The KX2 has internal filtering to reject frequencies below 3 MHz. The filter is 30 dB down at 1.5 MHz, and 56 dB down at 1 MHz. The KX3 does not have that filtering, probably because it would interfere with performance on 160 m.
There was some discussion of this a few years ago, including suggestions for commercial filters. http://elecraft.365791.n2.nabble.com/Broadcast-band-interference-td7568427.html <http://elecraft.365791.n2.nabble.com/Broadcast-band-interference-td7568427.html> http://www.digitalhams.net/ForumMsgs/msgsDisp.php?forum=KX3&subject=Broadcast+Band+Interference <http://www.digitalhams.net/ForumMsgs/msgsDisp.php?forum=KX3&subject=Broadcast+Band+Interference> Contact Elecraft support and they should send you a schematic for a high pass filter that rejects the AM broadcast band. wunder K6WRU Walter Underwood CM87wj http://observer.wunderwood.org/ (my blog) > On Aug 11, 2017, at 11:21 AM, Philip Anderson <[email protected]> > wrote: > > Hi everyone, > > I have been using a KX2 as my main rig for most of this year, it works very > well although the receiver sometimes struggles a bit from my favorite > portable location right next to the sea, where there's often a large amount > of very strong signals. > > Because of this, recent review comparisons of the KX2 with the KX3 tempted me > to buy a KX3 mostly for the extra receive performance. Unfortunately, when I > tried the KX3 from my favorite portable location next to the sea yesterday, I > had a problem with breakthrough of an AM broadcast station on 20m, the only > way I could completely eliminate the problem was by turning on RX SHIFT, > which unfortunately disables the roofing filter (a big reason for buying the > KX3) and dual watch. > > I understand from comments I have read that this issue is an inherent > weakness of the direct conversion architecture, however - my KX2 never > suffers from this problem. > > So before surrendering to the possibility that I've spent $$$ on a larger KX2 > with disabled dual watch ;) I thought I'd explore alternatives to using the > RX SHIFT feature. > > Since I've never had this problem with my KX2, and since that radio does not > have the RX SHIFT feature, I'm assuming that for some hardware reason, the > problem of AM broadcast breakthrough is not expected on the KX2. > > Does anyone know what the difference between the two is? I suspect that the > KX2 has a more severe high pass filter, in which case a 3Mhz high pass filter > in the KX3 aerial lead might help sort out everything above top band. > > Has anyone tried that? > > Has anyone found any other solutions? > > Phil G4PWO > ______________________________________________________________ > 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 > Message delivered to [email protected] ______________________________________________________________ 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 Message delivered to [email protected]
