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