[Elecraft] Wider bandwidth while listening to AM SW on the KX3?

[Ray Sills]

Hi Guys:

Well, it is quite true that EU AM broadcast stations are spaced 9 KHz  
apart, and US stations are 10KHz apart, it's not true that the audio  
bandpass for those stations is about 5 KHz.  AM stations may very well  
modulate their transmitters so that audio frequencies up to 10 KHz (or  
more) are transmitted.  It simply depends on the design of the  
transmitter and the audio chain that feeds it.  Yes, this makes their  
signals broader, but the FCC rules for AM stations provide (in effect)  
that stations will be located far enough apart from one another that  
the "wide" sidebands are not interfering with other stations.  Or, the  
stations will need to use a directional pattern for their signals, so  
as to "protect" the other stations from interference.

In fact, at one time, many US AM stations would use high quality phone  
lines that were certified to pass up to 15 KHz, for their connection  
from a studio to a transmitter site, for those stations that had  
studios "in town" and a transmitter elsewhere.  If dedicated phone  
lines were not used, then often a microwave link of equivalent quality  
(or better) would be used.  Back when AM stations were part of a major  
network, like ABC, NBC, CBS, or Mutual, the phone lines used for the  
network programs would only be rated to 5KHz.  That's because of the  
cost per mile for the high grade lines was so much more.  Easy enough  
to justify for a mile or ten, but not hundreds or thousands of miles.

Since many AM stations now primarily have talk programming, some  
stations will deliberately limit audio response to 5K, so as to try to  
pack more "talk power" into the signal, just as hams do with AM and  
SSB rigs.  SSB, after all is AM, too.

73 de Ray
K2ULR

On Nov 1, 2013, at 4:21 PM, Andrew Robertson wrote:

> It’s true that, in the USA, the sidebands will be 5 KHz, at the  
> absolute maximum, which means that I am missing at most about .8 KHz  
> of audio at the very most.  However, in the shortwave bands (above  
> MW BCB) there are many broadcasters using 12 to even 15 KHz of  
> spectrum these days.  China, Cuba, Russia, and others have all  
> adopted a very hi-fi sounding very wide bandwidth in the past few  
> years.
>
> I use the same speakers for all my listening with different radios  
> so it’s not likely that this is the issue.
>
> Thanks.
>
> -Andy KE7TMA
>
> On Nov 1, 2013, at 7:31 AM, dave <ho13dave at gmail.com> wrote:
>
>>
>> The audio bandwidth of an AM radio station is something less than  
>> half the separation between stations on the dial. In the EU that  
>> separation is 9 kHz and in the US that is 10 kHz. So the max  
>> bandwidth one can hear on AM - at absolute most - is 5 kHz.  
>> Remember that AM is double sideband. The audio energy is both above  
>> and below the carrier (USB and LSB). The audio passband is approx  
>> half the RF bandwidth used.
>>
>> If the KX3 has an audio passband of ~ 4.2 kHz then you are  
>> effectively missing nothing in terms of bandwidth.
>>
>> If some other radio 'sounds' better that is likely due to listening  
>> to a different speaker with different freq response.
>>
>> 73 de dave
>> ab9ca/4
>>
>>
>>
>> On 11/1/13 5:25 AM, Andrew Robertson wrote:
>>> While I do enjoy the AM SWL capabilities of the KX3, I would really
>> like to be able to appreciate a more hi-fi sound from the unit.  I
>> do know that that roofing filter XFIL1 is probably the ultimate
>> limiter (I believe it’s 15 KHz?  or 10?) but I think the DSP
>> filter in software is actually what is reducing my bandwidth
>> to 4.2 KHz.  Since it is in software, I am hopeful that, perhaps,
>> a future software update could provide a wider bandwidth or even
>> shut off the DSP filter completely (pass-through mode).
>>>
>>> I’m sure I’m not alone in using my KX3 as a SWL rig, and I hope
>> that consideration could be given to this suggestion.  Thanks
>> Wayne and Eric and the rest of the gang at Elecraft for a
>> superb product!
>>>
>>> -Andy KE7TMA
>>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:Elecraft at mailman.qth.net
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>>
>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html