[Elecraft] PX3 Anomoly (bug?) on AM

[GRANT YOUNGMAN]

This may be.  I don’t know if this is a bug, or just the way it is.  

The fact is that it is an odd display for the mode.  The P3 by comparison is quite “normal” for AM.  It would be more logical to show the presumptive equivalent “IF” on either side of the carrier, or (if Elecraft ever implements the stub to a sync detector) just one sideband above or below the carrier.  As it is, the display is hard to interpret.  It does appear to depict the “audio” bandwidth.  For example, if you bring up the lower edge of the green band to the carrier it’s clear the effect is just cutting the low frequency audio — e.g., you can’t retune the radio to center the bandwidth on the AM signal — it jut cuts the lows and renders the thing unintelligible.  Now if there were a really good explanation for how to interpret it (and yours may be part of it), that would be fine, too.

When the receive bandwidth is NORM'ed, it is symmetric about the carrier.  But it ought to stay that way as the bandwidth is increased.  There may be a perfectly good reason why it behaves the way it does.  It just isn’t explained anywhere.

It also doesn’t explain why it seems at least, that the KX3 needs to be tuned slightly off frequency to “center” the signal when the bandwidth is fully maximized.

Grant NQ5T
K3 #2091, KX3 #8342




> On May 3, 2016, at 9:46 PM, Don Wilhelm <donwilh at embarqmail.com> wrote:
> 
> Grant,
> 
> It would appear that you are running up against the bandwidth limit of the
> KX3 audio when you widen the bandwidth with HiCut.
> I don't know what the limits are, but from your observations, it may be that the maximum bandwidth is in the vicinity of 6.4kHz.
> 
> So if you have 4.2 kHz on one side, you will be restricted to 2.2kHz on the low side.
> If you back off the high side to 3.1kHz, is the AM response centered?
> 
> I am just venturing a guess, the maximum audio bandwidth is not specified for the KX3.
>