Re: BITX20 made in brasil...!!

Chris van den Berg

Hi all,
some additional measurement results (all loaded with 50 ohm):
- The output power of the oscillator is about 3 mw.
While measuring the output after the first mixer and increasing the
LF level until the HF output is not incresed gave the following
results (between brackets the reference numbers of Arv):
- LF output (to mixer): 1 volt pp. (1).
- Output of mixer: 0.6 volt pp. (2).
- output of Q11: 1 mw. (3)

Strange that Arv has much more power then I have on these points.
AC Signal Measurements:
1) LF: This signal becomes non-linear when the output goes above
1.4 to 1.6 volts P-P (Peak-to-Peak).
2) At the BFO Balanced Mixer with measurements taken from
the wiper of the 100 ohm potentiometer:
Varying the audio input (signal generator connected to
microphone input) causes 0 to 5.4 V P-P DSB output.
Unbalancing the mixer potentiometer causes a reading of
3.5 to 4.0 V PP with no audio input.
3) At the collector of Q11 (Tx DSB amplifier) the DSB signal
can be varied from 0 to 2 V P-P.

What I said about the 'calculated level' makes sense: if the output
power of the oscillator is about 3 mw, an expected conversion loss
of about 7 dB (likely more), the attenuator of -4dB, indeed the
measured 0.2 mw at that point looks realistic.

It also gives me a clue that I should try to make more output from
the oscillator (if I increase the 3 mw to 30 mw makes 10 dB
difference to the total output signal?).

The output of Q14 is 0.3 mw, output of the 2N2219 about 150 mw (with
much LF in the microphone stage). This means a gain of 27 dB (but I
am sure you should not measure it all with 50 ohm load).
What output do others have out of the local oscillator and the stage
with the 2N2219 (or 2N2218)?

Best regards,

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