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 <phil.ander...@invades.net> 
> 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
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