It's been a tough road or at least a long one. The basic kit went together
well but it soon became apparent that it suffered from many of the flaws
that had been mentioned. So I read and reread the threads on this list to
make sense of some of the diverse opinions about what worked and what
didn't. From this came coherence and here are the lessones learned and
solutions applied:
1) The chirp - I elected finally to just drop the RIT mod. That killed the
chirping. Instead of an RIT I used a multi-turn 100k pot that was lying
around and this will give me the resolution I need. If I regret this move
later I can always put in the modified RIT circuit with the saturated
transistor switches as suggested.
2) Poor sensitivity - I should have noticed this the first time around
because I've been bitten by this before: there was only one peak on TC1, a
give away that the circuit was not resonant. I took two turns off the
secondary of T-1 and voila, the same hot receiver people have been raving
about.
3) TiCK Telemetry Tone Mod - There was some diverse opinion about this
circuit. I put a 4.7K resistor from the right side of C32 (as seen in the
schematic) to the right side of R19; I cut the board connection between C32
and R19 first. This allows both the receiver and the TiCK sidetone to sum
at pin 6 of U5.
4) Diode biasing [note that you need to do the TiCK mod because you need
U4C and U4D] - removing the 8v from the top of R1 and R2 and feeding that
point instead with the inverting output from pin 5 of U4, shuts down
forward bias to the diodes during transmit. Be certain that you jumper D8
which you removed during the TiCK mod. This jumper passes the R- output to
U4D.
5) Direct coupling for the IRF510 - everyone should do this mod. It reduces
idle current drain and helps to stabilize the final. While you're at it,
stick a 560pF silver mica cap in C505. There was some suggestion that the
ferrite bead should not be there so out it went.
6) Variable power output - replacing R12 with a 2K pot allows me to vary
the power output from zilch to five watts.
To all those whose experiments led me to trying these mods, I thank you
immensely. I'm a happy camper. The transmitter sounds good at 4 watts and
the receiver hears everything my Index Labs QRP++ hears. Now on to mounting
this radio in an enclosure (just as soon as I learn the size of the new
digital display kit).
What a group!
..073
Grover
K7TP
The following is an attached File item from cc:Mail. It contains
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--------------------------------- Cut Here ---------------------------------
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end
[
QRP-L Archive |
]
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