[Elecraft] KX3 PBT problem

[Al Duncan]

Hi Peter,
It is odd that the Weaver mode is used when I "uninstall" the roofing
filters and the display shows it is only using FL1. I just tried enabling
the 8 KHz RX shift, both with and without the roofing filter installed, but
the problem still shows up. I am exiting from the menu and power-cycling the
KX3 after I make any menu changes to ensure they are in effect.

73, AL - VE3RRD

-----Original Message-----
From: Peter Lambert [mailto:plambert at qa.com.au] 
Sent: Thursday, September 03, 2015 4:14 PM
To: 'Al Duncan'; elecraft at mailman.qth.net
Subject: RE: [Elecraft] KX3 PBT problem

Hi Al,

Haven't tried it or observed it but I think that what you see is the switch
to weaver mode demodulating.  I thought this would only occurred when the
filter was installed but from your observation I'd say that's not so.

I think what you're seeing is normal.  There's an IF shift (or something
similar) which moves the centre of the demodulated space up to 8KHz.  This
will also prevent the KX3 from switching to weaver mode and supress the hole
in the centre of the demodulated audio but will confirm there's nothing
un-natural going on.  Weaver mode is essential to provide the minimal
roofing filter width in direct conversion SDR architecture.

In SSB mode the hole is of no consequence and not audible.  In digital modes
it can be supressed by keeping the IF bandwidth high.

The 8KHz IF mode is really there to supress low frequency punch through from
things like local AM broadcast station interference.

73's Peter VK4JD

-----Original Message-----
From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Al
Duncan
Sent: Friday, 4 September 2015 12:56 AM
To: elecraft at mailman.qth.net
Subject: [Elecraft] KX3 PBT problem

I have RX xFIL set to "normal" in the menu so that the PBT control adjusts
bandwidth. When I use a BW of 1.8 KHz or higher in SSB mode, everything
looks good on a waterfall display. But when I reduce the BW to 1.7 KHz or
lower, a chunk approximately 250 Hz wide and centered at 1500 Hz is removed
from the waterfall display. I originally thought it was related to the
roofing filters as the effect happened at the same time that FL2 was
selected, but after I set the roofing filters to "not installed" so that FL1
was used for all bandwidths, the problems still occurs. Any suggestions
would be appreciated.

KX3-K serial #1691 with latest production release firmware installed. The
roofing filter option was ordered with the transceiver.  

73, AL - VE3RRD

 

 

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