KX3: use at <500-KHz

[w7aqk]

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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[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
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

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