Clear Channel reduces bandwidth on AM stations

[Len14043]

While traveling in the Columbus area recently, I noticed that WOR was easily receivable and not splattered by WLW. At the time I figured that WOR was just strong that night and simply outmuscled WLW's sideband. Then I came across this article written by a Clear Channel manager about their decision to use a 5 khz bandwidth instead of the usual 10 khz. As indicated in the article, they are not reducing the bandwidth in anticipation of the implementation of IBOC, but they merely realized the advantage of using a 5 khz bandwidth during IBOC testing. Whether or not IBOC becomes a reality on AM (personally, I believe IBOC will be successful on FM, but not for AM), I hope other radio groups follow suit because it will open up DX possibilities in large cities - unless of course nighttime AM IBOC becomes a reality. See the link below for the entire article.


http://www.rwonline.com/reference-room/iboc/05_rw_bandwidth.shtml<P ID="edit"><FONT class="small">Edited by Len14043 on 07/03/05 12:36 AM.</FONT></P>

 

[Tom_]

***Very*** Interesting article...

*****What do the terms "audio response" and "rolled off" mean in these selectons below (quoted from the link)?

Quoted text from the article:

"The result is that an "above average" receiver today has audio response that is less than 4.5 kHz. In fact most have audio response that is down 10-12 dB at 5 kHz - and the rolloff can start at around 2 kHz...(...)...As far as I am aware, there is only one commonly manufactured radio that has more than 4.5 kHz audio bandwidth, the GE SuperRadio (in Wide Band mode); that one is good to about 6 kHz before it's significantly rolled off..."

*****Does this mean that the GE Superradio recieves an AM signal over a 12kHz bandwidth?

In other words, would the GE Superradio receive 1000kHz from 988 to 1012?

At first this doesn't make sense (to me) since for DX-ing, wouldn't you want *less* than this...in order to hear signals on adjacent channels that interfere from different markets? (e.g. 620/630, 710/720, 1150/1160).

On the other hand, would receiving the signal over a greater bandwidth be advantageous for increasing the signal strength of distant stations?

And consequentially, a wide/narrow filter would be beneficial to a radio that receives signals over 12kHz?

My Sangean 606A can detect adjacent channels better than my old Radio Shack DX375, Sangean DT-200V, Grundig FR-200, GE-4622D...

On the other hand, the 606A has a poor AM antenna so you have to use a loop antenna...

Source of quoted text was from the previous post's link:

http://rwonline.com/reference-room/iboc/05_rw_bandwidth.shtml

<P ID="edit"><FONT class="small">Edited by this Tom: on 07/03/05 06:52 AM.</FONT></P>

 

[Eli Polonsky]

This is why some of the wideband AM stereo receivers from the 80's and 90's had a bandwidth switch. On wideband mode, you'd hear far superior frequency response. A clean, strong AM stereo signal on wideband mode sounds almost as good as FM stereo.

However, wideband mode is no good for DX'ing. The selectivity is shot, and the increased frequency response results in exaggerated background noise. For hearing more distant stations and stations that are adjacent to others, you'd switch to narrow bandwidth (conventional) mode.


> "The result is that an "above average" receiver today has
> audio response that is less than 4.5 kHz. In fact most have
> audio response that is down 10-12 dB at 5 kHz - and the
> rolloff can start at around 2 kHz...(...)...As far as I am
> aware, there is only one commonly manufactured radio that
> has more than 4.5 kHz audio bandwidth, the GE SuperRadio (in
> Wide Band mode); that one is good to about 6 kHz before it's
> significantly rolled off..."
>
> *****Does this mean that the GE Superradio recieves an AM
> signal over a 12kHz bandwidth?
>
> In other words, would the GE Superradio receive 1000kHz from
> 988 to 1012?
>
> At first this doesn't make sense (to me) since for DX-ing,
> wouldn't you want *less* than this...in order to hear
> signals on adjacent channels that interfere from different
> markets? (e.g. 620/630, 710/720, 1150/1160).
>
> On the other hand, would receiving the signal over a greater
> bandwidth be advantageous for increasing the signal strength
> of distant stations?
>
> And consequentially, a wide/narrow filter would be
> beneficial to a radio that receives signals over 12kHz?
>
> My Sangean 606A can detect adjacent channels better than my
> old Radio Shack DX375, Sangean DT-200V, Grundig FR-200,
> GE-4622D...
>
> On the other hand, the 606A has a poor AM antenna so you
> have to use a loop antenna...
>
> Source of quoted text was from the previous post's link:
>
h> ttp://rwonline.com/reference-room/iboc/05_rw_bandwidth.shtml
>

 

[Ai4i]

Selectivity is not always that simple. There is the skirt factor which determines how far out the audio response goes and how drastically it falls off after that point. Here, we have three types of filters: crystal, ceramic, and mechanical, in increasing order of expense and performance. A cheaper way to "steepen" the skirt curve is to stagger tune the IF amplifiers. In other words, you peak those IF amps at 445KHz, 448KHz, 451KHz, 454KHz, 456KHz, 459KHz, 462KHz, 465KHz, in stead of all at 455KHz.<P ID="signature">______________
_____________________________________________
Proud 2 B a pioneering satellite radio subs¢riber
Ai4i is always on the trailing edge of technology</P>