[Elecraft] KX3 AM breakthrough (&KX2)

[Vic Rosenthal]

I live in line of sight of a 50 kW AM BC station and I had interesting problems with my K3 when I was using a vertical antenna. I made a 3 MHz highpass filter which fixed it. Note also that the common T network style antenna tuner also is a highpass filter, so that could be a simple solution. Switching to a horizontally polarized antenna will also help if practical.

Vic 4X6GP 

> On 11 Aug 2017, at 21:21, Philip Anderson <phil.anderson at 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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