[Elecraft] KX3: use at <500-KHz

[Wayne Burdick]

Dave,

If the KXAT3 ATU is installed, and you tune below about 1.3 MHz, a  
special broadcast-band filter is selected on the ATU that improves  
suppression of harmonic images. The LC network is adjusted as you tune  
below this frequency. The LC network values used are a compromise  
since we don't know what type of antenna is being used; we selected  
the values while using a 40-meter dipole. This special BC band  
filtering won't necessarily improve sensitivity in this low range --  
it is there only to improve rejection of images that are  
characteristic of a quadrature downconversion IF receiver (like the  
KX3, Flex radios, etc.).

73,
Wayne
N6KR

On Jul 8, 2012, at 9:51 AM, Dyarnes wrote:

> Hi All,
>
> This issue seems to come up with just about every rig that offers  
> general
> coverage.  I know it was a topic of discussion with the K3 when it  
> first
> arrived.  It has always been my understanding that offering general  
> coverage
> on a ham rig meant compromise somewhere.  Most of the earlier rigs  
> that
> started offering general coverage tended to compromise on the ham band
> performance in order to accomplish the wide RX capability.  That's  
> why many
> didn't even try to offer it.  I think Elecraft's approach has been  
> to offer
> it, but without degrading the ham band performance, which means the  
> wide
> band stuff may be a bit lacking, particularly at the low end.
>
> I've only checked the BC band performance on my KX3 once or twice,  
> and just
> to see if I heard much of anything!  Actually, I could hear things  
> pretty
> well, but probably not like I would on a more specifically designed  
> radio.
> I also suspect the antenna I was using wasn't a very good match.   
> Wayne's
> explanation seems to at least make good sense to me, and I'm sure the
> technical issues involved are real.  Heck--just about every radio I  
> own
> drops off somewhere!  I just want the least adverse effect to occur  
> on the
> ham bands.  Also, I wonder what the internal ATU does (or is capable  
> of
> doing), if anything, when I tune down to the BC band.  From a strictly
> intuitive standpoint, I know that a lot of tuners tend to lose  
> capability
> below 80 meters, so I wonder if the KX3 ATU can/does even function  
> at the BC
> band.  My guess is that it doesn't!  You can't activate it down  
> there, so I
> don't know what's happening.  Does that mean you really need an  
> antenna that
> is reasonably resonant at that frequency?  I suspect there have been  
> some
> "tricks" applied to generate some sort of performance that low, but  
> I really
> don't expect much.  Seems like we may be chasing ghosts to expect  
> too much.
>
> Dave W7AQK
>
>
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