40M band pass filter alignment - very little signal getting through

[Vic Dively]

Well, I finished up the assembly Part 2, and everything seems to be going
perfect except for the very last step - the 40M bandpass filter
alignment.  All of the checks were in the expected range, except for U6
pin 8, which was 36.8 ohms instead of greater than 100 ohms.  Everything
else works perfect.  I think the receiver itself is working perfectly,
because I am able to hear several stations with no antenna connected at
all; when I try that with my FT 817 and my Argonaut 509, I couldn't pick
up anything without an antenna attached.  On the other hand, with my
antenna attached, I'm picking up lots of stuff with either the FT-817 or
the Argonaut, and almost nothing additional, when attached to the K2.  I
assume the receiver for 40M is supposed to be fully functional at this
stage.  However, I seem to be having very severe attenuation between the
antenna input and the receiver itself.  So while the receiver seems to be
nearly "deaf" I think the problem is in the path from the antenna jack to
the receiver, not the receiver proper.

Unfortunately, just before performing the 40M band pass filter
adjustment, my Pug started choking on something, so I jumped up to see,
and naturally the headphone cord was wrapped around my leg so I yanked
the K2 off the table onto the floor... I could kick myself!  I redid the
checks, and it all seems to be the same, so I don't think I broke
anything new, I suspect my problem is something that already existed.

L34 seemed to perform as expected, a very mild peak, near the top of the
can... the L1/L2 peaking seemed to work, I could definitely make the
signal come and go, with the antenna attached.... there is a very mild
improvement when the antenna is attached, but as I noted, the signal is
quite severely degraded, compared to attaching the antenna to one of my
other two qrp radios...

I did check my toroids for continuity from the pads, not touching the
lead wire, to be sure that the wires had good connections to the solder,
so....its now on to the signal tracing, a new experience for me.  If the
answer is obvious to anyone, let me know!    Thanks.
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[Don Wilhelm-3]

It is not normal to hear signals with the K2 antenna disconnected unless you
have something connected that is acting like an antenna.

You may want to check the T/R switch area closely making certain everything
is properly soldered, and has the proper value components -- likewise for
the Low Pass Filter.  Especially check to be certain you have good tinning
and solder joints on L25 and L26.  Don't forget to check the soldering of
the relays carefully too.

Since you said you found a nice peak when tuning L1 and L2, I would expect
the bandpass filter to be OK.

You should find your K2 to be more quiet than your other transceivers, how
much so depends on the other transceivers.  How much extra 'junk' is heard
will (of course) depend on the bandwidth of the filters - it also could be
that your BFO is not yet adjusted properly.  You can do the complete CW
Filter/BFO alignment right now if you choose, it will not change when you
complete the K2.  If you want to do that, I highly recommend the use of
Spectrogram as an aid in doing the filter alignment (see my website
www.qsl.net/w3fpr article on K2 Dial Calibration - you need only look at
Step 3, CAL FIL for now, that part covers the filter alignment).

Yes, I would encourage you to check further into that low resistance reading
on U6 pin 8.  That is the 8B voltage rail and may be drawing excessive
current somewhere.  Check the schematic for all components that connect to
the 8B rail and be certain they are the correct value and are nicely
soldered with no solder bridges.

73,
Don W3FPR

> -----Original Message-----
>
>
> Well, I finished up the assembly Part 2, and everything seems to be going
> perfect except for the very last step - the 40M bandpass filter
> alignment.  All of the checks were in the expected range, except for U6
> pin 8, which was 36.8 ohms instead of greater than 100 ohms.  Everything
> else works perfect.  I think the receiver itself is working perfectly,
> because I am able to hear several stations with no antenna connected at
> all; when I try that with my FT 817 and my Argonaut 509, I couldn't pick
> up anything without an antenna attached.  On the other hand, with my
> antenna attached, I'm picking up lots of stuff with either the FT-817 or
> the Argonaut, and almost nothing additional, when attached to the K2.  I
> assume the receiver for 40M is supposed to be fully functional at this
> stage.  However, I seem to be having very severe attenuation between the
> antenna input and the receiver itself.  So while the receiver seems to be
> nearly "deaf" I think the problem is in the path from the antenna jack to
> the receiver, not the receiver proper.
>
> Unfortunately, just before performing the 40M band pass filter
> adjustment, my Pug started choking on something, so I jumped up to see,
> and naturally the headphone cord was wrapped around my leg so I yanked
> the K2 off the table onto the floor... I could kick myself!  I redid the
> checks, and it all seems to be the same, so I don't think I broke
> anything new, I suspect my problem is something that already existed.
>
> L34 seemed to perform as expected, a very mild peak, near the top of the
> can... the L1/L2 peaking seemed to work, I could definitely make the
> signal come and go, with the antenna attached.... there is a very mild
> improvement when the antenna is attached, but as I noted, the signal is
> quite severely degraded, compared to attaching the antenna to one of my
> other two qrp radios...
>
> I did check my toroids for continuity from the pads, not touching the
> lead wire, to be sure that the wires had good connections to the solder,
> so....its now on to the signal tracing, a new experience for me.  If the
> answer is obvious to anyone, let me know!    Thanks.
>

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