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I tried a similar approach tonight in
my simulator. Seems promising to me also. Once I fix my uBitx, the
Arduino died, I will try it.
On 8/8/2018 10:50 PM, K5ESS wrote:
is the filter approach taken by Wes Hayward W7ZOI for his
“Updated Universal QRP Transmitter” (QST April 2006)
although Wes didn’t add in the series resistors to broaden
the notch.. Wes has a table of component values for all the
ham bands 80 through 10 meters (including the WARC bands)
BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of
Sent: Tuesday, August 7, 2018 10:46 AM
Subject: Re: [BITX20] BITX40 LPF mod
I added the parallel capacitance to notch out the 3rd
harmonic the simulator showed
very narrow notch. Today I tried adding a resistance in
series with that parallel capacitor.
result is a much broader notch at approximately 21 MHz,
but still with 63 db of attenuation.
upper trace is frequency response and the lower trace
shows phase shift. Adding the resistor seems to have
the phase shift so it does not show a dramatic
transition at resonance of L7 and C3.
possibly illogical step is to notch out any 2nd
harmonic energy at 14 MHz. This was done with a
C1, L4). With R3 at 1.5 ohms this looks promising.
trace shows frequency response and lower trace is
Results look like (1) no additional insertion loss,
(2) Reasonably broad notch at 14 MHz, and
at 21 MHz is still there, and (4) overall LPF roll
off still starts at 10 MHz.
this actually work in a real-world circuit? It will
be interesting to find out. If it does work it
insure that 2nd and 3rd harmonics can be reduced to
way below FCC requirement for the
transceiver. The trap idea is interesting because
more traps could possibly be added
take care of any 12 MHz IF leak-through, or any
other spurious signal that looks like it might
this approach be applied to the uBITX filter
problem...maybe, but I will leave that to people
much smarter than myself.
is something that can be tested. It doesn't show in
the simulator, but real-world
be different. When I get to actually wiring this it
will be easy to test.
On Mon, Aug 6, 2018 at 10:18 PM
I read somewhere that its a good idea to drop the
inductor value by 25% or so, (cant recall exact %)
then calculate the parallel Cap value for the required
notch. Otherwise i think the RL is compromised.
Or my memory is suspect, quite possible........