For those of you out there who are still playing with the Pixie 2, I'd suggest
that you do yourself a favor and add a TiCK keyer chip. I added the TiCK to
one of my Pixie's and got the following results for a comparatively small
amount of effort:
1) A relatively full featured electronic keyer (no memory of course).
2) Sidetone
3) Keyed offset frequency.
In the "just do it if it works" tradition of the Pixie (exemplified by the
way the audio power amp is keyed), I simply connected the audio line of the
TiCK keyer (through the resistive divider and capacitor that Embedded Research
recommends, using 2.2K and 8.2K resistors) directly to the headphone jack.
Works fine, despite the fact that the keyer audio is "fighting" against the
low impedance of the audio power amp.
For offset, I duplicated the keying transistor circuit (one transistor and one
resistor), with the collector/emitter junction connected across a 33pF
capacitor that is in series with the crystal to ground. This works well, with
no apparent chirp or other problem reported
Actually, I also use an SPDT switch to select either the 33pF capacitor or a
39uH choke. This gives me a kind of simple RIT feature that
allows me to listen to the received 3686 signal from either side of the
transmit frequency. This may be useful in certain QRM situations (e.g., when
the QRM is "on the other side" of your receive frequency by an amount equal to
the difference frequency with the signal you're trying to receive) or when the
other station is transmitting on a frequency close to your normal receive
frequency.
These changes give a whole different flavor to the Pixie. Well worth the
effort. I'm now getting 589's rather than 229's.....HI.....Actually makes no
difference in XMT or RCV performance, but feels like it does.
One other slight mod: If you have not implemented any audio filtering, you
can get some improvement by placing a .01 to .022 uF capacitor across pins 5
and 1 on the LM386. This causes gain to decrease with frequency above 500-
1000 Hz (down to the minimum gain of 20 dB). Although not a large improvement,
this does cut back on a lot of the high frequency noise and signals.
72, Chuck
K1CL
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