Story Problem

[kl7aj]

Here's another broadcast one....a real toughie. Again, this one's from actual case files.

Pil Flanktorquer is chief engineer of WWWW, a 50KW Norheastern regional oldies AM station. WWWW has a six tower parallelogram array, with fairly sharp nulls towards Hartford Connecticut and Newark, New Jersey. The array has been up for forty years.

WWWW has, with much mixed emotion, replaced their beloved but ancient High Level iron horse, with a new solid state AM transmitter and audio processing equipment.

Pil is elated with the results, the modulation monitor, tapped off the common point, sounds marvelous, just like FM.

For the first time in its long history, WWWW is capable of consistently hitting 130% on positive peaks...the FCC limit.

After a few days, though, Pil starts getting some strange reports. Listeners to the southwest tell him his signal sounds "bassy." Listeners to the north say there's "no bottom end." Listeners in Hartford, who usually had rather weak but listenable signals, now report the signal is highly distorted. The description by one elderly woman sounds very much like a layman's description of single sideband. Yet, the modulation monitor sounds beautiful.

What IS the problem? (This is a REAL bugaboo)

eric

[kr9d]

Quote[/b] (kl7aj @ May 04 2007,09:33)]Here's another broadcast one....a real toughie. Again, this one's from actual case files.

Pil Flanktorquer is chief engineer of WWWW, a 50KW Norheastern regional oldies AM station. WWWW has a six tower parallelogram array, with fairly sharp nulls towards Hartford Connecticut and Newark, New Jersey. The array has been up for forty years.

WWWW has, with much mixed emotion, replaced their beloved but ancient High Level iron horse, with a new solid state AM transmitter and audio processing equipment.

Pil is elated with the results, the modulation monitor, tapped off the common point, sounds marvelous, just like FM.

For the first time in its long history, WWWW is capable of consistently hitting 130% on positive peaks...the FCC limit.

After a few days, though, Pil starts getting some strange reports. Listeners to the southwest tell him his signal sounds "bassy." Listeners to the north say there's "no bottom end." Listeners in Hartford, who usually had rather weak but listenable signals, now report the signal is highly distorted. The description by one elderly woman sounds very much like a layman's description of single sideband. Yet, the modulation monitor sounds beautiful.

What IS the problem? (This is a REAL bugaboo)

eric
Sounds like their phasing networks aren't broadbanded enough for their increased bandwidth. Some nodes are getting only part of the bandwidth.

Rick "a little afraid to even play this game" Denney

[kl7aj]

Quote[/b] (kr9d @ May 04 2007,11:10)]Quote[/b] (kl7aj @ May 04 2007,09:33)]Here's another broadcast one....a real toughie. #Again, this one's from actual case files.

Pil Flanktorquer is chief engineer of WWWW, a 50KW Norheastern regional oldies AM station. #WWWW has a six tower parallelogram array, with fairly sharp nulls towards Hartford Connecticut and Newark, New Jersey. #The array has been up for forty years.

WWWW has, with much mixed emotion, replaced their beloved but ancient High Level iron horse, with a new solid state AM transmitter and audio processing equipment.

Pil is elated with the results, the modulation monitor, tapped off the common point, sounds marvelous, just like FM.

For the first time in its long history, WWWW is capable of consistently hitting 130% on positive peaks...the FCC limit.

After a few days, though, Pil starts getting some strange reports. #Listeners to the southwest tell him his signal sounds "bassy." #Listeners to the north say there's "no bottom end." #Listeners in Hartford, who usually had rather weak but listenable signals, now report the signal is highly distorted. #The description by one elderly woman sounds very much like a layman's description of single sideband. #Yet, the modulation monitor sounds beautiful.

What IS the problem? # (This is a REAL bugaboo)

eric
Sounds like their phasing networks aren't broadbanded enough for their increased bandwidth. Some nodes are getting only part of the bandwidth.

Rick "a little afraid to even play this game" Denney
Hmmmm.....so far, you have the closest answer submitted. Wait! You have the ONLY answer submitted.

Let's see who else chimes in. http://www.qrz.com/iB_html/non-cgi/emoticons/smile.gif

eric

[kl7aj]

Be sure to check out the other exciting story problems!

Gold star rewards are available!

[N2RJ]

My guess? Due to the audio gear, more bandwidth was being delivered to the transmitter.

So, because of this, some third order products (splatter?) a few KC's up and down were being delivered to the antennae. When these mixed together with the main carrier, in the air, it canceled out the low end to the North, and the high end to the South.

Or something like that.

That's all I got.

[kl7aj]

Next?

[N2RJ]

Clue?

[kl7aj]

Think about the directional characteristics

[ab0wr]

what you are describing sounds like detection of double sideband without a syncronous detector. Depending on the phase relationships of any specfici frequency in the sidebands at any physical point, the two sidebands can combine in the detector to zero (phi of 90deg, i.e. totally out of phase) or to the original signal (phi of 0 deg, i.e. exactly in phase).

This causes some stations to say you sound good and some stations to say you sound bad and other stations to say you sound distorted (selective fading perhaps?).

tim ab0wr