[Elecraft] K3 AM reception

[Joe Subich, W4TV]

Jim, 

> He also says that "Re the bandwidth, a short time ago 
> Elecraft made a mod to the firmware so that audio bandwidth 
> and not IF bandwidth was displayed on the K3's screen. If 
> you're seeing 5KHz and you don't have FM filter installed 
> then it sounds like yet another bug."

This isn't a bug.  The DSP bandwidth is simply wider than the 
IF filter.  In practice the user will see audio out to 4 KHz 
or so at a reduced level following the filter skirts.  

> (2) What does the LCD BW actually read? 
> Is it an IF BW, an audio BW, or what, and does the displayed 
> BW actually corresond to reality? 

For wide modes the best way to display the bandwidth is LO/HI. 
Those are the numbers that correspond to the "real world."  If 
you are looking at FC/BW, the BW number will be  2 * (HI-FC).
Where FC is less than HI/2, BW will typically be overstated. 
In AM for example, "NORM" is BW=5.00 and FC=1.50.  If you 
toggle to the LO/HI display you will find it showing LO=0.00 
and HI=4.00.  Most users would consider that to be BW=4.00. 

It is most convenient to consider that (other than in CW) the 
the audio DSP limits are FC<=2.20, HI<=4.20. 

73, 

   ... Joe, W4TV 
 



> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Jim Garland
> Sent: Sunday, February 01, 2009 10:08 AM
> To: elecraft at mailman.qth.net
> Subject: [Elecraft] K3 AM reception
> 
> 
> I've been reading a thread on another email reflector about 
> the K3's audio response on AM. One of the reflector 
> participants is a serious SWBC listener and is very 
> dissatisfied with his K3's AM audio. He has pointed out a few 
> things about the K3 AM response which puzzle me. Here they are:
> 
> "My K3 sounds the same as others I've heard which I consider 
> to be absolutely terrible when using an external speaker and 
> beyond absolutely terrible when using the internal speaker! 
> The 6KHz roofing filter in the K3 will provide an audio 
> bandwidth of up to 3KHz and the FM 13KHz roofing filter will 
> enable the DSP to provide the user with an audio bandwidth of 
> approximately 4.5KHz I've been told by Elecraft." 
> 
> He also says that "Re the bandwidth, a short time ago 
> Elecraft made a mod to the firmware so that audio bandwidth 
> and not IF bandwidth was displayed on the K3's screen. If 
> you're seeing 5KHz and you don't have FM filter installed 
> then it sounds like yet another bug."
> 
> His particular complaint is audio clicks on AM when hard 
> consonants (Ts, Ks,
> etc) are spoken, a problem that he says has been confirmed by 
> other users. He has installed all the audio mods in his 
> radio, but they didn't fix the problem.
> 
> This was all news to me. I've not used my K3 extensively on 
> AM, and maybe my ears aren't as sensitive as his, but I've 
> not noticed any problem. I have the 6 kHz roofing filter in 
> my radio, and the DSP BW goes up to 5 kHz, which he says is a 
> bug, and that the actual BW is only 3kHz.
> 
> So my questions are: (1) Is audio distortion on AM a known 
> problem with the K3? (2) What does the LCD BW actually read? 
> Is it an IF BW, an audio BW, or what, and does the displayed 
> BW actually corresond to reality?
> 
> Tnx,
> 
> Jim W8ZR
> 
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