation is that AM is double-sideband full carrier - the spectra are mirrored around the full carrier. In the US, the NRSC-2 specification limits broadcast AM to a 10 kHz audio bandwidth - audio frequencies above 10 kHz must be attenuated well below the carrier level. Therefore, the actual bandwidth occupied for WCNN at 680 kHz would start about 10 kHz below the carrier (670) and end about 10 kHz above (690).
The spectra are created relative to the carrier. A 1 kHz tone would give you spikes at 679 kHz and 681 kHz, a 2 kHz tone at 678 kHz and 682 kHz, and on and on. The spectra closest to the carrier correspond to bass audio frequencies, and the spectra farthest from the carrier correspond to the treble audio frequencies.
Depending on the bandwidth of your receiver, when you tune to 670, you're actually going to receive a portion of the energy from 680 - mostly the energy from those treble audio frequencies. So when a music bumper plays, or when there's a lot of sibilance or other material with a lot of high frequency energy, you'll hear the splatter increase.
Some stations have voluntarily reduced their audio bandwidth to less than 10 kHz (I recall reading a directive from Jeff Littlejohn at Clear Channel some years ago). However, most of the stations in this market still run the full 10. HD Radio further increases the occupied bandwidth of AM stations, but since 790 is the only game in town doing HD right now, that doesn't apply as much here.
Hopefully that makes some sense.
The degree of splatter is also dependent upon the power level of the station - stronger signals will have stronger splatter. Along the same lines, distance has the same effect - the closer you are to the tower, the stronger the signal will be, and the more splatter you'll hear.
In the case of WCNN, they have a very strong signal, and they also apply a lot of high frequency equalization.
The more technical explanation is that AM is double-sideband full carrier - the spectra are mirrored around the full carrier. In the US, the NRSC-2 specification limits broadcast AM to a 10 kHz audio bandwidth - audio frequencies above 10 kHz must be attenuated well below the carrier level. Therefore, the actual bandwidth occupied for WCNN at 680 kHz would start about 10 kHz below the carrier (670) and end about 10 kHz above (690).
The spectra are created relative to the carrier. A 1 kHz tone would give you spikes at 679 kHz and 681 kHz, a 2 kHz tone at 678 kHz and 682 kHz, and on and on. The spectra closest to the carrier correspond to bass audio frequencies, and the spectra farthest from the carrier correspond to the treble audio frequencies.
Depending on the bandwidth of your receiver, when you tune to 670, you're actually going to receive a portion of the energy from 680 - mostly the energy from those treble audio frequencies. So when a music bumper plays, or when there's a lot of sibilance or other material with a lot of high frequency energy, you'll hear the splatter increase.
Some stations have voluntarily reduced their audio bandwidth to less than 10 kHz (I recall reading a directive from Jeff Littlejohn at Clear Channel some years ago). However, most of the stations in this market still run the full 10. HD Radio further increases the occupied bandwidth of AM stations, but since 790 is the only game in town doing HD right now, that doesn't apply as much here.
Hopefully that makes some sense.
WOW, thank you,,,that makes sense, but I have heard lower power still having a lot of hshdhhfhdhfhssssh sounds when you are off of the frequency. WSB which is a full time 50k does not have a lot of that has sound anymore-they use too...--have they tweaked their transmitter to do this??? And what is all of that "white" noise from 790 WQXI during the day..It almost overtakes WSB, especially where I live in VA Highland..
WSB may have reduced their audio bandwidth to below 10 kHz. I don't know if David or Bob browse the boards, but they may be able to chime in.
The white noise from 790 is a result of their digital (HD Radio) carriers. These digital carriers extend beyond the 10 kHz audio bandwidth limit, and even though they are at a much lower level, still create quite the noise.
I've listened to their HD signal, and it sounds atrocious - something is being horribly overdriven. If I were Lincoln Financial, I would be very embarrassed to have this on the air.
The white noise from 790 is a result of their digital (HD Radio) carriers. These digital carriers extend beyond the 10 kHz audio bandwidth limit, and even though they are at a much lower level, still create quite the noise.
I've listened to their HD signal, and it sounds atrocious - something is being horribly overdriven. If I were Lincoln Financial, I would be very embarrassed to have this on the air.
You are the man with the answers, this has always fascinated me even when I was a kid and kind of liked to hear that Hash sound from far off stations at night, like WLS, WLW, etc. I am a true radio Dxer from way back and to this day I still like to scan the AM band at night and even during the day, especially in the winter . I have many old, well 80's circa radio's that have amazing sensitivity on FM, but especially AM.. Yes WQXI is a mess with that horrifying sound right now..........
Besides the GE Superadios, what else would you recommend? I have the Optimus (Radio Shack) Superadio knockoff from the 1990s (http://mysite.verizon.net/vze20h45/radio/superadio/gesr_tech.html#N5A ) ...not as good as the real thing but still outstanding.BRENT said:
There are many people nowadays referring to the 1970s and 1980s as the "golden age of Japanese electronics"...
I also have a 1960s Motorola tube clock radio that is great on FM (and sounds great, too)...the AM side has quit (time to check those tubes)...
If you would like a lesson in harmonics, tune your radio to 1500AM when you're in the LaVista Road/285 area and you will pick up WSB better than when you're on 750AM.
BRENT said:
What's the "cadence" of the hash? If you tune to 670 on one radio and 680 on another, does the hash on 670 seem to vary in step with the programming on 680? Or is it pretty much continuous & unvarying?
HD Radio transmits the digital signal in the adjacent channels. If WCNN 680 were using HD (I'm in Nashville so I don't know..) I would expect to hear the HD carriers on 660, 670, 690, and 700. The HD hash is pretty much unvarying, there's no correlation to the analog audio. I suppose the closest analogy is to what you hear on an FM radio tuned to a frequency with no station.
Admittedly, HD is disappearing from AM stations, I'd be surprised if more than two AMs in the Atlanta market are still using it.
I've often heard the sound of hash at the Waffle House.
w9wi said:
WCNN does not employ HD Radio. Only a few AM's in the area ever installed IBOC equipment - the few I can recall are WSB 750, WQXI 790, WAEC 860, and WWWE 1100. To my knowledge, WQXI is the only one currently transmitting digital carriers - daytime only.
I heard that someone at the FCC admitted it was a mistake to assign 1500 to Dallas, GA and the station did have problems in that area.
Back in the 60's, WLCY/1380 in St. Pete put out a signal that was really heavy on the bass. All you had to do was manually tune it to the right (approx. 1382) to get some highs, and when it was done right, it sounded like an FM station.
Lawrenceville used to have a 1360 khz assignment which suffered from the 680 second harmonic.
I want to know why 680 bleeds all over the low end of the AM dial (640, 750, 920, 970), even with a decent radio with a digital tuner, around the high-voltage power lines on Pleasant Hill Road (near PIB, in Duluth). Do those power lines serve the WCNN transmitter in Peachtree Corners? Or is it just simple proximity to the WCNN array (relative to any other signal)?taylorengineer said:
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