PX3 -- AM Mode Display

[Grant Youngman]

Something is funky on the PX3 when the KX3 is in AM mode.

I have my PBT SSB menu item set for Hi/Lo Cut.  When set to NOR there minor differences in behavior in the AM mode, but the end result is the same.

If the bandwidth/shift or Hi/Lo cut is NORMalized, the green bandwidth band on the PX3 sits with it’s edges about 3 KHZ above and 3 KHz below the carrier frequency as you might expect.  It’s symmetrical around the carrier.  If I open up the HI setting to max (4.2 KHz) and set the LO to minimum, the green band is offset to the high frequency side of the carrier — with the low boundary about 2.2 KHz below the carrier, and the high boundary about 4.4 KHz above the carrier.  These points may not be exact, but they were roughly measured using the VFO A marker — close enough to make the point.  And just using the usual reduction in background hiss to retune the carrier, it appears most closely tuned when the VFO is set about 0.9 KHZ above the actual carrier frequency, although even then the green band is offset from either the actual or tuned carrier freq.

So can anyone explain what is going on, and why the PX3 display (and maybe the KX3) behavior appears so odd in AM mode.  Must be something I missed somewhere along the line.

Grant NQ5T
K3 #2091, KX3 #8342


PS — Sure would be a good thing to port the K3/K3S sync detector to the KX3 …

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[Grant Youngman]

No, I’m not missing any points here. Actually LO cut doesn’t really make much sense in this context in any case, just mentioned it.  It simply maximizes the available bandwidth.

The point — is that if one increases bandwidth, one would expect the bandwidth to generally increase symmetrically about the tuned frequency.  Obviously, if the AM detector is intentionally designed to receive only one sideband (plus carrier), aka the K3 sync mode, that wouldn’t happen.  One would not expect increasing bandwidth to both increase the bandwidth AND apparently shift the bandwidth always to favor the upper sideband.  That may not be what is actually happening, but that is what the KX3 display is showing.

So let’s say that IS what happens.  Then by shifting the low frequency side of the bandwidth upward (using the Lo Cut control, etc.) you can get to what looks like a bandwidth band that covers just the upper sideband of the AM signal. But when you do that (try it), the signal becomes pinched and unreadable, and it is not possible to “retune” the receiver to recover copy.

I’m not bitchig here, just trying to relate the odd PX3 display to what the KX3/PX3 is doing.

Grant NQ5T
K3 #2091, KX3 #8342

> On Apr 19, 2016, at 6:49 PM, Nr4c <[hidden email]> wrote:
>
> I think you are missing the point of AM.
> Remember, the extremes are Hi and if you mess with LO Cut doesn't it open a hole at the center?  
>
> Sent from my iPhone
> ...nr4c. bill
>
>
>> On Apr 19, 2016, at 3:53 PM, GRANT YOUNGMAN <[hidden email]> wrote:
>>
>> Something is funky on the PX3 when the KX3 is in AM mode.
>>

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