[Elecraft] KX-1: Broadcast breakthrough on 20m

[Peter, DL2FI]

Good morning all,
I assume there is nothing defect nor misalignment in the KX1 but a special
situation as we find it in some European Areas during winter conditions. At
different places in Europe we have different levels of Broadcast signals. It
depends on the distance between your actual location and the BC stn
location. Especially BC stn located somewhere in Russia can produce extreme
high field strength in the evening because if it is the right distance and
if it is darkness between them and you. For example I measured more the
350mV sum RF at 50 Ohm using a 2x 20m dipole here in Berlin. 

The KX1 is an excellent little transceiver but for such situations it´s
preselect ion sometimes is not good enough to handle such strong off band
signals without producing some intermodulations. Remember, even for the much
bigger K2 we published a "European 40m Band Modification" because in seldom
cases even the fantastic K2 suffered by Intermodulations.

The KX1 is as it is, it would be a hard job to give it some extra front end
selectivity, but an easy way to avoid this intermodulations is to use a
selective ATU. Normal T or L ATU designs do add only poor extra selectivity,
but if you use a parallel design like the ZM2 or ZM4
(http://www.qrpproject.biz/UK/ZM4.html) or the "Fuchs ATU"
(http://www.qrpproject.biz/UK/multifuchs.htm) you will have the same amount
of selectivity as with a complete preselector. 

73/2 de Peter, DL2FI

> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net [mailto:elecraft-
> bounces at mailman.qth.net] On Behalf Of Stephen Prior
> Sent: Tuesday, October 27, 2009 11:02 PM
> To: don at w3fpr.com; elecraft
> Subject: Re: [Elecraft] KX-1: Broadcast breakthrough on 20m
> 
> Many thanks Don, I have also had some input from Wayne on this one and
> have
> some things to check with the scope.  I shall combine your reply with
> his
> and see where it takes me.
> 
> Thanks again
> 
> 73 Stephen
> 
> 
> On 27/10/2009 21:57, "Don Wilhelm" <w3fpr at embarqmail.com> wrote:
> 
> >
> > Stephen,
> >
> > The first thing I would suggest is to see if the KX1 is really
> receiving
> > on 20 meters, or perhaps on some other frequency band.  What I am
> > thinking is that the firmware chip may not be fully seated in the
> > socket, which will cause to DDS output to be on some unknown
> frequency.
> >
> > Another thing that could cause similar problem is a distorted DDS
> output
> > waveshape - check inductors L4 and L5 for damage and capacitors C50,
> C51
> > and C52.
> >
> > The other possibility is that the KX1 was actually responding to the
> > image.  When tuned to USB at 14.2, the DDS output is 4.9 kHz below
> the
> > received frequency, and there could be leak-through of strong signals
> > near 4.4 MHz.
> >
> > 73,
> > Don W3FPR
> >
> 
> 
> 
> 
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