Re: BITX20 made in brasil...!!

Arvid Evans <arvevans@...>


There is an error in the info I sent you. I apparently
transposed the voltage readings for Base & Emitter of Q10.

The correction is shown below:

DC Voltage Measurements:

Q10 (Microphone Amplifier):
C = 7.0 V DC
* B = 2.3 V DC Actually is 3.0 V DC
* E = 3.0 V DC Actually is 2.3 V DC

Q11 (Tx DSB Amplifier)
C = 7.1 V DC
B = 2.4 V DC
E = 1.7 V DC

Sorry, 8-(

--- In BITX20@..., Rahul Srivastava <vu3wjm@y...> wrote:

From what I remember from my yester years of setting the diode bal
Mod ( In my SB 102) idealy the AF signal level should be 1/10 of
carrier level. ( A thumbrule I guess).

I may be wrong but possibly we need to have a defined optimum OSC
level as well as BFO levels as these very much effect the conversion
gain/ loss.


Rahul VU3WJM

Arv Evans <arvevans@e...> wrote:

As promised, here are some measurements from my BITX40 circuit board:

AC Signal Measurements:

1) Microphone Amplifier output (Q10 collector) is 8V PP with
the input totally over-driven by my AF signal generator at
700 Hz.
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.

DC Voltage Measurements:

Q10 (Microphone Amplifier):
C = 7.0 V DC
B = 2.3 V DC
E = 3.0 V DC

Q11 (Tx DSB Amplifier)
C = 7.1 V DC
B = 2.4 V DC
E = 1.7 V DC

Transistors for Q10 and Q11 are 2N2222 (FT=150 MHz),
with measured DC gain of about 150.

OK, I hope this helps.


On Fri, 2004-09-10 at 18:48, py1pe@a... wrote: hello Arv,

thank you for the clues
I don't have 100mw in the exit... 8 - (
I will verify all the points that you wrote, later I say the
the transistors are BCs549 (freq 300mhz)
I distrust the 1st mixer seriously, because the production DSB is
already low, I imagine that the audio low seje too much, but I didn't
still move for not knowing which the appropriate levels.
thank you and good weekend!
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