Hi All,
beeing a happy user of this fantastic little rig I still missed the
slight bandnoise on quiet days on 20m and 30m. One can blame several
things to the 602 devices - bot not a lack of sensitivity. so I went on
and entered Steves component values into the free rf- simulation
software rfsim99. At least for my european needs there was some room
for
improvement. Generally I achieved a better coincidence of the resonance
peaks of the series- and the parallel circuit. Response curve is
sharper, narrower at the base and passive gain even higher. These
properties may not be wanted by all. Anyway.....
C* is a series C to C1(22p) on the mainboard ***
20m:
---------
C5F=27p (+4p7 NP0chip)
C*=3p3 (cut the lead to PIN1 and bridge it with this C)
30m:
---------
C5F=37p (+3p3 NP0chip)
C8F=none
80m:
---------
C5F=125p (120p NP0 + 4p7 NP0chip)
C7F=37p (+3p3 NP0chip)
C8F=47p (NP0 leaded)
C*=15p (chip NP0)
Sensitivity increases by abt. 10db - by far too much on 80m. To restore
the original value of sensitivity while retaining the improved
selection
a 1k chip resistor is added between C5F and L3 (P4) in parallel to
D3/D4
to ground. Nice sideeffect is relaxed IM- situation because impedance
of
this "hot" point is lowered.
40m:
---------
Unfortunately reception was impossible at all in the evenings with the
original band module :-) but this one was expected...
Complete RX preselection was replaced by an MURATA SFE 7,02 Filter with
suiteable highpass - T matching networks. (please mail me if somebody
needs it -> l.bergner at ixadmin.de ). C1 on the
mainboard (22p) is part of the matching network. The first coil of the
T
-highpass is the 10uH SMCC gained from the original parts. The second
one is 15uH SMCC or 56 turns on AMIDON T30-2 fixed by _some_
beewax.Tuning is not necesary as Qs are relatively low.
Peter DL2FI at QRP-project has the filters on stock and could probably
help every one who needs one.
72/3s
Lutz, DL2HRP
Here is a subsequent email to me and pictures
Hi Mike,
Please post it on your website if you like. Here are some additional
pics about the 40m mod. There are photos from both sides of the module
and a little schematic.
There is one issue remaining that I want to cure. - The BK - diodes.
Especially with the murata filter added - it is so clean and quiet in
the evenings if there weren't those carriers and artefacts...
Still I have not made the final decision about it.
many thanks
73s
Lutz
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