Wunder,

The KX3 does have high-pass filtering integrated into the T/R switch, like the 
KX2. But it starts rolling off below the 160 m band. The KX2’s rolloff starts 
somewhat higher, as you noted.

73,
Wayne
N6KR



> On Aug 11, 2017, at 11:53 AM, Walter Underwood <wun...@wunderwood.org> wrote:
> 
> 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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> 
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