[Elecraft] Filtering

Fri Mar 1 12:03:01 2002

John,

I agree, K2's xtal filters on CW are as you stated-very high rejection few KHz away from received
signal.
I was able to confirm that yesterday evening.
However, in my K2 I'm hearing signal for few KHz on both sides of center frequency. This signal is
bypassing crystal
filter. This signal is not very strong but strong enough. I'm very happy that this is not the
problem with the cw filter.
I have found the solution for this problem and I will publish this hopefully over the weekend. Now
my K2 CW filtering
works like on FT1000D- no bypassing.
If this is just in my radio then is OK with me.
Please confirm the following. Insert the signal from the generator or  from second radio to the K2
so the S meter
shows S +35 to 40db on K2 (I calibrated K2 S meter using my FT1000D as a reference).
Put K2 in CW mode, try  any filter bandwidth. Tune up and down +/_ 10kHz from the center freq.
and let me know the results.
Perhaps other owners of K2 could do this experiment and send me email, so if there is no problem
than I wouldn't have to
waste my time describing the solution that eliminates the "bypassing"issue completely just in my
radio  SN2507.
I HAVE SO MUCH FUN WITH MY K2. Reminds me old days(you know-being very young) when I designed and
build my own Transceivers.

73!  Mark WQ7X

                    [email protected]                                                                 
                    Sent by:                    To:     [email protected]                      
                    elecraft-admin@mailm        cc:                                                   
                    an.qth.net                  Subject:     Re: [Elecraft] Filtering                 

                    02/28/2002 10:42 PM                                                               

Mark;
Measurements I have done on the K2's Xtal filters indicate that they would
have extremely high rejection at 6 kHz away from the received signal.  They
would certainly be down over 80 dB, and probably over 100 dB.  I have also
checked the oscillator phase noise and it is good enough that it does not
degrade the SSB filter response.  The problem is not likely in the K2 unless
there is a flaw in the radio.

However, on the transmit side, the FCC only requires that spurious signals
be down by 40 dB.  I would expect that most transmitters 6 kHz away from
their transmission frequency will be down more than that.  Suppose the
transmitter has spurious signals down 60 dB at a 6 kHz offset.  If your
S9+20 signal follows standard S-units, the spurious signal 6 kHz away will
be copied at an S2 level.  There is one well known Texas station that runs
at least a kW whose spurious output I can hear 50 kHz from his transmission
frequency.

-John
 KI6WX

----- Original Message -----
From: "Mark Rozmilowski" <[email protected]>

> Does anybody know why when you tune K2  away (6 kHz for example)  from
strong signal 59 +20db and
> there are many of those on SSB  you can still  hear high freq. "noise"
from that station.
> Is it because filter doesn't attenuate enough or signal is going around
the filter.
> I would like to eliminate this problem but not by adding audio filtering.
This should be eliminated
> at its origin.
> I think that there is similar problem on CW but I have to do more
experiments.
>
> Thanks and 73! Mark WQ7X
> K2 SN#2507
>
>
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